Detection of Shiga Toxin – Producing Escherichia coli in Raw and Pasteurized Milk

Abstract

One hundred random samples of raw buffalo and pasteurized cow milk (50, each) were collected from different localities of Sharkia Governorate for the detection of E. coli . The isolates were screened by PCR for virulence associated genes as well as antibiotic sensitivity test to determine the most effective antimicrobial agent. Furthermore, an experimental study was carried out to detect the influence of pasteurization and processing of kariesh cheese and yoghurt on E. coli O 111 :H 8 inoculated in milk with the concentration of 10 8 CFU/mL. The obtained results showed that the occurrence of E. coli in the examined raw buffalo and pasteurized cow milk samples were 66% and 30%, respectively. Serogrouping of E. coli isolates revealed that O128, O26 and O111 were recorded as the most frequent O-serogroups. The sensitivity test showed that E. coli isolates were more sensitive to gentamicin (79.2%), followed by ciprofloxacin (70.8%) and colistin (68.8%). However, the examined isolates were completely resistant to erythromycin (100%) followed by sulphamethazole- trimethoprim (79.2%). Molecular identification of virulence associated genes revealed stx 1, stx 2 and eae A genes. The experimental study showed that milk pasteurization was more effective on E. coli O 111 :H 8 survival at refrigeration temperature compared with processed products such as kariesh cheese and yoghurt.