Abstract
The aim of this study was to describe the prevalence, serotypes and virulence genes of Shiga toxin-producing Escherichia coli (STEC) isolated from raw milk cheese samples collected at producer level with the purpose of determining whether raw milk cheeses in Switzerland represent a potential source of STEC pathogenic for humans.
Raw milk cheese samples (soft cheese n=52; semi-hard and hard cheese n=744; all produced from Swiss cows’, goats’ and sheep milk) collected at producer level throughout Switzerland within the national sampling plan during the period of March 2006 to December 2007 were analyzed.
Of the 432 cheese samples obtained in the year 2006 and the 364 samples obtained in the year 2007, 16 (3.7%) and 23 (6.3%), respectively were found to be stx positive. By colony dot-blot hybridization, non-O157 STEC strains were isolated from 16 samples. Of the 16 strains 11 were typed into seven E. coli O groups (O2, O15, O22, O91, O109, O113, O174), whereas five strains were non-typeable (ONT). Among the 16 STEC strains analyzed, stx1 and stx2 were detected in one and 15 strains. Out of the 15 strains with genes encoding for the Stx2 group, four strains were positive for stx2, six strains for stx2d2, two strains for stx2-O118, one strain for stx2-06, one strain for stx2g, one strain for stx2 and stx2d2, and one strain for stx2 and stx2g. Furthermore, three STEC strains harbored E-hlyA as a further putative virulence factor. None of the strains tested positive for eae (intimin).
Results obtained in this work reinforce the suggestion that semi-hard raw milk cheese may be a potential vehicle for transmission of pathogenic STEC to humans.
Stephan, Roger