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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: 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
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
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