Phylogenetic relationship, genomic heterogeneity, and population structure of Yersinia enterocolitica biotype 1A isolated from pork and poultry meat.

Yersinia enterocolitica is a zoonotic pathogen commonly found in livestock and poultry and their meat products. It causes enteric yersiniosis in humans, primarily through contaminated food consumption. In this study, 352 retail meat samples, including raw and cooked pork and poultry, were collected from Weifang City, Shandong Province, China. The overall prevalence of Y. enterocolitica was 9.7 % (34/352), with pork samples showing the highest rate (14.0 %; 7/50), followed by chicken (9.6 %; 27/280). No isolates were detected in duck meat. The highest prevalence was observed in spring (22.2 %; 22/99). All 36 isolates were identified as biotype 1A, with serotypes including O:5, O:8, O:9, and O:3. These isolates exhibited high resistance to ampicillin (69.4 %; 25/36), followed by nalidixic acid (25.0 %; 9/36) and ampicillin/sulbactam (22.2 %; 8/36). Some isolates from chicken were resistant to ciprofloxacin, polymyxin E, and cefotaxime. All isolates carried the antimicrobial resistance genes (ARGs), such as blaA, vatF, rosAB, and crp. Phylogenetic analysis revealed that the 36 isolates formed a tight cluster on the core gene maximum-likelihood phylogenetic tree but were distantly related to some isolates collected in 2015-2016. Only three isolates (pathogenic biotype 3, serotype O:3) carried pathogenic type III secretion system effector yop genes. While the phylogenetic tree showed close clustering of host isolates, the associated plasmids exhibited greater heterogeneity. The Y. enterocolitica isolates from Shandong Province and across China contained very small soft core genes and large cloud genes, indicating genomic plasticity and wide phenotype diversity within the Y. enterocolitica species. Among them, substantial genotypic heterogeneity was observed. The most common sequence types (STs) in China were ST429, ST3, ST157, and ST178. Biotype 1A isolates accounted for 75.6 % (382/505) of the total Chinese isolates. Certain STs (ST3, ST157, and ST178) were found across various sources, including humans, livestock, meat products, and wildlife, indicating zoonotic transmission via the fecal-oral route, contact with animals, and consumption of contaminated food. This study highlights the potential pathogenicity and antimicrobial resistance of biotype 1A Y. enterocolitica isolates. Continuous surveillance of antimicrobial resistance and food contamination is essential to mitigate infection risks and prevent yersiniosis outbreaks.