History and Objectives: Food toxicity is an acute disease arising from the lack of attention to the health related food regulations. One of the indices for determination of bacterial food contamination is total bacterial counting, examination for existence of Escherichia coli (E.coli) and other pathogenic agents. Since E.coli induce diarrhea by different mechanisms, the present research was performed in order to determine the distribution and prevalence of there mechanisms of E.coli contamination isolated from different food sources referred to the microbial laboratory of Iran University of Medical Sciences and Health Service in 1998-1999.

Materials and Methods: A descriptive study was performed on 2119 samples from food sources within one year and 300 isolated E.coli samples were examined in order to observe how they cause disease. E.coli diagnostic enteropathogen antiserum was used to detect enteropathogenic E.coli (EPEC). SMA biologic techniques and newborn mice were used to detect heat-stable enterotoxin producing E.coli (ETEC). Sereny biologic test and enterohemorrhagic E.coli antiserum 0157:H7 were used for detection of invasive type E.coli and enterohemorrhagic E.coli (EHEC) respectively.

Results: 23 cases (2.7%) of E.coli isolated from various food sources, showed EPEC whereas 13 cases (1.5%) were ETEC and 1 case was EHEC.

Conclusion: The rate of E.coli isolation in spring and summer compared to other seasons were higher. Milk, other diary products, juices traditional ice cream and candies were the most frequent food sources with E.coli contamination. These findings strongly recommended monitoring and surveillance of food industries for microbial contamination.