MICR 454L Emerging and Re-Emerging Infectious Diseases Lecture 6: E. coli Dr. Nancy McQueen & Dr. Edith Porter

Overview Morphology Growth and metabolic characteristics O and H antigens Pathogenicity factors including toxins Diseases Diagnostic 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 inoculatedE. coli

O- Antigens and H- Antigens in Enterobacteriaceae Refer to surface structures H-antigen is part of flagella “Hauch” [extremely thin layer, caused by swarming] O-antigen located on LPS “Ohne Hauch” [“without breeze”, without extremely thin layer] High antigenic variability Serotyping with antibodies against O- and H-antigen For example > 2,000 serotypes of S. enteritidis

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 for Serological Assays Diagnostic tests that are based on antigen- antibody reactions Agglutination Immunofluorescence ELISA Western Immunoblotting

E. coli: Pathogenicity Factors Pili Adherence to urothel Urinary tract infection Capsules New born meningitis (K1 serotype) Toxins Various enterotoxins Various types of diarrhea Hemolysins

E. coli and Gastroenteritis DesignationToxinSymptoms EnterotoxigenicETECEnterotoxin,watery (traveler’s) diarrhea EnteroinvasiveEIECType III secretion system invasive, bloody diarrhea EnteropathogenicEPECAttachment to enterocytes via pili bundles mucoid diarrhea EnteroaggregativeEAECBiofilm formation Enterotoxin watery diarrhea EnterohemorrhagicEHECShiga-like toxincytotoxic, bloody diarrhea

Association of Serotype with Pathogenicity Hemorrhagic uremic syndrome (HUS) Acute renal failure in children (and adults) Microangiopathic anemia Thrombotic thrombocytopenia Renal failure Shiga toxin-producing EHEC Escherichia coli serotype O157:H7 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

Kidney Damage in Hemolytic Uremic Syndrome DiseasedNormal

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 risk

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 Outbreak of E. coli O157:H7 26 states were affected, with at least 200 cases 3 deaths were Traced to organic bagged fresh spinach - sold as conventional produce Originated from irrigation water contaminated with cattle feces or from grazing deer

2007 Multistate Outbreak of E. coli O157:H7 Infections Linked to Topp's Brand Ground Beef Patties 21.7 millions pounds of frozen ground beef patties recalled 33 ill persons for whom hospitalization status is known 21 (64%) were hospitalized 2 developed hemolytic-uremic syndrome (HUS) No deaths 18 (45%) patients were female 50% were between 15 and 24 y only 14% of the US population is in this age group

Enjoy Your Meals?

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.

Additional Resources ASM Microbe library Madigan & Matinko, Brock Biology of Microorganism, 11 th edition.