Application of multiplex PCR assay based on uidR and fliCH7 genes for detection of Escherichia coli O157:H7 in milk

A highly sensitive and specific multiplex PCR assay has been developed to detect the presence of Escherichia coli O157:H7 from naturally contaminated raw milk samples within 10 h. The primers explored in the assay were targeted against the uidR gene specific for all types of E. coli and the fliCH7 gene specific for the h7 flagellar antigen of E. coli O157:H7. The multiplex PCR assay developed was found to be highly specific as it produced PCR products of 152 bp (E. coli specific) and 625 bp (E. coli O157:H7 specific). The assay was tested for its specificity against different serotypes of E. coli as well as other pathogenic strains like Salmonella, Shigella, Klebsiella, Enterobacter, Staphylococcus aureus, Lactobacillus and Lactococcus etc. When this multiplex PCR assay was directly applied to 24 raw milk samples collected from different sources, E. coli O157:H7 could be detected in one of the milk samples without 4 h enrichment in CT-SMAC broth and three samples after 4 h enrichment in CT-SMAC broth. However, all the pasteurized milk samples gave a negative signal for this organism.