Carbapenem Resistancean update on

essential learning Dr.T.V.Rao MD

Definition of Carbapenems • The term “carbapenem” is defined as the 4:5 fused ring lactam of penicillin's with a double bond between C-2 and C-3 but with the substitution of carbon for sulfur at C-1. The hydroxyethyl side chain of thienamycin is a radical departure from the structure of conventional penicillin's and cephalosporins, all of which have an acylamino substituent on the β-lactam ring; the stereochemistry of this hydroxyethyl side chain is a key attribute of carbapenems and is important for activity.

We have more stable Carbapenems

• Along the journey to the discovery of more-stable carbapenems with a broader spectrum, the other currently available compounds, Meropenem, biapenem, ertapenem, and doripenem were developed, and several novel carbapenems were also identified

Synthetic journey of Carbapenems • A major advance in this

“synthetic journey” was the addition of a methyl group to the 1-β position . This modification was found to be protective against DHP-I hydrolysis . Several carbapenems were identified with this modification in the subsequent 2 decades; many were similar to the currently available carbapenems, having a 1-β-methyl and a pyrrolidine ring at C-2

Newer use of Carbapenems • These novel carbapenems

included antipseudomonal carbapenems, anti-methicillin-resistant S. aureus (MRSA) carbapenems (i.e., cationic and dithiocarbamate carbapenems), orally available carbapenems, trinem carbapenems, a dual quinolonyl-carbapenem, and others.

Mechanism of action of Carbapenams

• Mechanism of action. As a class of β-lactams, carbapenems are not easily diffusible through the bacterial cell wall . Generally speaking, carbapenems enter Gram-negative bacteria through outer membrane proteins (OMPs), also known as porins. After transversing the periplasmic space, carbapenems “permanently” acylate the PBPs (for the mechanism, . PBPs are enzymes (i.e., transglycolases, transpeptidases, and carboxypeptidases) that catalyse the formation of peptidoglycan in the cell wall of bacteria

What are Current Insights • Current insights into this

process suggest that the glycan backbone forms a right-handed helix with a periodicity of three per turn of the helix . Carbapenems act as mechanism-based inhibitors of the peptidase domain of PBPs and can inhibit peptide cross-linking as well as other peptidase reactions.

What are Current Insights • A key factor of the efficacy of

carbapenems is their ability to bind to multiple different PBPs . Since cell wall formation is a dynamic “three-dimensional process” with formation and autolysis occurring at the same time, when PBPs are inhibited, autolysis continues . Eventually the peptidoglycan weakens, and the cell bursts due to osmotic pressure.

Microbiological activity• Carbapenems demonstrate an

overall broader antimicrobial spectrum in vitro than the available penicillin's, cephalosporins, and β-lactam/β-lactamase inhibitor combinations . In general, imipenem, panipenem, and doripenem are potent antibiotics against Gram-positive bacteria

Every Carbapenem has Different potentials

• Meropenem, biapenem, ertapenem, and doripenem are slightly more effective against Gram-negative organisms . Important considerations here are the following: (i) ertapenem has a more limited spectrum, because it is not as active as imipenem or Meropenem against P. aeruginosa ; (ii) Meropenem is not as potent as imipenem or doripenem against Acinetobacter baumannii

Meropenem in Resistant Mycobacterial Infections

• A unique application of Meropenem is that when combined with clavulanic acid, it is potent at killing MDR Mycobacterium tuberculosis, a bacterium that typically is not susceptible to β-lactams due to a chromosomally expressed β-lactamase . This ability to inhibit or kill M. tuberculosis is likely to be a property of other carbapenems as research in this area grows.

Carbapenems can be Combined with other

Antimicrobials • Carbapenems can also be

combined with other antimicrobials to treat serious infections. Combination therapy is a subject of intense interest, since the emergence of MDR pathogens often requires us to treat patients with more than one antibiotic

Safety and Tolerability• Nephrotoxicity, neurotoxicity,

and immunomodulation have been reported with the use of carbapenems, and thus predisposing factors should be considered when administering any carbapenem . In addition, the use of carbapenems can alter the intestinal microflora and select for carbapenem-resistant isolates

Carbapenems are Important Antibiotics in clinical care

• Carbapenems play a critically important role in our antibiotic armamentarium. Of the many hundreds of different β-lactams, carbapenems possess the broadest spectrum of activity and greatest potency against Gram-positive and Gram-negative bacteria.

Used as last line life saving Drugs

• They are often used as “last-line agents” or “antibiotics of last resort” when patients with infections become gravely ill or are suspected of harbouring resistant bacteria . Unfortunately, the recent emergence of multidrug-resistant (MDR) pathogens seriously threatens this class of lifesaving drugs

Recent studies show • Several recent studies clearly

show that resistance to carbapenems is increasing throughout the world . Despite this menacing trend, our understanding of how to best use these agents is undergoing a renaissance, especially concerning their role with regard to β-lactamase inhibition

Major Mechanism of Drug Resistance in Bacteria

Spectrum of ActivityDrug

Strep spp. &MSSA

Entero-bacteriaeae

Non-fermentors Anaerobes

Imipenem + + + +

Meropenem + + + +

Ertapenem + + Limited activity +

Doripenem + + + +

MECHANISMS OF RESISTANCE AGAINST

CARBAPENEMS• Many nonterminating Gram-negative bacteria (e.g., Pseudomonas spp., Acinetobacter spp., and Stenotrophomonas spp.), as well as the Enterobacteriaceae (e.g., Klebsiella spp., Escherichia coli, and Enterobacter spp.) and Gram-positive bacteria (e.g., Staphylococcus spp., Streptococcus spp., Enterococcus spp., and Nocardia spp.), are or are becoming resistant to most clinically available carbapenems. This distressing pattern poses a major public health threat.

MECHANISMS OF RESISTANCE AGAINST CARBAPENEMS

• Mechanisms of resistance to carbapenems include production of β-lactamases, efflux pumps, and mutations that alter the expression and/or function of porins and PBPs . Combinations of these mechanisms can cause high levels of resistance to carbapenems in certain bacterial species, such as Klebsiella pneumoniae, P. aeruginosa, and A. baumannii

How are Carbapenems Used?Uses by Clinical Syndrome• Bacterial meningitis• Hospital-associated sinusitis• Sepsis of unknown origin• Hospital-associated

pneumonia

Use by Clinical Isolate Acinetobacter spp. Pseudomonas aeruginosa Alcaligenes spp. Enterobacteriaceae

Mogenella spp. Serratia spp. Enterobacter spp. Citrobacter spp. ESBL or AmpC + E. coli

and Klebsiella spp.Reference: Sanford Guide

Emerging Carbapenem Resistance in Gram-Negative

Bacilli• Significantly limits treatment options for life-threatening

infections

• No new drugs for gram-negative bacilli

• Emerging resistance mechanisms, carbapenemases are mobile,

• Detection of carbapenemases and implementation of infection control practices are necessary to limit spread

Carbapenem Resistance: MechanismsEnterobacteriaceae Cephalosporinase + porin loss

Carbapenemase

P. aeruginosa Porin loss

Up-regulated efflux

Carbapenemase

Acinetobacter spp. Cephalosporinase + porin loss

Carbapenemase

CarbapenemasesClassification Enzyme Most Common Bacteria

Class A KPC, SME, IMI, NMC, GES

Enterobacteriaceae(rare reports in P. aeruginosa)

Class B(metallo-b-lactamse)

IMP, VIM, GIM, SPM

P. aeruginosaEnterobacteriaceaAcinetobacter spp.

Class D OXA Acinetobacter spp.

Klebsiella Pneumoniae Carbapenemase

• KPC is a class A b-lactamase• Confers resistance to all b-lactams including extended-

spectrum cephalosporins and carbapenems

• Occurs in Enterobacteriaceae• Most commonly in Klebsiella pneumoniae• Also reported in: K. oxytoca, Citrobacter freundii,

Enterobacter spp., Escherichia coli, Salmonella spp., Serratia spp.,

• Also reported in Pseudomonas aeruginosa (Columbia)

Susceptibility Profile of KPC-Producing K. pneumoniae

( Learn from Antibiograms ) Antimicrobial Interpretation Antimicrobial InterpretationAmikacin I Chloramphenicol RAmox/clav R Ciprofloxacin RAmpicillin R Ertapenem RAztreonam R Gentamicin RCefazolin R Imipenem RCefpodoxime R Meropenem RCefotaxime R Pipercillin/Tazo RCetotetan R Tobramycin RCefoxitin R Trimeth/Sulfa RCeftazidime R Polymyxin B MIC >4mg/mlCeftriaxone R Colistin MIC >4mg/mlCefepime R Tigecycline S

KPC Enzymes• Located on plasmids; conjugative

and nonconjugative

• blaKPC is usually flanked by transposon sequences

• blaKPC reported on plasmids with:• Normal spectrum b-lactamases• Extended spectrum b-lactamases• Aminoglycoside resistance

KPC’s in EnterobacteriaceaeSpecies Comments

Klebsiella spp. K. pneumoniae-cause of outbreaksK. oxytoca-sporadic occurrence

Enterobacter spp.

Sporadic occurrence

Escherichia coli

Salmonella spp.

Citrobacter freundii

Serratia spp.

Pseudomonas aeruginosa – Columbia & Puerto Rico

Laboratory Detection of KPC-

ProducersProblems:1) Some isolates

demonstrate low-level carbapenem resistance

2) Some automated systems fail to detect low-level resistance

Can Carbapenem Susceptibility of I or R Detect

KPC-Producers?Method

Sens/Spec (%) for Detection of KPC-mediated R*

Imipenem Meropenem Ertapenem

Ref BMD 94/93 94/98 97/89

Disk Diffusion 42/96 71/96 97/82

Etest 55/96 58/96 90/84

Vitek Legacy 55/96 52/98 N/A

Vitek 2 71/98 48/96 94/93

MicroScan 74/96 84/98 100/89

Phoenix 81/96 61/98 N/A

*N = 76 K. pneum, K. oxy, E. coli; 31 KPC-producers & 45 non-KPC producers

CAP Results (D-05)KPC-producing Klebsiella

pneumoniaeSusceptible Results

MIC Method Disk Method

Imipenem 63 57

Meropenem 63 18

Ertapenem 0 0

Phenotypic Tests for Carbapenemase Activity

• Modified Hodge Test

• 100% sensitivity in detecting KPC; also positive when other carbapenemases are present

• 100% specificity

Procedure described by Lee et al. CMI, 7, 88-102. 2001.

Modified Hodge TestLawn of E. coli ATCC 25922 1:10 dilution of a 0.5 McFarland suspension

Imipenem disk

Test isolates

Described by Lee et al. CMI, 7, 88-102. 2001.

Modified Hodge Test

• Preliminary results suggest that any of the three carbapenem disks work in the Modified

Hodge Test

What Labs Should Do Now• Look for isolates of Enterobacteriaceae (especially K.

pneumoniae), with carbapenem MIC ≥ 2 mg/ml or nonsusceptible to ertapenem by disk diffusion

• Consider confirmation by Modified Hodge Test• Can submit initial isolate to CDC via NJ State Lab for

confirmation by blaKPC PCR if KPC-producers not previously identified in hospital’s isolate, or any other reference laboratories experienced with genomic methods Alert clinician and infection control practitioner to possibility of mobile carbapenems in isolate

We have no Appropriate Documentation on Carbapenem

resistance • Outbreaks of carbapenem-

resistant Escherichia coli and Klebsiella pose significant public health threats, but there is currently no surveillance network that alerts public health officials when outbreaks occur or provides easily-accessible information about the strains involved.

Documentation of Antibiograms is Highly

essential to reduce Antibiotic Resistance

Scientific Documentation is highly Essential

• The Weissman Lab and collaborators created CaseFinder.org, which tracks Carbapenem-resistant Enterobacteriaceae (CRE) infections in the continental United States.

• Hope India urgently needs one to forecast trends in our own country

Why Carbapenems cannot be Misused

• The discovery of a β-lactam (e.g., carbapenem) with PBP and β-lactamase inhibitory properties was a major breakthrough in infectious disease therapeutics. The carbapenems are often agents of “last resort” for many complicated bacterial infections. As MDR pathogens continue to emerge, the sustained study of the development of novel carbapenems is an essential undertaking.

References and Adopted from • Carbapenem Resistance in Enterobacteriaceae Jean B.

Patel, PhD, (D)ABMM Leader, Antimicrobial Resistance Team Division of Healthcare Quality Promotion CDC

• Carbapenems: Past, Present, and Future Krisztina M. Papp-Wallace1,2, Andrea Endimiani1,2,3, Magdalena A. Taracila2 and Robert A. Bonomo American Society for Microbiology Antimicrobial Agents and Chemotherapy

Dr.T.V.Rao MD 41

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