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Lec 1 Enterobacteriaceae

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    Enterobacteriaceae

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    Enterobacteriaceae

    Classification more than15 different genera Escherichia

    Shigella

    Salmonella Citrobacter

    Klebsiella

    Enterobacter

    Serratia

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    Enterobacteriaceae

    Proteus

    Providencia

    Morganella

    Yersinia

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    Enterobacteriaceae

    Morphology and General Characteristics

    Gram-negative, non-sporing, rod shaped bacteria

    Oxidase

    Ferment glucose and may or may not produce gasin the process (aerogenic vs anaerogenic)

    Reduce nitrate to nitrite (there are a fewexceptions)

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    Enterobacteriaceae

    Are facultative anaerobes

    If motile, motility is by peritrichous flagella

    Many are normal inhabitants of the intestinal tract

    of man and other animals Some are enteric pathogens and others are urinary

    or respiratory tract pathogens

    Differentiation is based on biochemical reactions

    and differences in antigenic structure

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    Enterobacteriaceae

    Some are found primarily in the colon of thehuman and other animals, many as part of thenormal flora; e.g. Escherichia, Klebsiella,

    Enterobacter, Serratia, and Citrobacter(collectively called the coliform bacilli).

    They are opportunistic pathogens that causenosocomial infections.

    Salmonella, Shigella, Proteusand Yersiniaarepathogenic.

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    Enterobacteriaceae

    Most grow well on a variety of lab media includinga lot of selective and differential media originallydeveloped for the the selective isolation of entericpathogens.

    Most of this media is selective by incorporation ofdyes and bile salts that inhibit G+ organisms andmay suppress the growth of nonpathogenicspecies of Enterobacteriaceae.

    Many are differential on the basis of whether ornot the organisms ferment lactose and/or produceH2S.

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    Enterobacteriaceae

    On BA they may or may not be hemolytic.

    The antigenic structure is used todifferentiate organisms within a genus or

    species. Three major classes of antigens are found:

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    Enterobacteriaceae

    Somatic Oantigens these are the heat stablepolysaccharide part of the LPS.

    Variation from smooth to rough colonial forms isaccompanied by progressive loss of smooth O Antigen.

    Flagellar H antigens are heat labile

    Envelope or capsule K antigens overlay thesurface O antigen and may block agglutination by

    O specific antisera. Boiling for 15 minutes will destroy the K antigen and

    unmask O antigens.

    The K antigen is called the Vi (virulence) antigen in

    Salmonella typhi.

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    Enterobacteriaceae

    Diseases caused by members of Enterobacteriaceae

    Major Pathogen and Disease

    E. coli: Urinary Tract (UT) Infection, neonatal meningitis,traveler's diarrhea.

    Shigella: Dysentery

    Salmonella: Typhoid fever, enterocolitis

    Klebsiella, Enterobacter, Serratia: Pneumonia, UT

    infections. Proteus: UT infections

    Yersinia: Plague, entercolitis

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    Enterobacteriaceae

    Escherichia coli Normal inhabitant of the G.I. tract.

    Some strains cause various forms ofgastroenteritis.

    Is a major cause of urinary tract infection andneonatal meningitis and septicemia.

    May have a capsule.

    Biochemistry Most are motile.

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    E. coli

    May be hemolytic on BA more commonin pathogenic strains

    KEY tests for the normal strain: TSI is A/A + gas

    Urea

    Indole +

    Citrate

    Motility +

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    E. coli

    E. coliand related bacteria possess theability to transfer DNA via bacterialconjugation, transduction or

    transformation, which allows geneticmaterial to spread horizontally throughan existing population. This process led

    to the spread of the gene encoding shigatoxin from Shigellato E. coliO157:H7,carried by a bacteriophage.

    http://en.wikipedia.org/wiki/Shigellahttp://en.wikipedia.org/wiki/E._coli_O157:H7http://en.wikipedia.org/wiki/E._coli_O157:H7http://en.wikipedia.org/wiki/Bacteriophagehttp://en.wikipedia.org/wiki/Bacteriophagehttp://en.wikipedia.org/wiki/E._coli_O157:H7http://en.wikipedia.org/wiki/E._coli_O157:H7http://en.wikipedia.org/wiki/E._coli_O157:H7http://en.wikipedia.org/wiki/E._coli_O157:H7http://en.wikipedia.org/wiki/E._coli_O157:H7http://en.wikipedia.org/wiki/Shigella
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    E. coli

    Antigenic structure - has O, H, and K antigens. K1has a strong association with virulence, particularly

    meningitis in neonates.

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    E. coli

    Virulence factors Toxins: Enterotoxins produced by enterotoxigenic

    strains of E. coli(ETEC). Causes a movement of waterand ions from the tissues to the bowel resulting in waterydiarrhea.

    There are two types of enterotoxin:

    LT is heat labile and stimulates adenylate cyclase toincrease production of cAMP. Increased cAMP alters theactivity of sodium and chloride transporters producing an

    ion imbalance that results in fluid transport into thebowel.

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    E. colitoxins

    ST

    is heat stable and binds tospecific receptors to stimulate the

    production of cGMP with the sameresults as with LT.

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    LT vs ST activity

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    E. colitoxins

    Both enterotoxins are composed offive beta subunits (for binding) and1 alpha subunit (has the toxic

    enzymatic activity).

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    E. colitoxins

    Shiga-type toxin also called the verotoxin -produced by enterohemorrhagic strains of E.coli(EHEC) is cytotoxic, enterotoxic,neurotoxic, and may cause diarrhea and

    ulceration of the G.I. tract.

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    E. colitoxins

    Enteroaggregative ST-like toxin produced byenteroaggregative strains of E. coli(EAEC)causes watery diarrhea.

    Hemolysins

    They lyse RBCs and leukocytes and may help toinhibit phagocytosis when cell bound.

    Endotoxin

    Involved in inducing uptake of EIEC into intestinalcells.

    Involved in development of an attachment andeffacing lesion in EPEC characterized by microvilli

    destruction and pedestal formation.

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    Pedestal formation

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    E. coli

    Adhesions are also called colonizationfactors and include both pili or fimbriaeand involved in attachment

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    E. coli

    Clinical significance Is the leading cause of urinary tract

    infections which can lead to acutecystitis (bladder infection) andpyelonephritis (kidney infection).

    the source of the E. colithatcauses urinary tract infections is

    the patient's own colonic florathat colonizes the urogenital

    area.

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    E. coliinfections

    Neonatal meningitis

    is the leading cause of neonatalmeningitis and septicemia with a high mortality rate.

    Usually caused by strains with the K1 capsular antigen.

    Gastroenteritis there are several distinct types of E.

    colithat are involved in different types ofgastroenteritis:

    Enterotoxigenic E. coli(ETEC),

    Enteroinvasive E. coli(EIEC),

    Enteropathogenic E. coli(EPEC) , Enteroaggregative E. coli(EAEC), and

    Enterohemorrhagic E. coli(EHEC).

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    E. coli gastroenteritis

    Transmission of E. colicausing diarrheais by the fecal-oral route.

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    E. coli gastroenteritis

    ETEC is a common cause of travelersdiarrhea and diarrhea in children in developingcountries.

    The organism attaches to the intestinal mucosa

    via colonization factors and then liberatesenterotoxin. The disease is characterized by a watery

    diarrhea, nausea, abdominal cramps and low-grade fever for 1-5 days.

    Transmission is via contaminated food orwater.

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    E. coli gastroenteritis

    EPEC The exact mode of pathogenesis is unclear, but it

    is probably due to the attachment and effacement. Diarrhea with large amounts of mucous without

    blood or pus occurs along with vomiting, malaiseand low grade fever. This is a problem mainly in hospitalized infants

    and in day care centers.

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    E. coli gastroenteritis

    EIEC The organism attaches to the intestinalmucosa via pili and outer membrane proteinsare involved in direct penetration, invasion ofthe intestinal cells, and destruction of the

    intestinal mucosa. Symptoms include fever,severe abdominal

    cramps, malaise, and watery diarrhea followedby scanty stools containing blood, mucous, andpus.

    occasional abdominal pain.

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    E. coli gastroenteritis

    EAEC Mucous associated autoagglutininscause aggregation of the bacteria at the cellsurface and result in the formation of amucousbiofilm.

    The organisms attach via pili and liberate acytotoxin distinct from, but similar to the STand LT enterotoxins liberated by ETEC.

    Symptoms include watery diarrhea, vomiting,

    dehydration and occasional abdominal pain.

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    E. coli gastroenteritis

    EHEC The organism attaches via pili to theintestinal mucosa and liberates the shiga-liketoxin.

    a watery diarrhea that progresses to bloodydiarrhea without pus with no fever or a low-gradefever.

    This may progress to hemolytic-uremic syndromethat is characterized by low platlet count,hemolytic anemia, and kidney failure.

    This is most often caused by serotypesO157:H7.

    This strain of E. colican be differentiated fromother strains of E. coli by the fact that it does not

    ferment sorbitol

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    Different E. colistrains that cause diarrhea

    EPECEHEC

    EIEC

    ETEC

    No exotoxins

    Verotoxin or"shiga like"

    exotoxin

    No exotoxin,only the

    cytotoxic effectof the endotoxin

    Produce twoexotoxins

    heat labile andheat stable toxin.

    Not invasive, noinflammation

    Not invasive, noinflammation

    Invasive,inflammation

    Not invasive, noinflammation

    Watery diarrhea

    with fever,nausea and

    vomiting.

    Haemorrhagic

    colitis, bloodystool, mild fever

    and severeabdominalcramps.

    Dysentery

    bloody stool.

    Traveler's

    diarrhea,dehydration in

    infants.

    EAEC

    Hemolysinand ST

    enterotoxin

    Not invasive

    Watery

    diarrheawithout fever

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    E.coli

    Antimicrobic therapy- E. coliis usuallysusceptible to a variety of chemotherapeuticagents, though drug resistant strains are

    increasingly prevalent. It is essential to do susceptibility testing.

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    Enterobacteriaceae

    Citrobacter Are opportunistic pathogens causing urinary

    tract or respiratory tract infections

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    Enterobacteriaceae

    Klebsiella NF of GI tract, but potential pathogen in other areas

    Has both O and K antigens

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    Klebsiella

    Virulence factors

    Capsule

    Adhesions

    Clinical significance

    Causes pneumonia, mostly in immunocompromised hosts.

    Permanent lung damage is a frequent occurrence (rare inother types of bacterial pneumonia)

    A major cause of nosocomial infections such assepticemia and meningitis

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    Enterobacteriaceae

    Enterobacter NF of GI tract

    Citrate +

    Clinical significance Nosocomial infections

    Bacteremia in burn patients

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    Enterobacteriaceae

    Serratia A free-living saprophyte

    Has been found in RT and UT infections

    Is resistant to many antimicrobics

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    Enterobacteriaceae

    Proteus, Providencia, and Morganella Are all part of the NF of the GI tract (except

    Providencia).

    All motile, with Proteusswarming

    Urea + for most, strongly + for Proteus

    TSI variable (know the reactions for each in thelab!)

    Indole only P. mirabilisis -

    Proteus Providencia and

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    Proteus, Providencia, andMorganella

    Virulence factors Urease the ammonia produced may damage the

    epithelial cells of the UT

    Clinical Significance

    UT infections, as well as pneumonia, septicemia, andwound infections

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