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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/Shigella8/2/2019 Lec 1 Enterobacteriaceae
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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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