Identification and molecular characteristics of verotoxin-producing Escherichia coli (VTEC) from bovine and pig carcasses isolated in Poland during 2014-2018

The presence of verotoxin-producing Escherichia coli (VTEC) on bovine (n = 330) and pig (n = 120) carcasses in Poland was investigated using the ISO/TS 13136 standard. A total of 115 (34.8%) and 37 (30.8%) cattle and pig samples were positive in real-time PCR, respectively. Isolation of the bacteria revealed that from bovine carcasses 37 (32.2%) VTEC were obtained whereas only 5 (13.5%) pig carcasses were positive for the stx gene. The VTEC were characterized using whole genome sequencing (WGS) and bovine isolates were classified into 25 serotypes with the most prevalent 0113:H21 (5 strains) whereas pig strains belonged to 5 different semtypes which were not identified among cattle strains. The majority of bovine VTEC (35; 94.6% isolates) were positive for the stx2 gene, either alone or together with the stx/gene. All strains isolated from pig carcasses resulted positive for the stx2 gene only. Only two isolates of bovine origin contained the eaeA intimin gene, together with the ehxA and 1pfA markers. VTEC were highly molecularly diverse as shown by classification into 29 different MLST STs. The obtained results suggest that further studies related to cattle and pig carcasses are needed to assess the role of these sources for human VTEC infections.