بررسي منشاء ژنتيك شيگاتوكسين در اشريشيا كلي انتروهموراژيك

Assessment of the genetic origin of shiga toxin in enterohemorrhagic Escherichia coli

Background and Aim: EHEC has been known as one of the most dangerous pathogenic agents, with a high rate of mortality and morbidity at the time of epidemic food poisoning. It produces cytotoxins named shiga toxins which cause human and animal diseases. Determination of the genetic origin of shiga toxin is important for controlling its dissemination among different species of E.coli. To produce large amounts of this toxin for medical purposes, it is important to determine its genetic origin to evaluate its expression level. Materials and Methods: 400 samples of fecal material of cows and calves from three farms in Tehran were collected in sterile tubes. Total DNA extracted from each isolate was prepared for PCR. Phage induction method using ciprofloxacin was done to extract lysogenic phages from isolates. Then the phages were purified through enzymatic hydrolysis and filtration. PCR was done again to demonstrate the existence of shiga toxin gene on the phage genome. Results: From 34 shiga toxin producing isolates, 24 isolates (70.5%) produced shiga toxin 1, 8 isolates (23.5%) produced shiga toxin 2 and 2 isolates (6%) produced both toxins. Also the frequency of shiga toxin encoding gene on phage genum was determined. 26 isolates (76.5%) out of 34 shiga toxin producing isolates had lysogenic phages. Conclusion: It is demonstrated that shiga toxin can be encoded through chromosome, plasmid or phage. If there is a receptor for the phage on the bacterial surface, it can enter into the bacteria. Shiga toxin encoding gene can spread among different strains of a bacterium or different bacteria if it is carried on phage genome. In order to control toxin production among different species of E.coli, determination of shiga toxin gene origin is necessary. On the other hand, shiga toxin has anti cancer effects and if shiga toxin is to be used as an anti cancer drug, it is desirable to produce large amounts of this toxin. Therefore its genetic origin should be determined. Conflict of Interest: Nill Received: July 2, 2008 Accepted: August 4, 2008