Prevalence and distribution of the stx1 and stx2 genes of Shiga toxin producing E. coli (STEC) in vegetables, beef caracasse and patients with acute diarrhea

Background and Objectives: Shiga toxin-producing Escherichia coli (STEC) are one of the major causes of food-borne diseases worldwide. Human diseases ranging from mild diarrhea to hemorrhagic colitis and hemolytic uremic syndrome (HUS) can be caused by STEC. Cattle are being known as the main source of STEC, bacteria commonly transferred by the consumption of contaminated foods. Shiga toxins are of two major classes: stx1 and stx2. The present study was conducted to evaluate the prevalence of both genes in stool samples of patients with acute diarrhea, and in raw beef, and fresh vegetables sampled at different markets in Shiraz. Materials and methods: In this study, 750 samples (250 of stool, 400 of fresh vegetables and 100 of beef carcasses) were collected. Following enrichment in Trypticase Soy broth (TSB) supplemented with Novobiocin, DNA extraction was done through boiling method. Stx1 and stx2 genes were detected through multiplex PCR method using specific primers. Results: A total of 104 samples were positive for at least one toxin gene. Fifty four (54%) beef carcasses were positive for STEC virulence genes, with 17 (31.5%) being positive for either stx1 or stx2, and 37 (68.5%) for both. Concerning vegetable samples, 33 (8.25%) proved positive for STEC genes, among which 24 (72.1%) were positive for either stx1 or stx2 and 9 (27.3%) for both. Finally, PCR showed that 17 (6.8%) of stool samples were positive for STEC genes. While all STEC positive stool samples were positive for stx1, only 7 (41.2%) were positive for stx2 as well. Conclusion: Our data confirm that cattle still could be considered as a main reservoir of STEC, however, vegetables could also have a role.