Lec 1 Enterobacteriaceae

8/2/2019 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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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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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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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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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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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


Invasive,inflammation


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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Lec 1 Enterobacteriaceae