Detection of cytolethal distending toxin (cdt) and cytotoxic necrotizing factor (cnf) genes among Escherichia coli isolates from Iranian sheep carcasses

Escherichia coli is a Gram-negative, nonspore-forming bacillus, usually motile, and a member of the family Enterobacteriaceae. Virulence factors such as CDT and CNF are associated with the capacity of E. coli strains to cause intestinal and extraintestinal infections, and sheep and mutton are important sources for transmission of this infection to human. The purposes of this study were to determine the presence of E. coli at the first step and to examine samples for detection of virulence genes using specific primers in Iranian sheep carcasses. One hundred fifty muttons were collected randomly from slaughterhouse industries in southwest Iran, and bacterial DNA was extracted. For gene amplification, PCR reaction was performed using 16srRNA primer for the presence of E. coli DNA, and then specific primers were used for the detection of cdt and cnf genes in positive samples. The amplification products were analyzed in 1% agarose gel electrophoresis. E. coli DNA was found to be positive in 32/150 (21.33%) mutton specimens, and cdt, cnf, and both genes were identified in 10/32 (31.25%), 16/32 (50%), and 6/32 (18.75%) of positive samples, respectively. The results showed a significantly frequent presence of cdt and cnf genes in E. coli strains isolated from mutton. These findings indicated that sheep is an important carrier of these infectious agents to humans, and examinations of these animals are significant for food safety and public health in Iran.