Escherichia Coli Flashcards
E. coli
E. coli is an enteric like Salmonella and Shigella
- part of the normal microflora, synthesizes vitamin K and protects against other pathogens
- specific strains have evolved to become serious GI pathogens by acquiring virulence genes
E. coli pathogens
Enterohemorrhagic and Shiga Toxin E. coli (EHEC and STEC) Enteropathogenic E. coli (EPEC) Enteroaggregative E. coli (EAEC) Enteroinvasive E. coli (EIEC) Enterotoxigenic E. coli (ETEC)
Overview of E. coli epidemiology relating to intestinal disease
2-4 billion episodes of diarrhea in developing countries
3-5 million deaths
25-50% of cases are due to E. coli
important agents of food poisoning
Enterohemorrhagic E. coli (STEC) general features
Main serogroup is 0157:H7 sources of infection: food (undercooked, contaminated ground beef, leafy vegetables, unpasteurized apple cider/juice, raw milk./dairy) petting zoos person-person contact low infectious dose
Enterohemorrhagic E. coli (STEC) –Clinical Syndrome
Ab pain
Bloody diarrhea
Toxins can spread leading to hemolytic uremic syndrome (HUS)–Results in 7% of cases due to destruction of RBCs adn damage to lining blood vessel walls
acute renal failure in severe cases (usually in children under 10 or elderly)
cells remain largely extracellular (some strains can invade mucosal cells) but does not become systematic
Enterohemorrhagic E. coli (STEC) –virulence determinants and pathogenicity
Pili-mediated attachment (relatively weak)
-E. coli common pilus
T3SS induces formation of attaching.effacing lesions
genes for T3SS dncoded on LEE patho island
-LEE (locus for enterocyte effacement) encodes intimin and tir.
Tir: a T3SS-secreted bacterial protein that is delivered to surface of epithelial cells to allow for E. coli attachment
Intimin: Tir binding protein on surface of E. coli
Other E. coli proteins can recruit host cell actin, causing altered morphology and impact signal transduction leading to lesions
lesions lead to effacment (destruction of host cell microvilli)
Shiga-like toxin:
similar to shiga toxin
gene found on phage
disrupts eurkaryotic protein sytnethesis and is cytotoxic
-via RNA cleavage activity
-HUS is due to shiga-like toxin
hemolysin
-pore forming protein that inserts into host cell membranes-common in E. coli strains that cause meningitis - present in other gram-negative pathogens
Capsule (K-antigen)- LPS and nutrient acquisitions pathways
Diarrheagenic E. coli
Enteropathogenic E. coli (EPEC)
transmitted person-person
leading cause of childhood diarrhea in developing countries- over 100 million cases per year
forms A/E lesions
localized adherence by bundle forming pili
toxins not detected in stool of infected human volunteers
Diarrheagenic E. coli
Enterotoxigenic E. coli (ETEC)
traveler’s diarrhea and problematic in infants in the developing world
fimbriae adhere to specific receptors on enterocytes in small intestine
Heat-labile toxin (LT) which targets adenlyate cyclase leading to increased cAMP —results in excess Cl ion secretion and blocked sodium ion uptake–leads to net loss of fluid and electrolytes into lumen of the gut and watery diarrhea
Heat-stable toxin (ST)-= alters cGMP levles with similar outcome to LT enterotoxin
Diarrheagenic E. coli
Enteroaggregative E. coli (EAEC)
Childhood diarrhea similar to EPEC, common in developing countries
can cause persistent diarrhea that can lead to weight loss
Somewhat more aggressive than EPEC due to different colonziation factors that lead to more aggressive epithelial cell attachment
No A/E lesions and non-invasive
Heat-stable like toxin called enteroaggregative stable toxin (EAST), a poorly characterized plasma encoded toxin (pet) and hemolysin produced
Diarrheagenic E. coli
Enteroinvasive E. coli (EIEC)
Less common in industrial countries
attaches to cells within the colon by non-fimbrial adhesins
invades mucosal cells, multiplies within these cells but does not become systemic
cliinical syndrome is similar to shigella dysentary with water diarrhea that can have blood/mucus
genes for invasion, replication within host and survival encoded by a plasmid that contains genes very similar to those in Shigella
EIEC strains do not produce ST and LT
Diarrheagenic E. coli
Diffuse adhering E. coli (DAEC)
Diarrhea in older children in developing countries
poorly characterized, may be a heterogeneous collection of strains
Diagnostics
E. coli is Lac+, easily discerned on EMB or MacConkey agar
main diagnostic tools for 0157:H7
-Cannot grow on sorbitol
-serology- direct or latex agglutination tests (to identify 0157 antigen)
immunoassay for shiga like toxin
PCR or DNA probe analysis of virulence genes is importnat to identify strains
tissue culture assays
strain typing (Pulse field electrophoresis) important in tracing outbreak
Prevention
2010 FDA report finds 28% of cattle shed EHEC
grain fed cattle harbor more E. coli and are more resistant to acid shock, hay feeding leads to higher pH and lack of acid adaption of pathogenic E. coli
hygiene is key
