Esherichia coli

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Esherichia coliGram-negative rodFacultative anaerobe

Named for Theodor EscherichGerman physician (ca. 1885)Demonstrated that particular strains were responsible for infant diarrhea and gastroenteritis

Normal flora of the mouth and intestine Protects the intestinal tract from bacterial infectionAssists in digestionProduces small amounts of vitamins B12 and K

Colonizes newborns GI tract within hours after birth

There are more than 700 different serotypes of E. coliDistinguished by different surface proteins and polysaccharides

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Escherichia

• Escherichia coli– coli- large intestine, colon– Mammalian large intestine

• Escherichia blattae– blattae. L. n. blatta cockroach – Hindgut of cockroach Blatta orientalis

Bergey’s Manual of Systematic Bacteriology

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Escherichia coli K-12 strain • The original E. coli strain K-12 was

obtained from a stool sample of a diphtheria patient in Palo Alto, CA in 1922

• Strain K-12 was used for biochemical and genetic studies for many years – Metabolism– F+ plasmids– Bacteriophages– Operons– Genome sequencing

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Many strains• O antigen

– Somatic (on LPS)– 171 antigens

• H antigen– Flagella– 56 antigens

• K antigen– Capsule and or

fimbrial antigen– 80 antigens

SerotypesAntibody – antigen rxn

O18ac:H7:K1

18th O antigen 1st K antigen

7th H antigen

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EPECEnteropathogenic E. coli

ETECEnterotoxigenic E. coli

EIECEnteroinvasive E. coli

Bergey’s Manual of Systematic Bacteriology

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Summary of the virulence factors of pathogenic strains of E. coli

Fimbriae (Pili)Hemolysins Siderophores FlagellaToxins Endotoxin LPSCapsules K antigens LPSAntigenic variationDrug resistance plasmids Toxin and other virulence plasmids

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Thermolabile toxin (LT)

Thermostable toxin (ST)

Found alone or together

Both are plasmid borne

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Pathogenic Agent

• Urinary Tract Infections• Sepsis / neonatal meningitis • Enteric / diarrheal diseases

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Uropathogenic E. coli UPEC

• Most common form of extraintestinal E. coli infection

• Acute symptomatic UTI– 12% of all men– 10-20% of women– 100,000 patients hospitalized for renal

infections

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Urovirulence Factors AdherenceFimbriae

AerobactinSiderophore

Hemolysis

Capsule

K antigensResist phagocytosisResist complement proteins

Endotoxin

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Neonatal Meningitis E. coli NMEC• Meningitis in an infection of the fluid and membranes that cover the

brain and spinal cord– Bacteria – Viruses – Fungi

• E. coli incites between 1/4 and 1/3 of meningitis cases in newborns– Less than 2% of cases of meningitis at all other ages

• Approximately 1 out of 5 newborns with E. coli meningitis dies – Survivors frequently sustain permanent brain damage

• The majority of cases occur in premature babies• K-1

– 80% of NMEC E. coli strains produce K-1 capsular antigens – K1 capsular polysaccharide – O18ac:H7:K1 – Inhibits phagocytosis

• Siderophore production – Sequesters Fe

• Endotoxin

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Enteric / diarrheal diseases

E. coli can adhere to the mucosa of the large intestine

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Combinations of the O & H antigens identify the serotype

Clinical Microbiology Reviews 1998 11:142-201

ETECEnterotoxigenic E. coli

EPECEnteropathogenic E. coli

EHECEnterohemorrhagic E. coliEAECEnteroaggregative E. coli

EIECEnteroinvasive E. coli

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Enterotoxigenic E. coli ETEC• Adhere to intestinal mucosa by fimbriae• Produce enterotoxins

– Plasmids contain genes for enterotoxins– Cause leakage of intestinal epithelial cells

• Loss of electrolytes & water

• Attach by fimbriae• Cause diarrhea in children & adults• Toxins increase intracellular levels of cAMP• Causes cell leakage• Traveler’s diarrhea• Weanling diarrhea

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Enteropathogenic E. coli EPEC• Attaching & effacing

– Effacement of microvilli

– Adherence between bacterium and epithelial cells

– Unique histopathology

– Locus of enterocyte effacement

Clinical Microbiology Reviews 1998 11:142-201

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Clinical Microbiology Reviews 1998 11:142-201

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Enteroaggregative E. coli EAEC• Adhere to HEp-2

cells– Human laryngeal

carcinoma cells

• Bacterial cells autoagglutinate– Stick to one

another• Do not secrete

enterotoxins

Clinical Microbiology Reviews 1998 11:142-201

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Clinical Microbiology Reviews 1998 11:142-201

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Enteroinvasive E. coli EIEC• Biochemically, genetically, and pathogenetically

closely related to Shigella spp.• Cause watery diarrhea

– Not bloody

• EIEC cells invade intestinal epithelial cells, lyse the phagosomal vacuole, spread through the cytoplasm and infect adjacent cell– Shigella does the same thing

• Plasmid encoding a gene for a K surface antigen– Attach and invade mucosal cells

20Clinical Microbiology Reviews 1998 11:142-201

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Enterohemorrhagic E. coli EHEC

• Severe gastrointestinal distress• Hemorrhagic colitis

– Crampy abdominal pain– Watery diarrhea– Little or no fever– Bloody diarrhea

• New serotype O157:H7– 1983– Undercooked hamburgers

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E. coli 015:H7 Distinguished by serologyCannot be distinguished from all other strains of E. coli using other standard microbiological tests

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E. coli 015:H7• 157th somatic O antigen• 7th flagellar H antigen• Hemorrhagic colitis

– Abdominal cramps, blood stools, with minor or no fever

• Post diarrheal hemolytic ureamic syndrome– Acute renal injury– Thrombocytopenia

• An abnormal decrease in the number of platelets in circulatory blood.

– Microangiopathic hemolytic anemia• The fragmentation of red blood cells

because of narrowing or obstruction of small blood vessels.

• Enterohemorrhagic E. coli– EHEC

• Among the most dangerous enteric pathogens

The Lancet 1998 352:1207-1212

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Reservoir• Healthy cattle are the major

reservoir for human infection– Deer, sheep, goats, horses, dogs, birds

and flies• Bacterial cells can survive in manure

and water troughs• Infection is more common during the

summer in both the northern and southern hemisphere

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• Transmitted via food– Ground beef– Raw milk– Lamb meat– Venison jerky– Salami and other fermented dried meat products– Lettuce, spinach, alfalfa sprouts– Unpasteurized apple cider

• Transmitted via water– Drinking and swimming in unchlorinated water

• Direct person to person contact– Diaper changing– Improper sanitation– Day care & chronic adult care facilities

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Clinical Features• Average interval

between exposure & illness is 3 days

• Most patients recover with 7 days

• 70% of patients report bloody stools

• 30-60% of patients report vomiting

• Approx 5% of patients develop HUS

The Lancet 1998 352:1207-1212

SequelaeA condition following as a consequence of a disease.

ProteinuriaExcess protein in the urine.

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Identification

• MacConkey agar (SMAC)– Does not ferment sorbitol rapidly– Forms colorless colonies on sorbitol

containing MacConkey agar

• Serology– Colorless colonies on SMAC are

screened for the 0157 antigen

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Shiga Toxins• Exotoxin• Very similar to toxin produced by Shigella

dysenteriae– Inhibits protein synthesis in host cell– A subunit inactivates the 60S ribosomal subunit

• Shiga toxin producing E. coli (STEC)– Verotoxins

• Most OH157 strains produce Shiga toxin 2– 25% produce Shiga toxin 1

• Identical to Shigella toxin

• A B exotoxin– A subunit exists on a temperate bacteriophage

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• Cells leak Na+, Cl-, K+, HCO3- and

water• Watery diarrhea• Cramps• Nausea• Vomiting• Bloody stool

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Virulence Factors

• Virulence plasmid (pO157)– Encodes a hemolysin– O157 strains can use iron from blood

released into the intestine

• Locus of enterocyte effacement– Adhesion proteins

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Non O157 Shiga Toxin Producing E. coli

• Several other serotypes of E. coli produce Shiga toxins– O111:nonmotile– O26:H11– O132:H2

• Incite diarrhea, hemorrhagic colitis & HUS

• Labs generally not prepared to identify these strains – Many times go undetected