Molecular Characterization of Non-O157 Shiga Toxin-producing E. coli Detected in Raw Milk and Some Dairy Products

Abstract

Aims: The aim of this study was to detect non-O157 Shiga toxin producing E. coli in raw milk and some of its products in Qena, Egypt. Study Design: An exploring, evaluating study.  Place and Duration of Study: The study was conducted at Department of Food Hygiene and Control, Faculty of Veterinary Medicine, South Valley University, Qena, Egypt. Methodology: A total of 90 samples of raw milk, white cheese and small scale ice cream sold in local markets in Qena city, Egypt were collected and investigated for the presence of non-O157 STEC. The tested products were screened for the presence of Shiga toxin by ELISA Kits. A loopful from samples that gave a positive reading in ELISA test was streaked onto SHIBAM plates for isolation of non-O157 STEC. Then the obtained isolates were molecularly characterized and serotyped. Results: Shiga toxin was detected in 12.2% of the examined samples by using ELISA. From the ELISA-positive samples, 28 non-O157 E. coli strains were isolated and molecularly characterized by the presence of stx1, stx2, eaeA and the genes. All non-O157 STEC obtained from raw milk samples carried stx2 gene only and lacked stx1, eaeA and hly genes. While 94.1% and 5.8% of the non-O157 STEC obtained from white cheese samples harbored stx1 and stx2, respectively, eaeA and hly genes also could be detected in 82.4, and 11.7% of non-O157 STEC strains isolated from white cheese, respectively. One non-O157 STEC isolates could be obtained from the ice cream samples, and it harbored stx1, eaeA and hly genes.  Conclusion: The presence of the non-O157 STEC in the examined samples reinforces the idea that these products exhibit a potential health hazard to the consumers since the hazard to the consumer is associated with the virulence of the detected strains in the investigated dairy products.