<i>Salmonella</i> and <i>Yersinia enterocolitica</i> through the pig meat chain in Sardinia: occurrence, antimicrobial resistance and genetic insight

This study aimed to characterize Salmonella and Yersinia enterocolitica detected in fattening pigs in Sardinia, examining genetic similarity and antimicrobial resistance of isolates from farms and slaughterhouses and evaluating carcass hygiene. Environmental samples were collected from six pig farms, and the same pigs were also sampled at the slaughterhouses. Palatine tonsils, mesenteric lymph nodes, colon content, and carcass surface samples were collected and tested for Salmonella and Y. enterocolitica. Antimicrobial resistance testing and whole genome sequencing were performed on all isolates. Carcass surface samples were tested for total aerobic colony count (ACC) and Enterobacteriaceae count (EBC). Y. enterocolitica was found in two farms (33%), while Salmonella was absent in environmental farm samples. At slaughterhouses, 13.1% of pigs were found positive for Salmonella (lymph nodes, colon content, and palatine tonsils samples), but Y. enterocolitica was not detected. Salmonella isolates were typed as monophasic S. Typhimurium ST34 and S. Goldcoast ST358, with few allelic differences among isolates of the same ST. Salmonella ST34 showed resistance towards ampicillin, streptomycin, sulfonamide, and tetracycline (blaTEM-1B, aph(3 )-Ib, sul2 and tetB genes, R-type ASSuT). Y. enterocolitica isolates (biotype 2, ST853, and ST859) showed resistance to ampicillin and amoxicillin-clavulanic acid (blaA gene). Process hygiene criteria were generally met, with mean (log10 CFU/cm2 ± standard deviation) values for ACC and EBC being 2.23±0.74 and 0.75±0.81. Pigs of Sardinia are confirmed carriers of Salmonella and Y. enterocolitica, but overall hygienic status in farms and slaughterhouses in Sardinia is acceptable. Monophasic S. Typhimurium and Y. enterocolitica isolates showed typical resistance patterns. Monophasic S. Typhimurium ST34 isolates with R-type ASSuT are confirmed as epidemic clones.