Prevalence and molecular characterisation of Shiga toxin-producing Escherichia coli in raw milk cheeses from Lazio region, Italy

In recent years, the incidence of foodborne diseases caused by Shiga toxin-producing Escherichia coli (STEC) has increased globally. For this reason, within the specific regional control plan for the detection of STEC in food products in Italy, the presence of STEC in unpasteurised milk cheeses was investigated. In total, 203 samples obtained from March 2011 to December 2013 were analysed, with two standard methods (ISO 16654:2001 and ISO 13136:2012). Two strains of E. coli O157 were isolated (2/161, 1.2%) but did not carry any virulence-associated genes and 22 stx-positive samples (22/146, 15.1%) were detected in enrichment cultures, mostly from ovine cheeses. Only two strains isolated from different ovine cheeses carried stx gene and none of these was eae-positive. This study confirms the presence of stx-positive E. coli and suggests that this type of food cannot be excluded as a potential vehicle of STEC.