During the last two decades we have witnessed the emergence and global dissemination of Gram-negative bacterial strains, including enterobacteria, producing the so-called ‘carbap-enemases’. The term refers to a variety of struc-turally and functionally diverse -lactamases, the most common being the Klebsiella pneumo-niae carbapenemase (KPC) enzymes (molecular class A), the metallo- -lactamases (M Ls) VIM, IMP and New Delhi M L (NDM; molecular class B) and the OXA-48 and its derivatives (molecular class D). These carbapenemases exhibit extensive hydrolysis spectra, includ-ing many of the clinically available -lactams. Additionally, they exhibit decreased suscepti-bility (KPC) or resistance to mechanism-based inhibitors (M Ls and OXA-48). In addition to the variety it shields, the term carbapenemase also does not accurately reflect these enzymes’ substrate preference. Unlike the ‘tailor-made’ penicillinases, such as the TEMs and SHVs, acquired carbapenemases do not have car-bapenems as their preferred substrate (TABLE 1). Indeed, the collective name of these particular
-lactamases reflects their clinical impact more than their hydrolytic properties.
From the epidemiological view, the situation with the carbapenemase-producing (CP) entero-bacterial species, especially CP K. pneumoniae (CP-Kp), is complex and evolving [1]. CP entero-bacteria continue to spread worldwide, currently affecting acute as well as long-term care facilities
in countries where, until recently, they occurred in a sporadic fashion if at all [1–3].
A systematic evaluation of the accumulated clinical data has already called for the revision of therapeutic approaches against severe infections caused by CP-Kp strains. For example, mono-therapy using either colistin (considered as the first-choice antimicrobial for these infections) or tigecycline, has been questioned [1,4–6]. Fur-thermore, a discussion on the benefits of using carbapenems – a possibility that would have been out of the question not so long ago – has been initiated [7]; in fact, in some settings, the therapeutic potential of carbapenem-based combinations against CP-Kp hospital-acquired infections has already been tested with positive results [8–10]. Nevertheless, systematic efforts (e.g., large-scale controlled trials) to define the optimal therapeutic regimens have not yet been undertaken. This is partly due to the fact that CP-Kp strains mostly affect severely ill, immu-nocompromised patients treated in intensive care units (ICUs), in whom numerous con-founding factors hamper a clear-cut evaluation of any antimicrobial regimens. There are also additional open issues regarding CPs, including their modes of transmission, detection methods and infection control policies.
In the present review, we have attempted a critical appraisal of the existing epidemiologi-cal, experimental and clinical data, focusing on issues that remain debatable. Novel anti-CP
Antonis Markogiannakis1, Leonidas S Tzouvelekis2, Mina Psichogiou3, Efi Petinaki4 & George L Daikos*3
1Department of Pharmacy, Laiko General Hospital, Athens, Greece 2Department of Microbiology, Medical School, University of Athens, Greece 3First Department of Propaedeutic Medicine, Medical School, University of Athens, Greece 4Department of Microbiology, Medical School, University of Thessaly, Larissa, Greece*Author for correspondence: Tel.: +30 210 746 2636 Fax: +30 210 746 2635 [email protected]
The ongoing spread of carbapenemase-producing (CP) multidrug-resistant enterobacteria, primarily Klebsiella pneumoniae, has undoubtedly caused a public health crisis of unprecedented dimensions. The scientific community has been struggling with these highly problematic nosocomial pathogens for more than a decade. Faced with the current situation, one cannot help but wish we could have done better, earlier. However, significant steps have been and are currently being made towards a better understanding of transmission routes of CP microorganisms and in designing strategies that could effectively curb this devastating epidemic. Most importantly, the systematic evaluation of accumulating experimental and clinical data has paved the way to a more rational management of CP-infected patients. In addition, systematic efforts of the industry have led to the development of novel antibacterial agents that are active against CP strains and expected to be introduced to clinical practice in the immediate future.
compounds that are in an advanced stage of development are also presented.
Antibiotic resistance patterns of CP-KpsResistance to -lactamsKPCs (KPC-2–KPC-15) are typical class A
-lactamases possessing the characteristic amino acid motifs of this family of enzymes. The arrangement of the active site residues allows the accommodation and efficient acylation of virtu-ally all -lactam antibiotics, including carbap-enems and cephamycins [11–13]. Consequently, KPC producers commonly exhibit high-level resistance to penicillins (with the exception of temocillin, a derivative of ticarcillin with lim-ited clinical usefulness), older cephalosporins, as well as newer oximino derivatives, cefamycins and aztreonam. The frequent coproduction of extended-spectrum -lactamases (ESBLs), such as SHV and CTX-M, as well as acquired AmpCs (mostly CMYs), contribute to the high MICs observed for the latter drugs. MICs of carbap-enems may vary considerably among CP-Kps, though according to the breakpoints of the Clin-ical and Laboratory Standards Institute (CLSI) most of them are classified as resistant [14].
The class B M Ls of VIM (VIM-1 –VIM-38), IMP (IMP-1–IMP-44) and NDM (NDM-1–NDM-8) types, though phylogenetically distant, exhibit similarities in their hydrolysis spectra being active against all -lactams except aztre-onam [15,16]. However, the frequent coproduction of ESBLs active against aztreonam, especially among VIM producers, precludes the use of this drug. Similarly to KPC producers, M L-positive K. pneumoniae strains display high-level resist-ance to penicillins and cephalosporins, while the range of carbapenem MICs is wide.
Of the acquired carbapenemases encountered in K. pneumoniae, OXA-48 and its point mutants
OXA-162, -163, -181, -204 and -232 exhibit the weakest activity against carbapenems as well as the least extensive substrate spectrum, sparing oximino-cephalosporins. Yet, the vast major-ity of OXA-48-positive K. pneumoniae isolates coproduce -lactamases such as CTX-M, which are capable of hydrolyzing the latter drugs [17,18].
Resistance to non- -lactamsVirtually all CP-Kps exhibit extensive resistance phenotypes that include most clinically available drug classes. This is due to the fact that the vast majority of CP-Kps, apart from carbapenemase-encoding genes, also possess a variety of other resistant determinants – mainly genes encod-ing aminoglycoside-modifying enzymes located either on the plasmid carrier of the carbapen-emase gene or on coresident resistance plasmids. Moreover, several chromosomal mutations fre-quently encountered among clinical K. pneu-moniae strains contribute to overall antibiotic resistance (e.g., by decreasing outer membrane permeability, upregulating efflux pumps and lowering the affinity between topoisomerases and quinolones, among others). Thus, with the exception of gentamicin (which retains some good activity, mainly against KPC producers), CP-Kps commonly exhibit in vitro resistance to most of the clinically important non- -lactam antimicrobial agents, such as aminoglycosides and fluorinated quinolones [19].
The good in vitro activity of colistin and tigecycline against CP enterobacteria has been shown in numerous studies. In vivo, however, these drugs are inherently problematic. Both exhibit complex pharmacokinetics that can-not be considered optimal for the treatment of bloodstream, lower respiratory and urinary tract infections caused by CP-Kps (as discussed below). Nevertheless, due to the dearth of drugs
Table 1. Hydrolytic efficiency of representative variants of the carbapenemase types encountered in Klebsiella pneumoniae clinical isolates against selected
Penicillin-G 1.90 0.04 0.62 0.68 6.10Data for KPC-2, VIM-1, IMP-1, NDM-1 and OXA-48 were derived from [11], [101–103] and [17], respectively. kcat: Turnover number; Km: Michaelis constant; ND: Not determined.
to which CP-Kps are susceptible in vitro, colis-tin and, to a lesser extent, tigecycline, readily become the choice antibiotics. Not surpris-ingly, the consequence of their systematic use, especially in endemic settings, has been the increasing isolation frequency of colistin- and/or tigecycline-resistant CP-Kps [20–23].
Global spread of CP-Kp strainsKPC producers: a single clone pandemic?The most widespread CP-Kp strains are those producing KPC-type -lactamases (predomi-nant variants KPC-2 and KPC-3). KPC-positive strains have caused extensive hospital outbreaks in the northeast regions of the USA during the last decade (mainly in the states of NY and NJ). However, sporadic isolations had already been noticed during the late 1990s in the south-eastern (NC) and the mid-Atlantic regions (MD), indicating that these pathogens had in fact been circulating unnoticed for some years [24,25]. According to a recent report from the CDC, the prevalence of CP-Kp in the USA has increased from 1.6% in 2001 to 10.4% in 2012 [26]. An increasing proportion of KPC-positive K. pneumoniae has also been reported in Latin America, though a clear link with the US epidemic has not been established [22,27]. It has been suggested that transfer of patients carrying KPC-producing K. pneumoniae from the USA to Israel [28] and then to northern and western European countries (where isolation frequency remains low [1]), supposedly through Greece, was one of the main transmission routes leading to these microorganisms becoming widespread [29]. This hypothesis appears to be in line with the common clonal origin (sequence type 258 [ST258]) of the majority of the respective iso-lates. Nevertheless, it should be emphasized that sequence typing delineates phylogenetic origins rather than epidemiological associations. Also, index cases supporting the proposed transmis-sion paths have not always been identified with certainty in the limited outbreaks described in Germany and The Netherlands [30,31]. Of note, in Chinese hospitals (also an endemic setting) KPC-producing K. pneumoniae isolates belong mainly to the likely founder of the clonal com-plex 258, ST11, differing from ST258 in a single locus [32]. Although we have sporadically identi-fied ST11 CP-Kps in Greece, we are not aware of ‘medical tourism’ cases from the latter coun-try to China. We believe that the issue regarding the rapid international spread of the ST258 clone should remain open and some of the explanations
discussed above should better serve as working hypotheses. Although isolates of clonal complex 258 remain predominant, KPC-Kps belonging to other lineages have emerged in many geographic areas due to the acquisition of blaKPC-encoding plasmids. The latter have been classified into sev-eral incompatibility groups such as FII, N and L/M, a fact reflecting the mobilization capacity of the blaKPC genes that are invariably associated with isoforms of Tn4401 as well as the impor-tant role played by transmissible plasmids in the further dispersion of these genes [33–35].
M L-producers: a continuous threatIn stark contrast to the KPC picture just described, the three acquired M L types, namely VIM, IMP, and NDM, have been encountered in a variety of phylogenetically distinct K. pneumo-niae strains causing polyclonal outbreaks. More-over, the respective bla genes have been identi-fied in a wide range of different plasmids [1,34,36]. Producers of IMP- and VIM-type enzymes were frequently isolated during the last decade in Far East and the Mediterranean countries, respec-tively, where they are still endemic [1,3,37]. The most affected country was Greece. VIM-positive K. pneumoniae predominated among multidrug-resistant strains isolated in Greek tertiary care hospitals until 2008 [38]. Their decline during 2008–2009 coincided with the rapid dissemi-nation of KPC producers in that setting [39]. Notwithstanding the repeated occurrence of IMP and VIM producers in various countries, these strains have largely remained confined in their original foci. NDM is the most recent M L type detected in K. pneumoniae. The epicenter of the NDM producers is the Indian subcontinent where, apart from their prevalence in the hospital setting, they have also been detected in various environmental niches. The recent emergence of these microorganisms in Europe, North America, the Far East and Australia (apparently associated with the transfer of patients from India, Pakistan and Bangladesh, as well as the high immigration rates from these areas), led some investigators to hypothesize that NDM producers may be capa-ble of achieving a global spread similar to that presently seen with KPC-producing enterobac-teria [40–42]. Hopefully, efforts to contain these microorganisms will be successful.
OXA-48 producers: the newcomersOXA-48-producing K. pneumoniae caused exten-sive hospital outbreaks in Turkey during the end of the last decade, though it had been isolated from clinical samples in this country since 2001.
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About the same time, such strains were also being isolated in other Middle Eastern and North Afri-can countries underscoring the lag time between emergence and detection of multidrug-resistant strains [43]. The Middle East and North Africa are still regarded as the most important foci of OXA-48 producers. There have been various studies suggesting that transfer of patients carry-ing OXA-48-positive K. pneumoniae from these areas to Europe has led to occasional outbreaks [18]. Moreover, the increasing number of studies reporting spread of OXA-48 producers in diverse geographic areas (e.g., Latin America, South Africa and the USA) clearly suggests that these pathogens have reached a global epidemic status.
Concluding remarksThe data summarized above show that the trans-fer of patients from endemic to nonendemic areas is of undeniable importance for the international spread of CP-Kps. Consequently, policies to curb cross-border diffusion have been proposed [44]. Notwithstanding the ethical and political issues (readers are reminded of the discussion regard-ing the ‘correctness’ of the designation NDM) arising, these approaches may need revision as indicated by the current dispersion patterns of CP-Kps. We do not argue against such measures. On the contrary, we believe that they should be redesigned and intensified based on international collaborative efforts that would include a drastic reallocation of the available resources: containing CP-Kps immediately and directly in their main foci is infinitely more efficient – not to mention beneficial to international public health – than trying to limit their subsequent spread towards other areas. What sounds like an ambitious project is bound to be extremely rewarding and effective in the mid-to-long term. It is also worth mentioning studies reporting the isola-tion of apparently autochthonous carbapenemase producers around the world, including western Europe and the Far East [45,46]. Assuming that the de novo emergence of such strains in diverse regions during the same time period is rather unlikely, these findings may indicate that the methods currently applied to trace transmission routes must be improved.
CP-Kp strains in the acute care health setting
Acquisition risks, transmission & control of CP-Kp strainsAlthough CP-Kps can affect any hospital-ized patient in endemic setting, these organ-isms cause life-threatening infections such as
bacteremia and pneumonia mostly in critically ill patients with severe underlying diseases and comorbidity conditions. Consequently, several variables commonly linked with this subset of hospitalized patients have been recognized as independent risk factors for CP-Kp acquisition, those most frequently reported being prolonged hospitalization, stay in an ICU, poor functional status, previous use of antibiotics, malignancies, solid organ or stem cell transplantation, use of multiple invasive devices among others. How-ever, the ‘independence’ of each of the above factors may be rather an overstatement, since risks for colonization/infection by CP-Kps have mainly been assessed in settings where these microorganisms had been established and, in most cases, had already reached epidemic, if not indeed endemic, status. Therefore, a straightfor-ward answer to the question: ‘Who is prone to acquire a CP-Kp?’ could well be the inevitable tautology: ‘The seriously ill patient treated in a facility where transmission of CP-Kps is largely uncontrolled’. A fraction of colonized patients will develop infection. The colonization/infec-tion ratio may vary from 10 to 30% depending mainly on patient characteristics [47,48] [D!"#$% GL,
U&'()*"%+,- D!.!].The modes of CP-Kp transmission do not
differ from those of other multiresistant enter-obacteria. Person-to-person transmission via the hands of nursing and medical staff is most probably the main route of dissemination in healthcare facilities (FIGURE 1). Involvement of environmental sources has also been proposed, but its contribution is probably less important. In the majority of cases, the first step is inges-tion of the microorganism followed by its estab-lishment in the patient’s gut flora. The median carriage time has been estimated to be at least several months, and in patients with invasive devices, poor functional status and comorbidity conditions appear to be longer [49,50]. This rela-tively long colonization time, when coupled with serious infection control shortfalls in a facility, will raise the number of colonized patients. In a study using the classic Ross–Macdonald model for vector-borne diseases, it was estimated that, in a setting with low compliance with standard hygiene practices, an average of two secondary cases may occur per primary case of CP-Kp colonization [51]. In a worst case scenario, the gradually increasing colonization pressure would eventually lead to the predominance of CP-Kps.
Until recently, the policies to control the spread of CP-Kps and other CP enterobacterial
species were those applied for other MDR Gram- negatives. However, experience from successful control attempts undertaken at vari-ous levels (from single wards to national health systems) has now allowed the formulation of more focused and detailed guidelines [44,52,53]. Some differences do exist, but there is a gen-eral agreement on the main actions that must be taken. Briefly, in order to be timely and effective, an intervention must include, at least, active surveillance cultures, isolation or cohort-ing of colonized/infected patients together with contact precautions and the appointment of dedicated nursing staff. Results must be evalu-ated on a regular basis, and, in case of failure, root-cause ana lysis must be performed. The potential effectiveness of the aforementioned measures has recently been supported by a mathematical model predicting that, in a high prevalence setting, a reduction of 60–90% in colonized patients on admission, through active surveillance cultures, contact precautions and isolation/cohorting, in combination with 60% compliance in hand hygiene, would result in a drastic decline in CP-Kp prevalence in a few months (FIGURE 2) [43].
Surveillance & detection: current trendsMethods aiming to detect carbapenemase pro-duction appeared in the literature almost simul-taneously with the emergence of CP Gram- negatives. There has been a wide variety of detec-tion approaches that can be grossly classified as phenotypic, biochemical and molecular. Based on published data, we support that the straight-forward recognition of carbapenemase-positive isolates by interpreting reading of phenotypes, including those obtained from automated sys-tems, should be avoided [54–56]. Of the pheno-typic methods, the modified Hodge test – still the only screening method recommended by the CLSI [14] – is based on the hydrolysis of ertap-enem or meropenem by whole cells of carbapen-emase producers. The major shortcoming of the modified Hodge test is its relatively low speci-ficity (frequent false positives among CTX-M and/or AmpC producers) [57]. Synergy between carbapenems and inhibitors (boronates for KPCs and chelating agents for M Ls) in a combined disk assay is a reliable approach despite some lim-itations, such as the requirement for additional time and the inability to detect OXA-48-type carbapenemases [1,57]. These problems can be overcome by the available molecular methods, which are mainly PCR-based. Numerous ‘in-house’ simplex, multiplex, and real-time PCR
assays have been employed in the identifica-tion of carbapenemase genes. The industry has also developed various reliable detection meth-ods based on PCR hybridization and real-time PCR as well as microarray technology [58–60]. A biochemical approach to detect carbapenemase production is the photometric monitoring of imi-penem hydrolysis by crude enzyme preparations derived from the suspected isolate. The method is considered as the ‘gold standard’ but can usu-ally only be applied in reference laboratories [57]. Also, matrix-assisted laser desorption ioniza-tion time of flight mass spectrometry, a method capable of identifying carbapenem hydrolysis products, has been used to confirm carbapen-emase activity in Gram-negative isolates [61]. At this point, it is worth mentioning the CarbaNP test, a recently developed rapid, reliable and low-cost chromogenic reaction based on imipenem hydrolysis by whole cell suspensions that can be readily integrated in the work flow of a clinical laboratory [62].
The routine application of carbapenemase detection techniques in the clinical laboratory is no longer recommended by the CLSI and the European Committee on Antimicrobial Suscep-tibility Testing (EUCAST) [14,201]. However, confirmation of the presence of carbapenemases should be performed for epidemiological pur-poses, for example, identification of positive isolates derived after CP carrier screenings. The latter rely increasingly on the use of commercially available selective culture media [63]. It is possible that these media – that are being continuously refined – could be routinely used in surveillance studies in the near future.
Uncolonized patients Colonized patients
Contaminated HCWUncontaminated HCW
Figure 1. Clonal transmission of carbapenemase-producing Klebsiella pneumonia strains from patient to patient through healthcare workers in a 40–50-bed ward during a relatively short time period (6–8 months). Boxes depict four population groups: uncolonized patients, colonized patients, uncontaminated HCWs and contaminated HCWs. Solid arrows depict movement between population groups and dashed arrows depict transmission of carbapenemase-producing Klebsiella pneumonia between patients and HCWs. HCW: Healthcare worker. Adapted from [51].
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Antibiotic therapy of CP-Kp infectionsAlthough numerous clinical studies have dealt with the antimicrobial treatment of CP-Kp-caused infections, controlled comparative trials are missing. Consequently, a systematic appraisal of the efficacy of the various treatment schemes used so far is quite difficult. Indeed, compilation of data from different types of studies, some of which include a fairly small number of patients, cannot lead to solid conclusions. The lack of a universally accepted definition for combination therapy is also problematic. Some investigators consider administration of at least two antibiotics as combination therapy, regardless of in vitro sus-ceptibility, while, for others, combination therapy is defined as the use of at least two in vitro-active
drugs. Further complications arise from the use of different carbapenem breakpoints (CLSI or EUCAST; TABLE 2) in clinical studies evaluating therapeutic efficacy of antibiotic schemes that include carbapenems. Apart from the difficulties in comparing clinical outcome data, applying different breakpoints may hamper the setting-up of large scale international efforts aiming to optimize therapeutic practices. In defining car-bapenem susceptibility status, EUCAST, based primarily on pharmacokinetic/pharmacody-namic (PK/PD) and clinical data, recommended higher values than the CLSI. However, lowering the breakpoints and reporting the CP-Kp isolates exhibiting, for instance, meropenem MICs of 4 or 8 µg/ml as resistant, decreases the opportunity
Table 2. Carbapenem clinical breakpoints for Enterobacteriaceae according to European Committee on Antimicrobial Susceptibility Testing and Clinical and Laboratory Standards Institute.
Carbapenem EUCAST CLSI
S R Screening cutoff
S I R
Imipenem !2 >8 >1 !1 2 "4
Ertapenem !0.5 >1 >0.125 !0.5 1 "2
Meropenem !2 >8 >0.125 !1 2 "4
Doripenem !1 >4 ND !1 2 "4Values (mg/l) are presented as in [14, 209]. CLSI: Clinical and Laboratory Standards Institute; EUCAST: European Committee on Antimicrobial Susceptibility Testing; I: Intermediate; ND: Not defined; R: Resistant; S: Susceptible.
20
22
18
16
14
12
10
8
6
4
2
00 30 60 90 120 150 180
Time (days)
CP
-Kp
colo
niza
tion
(%)
Figure 2. Impact of infection control measures on the prevalence of carbapenemase-producing Klebsiella pneumonia colonization in an hyperendemic setting. The evaluated scenarios include: (A) hand hygiene compliance of 60% (line with triangles); (B) hand hygiene compliance of 60% in combination with 60% reduction of colonized admissions by active surveillance cultures, isolation/cohorting and contact precautions (line with circles); and (C) hand hygiene compliance of 60% in combination with 90% reduction of colonized admissions by active surveillance cultures, isolation/cohorting and contact precautions (line with squares). CP-Kp: Carbapenemase-producing Klebsiella pneumonia. Adapted from [51].
for some patients to obtain the potential thera-peutic benefit of carbapenem-based combina-tion schemes. It should be also emphasized that, in certain clinical studies, carbapenem MICs have been determined by automated systems that have been repeatedly blamed for serious inconsistencies [54–56].
Notwithstanding these limitations, there have been ample data that justify a current shift to combination therapy. As we have discussed pre-viously, use of a single agent in treating patients with CP-Kp bloodstream infection (BSI) or pneumonia was associated with unacceptably high mortality rates, while combination therapy performed significantly better, though still sub-optimally [1,64]. Further support for the supe-riority of the combination regimens that may include up to three drugs was provided by two recent studies conducted in the USA and Italy that included cohorts of patients infected with KPC-producing K. pneumoniae [9,10]. Notably, in the Italian study, carbapenem-containing combinations appeared to be the most effica-cious even when used against CP-Kps resistant to these drugs according to the current criteria of the CLSI.
Therefore, using antibiotic combinations should clearly be regarded as a step towards a more efficacious treatment of CP-Kp infec-tions. On the other hand, it cannot be denied that the relevant data are largely observational and lacking in experimental support. Superior-ity of treatment with two or more drugs appar-ently results from synergy or additive effect. The potential synergistic activity of a wide variety of antibiotic combinations against CP-Kps, pro-ducing either KPCs or M Ls, has been exam-ined in many in vitro studies, using a variety of time-kill methodologies. These studies may provide some useful preliminary information. However, results are sometimes inconsistent and also depend heavily on the concentrations of the drugs tested. More valid data regarding synergy through drug combinations can be obtained by using animal infection models and controlled clinical trials, but the scarcity of such studies is remarkable. Lately, Hirsch and colleagues have documented a clear synergistic effect of dorip-enem–amikacin combination against CP-Kps fully resistant to both drugs in the neutropenic murine pneumonia model [65]. In addition, two multicenter prospective studies aiming to evalu-ate the therapeutic potential of imipenem–colis-tin [202] and meropenem–colistin [203] combi-nations are underway. In the meantime, the available experimental and clinical data can and
should be revisited in order to optimize the use of commonly used antimicrobial agents.
Although there is a clear trend towards increasing resistance to colistin among CP-Kps, this drug remains one of the most in vitro-active ones against these pathogens. It can be reason-ably expected that its use, mostly in combina-tion schemes, will continue. However, the low efficacy of colistin monotherapy suggests that the currently employed schemes, administered in two or three divided doses across the day, are suboptimal and should be reconsidered [1]. Indeed, the complex pharmacokinetics of colis-tin have not yet been fully elucidated. Conse-quently, the fine balance between efficacy and toxicity of colistin remains to be defined. As things stand, the design of dosing schemes in subsets of patients, such as the critically ill, trans-plant patients and those with impaired renal function, rests on what could, not unfairly, be described as guesswork. The commonly used schemes have been based primarily on data from animal infection models, indicating a correlation between exposure time and antibacterial activity [66]. Kinetic studies in humans have shown that it takes at least 2 days for the drug to achieve steady state [67]. An initial loading dose of 9 ml IU can overcome this disadvantage; this prac-tice is now widely accepted by clinicians. More to the point, colistin concentrations attained in serum are most probably insufficient for isolates with MICs >0.5 mg/l [68]. Also, its concentra-tions in bronchial secretions are significantly lower, even below detection levels [69,70]. Thus, testing colistin at higher dosages given at longer intervals may be worth trying. The long half-life of colistin, as well as its concentration-depend-ent killing and adaptive resistance phenomena [68,71,72], favor these suggested changes. However, the issues of nephro- and neuro-toxicity should be priorities, if any effort to enhance colistin efficacy by changing the dosing schemes is to be undertaken.
The shortage of active antimicrobials and the generally low MICs of tigecycline against CP-Kps have led to the use of this drug, occasion-ally as a single agent, in the treatment of CP-Kp BSIs and pneumonia, in spite of these not being included in the US FDA-approved indications of the drug (skin and skin structure infections, complicated intra-abdominal infections and community-acquired pneumonia). Efficacy of tigecycline monotherapy in the former infec-tions, however, seems to be poor, as expected from its PK/PD features [1]. Even so, the drug can be useful against various CP-Kp infections
Future Microbiol. (2013) 8(9)1154 future science group
including BSIs as part of combination regimens including a carbapenem and/or colistin but the relevant data are still limited [9,10]. Occasionally, tigecycline has been used at doses higher than those approved (e.g., 100 mg every 12 h) [73]. Notwithstanding its potential toxicity, the large volume of distribution of tigecycline [74] makes it unlikely that a meaningful increase in plasma and epithelial lining fluid concentration can be attained by doubling its daily dose.
One of the most debatable issues regarding therapy of infections caused by CP-Kps and other CP enterobacteria is the use of carbapen-ems [7,75]. We have previously supported the use of these antibiotics based on clinical observations as well as data from animal experimental infec-tions [1]. Lately, we have introduced (in a limited number of ICUs and hematology wards in Greek hospitals) an algorithm in which a carbapenem (preferentially meropenem) combined with a suitable aminoglycoside or colistin is the first choice for primary and secondary BSIs caused by CP-Kps, provided that the meropenem MIC of the infecting strain is !4 mg/l [64]. Results so far appear to be promising. Others, however, oppose the use of carbapenems against CPs irre-spective of the MIC value, with the argument that such practice is not justified by the avail-able clinical data [76]. Irrespective of this as-yet unresolved debate, for a carbapenem to be use-ful in a combination scheme it must be given at high doses and by prolonged infusion in order to exploit its PK/PD features and maximize its in vivo activity [77,78].
Other drug classes, mostly aminoglycosides that occasionally exhibit good in vitro activity against CP-Kps, have also been used in combi-nation regimens. Evidently, any active amino-glycosides should be among the first-choice anti-biotics for the treatment of urinary tract infec-tions caused by CP-Kps. There have also been indications from a limited number of clinical studies that carbapenem–aminoglycoside com-binations may exhibit satisfactory therapeutic efficacy against CP-Kp bloodstream and lower respiratory tract infections [1,64]. Parenteral fos-fomycin has been proposed as an adjunct to other active agents against serious CP-Kp infec-tions but clinical experience is limited to a few small studies producing conflicting results [79,80]. This drug may deserve more attention since it exhibits good in vitro activity against CP-Kps and seems to be well tolerated at relatively high doses. It should be stressed, however, that the selection rate of fosfomycin-resistant vari-ants among enterobacterial species is high [81].
Moreover, in the case of K. pneumoniae ST258, cross-resistance to -lactams is also possible [80].
Readers should bear in mind that the above discussion is based on studies mainly reporting on infections caused by KPC- and VIM-pro-ducing isolates. Similar data regarding infec-tions due to OXA-48 and NDM producers are still limited. As with the other CP-Kps, combi-nations including colistin and/or tigecycline are frequently employed in treating the respective infections [18,40]. However, the relatively low carbapenem MICs in a significant portion of OXA-48-producing K. pneumoniae should also allow treatment with carbapenem-based combi-nations [82,83]. Furthermore, oximino-cephalo-sporins may be an option for OXA-48-positive K. pneumoniae not coproducing an ESBL [84].
Novel antimicrobialsAntibioticsPlazomicinA derivative of sisomicin, plazomicin (FIGURE 3) is a new-generation aminoglycoside active against Gram-negative pathogens, mainly Enterobacte-riaceae. Most importantly, the in vitro activity spectrum of the drug also includes bacterial strains producing any of the clinically impor-tant aminoglycoside-modifying enzymes. Pla-zomicin, however, is inactive against strains producing ribosomal methyltransferases such as most of the NDM-positive Enterobacteriaceae [85]. The kinetic profile of plazomicin resembles that of other aminoglycosides, although at the currently tested dosing scheme in healthy indi-viduals (intravenous infusion of 15 mg/kg over 10 min), the Cmax of the drug is much higher and the T1/2 more prolonged compared with the clinically available aminoglycosides [86]. Also, animal and Phase I studies have indicated no oto- or nephro-toxicity [87]. Results from a Phase II study in patients with complicated uri-nary tract infection including cases with bac-teremia are expected to be published soon [204]. In a press release, the manufacturer announced that “all objectives met in Phase II plazomicin complicated urinary tract infections study”[205].
BAL30072This monocyclic -lactam (a siderophore mono-sulfactam; FIGURE 3) exhibits potent in vitro activ-ity against a wide range of Gram-negative spe-cies by inhibiting multiple penicillin binding proteins. BAL30072 overcomes decreased per-meability and resists hydrolysis by several clini-cally relevant -lactamases, including M Ls, OXA-48 and KPCs, though it is susceptible to
common ESBLs such as the SHV-type enzymes [88,89]. BAL30072, either alone or combined with meropenem, has shown promising activity against various Gram-negative species including M L-producing enterobacteria both in vitro and in experimental animal infections [90,91].
Carbapenemase inhibitorsAvibactamThis non- -lactam compound (a bridged diaz-abicyclo-octanone; FIGURE 3) is expected to be introduced soon in the clinic combined with ceftazidime, aztreonam or ceftaroline. Avibac-tam is capable of inhibiting virtually all serine
-lactamases, including KPCs, at low con-centrations [92], thus restoring – even in KPC producers – the activity of various -lactams, including oximino-cephalosporins. The thera-peutic efficacy of the ceftazidime–avibactam combination against KPC-positive K. pneu-moniae has been documented in murine infec-tion models [93]. The results of a Phase II study involving hospitalized patients with compli-cated urinary tract infections showed that its efficacy and safety were comparable to those of imipenem [94]. Additional clinical trials to evaluate ceftazidime–avibactam combinations in a variety of nosocomial infections have been designed [206].
MK-7655The second member of the diazabicyclo-octanone family of -lactamase inhibitors, MK-7655 (FIGURE 3), is a potent inhibitor of class A and C -lactamases [95]. A pronounced in vitro synergy between MK-7655 and imipenem against KPC-producing K. pneumoniae has been shown [96]. A Phase II study of the safety, toler-ability and efficacy of imipenem plus MK-7655 versus imipenem alone to treat complicated intra-abdominal infections is underway [207].
RPX7009This is a boron-containing compound with activity against class A -lactamases includ-ing KPC types, as well as most AmpC enzymes [97]. RPX7009 is being developed in combina-tion with biapenem, a carbapenem that is less vulnerable to M Ls and OXA-48 enzymes as compared with other carbapenems. A biap-enem/RPX7009 combination produced sig-nificant bacterial killing in experimental infec-tions caused by KPC-producing strains and a Phase I study evaluating the safety, tolerability, and pharmaco kinetics of RPX7009 in healthy adults is in progress [208].
ConclusionThe grave public health consequences of the ongoing worldwide dissemination of CP enter-obacteria, especially K. pneumoniae, have been exhaustively discussed [1,2,36,98]. Genes encoding distinct -lactamases, such as KPC and M Ls of the VIM, IMP and NDM types, capable of hydrolyzing virtually all -lactams, including carbapenems, have spread via mobile units to a variety of K. pneumoniae clones, some of which have achieved global dissemination. Although infections by these pathogens have been plagu-ing the healthcare sector for over a decade, too many critical issues – of epidemiology, detection, control measures and, most importantly, thera-peutic approach – remain open, and the need for these to be resolved, or at least adequately tackled, is urgent.
At present, the most widespread CP-Kps are the blaKPC-carrying strains, many of which belong to ST258. Additionally, in the last few years, pro-ducers of OXA-48 carbapenemase, which prob-ably emerged in the Middle East, are increasingly being isolated in various regions. On the other hand, producers of the M L types VIM, IMP and NDM, though also detected worldwide, are, so far, being isolated at high frequencies mostly
O
O
NH2
O
NHOH
NH2OH
O
NH
O
OH
NH2
NHCH3
OHCH3
OH
NS
N
N
O
OH
OHON
O
NNH2
O OSO3H
N
O
NH2
NO OSO3Na N
NH
NH
O
NO OSO3Na
S
O
NH
BO OH
O
OH
Plazomicin
BAL30072
Avibactam
MK-7655
RPX7009
Figure 3. Novel agents active against carbapenemase producers expected to be introduced to clinical practice soon.
Future Microbiol. (2013) 8(9)1156 future science group
in their original foci (the Mediterranean region, the Far East and the Indian subcontinent, respec-tively). Regardless of this epidemiological vari-ability, curbing the further spread of carbapen-emase producers is a clear international priority. Special measures aiming to limit cross-border diffusion from high- to low-prevalence countries have been implemented. The current epidemio-logical patterns of CP-Kps, however, suggest that these are not yet satisfactory, calling for a better elucidation of transmission routes.
Introduction of these pathogens in a particular setting does not necessarily lead to dominance and endemicity. Nevertheless, propagation of CP-Kps in a healthcare institution is a clear indicator of the inadequacy of currently applied infection control measures. Fortunately, sound studies have shown that successful containment of carbapenemase producers is feasible. Euro-pean expert committees and the CDC have recently issued detailed recommendations that include, among others, active surveillance cul-tures, isolation/cohorting of colonized/infected patients, contact precautions and assignment of dedicated nursing staff.
CP-Kp strains mainly affect hospitalized patients with severe underlying conditions, but are also spreading in long-term care facilities. Among the wide spectrum of infections they cause, BSI and pneumonia are the most life-threatening. Virtually all CP-Kps exhibit multi-drug resistance phenotypes. Thus, the dearth of treatment options has led to the extensive use of colistin and tigecycline, since these are the most active drugs in vitro. However, systematic assessment of clinical data accumulated over a decade has demonstrated beyond any doubt that the therapeutic potential of the aforementioned drugs, especially in monotherapy schemes, is suboptimal. It has been suggested that the com-monly used colistin dosage regimens are inappro-priate and hence associated with possible clinical failure. Indeed, while this drug’s toxicity is noto-rious, its complex pharmacokinetics have not yet been fully elucidated. Consequently, the balance between colistin’s efficacy and toxicity remains to be fine-tuned. Regarding tigecycline, its bacte-riostatic activity and, most importantly, its unfa-vorable kinetic properties (low concentrations in serum and epithelial lining fluid) may explain the poor efficacy of monotherapy in serious CP-Kp infections, including primary and sec-ondary BSIs. Adding to these quandaries, there is a notable trend towards increasing MICs for both colistin and tigecycline, evidently associated with the systematic use of these agents. Therapy with
carbapenems remains debatable. Nevertheless, it is reasonable to hypothesize that treating patients with prolonged infusion of maximum doses – thus exploiting the PK/PD features of carbapenems – may be effective against strains with relatively low MICs for these drugs.
The overall safer current trend in the therapy of CP-Kp infections is the use of combination schemes including up to three antibiotics. So far, carbapenem-based combinations (e.g., a carbap-enem plus either colistin or an aminoglycoside and/or tigecycline) seem to be the most effica-cious. Antibiotic combinations are clearly prom-ising as a more efficacious treatment of CP-Kp infections, though the available data are still limited. Large-scale controlled trials along with experimental studies are needed to validate and refine the combination schemes.
Novel antimicrobials active against CP entero-bacteria as well as inhibitors active against the most common carbapenemases have been devel-oped by the industry. Some of them, such as plazomicin (an aminoglycoside resistant to all clinically important modifying enzymes), the sulfactam BAL30072 (a monocyclic -lactam active against M L producers) and the non-
-lactam inhibitors avibactam and MK-7655 (both highly active against KPC -lactamases), are under advanced clinical testing and may prove valuable in the near future.
Future perspectiveWe may reasonably expect that application of the comprehensive infection control measures proposed by the USA and EU public health authorities could drastically limit the spread of CP enterobacterial pathogens, and possibly even eradicate them in low-prevalence settings in a relatively short time period. An utterly success-ful outcome, however, is far from certain. The recommended policies are demanding in both expertise and, more importantly, resources that are not available in many of the affected areas. Consequently, it would be safer to predict that the problem will persist, at least in the developing countries. One may be more optimistic regarding the future of antibiotic therapy for CP entero-bacteria infections. So far, attempts to assess clinical data, though fragmentary, have facili-tated the rationalization of patient management. Reaching a consensus regarding the minimum requirements for the presentation and evaluation of clinical data should become a priority. This is a prerequisite for the setting up of large-scale international trials aiming to define optimal antibiotic treatments for specific patient groups.
ReferencesPapers of special note have been highlighted as: of interest of considerable interest
1. Tzouvelekis LS, Markogiannakis A, Psichogiou M, Tassios PT, Daikos GL. Carbapenemases in Klebsiella pneumoniae and other Enterobacteriaceae: an evolving crisis of global dimensions. Clin. Microbiol. Rev. 25(4), 682–707 (2012).
Extensive review on microbiology, epidemiology, infection control and treatment for carbapenemase-producing
Enterobacteriaceae, with emphasis on Klebsiella pneumoniae.
2. Nordmann P, Dortet L, Poirel L. Carbapenem resistance in Enterobacteriaceae: here is the storm! Trends Mol. Med. 18(5), 263–272 (2012).
3. Cantón R, Akova M, Carmeli Y et al. Rapid evolution and spread of carbapenemases among Enterobacteriaceae in Europe. Clin. Microbiol. Infect. 18(5), 413–431 (2012).
4. Hirsch EB, Tam VH. Detection and treatment options for Klebsiella pneumoniae carbapenemases (KPCs): an emerging cause
The introduction of novel antibacterial agents will also provide additional therapeutic options. Considering the recent development of several promising compounds that are highly active against CPs as well as potent carbapenemase inhibitors (some of which are to be used in clini-cal practice quite soon), it is expected that the renewed interest of the industry in producing novel antimicrobials will continue and, prob-ably, be intensified. Technological progress in various relevant areas such as organic synthe-sis, modeling and high-throughput screening are most likely to facilitate this process. It can safely be surmised that the conventional, though still successful, strategy to design new improved molecules belonging to already established drug
classes (recent examples being plazomicin and BAL30072) will remain prevalent in the near future [99]. Nonetheless, there have been system-atic efforts to produce innovative compounds capable of interfering with metabolic path-ways of the Gram-negative cell that have not yet been exploited. Notable among others are various hydroxamic acid derivatives that can arrest the growth of a wide variety of Gram-negative species including K. pneumoniae, by impeding the biosynthesis of lipid A [100]. In this respect, development of -lactamase inhibitors is a step ahead: the diazabicyclooctanes avibac-tam and MK-7655 may indeed be the precur-sors of a brand new family of non- -lactam broad-spectrum inhibitors.
Executive summary
Antibiotic resistance patterns of carbapenemase-producing Klebsiella pneumoniae strainThe global spread of carbapenemase-producing (CP) and extensively drug-resistant enterobacteria of clinical importance, especially Klebsiella pneumoniae (CP-Kp), is currently one of the most pressing public health problems.
Global spread of CP-Kp strainHigh incidence of CP-Kps is commonly seen in developing countries, though increasing isolation frequencies are also being observed in industrialized countries. Cross-border transfer has been recognized as an important contributor to the ongoing evolution of this epidemic.
CP-Kp strain in the acute care settingCP-Kp colonizations and infections occur mainly in acute healthcare settings and, to a lesser extent, in long-term care facilities. Claims of community-acquired CP-Kp infections have not been effectively documented.Numerous ‘independent’ risk factors for CP-Kp colonization/infection have been reported. Most relevant studies, however, have been conducted in endemic settings, suggesting that the key factor is the inadequacy of infection-control measures.CP-Kps preferentially affect hospitalized patients with severe underlying conditions causing a variety of life-threatening infections, such as bacteremia and pneumonia, with high mortality rates.
Antibiotic therapy of CP-Kp infectionsThe dearth of therapeutic options has led to the extensive use of colistin and tigecycline owing to their in vitro activity against CP-Kps. Yet, the efficacy of these drugs, especially when used in monotherapy, is disappointing. Moreover, colistin- and tigecycline-resistant CP-Kps are being increasingly reported.Currently, there is a shift towards therapy with antibiotic combination regimens. The hitherto available clinical data clearly indicate the superiority of this approach, where carbapenem-based combinations are the most efficacious, presumably because of carbapenems’ favorable pharmacokinetic/pharmacodynamic characteristics, especially when bloodstream infection and pneumonia are being treated.
Novel antimicrobialsNovel antibiotics active against CP enterobacteria as well as compounds with potent inhibitory activity against carbapenemases are expected to be available soon.
Financial & competing interests disclosureThe authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials dis-cussed in the manuscript. This includes employ-ment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.
No writing assistance was utilized in the production of this manuscript.
Future Microbiol. (2013) 8(9)1158 future science group
of multidrug-resistant infection. J. Antimicrob. Chemother. 65(6), 1119–1125 (2010).
5. Akova M, Daikos GL, Tzouvelekis L, Carmeli Y. Interventional strategies and current clinical experience with carbapenemase-producing Gram-negative bacteria. Clin. Microbiol. Infect. 18(5), 439–448 (2012).
6. Lee GC, Burgess DS. Treatment of Klebsiella pneumoniae carbapenemase (KPC) infections: a review of published case series and case reports. Ann. Clin. Microbiol. Antimicrob. 11, 32 (2012).
7. Daikos GL, Markogiannakis A. Carbapenemase-producing Klebsiella pneumoniae: (when) might we still consider treating with carbapenems? Clin. Microbiol. Infect. 17(8), 1135–1141 (2011).
8. Daikos GL, Petrikkos P, Psichogiou M et al. Prospective observational study of the impact of VIM-1 metallo- -lactamase on the outcome of patients with Klebsiella pneumoniae bloodstream infections. Antimicrob. Agents Chemother. 53(5), 1868–1873 (2009).
9. Qureshi ZA, Paterson DL, Potoski BA et al. Treatment outcome of bacteremia due to KPC-producing Klebsiella pneumoniae: superiority of combination antimicrobial regimens. Antimicrob. Agents Chemother. 56(4), 2108–2113 (2012).
10. Tumbarello M, Viale P, Viscoli C et al. Predictors of mortality in bloodstream infections caused by Klebsiella pneumoniae carbapenemase-producing K. pneumoniae: Importance of combination therapy. Clin. Infect. Dis. 55(7), 943–950 (2012).
Presentation of sound data indicating the superiority of antibiotic combinations, preferentially those including a carbapenem, over monotherapy against bloodstream infections caused by Klebsiella pneumoniae carbapenemase-producing K. pneumoniae.
11. Yigit H, AM Queenan JK Rasheed et al. Carbapenem-resistant strain of Klebsiella oxytoca harboring carbapenem-hydrolyzing
12. Alba J, Ishii Y, Thomson K, Moland ES, Yamaguchi K. Kinetics study of KPC-3, a plasmid-encoded class A carbapenem-hydrolyzing beta-lactamase. Antimicrob. Agents Chemother. 49(11), 4760–4762 (2005).
13. Ke W, Bethel CR, Thomson JM, Bonomo RA, van den Akker F. Crystal structure of KPC-2: insights into carbapenemase activity in class A -lactamases. Biochemistry 46(19), 5732–5740 (2007).
14. Clinical and Laboratory Standards Institute (CLSI). Performance standards for
antimicrobial susceptibility testing: twenty-first informational supplement. CLSI document M100-S21. Clinical and Laboratory Standards Institute, Wayne, PA, USA (2011).
15. Bebrone C. Metallo- -lactamases (classification, activity, genetic organization, structure, zinc coordination) and their superfamily. Biochem. Pharmacol. 74(12), 1686–1701 (2007).
16. Palzkill T. Metallo- -lactamase structure and function. Ann. N. Y. Acad. Sci. 1277, 91–104 (2012).
17. Poirel L, Héritier C, Tolün V, Nordmann P. Emergence of oxacillinase-mediated resistance to imipenem in Klebsiella pneumoniae. Antimicrob. Agents Chemother. 48(1), 15–22 (2004).
18. Poirel L, Potron A, Nordmann P. OXA-48-like carbapenemases: the phantom menace. J. Antimicrob. Chemother. 67(7), 1597–1606 (2012).
19. Livermore DM, Warner M, Mushtaq S, Doumith M, Zhang J, Woodford N. What remains against carbapenem-resistant Enterobacteriaceae? Evaluation of chloramphenicol, ciprofloxacin, colistin, fosfomycin, minocycline, nitrofurantoin, temocillin and tigecycline. Int. J. Antimicrob. Agents 37(5), 415–419 (2011).
20. Anthony KB, Fishman NO, Linkin DR, Gasink LB, Edelstein PH, Lautenbach E. Clinical and microbiological outcomes of serious infections with multidrug-resistant Gram-negative organisms treated with tigecycline. Clin. Infect. Dis. 46(4), 567–570 (2008).
21. Capone A, Giannella M, Fortini D et al. High rate of colistin resistance among patients with carbapenem-resistant Klebsiella pneumoniae infection accounts for an excess of mortality. Clin. Microbiol. Infect. 19, E23–E30 (2013).
22. Pereira PS, de Araujo CF, Seki LM, Zahner V, Carvalho-Assef AP, Asensi MD. Update of the molecular epidemiology of KPC-2-producing Klebsiella pneumoniae in Brazil: spread of clonal complex 11 (ST11, ST437 and ST340). J. Antimicrob. Chemother. 68(2), 312–316 (2013).
23. Spanu T, De Angelis G, Cipriani M et al. In vivo emergence of tigecycline resistance in multidrug-resistant Klebsiella pneumoniae and Escherichia coli. Antimicrob. Agents Chemother. 56(8), 4516–4518 (2012).
24. Bratu S, Mooty M, Nichani S et al. Emergence of KPC-possessing Klebsiella pneumoniae in Brooklyn, New York: epidemiology and recommendations for detection. Antimicrob. Agents Chemother. 49(7), 3018–3020 (2005).
25. Kitchel B, Rasheed JK, Patel JB et al. Molecular epidemiology of KPC-producing Klebsiella pneumoniae in the United States: clonal expansion of MLST sequence type 258. Antimicrob. Agents Chemother. 53(8), 3365–3370 (2009).
27. Castanheira M, Costello AJ, Deshpande LM, Jones RN. Expansion of clonal complex 258 KPC-2-producing Klebsiella pneumoniae in Latin American hospitals: report of the SENTRY Antimicrobial Surveillance Program. Antimicrob. Agents Chemother. 56(3), 1668–1669 (2012).
28. Navon-Venezia S, Leavitt A, Schwaber MJ et al. First report on a hyperepidemic clone of KPC-3-producing Klebsiella pneumoniae in Israel genetically related to a strain causing outbreaks in the United States. Antimicrob. Agents Chemother. 53(2), 818–820 (2009).
29. Wernli D, Haustein T, Conly J, Carmeli Y, Kickbusch I, Harbarth S. A call for action: the application of The International Health Regulations to the global threat of antimicrobial resistance. PLoS Med. 8, e1001022 (2011).
30. Wendt C, Schütt S, Dalpke AH et al. First outbreak of Klebsiella pneumoniae carbapenemase (KPC)-producing K. pneumoniae in Germany. Eur. J. Clin. Microbiol. Infect. Dis. 29(5), 563–570 (2010).
31. Meessen N, Wiersinga J, van der Zwaluw K, van Altena R. First outbreak of carbapenemase-producing Klebsiella pneumoniae in a tuberculosis care facility in The Netherlands. Presented at: Proceedings of the 20th European Congress of Clinical Microbiology and Infectious Diseases (ECCMID). Vienna, Austria 10–13 April 2010 (Abstract P1283).
32. Qi Y, Wei Z, Ji S, Du X, Shen P, Yu Y. ST11, the dominant clone of KPC-producing Klebsiella pneumoniae in China. J. Antimicrob. Chemother. 66(2), 307–312 (2011).
33. Cuzon G, Naas T, Truong H et al. Worldwide diversity of Klebsiella pneumoniae that produce beta-lactamase blaKPC-2 gene. Emerg. Infect. Dis. 16(9), 1349–1356 (2010).
34. Patel G, Bonomo RA. “Stormy waters ahead”: global emergence of carbapenemases. Front. Microbiol. 4, 48 (2013).
35. Richter SN, Frasson I, Franchin E et al. KPC-mediated resistance in Klebsiella pneumoniae in two hospitals in Padua, Italy, June 2009–December 2011: massive spreading of a KPC-3-encoding plasmid and involvement of non-intensive care units. Gut Pathog. 4(1), 7 (2012).
38. Psichogiou M, Tassios PT, Avlamis A et al. Ongoing epidemic of blaVIM-1-positive Klebsiella pneumoniae in Athens, Greece: a prospective survey. J. Antimicrob. Chemother. 61(1), 59–63 (2008).
39. Giakkoupi P, Papagiannitsis CC, Miriagou V et al. An update of the evolving epidemic of blaKPC-2-carrying Klebsiella pneumoniae in Greece (2009–2010). J. Antimicrob. Chemother. 66(7), 1510–1513 (2011).
40. Kumarasamy KK, Toleman MA, Walsh TR et al. Emergence of a new antibiotic resistance mechanism in India, Pakistan, and the UK: a molecular, biological, and epidemiological study. Lancet Infect. Dis. 10(9), 597–602 (2010).
41. Nordmann P, Poirel L, Toleman MA, Walsh TR. Does broad-spectrum -lactam resistance due to NDM-1 herald the end of the antibiotic era for treatment of infections caused by Gram-negative bacteria? J. Antimicrob. Chemother. 66(4), 689–692 (2011).
43. Carrër A, Poirel L, Yilmaz M et al. Spread of OXA-48-encoding plasmid in Turkey and beyond. Antimicrob. Agents Chemother. 54(3), 1369–1373 (2010).
44. European Centre for Disease Prevention and Control. Risk assessment on the spread of carbapenemase-producing Enterobacteriaceae (CPE) through patient transfer between healthcare facilities, with special emphasis on cross-border transfer. ECDC, Stockholm, Sweden (2011).
Systematic review of risk factors associated with carbapenemase-producing Enterobacteriaceae and detailed guidance for prevention and control.
45. Nordmann P, Couard JP, Sansot D, Poirel L. Emergence of an autochthonous and community-acquired NDM-1-producing Klebsiella pneumoniae in Europe. Clin. Infect. Dis. 54(1), 150–151 (2012).
46. Kim MN, Yong D, An D et al. Nosocomial clustering of NDM-1-producing Klebsiella pneumoniae sequence type 340 strains in four patients at a South Korean tertiary care hospital. J. Clin. Microbiol. 50(4), 1433–1436 (2012).
47. Borer A, Saidel-Odes L, Eskira S et al. Risk factors for developing clinical infection with
carbapenem-resistant Klebsiella pneumoniae in hospital patients initially only colonized with carbapenem-resistant K. pneumoniae. Am. J. Infect. Control 40 (5), 421–425 (2012).
48. Schechner V, Kotlovsky T, Kasma M et al. Carbapenem-resistant Enterobacteriaceae : who is prone to become clinically infected? Clin. Microbiol. Infect. 19 (5), 451–456 (2013).
49. Saidel-Odes L, Polachek H, Peled N et al. A randomized, double-blind, placebo-controlled trial of selective digestive decontamination using oral gentamicin and oral polymyxin E for eradication of carbapenem-resistant Klebsiella pneumoniae carriage. Infect. Control Hosp. Epidemiol. 33(1), 14–19 (2012).
50. Feldman N, Adler A, Molsatzki N et al. Gastrointestinal colonization by KPC-producing Klebsiella pneumoniae following hospital discharge: duration of carriage and risk factors for persistent carriage. Clin. Microbiol. Infect. 19(4) E190–E196 (2013).
51. Sypsa V, Psichogiou M, Bouzala GA, Hadjihannas L, Hatzakis A, Daikos GL. Transmission dynamics of carbapenemase-producing Klebsiella pneumoniae and anticipated impact of infection control strategies in a surgical unit. PLoS ONE 7(7), e41068 (2012).
52. CDC. Guidance for control of carbapenem-resistant Enterobacteriaceae (CRE). 2012 CRE Toolkit. CDC, Atlanta, GA, USA (2012).
Detailed guidance for the prevention and control of carbapenem-resistant Enterobacteriaceae.
53. Schwaber MJ, Lev B, Israeli A et al. Containment of a country-wide outbreak of carbapenem-resistant Klebsiella pneumoniae in Israeli hospitals via a nationally implemented intervention. Clin. Infect. Dis. 52(7), 848–855 (2011).
First successful nationwide effort to curb the dissemination of carbapenemase-producing enterobacteria.
54. Giakkoupi P, Tzouvelekis LS, Daikos GL et al. Discrepancies and interpretation problems in susceptibility testing of VIM-1-producing Klebsiella pneumoniae isolates. J. Clin. Microbiol. 43(1), 494–496 (2005).
55. Tenover FC, Kalsi RK, Williams PP et al. Carbapenem resistance in Klebsiella pneumoniae not detected by automated susceptibility testing. Emerg. Infect. Dis. 12(8), 1209–1213 (2006).
56. Woodford N, Eastaway AT, Ford M et al. Comparison of BD phoenix, Vitek 2, and MicroScan automated systems for detection and inference of mechanisms responsible for
carbapenem resistance in Enterobacteriaceae. J. Clin. Microbiol. 48(8), 2999–3002 (2010).
57. Nordmann P, Gniadkowski M, Giske CG et al. Identification and screening of carbapenemase-producing Enterobacteriaceae. Clin. Microbiol. Infect. 18(5), 432–438 (2012).
58. Avlami A, Bekris S, Ganteris G et al. Detection of metallo- -lactamase genes in clinical specimens by a commercial multiplex PCR system. J. Microbiol. Methods 83(2), 185–187 (2010).
59. Spanu T, Fiori B, D’Inzeo T et al. Evaluation of the New NucliSENS EasyQ KPC test for rapid detection of Klebsiella pneumoniae carbapenemase genes (blaKPC). J. Clin. Microbiol. 50(8), 2783–2785 (2012).
60. Cuzon G, Naas T, Bogaerts P, Glupczynski Y, Nordmann P. Evaluation of a DNA microarray for the rapid detection of extended-spectrum -lactamases (TEM, SHV and CTX-M), plasmid-mediated cephalosporinases (CMY-2-like, DHA, FOX, ACC-1, ACT/MIR and CMY-1-like/MOX) and carbapenemases (KPC, OXA-48, VIM, IMP and NDM). J. Antimicrob. Chemother. 67(8), 1865–1869 (2012).
61. Hrabák J, Studentová V, Walková R et al. Detection of NDM-1, VIM-1, KPC, OXA-48, and OXA-162 carbapenemases by matrix-assisted laser desorption ionization-time of flight mass spectrometry. J. Clin. Microbiol. 50(7), 2441–2443 (2012).
62. Nordmann P, Poirel L, Dortet L. Rapid detection of carbapenemase-producing Enterobacteriaceae. Emerg. Infect. Dis. 18(9), 1503–1507 (2012).
Presents an inexpensive, sensitive and specific method for the rapid detection of carbapenemases in Enterobacteriaceae.
63. Gazin M, Paasch F, Goossens H, Malhotra-Kumar S; MOSAR WP2 and SATURN WP1 study teams. Current trends in culture-based and molecular detection of extended-spectrum- -lactamase-harboring and carbapenem-resistant Enterobacteriaceae. J. Clin. Microbiol. 50(4), 1140–1146 (2012).
64. Daikos GL, Markogiannakis A, Souli M, Tzouvelekis LS. Bloodstream infections caused by carbapenemase-producing Klebsiella pneumoniae: a clinical perspective. Expert Rev. Anti Infect. Ther. 10(12), 1393–1404 (2012).
65. Hirsch EB, Guo B, Chang K-T et al. Assessment of antimicrobial combinations for KPC-producing Klebsiella pneumoniae. J. Infect. Dis. 207(5) 786–793 (2013).
66. Dudhani RV, Turnidge JD, Nation RL, Li JJ. fAUC/MIC is the most predictive pharmacokinetic/pharmacodynamic index of colistin against Acinetobacter baumannii in
Future Microbiol. (2013) 8(9)1160 future science group
murine thigh and lung infection models. J. Antimicrob. Chemother. 65(9), 1984–1990 (2010).
67. Plachouras D, Karvanen M, Friberg LE et al. Population pharmacokinetic analysis of colistin methanesulfonate and colistin after intravenous administration in critically ill patients with infections caused by Gram-negative bacteria. Antimicrob. Agents Chemother. 53(8), 3430–3436 (2009).
Pioneer study introducing the necessity of a loading dose of colistin for rapid attainment of steady-state serum drug concentrations.
68. Garonzik SM, Thamlikitkul V, Paterson DL et al. Population pharmacokinetics of colistin methanesulfonate and formed colistin in critically ill patients from a multicenter study provide dosing suggestions for various categories of patients. Antimicrob. Agents Chemother. 55(7), 3284–3294 (2011).
Provides recommendations for colistin dosing for various categories of patients.
69. Imberti R, Cusato M, Villani P et al. Steady-state pharmacokinetics and BAL concentrations of colistin in critically ill patients after IV colistin methanesulfonate administration. Chest 38(6), 1333–1339 (2010).
70. Markou N, Fousteri M, Markantonis SL, Boutzouka E, Tsigou E, Baltopoulos G. Colistin penetration in the alveolar lining fluid of critically ill patients treated with IV colistimethate sodium. Chest 139(1), 232–233 (2011).
71. Daikos GL, Skiada A, Pavleas J et al. Serum bactericidal activity of three different dosing regimens of colistin with implications for optimum clinical use. J. Chemother. 22(3), 175–178 (2010).
72. Fernández L, Breidenstein EB, Hancock RE. Creeping baselines and adaptive resistance to antibiotics. Drug Resist. Updat. 14(1), 1–21 (2011).
73. Humphries RM, Kelesidis T, Dien Bard J, Ward KW, Bhattacharya D, Lewinski MA. Successful treatment of pan-resistant Klebsiella pneumoniae pneumonia and bacteraemia with a combination of high-dose tigecycline and colistin. J. Med. Microbiol. 59(11), 1383–1386 (2010).
74. Rodvold KA, Gotfried MH, Cwik M et al. Serum, tissue and body fluid concentrations of tigecycline after a single 100 mg dose. J. Antimicrob. Chemother. 58(6), 1221–1229 (2006).
75. van Duin D, Kaye KS, Neuner EA, Bonomo RA. Carbapenem-resistant Enterobacteriaceae: a review of treatment and outcomes. Diagn. Microbiol. Infect. Dis. 75(2), 115–120 (2013).
76. Livermore DM, Andrews JM, Hawkey PM et al. Are susceptibility tests enough, or should laboratories still seek ESBLs and carbapenemases directly? J. Antimicrob. Chemother. 67(7), 1569–1577 (2012).
77. Bulik CC, Christensen H, Li P, Sutherland CA, Nicolau DP, Kuti JL. Comparison of the activity of a human simulated, high-dose, prolonged infusion of meropenem against Klebsiella pneumoniae producing the KPC carbapenemase versus that against Pseudomonas aeruginosa in an in vitro pharmacodynamic model. Antimicrob. Agents Chemother. 54(2), 804–810 (2010).
78. Bulik CC, Nicolau DP. In vivo efficacy of simulated human dosing regimens of prolonged-infusion doripenem against carbapenemase-producing Klebsiella pneumoniae. Antimicrob. Agents Chemother. 54(10), 4112–4115 (2010).
79. Michalopoulos A, Virtzili S, Rafailidis P, Chalevelakis G, Damala M, Falagas ME. Intravenous fosfomycin for the treatment of nosocomial infections caused by carbapenem-resistant Klebsiella pneumoniae in critically ill patients: a prospective evaluation. Clin. Microbiol. Infect. 16(2), 184–186 (2010).
80. Karageorgopoulos DE, Miriagou V, Tzouvelekis LS, Spyridopoulou K, Daikos GL. Emergence of resistance to fosfomycin used as adjunct therapy in KPC Klebsiella pneumoniae bacteraemia: report of three cases. J. Antimicrob. Chemother. 67(11), 2777–2779 (2012).
81. Nilsson A, Berg OG, Aspevall O, Kahlmeter G, Andersson DI. Biological costs and mechanisms of fosfomycin resistance in Escherichia coli. Antimicrob. Agents Chemother. 47(9), 2850–2858 (2003).
82. Maherault AC, Nordmann P, Therby A, Pangon B. Efficacy of imipenem for the treatment of bacteremia due to an OXA-48-producing Klebsiella pneumoniae isolate. Clin. Infect. Dis. 54(4), 577–578 (2012).
83. Navarro-San Francisco C, Mora-Rillo M, Romero-Gómez MP et al. Bacteremia due to OXA-48-carbapenemase-producing Enterobacteriaceae: a major clinical challenge. Clin. Microbiol. Infect. 19(2), E72–E79 (2013).
84. Mimoz O, Grégoire N, Poirel L, Marliat M, Couet W, Nordmann P. Broad-spectrum
-lactam antibiotics for treating experimental peritonitis in mice due to Klebsiella pneumoniae producing the carbapenemase OXA-48. Antimicrob. Agents Chemother. 56(5), 2759–2760 (2012).
85. Livermore DM, Mushtaq S, Warner M et al. Activity of aminoglycosides, including ACHN-490, against carbapenem-resistant Enterobacteriaceae isolates. J. Antimicrob. Chemother. 66(1), 48–53 (2011).
86. Van Wart S, Bhavnanil SM, Forrest A, Bruss J, Cass R, Ambrose PG. Population pharmacokinetics of ACHN-490 injection in healthy subjects. Presented at: 48th Annual Meeting of the Infectious Diseases Society of America. Vancouver, BC, Canada, 21–24 October 2010.
87. Zhanel GG, Lawson CD, Zelenitsky S et al. Comparison of the next-generation aminoglycoside plazomicin to gentamicin, tobramycin and amikacin. Expert Rev. Anti Infect. Ther. 10(4), 459–473 (2012).
88. Page MG, Heim J. New molecules from old classes: revisiting the development of
-lactams. IDrugs 12 (9), 561–565 (2009).
89. Page MG, Dantier C, Desarbre E. In vitro properties of BAL30072, a novel siderophore sulfactam with activity against multiresistant Gram-negative bacilli. Antimicrob. Agents Chemother. 54(6), 2291–2302 (2010).
90. Miriagou V, Papagiannitsis C, Kotsakis S et al. Efficacy of BAL30072, alone and combined with meropenem, against VIM-producing enterobacteria in a murine thigh infection model. Program and Abstracts of the 20th European Congress of Clinical Microbiology and Infectious Diseases ECCMID. Vienna, Austria, 10–13 April 2010 (Poster P1240).
91. Walsh TR, Weeks J, Toleman M et al. Activity of the novel sulfactam BAL30072, alone and in combination with meropenem, against Enterobacteriaceae harbouring NDM-1 beta-lactamase. Program and Abstracts of the 21st European Congress of Clinical Microbiology and Infectious Diseases ECCMID, 27th International Congress of Chemotherapy ICC. Milan, Italy, 7–10 May 2011 (Poster P1146).
92. Stachyra T, Levasseur P, Pechereau MC et al. In vitro activity of the -lactamase inhibitor NXL104 against KPC-2 carbapenemase and Enterobacteriaceae expressing KPC carbapenemases. J. Antimicrob. Chemother. 64(2), 326–329 (2009).
93. Endimiani A, Hujer KM, Hujer AM, Pulse ME, Weiss WJ, Bonomo RA. Evaluation of ceftazidime and NXL104 in two murine models of infection due to KPC-producing Klebsiella pneumoniae. Antimicrob. Agents Chemother. 55(1), 82–85 (2011).
94. Vazquez JA, González, Patzán LD et al. Efficacy and safety of ceftazidime-avibactam versus imipenem-cilastatin in the treatment of complicated urinary tract infections, including acute pyelonephritis, in hospitalized adults: results of a prospective, investigator-blinded, randomized study. Curr. Med. Res. Opin. 28(12), 1921–1931 (2012).
95. Young K, Raghoobar SL, Hairston NN et al. In vitro activity of the class A and C
-lactamase inhibitor MK-7655. Program and Abstracts of the 50th Interscience Conference on
Antimicrobial Agents and Chemotherapy. Boston, MA, USA 12–15 September 2010 (Abstract F1–2139).
96. Hirsch EB, Ledesma KR, Chang KT, Schwartz MS, Motyl MR, Tam VH. In vitro activity of MK-7655, a novel -lactamase inhibitor, in combination with imipenem against carbapenem-resistant Gram-negative bacteria. Antimicrob. Agents Chemother. 56(7), 3753–3757 (2012).
97. Livermore DM, Mashtaq S. Activity of biapenem (RPX2003) combined with boronate -lactamase inhibitor RPX7009, against carbapenem-resistant Enterobacteriaceae. J. Antimicrob. Chemother. 68(8), 1825–1831 (2013).
98. Walsh TR. Emerging carbapenemases: a global perspective. Int. J. Antimicrob. Agents 36(Suppl 3), S8–S14 (2010).
99. Bush K. Improving known classes of antibiotics: an optimistic approach for the future. Curr. Opin. Pharmacol. 12(5), 527–534 (2012).
100. Zhang J, Zhang L, Li X, Xu W. UDP-3-O-(R-3-hydroxymyristoyl)-N-acetylglucosamine deacetylase (LpxC) inhibitors: a new class of antibacterial agents. Curr. Med. Chem. 19(13), 2038–2050 (2012).
101. Franceschini N, Caravelli B, Docquier JD et al. Purification and biochemical characterization of the VIM-1 metallo-
102. Laraki N, Franceschini N, Rossolini GM et al. Biochemical characterization of the Pseudomonas aeruginosa 101/1477 metallo-
-lactamase IMP-1 produced by Escherichia coli. Antimicrob. Agents Chemother. 43(4), 902–906 (1999).
103. Yong D, Toleman MA, Giske CG et al. Characterization of a new metallo-
-lactamase gene, blaNDM-1, and a novel erythromycin esterase gene carried on a unique genetic structure in Klebsiella pneumoniae sequence type 14 from India. Antimicrob. Agents Chemother. 53(12), 5046–5054 (2009).
Websites201. European Committee on Antimicrobial
Susceptibility Testing. EUCAST guidelines for detection of resistance mechanisms and specific resistances of clinical and/or epidemiological importance. www.eucast.org/fileadmin/src/media/PDFs/EUCAST_files/Consultation/EUCAST_
205. Press release: Achaogen Announces All Objectives Met in Phase 2 Plazomicin Complicated Urinary Tract Infections Study and Start of First-in-Human Study with ACHN-975. www.achaogen.com/news/148/15
