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MICR 454L
Emerging and Re-EmergingInfectious Diseases
Lecture 6:E. coli
Dr. Nancy McQueen & Dr. Edith Porter
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Overview
Morphology Growth and metabolic characteristics O and H antigens Pathogenicity factors including toxins Diseases Diagnostic
Culture Serotyping Cytotoxicity PCR: toxin production
Therapy Threats
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E. coli
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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
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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
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Gram-Negative Cell Wall
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Lipopolysaccharide (LPS)
O-Antigen
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The Gram-Negative Flagella and Flagellin
H-antigen
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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.
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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
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Examples for Serological Assays
Diagnostic tests that are based on antigen-antibody reactions
Agglutination Immunofluorescence ELISA Western
Immunoblotting
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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
http://library.med.utah.edu/WebPath/CNSHTML/CNS061.html
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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
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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
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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%
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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
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Kidney Damage in Hemolytic Uremic Syndrome
http://www.gamewood.net/rnet/renalpath/t14.jpg
DiseasedNormal
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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
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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
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The 2006 North American Outbreakof 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
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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
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Enjoy Your Meals?
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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.
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Additional Resources
ASM Microbe library Madigan & Matinko, Brock Biology of
Microorganism, 11th edition. www.cdc.org