MICR 420

Emerging and Re-EmergingInfectious Diseases

Lecture 5:E. coli

Dr. Nancy McQueen & Dr. Edith Porter

Overview

Morphology Growth and metabolic characteristics O and H antigens Virulence factors including toxins Diseases Diagnosis

Culture Serotyping Cytotoxicity PCR: toxin production

Therapy Threats

E. coli

E. coli: Morphology and Metabolic Characteristics

Gram-negative rods LPS: O-antigen

Motile Flagella: H-antigen

Enterobacteriaceae Facultative anaerobic Nitrate positive Oxidase negative

Lactose positive Normal flora in intestine

(non-toxigenic strains)

TSI

Not inoculated E. coli

O- Antigens, H- Antigens and K- Antigens in Enterobacteriaceae

Refer to surface structures H-antigen is part of flagella O-antigen located on LPS K or Vi- (Samonella) antigen - capsule

High antigenic variability

Gram-Negative Cell Wall

Lipopolysaccharide (LPS)

O-Antigen

The Gram-Negative Flagella and Flagellin

H-antigen

Antigens and Antibodies

Antigen is a molecule (free or cell associated) that induces the production of measurable antibody titers.

Antibodies are glycoproteins that specifically bind to their antigens.

Serotyping: Generation of Specific Antibodies

Purified antigens (e.g., O157 or H7) are injected repeatedly into an animal Rabbit

Animal produces high levels of antibodies against the specific antigen

Blood is drawn and serum prepared

Serum contains high concentrations of specific antibodies

Examples of Serological Assays

Diagnostic tests that are based on antigen-antibody reactions

Agglutination Immunofluorescence ELISA Western

Immunoblotting

E. coli: Virulence Factors and Diseases

Pili Adherence to epithelial

cells of urethra Urinary tract infection

Capsules New born meningitis (K1

serotype) Toxins

Various enterotoxins Various types of

diarrhea Hemolysins

http://library.med.utah.edu/WebPath/CNSHTML/CNS061.html

E. coli and Gastroenteritis

Designation Toxin Symptoms

Enterotoxigenic ETEC Enterotoxin, watery (traveler’s)

diarrhea

Enteroinvasive EIEC Type III secretion system

invasive, bloody diarrhea

Enteropathogenic EPEC Attachment to enterocytes via pili bundles

mucoid diarrhea

Enteroaggregative EAEC Biofilm formation

Enterotoxin

watery diarrhea

Enterohemorrhagic EHEC Shiga-like toxin cytotoxic, bloody diarrhea

Various types of E. coli

Association of Serotype with Pathogenicity

Shiga toxin-producing EHEC Escherichia coli serotype O157:H7

Hemorrhagic uremic syndrome (HUS)

Acute renal failure in children (and adults) Microangiopathic anemia Thrombotic thrombocytopenia Renal failure

Sorbitol negative

Phase contrast

Anti-O157:H7

Main Sympotms of HUS

Episode of diarrhea Acute and severe onset Bleeding (hematemesis or melena) Severe oliguria (no urine production) Hematuria (blood in urine) Neurologic changes in 1/3 Hypertension in 50%

Pathogenesis of Hemolytic Uremic Syndrome Shigatoxin mediated Locally produced Absorbed across the gut

epithelium into the circulation

Transported to small vessel endothelial cells

Microvascular endothelial damage Inhibition of protein

synthesis Apoptosis Platelet activation

K. S. Sandhu and C. L. Gyles (2002)

Normal Villus

+Stx

+Stx +Stx

Kidney Damage in Hemolytic Uremic Syndrome

http://www.gamewood.net/rnet/renalpath/t14.jpg

DiseasedNormal

E. coli: Diagnosis

Culture using Sorbitol Mac ID using biochemicals Serotyping

Cytotoxicity assay PCR to identify toxin genes

Therapy

Symptomatic Non-specific supportive therapy

Hydration Electrolytes

Antibiotics should not be used No evidence that treatment with antibiotics is

helpful Taking antibiotics may increase the risk of HUS Antidiarrheal agents like Imodium® may also

increase that riskhttp://www.cdc.gov/nczved/dfbmd/disease_listing/stec_gi.html#14

Threats by E. coli O157

An estimated 73,000 cases occur annually in the United States

2,100 hospitalizations annually Estimated 61 fatal cases annually Major sources: spinach and undercooked

ground beef Easily spread from person to person Nationally reportable

The 2006 North American Outbreakof E. coli O157:H7

26 states were affected, with at least 200 cases

3 deaths Traced to organic bagged

fresh spinach - sold as conventional produce

Originated from irrigation water contaminated with cattle feces or from grazing deer

2009 Multistate Outbreak of E. coli O157:H7 Infections 2009: recall of approximately 545,699 pounds of ground beef

products from Fairbank Farms that may be contaminated with E. coli O157:H7.

A cluster of individuals including 26

persons from 8 states were infected

with matching strains of E. coli O157:H7. Nineteen hospitalized

Five developed HUS Two deaths

50% of patients male 38% less than 18 years old

Less than 14% of the US population is

in this age group

Other recent E. coli O157 H7 outbreaks Prepackaged Cookie Dough (June, 2009)

72 infected 34 hospitalized 10 HUS No deaths Beef from JBS Swift Beef Company (July 2009) 23 infected 12 hospitalized 2 HUS No deaths

Daycare Center in Washington (March- April, 2010) 4 children hospitalized 1 death

Take Home Message

E. coli part of normal flora but toxin producing strains can cause great damage

Various toxins lead to characteristic diseases. Major public threat is strain O157:H7 because of

possible fatal outcome and frequent outbreaks. Note – other strains of E. coli are now reported

to produce the Shiga-like toxin and cause HUS

Additional Resources

ASM Microbe library Madigan & Matinko, Brock Biology of

Microorganism, 11th edition. www.cdc.org