Mechanism of action
Factors affects growth
Enterohemorrhagic Escherichia coli
E.coli is a gram negative bacteria present in the form of rods(bacillus) in the Enterobacteriaceae. Mostly E.coli are normal commensals of intestines so that isolation of pathogenic strains on the basis of Virulence factors e.g toxins. EHEC group produces shiga-like toxins (stx), enterohemolysin, ...view middle of the document...
Bacteria mostly present in animal feces e.g cattle. Contact to feces lead to contamination of food and fruit.
In 2010, FDA recalled different beef productions e.g beef placed in pet animal.
Mechanism of action
• Consumption of contaminated food or water, bacteria colonize the intestine by attaching to epithelial cells
• Intimin helps intimate adhesion by forming a pedestallike structure a characteristic lesion on microvilli.
• Destruction of villi results in malabsorption and lesion as EPEC
• Hemorrhagic colitis caused by damaging of colon epithelial cells due to production of toxins (stx).
• Toxins absorbed by blood cause damaging of blood vessels in kidneys, intestines, and brain.
• Destruction of large intestine lining cause bleeding.
• Toxins cause kidney damage to kidney failure, destroy RBC,s and clotting of kidney blood vessels lead to HUS, TTP.
Factors affecting survival and growth
Factors as Temperature, pH, Water activity, Antimicrobials.
It shows high degree of acid tolerance, survive at 37°C and pH 2.5 for 2-7hr exposure.
Water activity, NaNO2 conc. (0.5-5.0%), Temp. pH affects growth kinetics of E.coli.
It shows no resistence against antimicrobial foods.
• E.coli produces verotoxins (VTEC), shiga-like toxins (STEC). Stx produces as stx1 and stx2 which binds with Gb3 receptor located in kidney and intestine cells.
• Verotoxins shows cytotoxic effect and derived from kidney of African green monkey.
• Toxins prevent protein synthesis leads to cell death.
• Stx is 70,000 daltons comprises of two subunits as: Subunit B (7.7k dal) helps in specific binding toGb3 receptors and Subunit A (32k dal) has N-glucosidase which inactivates 28S ribosome and inhibit protein synthesis.
• It produces enterohemolysin which encoded by 60-MDa plasmid.
• Indirectly toxins damage cells by releasing cytokines e.g tumor necrosis factor and alone not sufficient to cause infection.
• eae chromosomal gene encoded by outer membrane protein responsible for attachment.
EHEC Infection is contagious and spread person to person by oral-fecal route. CDC shows transmission manners as:
Contaminated meat e.g beef does not smell and looks normal while require proper cooking.
Infection caused by contaminated drinking or swimming water.
Person to person in hospitals and day-care centers.
Usually symptoms appears 3 to 5 days after consumption of contaminated food or water and last 8 days.
• Abdominal pain
• Severe bloody diarrhea
• No fever
Complications, severe forms of EHEC
Three different forms of EHEC as
Hemorrhagic Diarrhea (Hemorrhagic enterocolitis)
• Incubation period and onset of symptoms appears in three to five days or may longer.
• Symptoms as abdominal tenderness, abdominal pain, bloody diarrhea which lasts 6 to 8 days, and little to no fever.
• Dehydration or blood loss cause death.