Prevalence and quantification of Shiga-toxin producing Escherichia coli along the lamb food chain by quantitative PCR

Shiga-toxin producing Escherichia coli (STEC), which is responsible for numerous food-borne disease outbreaks, is the most important human pathogen found in ruminants. In this study, conventional microbiology and quantitative PCR (qPCR) were used to detect and quantify STEC along the lamb food chain, from slaughterhouses to butcheries, in both meat and environmental samples. Microbial Assessment Scheme (MAS) was used to select Critical Sampling Locations (CSLs) in each establishment. The rpoB gene was used to enumerate total E. coli by qPCR, whereas the genes stx(1), stx(2) and eae were directly amplified for quantification of E. coli virulent populations. The results obtained show that E. coli carrying all three virulence genes were the most prevalent in slaughterhouses (69%), whereas E. coli with the eae gene alone were found more frequently in the processing plant (32%), and stx(1)- and stx(2)-positive E. coli were predominant in butcheries (9-10%). E. coli virulent populations were not common in butcheries. Samples determined to be positive for E. coli virulent populations after enrichment were quantified by qPCR and compared with conventional microbiology counts using validated methods. The results showed a higher number of positive CSLs for E. coli virulent populations, and higher counts were obtained when qPCR was used than when using conventional methods.