Microbe of the Month – E.coli

The following is from The Bug Bible - http://www.safefood.net.au/AudienceHierarchy/TheBugBible/Default.htm

Many strains of E. coli are harmless and are found naturally in the gut of humans and animals. Traditionally its presence in foods has been an indication of faecal contamination however, a number of serotypes are now known to be pathogens. Humans are known to be the major if not the only source of some strains. Other strains can be present in the intestinal tract of cattle and sheep. They have also been detected in pigs, buffalo, goat, deer and various birds and dogs and cats.

These strains are described by their pathogenicity action:

EIEC Enteroinvasive E coli

ETEC Enterotoxigenic E coli

EPEC Enteropathogenic E coli

EHEC Enterohaemorrhagic E coli

The infective dose varies however, for some serotypes this appears to be very low.

Dairy products, vegetables, salads and contaminated water have all been implicated in human illness.

These organisms may enter the kitchen on raw meats and also from domestic pets. If animal manures are used for fertilization this can also result in the transfer of these organisms to vegetable and fruit tissues. Similarly contaminated water can become a vehicle for transfer of the organism from a faecal source to other foods.

Human and animal faecal material is the primary source and a point of entry of E. coli into the food chain. It is important to note that vegetables and fruits may be contaminated internally and externally. If the organisms attach to the internal tissues during development or through damaged tissue, it is difficult to remove these by washing.

E. coli are not heat resistant and will be destroyed by normal cooking temperatures. Mincing meat increases the surface area and also increases the bacterial load. Therefore, it is very important that mince meat is thoroughly cooked prior to consumption. Improperly cooked hamburgers have been implicated in a number of food poisoning outbreaks.

It is also important to keep foods properly chilled below 5ºC.

Many foods will support the growth of these strains of E. coli. So good hygienic practices should be adopted to minimize the possibility of cross-contamination.

  • Obtain food from safe sources and ensure as far as possible that unprocessed animal manures are not used on fruits and vegetables.
  • Store perishable foods either chilled or frozen.
  • In the refrigerator store cooked foods above raw foods.
  • Wash vegetables and fruit well and do not use vegetables and fruits showing obvious tissue damage.

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