Fish Microbiology and Quality Assurance

5.4. Foodborne gastroenteritis caused by E. coli

Unit 5 - Foodborne pathogens

5.4. Foodborne gastroenteritis caused by E. coli
E. coli is the most common aerobic organism in the intestinal tract of humans and warm blooded animals. Generally the E.coli strains that colonize the gastrointestinal tract are harmless commensals, and they play an important role in maintaining intestinal physiology. However, certain strains of E. coli are pathogenic and cause gastrointestinal disturbances.

Pathogenic strains
Within the species of E. coli there are at least 4 types of pathogenic strains

• Enteropathogenic E. coli (EPEC)
• Enterotoxigenic E. coli (ETEC)
• Enteroinvasive E. coli (ETEC) or shiga dysentery-like E. coli
• Enterohaemorrhagic E. coli (EHEC) or Verocytotoxin producing E. coli (VTEC) or E. coli 0157:H7

Charcters

• Various E. coli types can be separated by serotyping, phage typing and genetic methods.
• No specified phenotypic marker is available to separate between pathogenic and non-pathogenic strains.
• However, some atypical properties such as being lactose-negative or failure to produce indole at 44ºC are more common between the pathogenic strains.
• VTEC strains do not grow at all on selective media at a 44ºC.
• Disease conditiond produced by pathogenic E. coli strains vary in severity from extremely mild to life-threatening depending on type of pathogenic strains involved, susceptibility of victim and degree of exposure.
• E. coli can be isolated from environments polluted by faecal material or sewage, and the bacterium can multiply and survive for a long time in the environment. There are reports of occurrence of E. coli in unpolluted warm tropical waters.
• Most infections are related to contamination of water or handling of food under unhygienic conditions. Seafoods have not been reported as important source of E. coli infection.

Prevention of food poising outbreaks

• Good personal hygiene and health education of food handlers are essential in the control of disease.
• Proper treatment (e.g. chlorination) of water and sanitary disposal of sewage.
• Risk of infection can be minimized or eliminated by proper cooking before consumption.
• The growth is generally inhibited in the presence of 4-5% NaCl. Increased inhibition is seen at low temperature/ or reduced pH.