Shiga toxin-producing Escherichia coli in slaughtered pigs and pork products

Abstract

During the years 2015-2016, 83 faecal samples were collected at slaughter from pigs reared in farms located in Central-Northern Italy. During the years 2014-2016 a total of 562 pork products [465 not-readyto-eat (NRTE) and 97 ready-to-eat (RTE) products] were collected from retail outlets, large retailers and processing plants. The samples were analysed according to ISO TS 13136:2012. Out of 83 swine faecal samples, 77 (92.8%) resulted stx-positive by real time polymerase chain reaction (PCR), 5 <i>stx2+</i> and 1 <i>stx1+</i> Shiga toxin-producing <i>Escherichia coli</i> (STEC) strains were isolated. Among the 465 NRTE samples, 65 (14.0%) resulted stx-positive by real time PCR and 7 <i>stx2+</i> STEC strains were isolated. The <i>stx2</i> gene was detected more frequently than the <i>stx1</i> gene both in faecal samples (90.4 vs 8.4%) and in NRTE pork products (13.3 vs 1.3%). All the RTE samples included in the analysis resulted <i>stx-</i>negative. Among the samples resulted positive for <i>stx</i> and <i>eae</i> genes, serogroup-associated genes were detected at high frequency: O26 resulted the most frequent in faecal samples (81.3%) and O145 in pork products (88.1%). The O157 serogroup resulted positive in 83.3 and 78.1% of pork products and faecal samples, respectively. Despite the frequent detection by real time PCR of genes indicating the possible presence of STEC strains belonging to the six serogroups, the bacteriological step did not confirm the isolation of any such strains.