Emergence of polymyxin-resistant Yersinia enterocolitica strains in natural aquatic environments.

Aquatic environments serve as ideal reservoirs for antibiotic-resistant bacteria and resistance genes. However, the presence of polymyxin-resistant Yersinia enterocolitica, the pathogen responsible for human yersiniosis, in aquatic environments remains poorly understood. Herein, we isolated polymyxin-resistant Y. enterocolitica strains from natural water for the first time. In addition to intrinsic resistance to ampicillin and cefazolin, the strains demonstrated high resistance to polymyxin B and polymyxin E. All isolates were capable of biofilm production and exerted high virulent effects in Galleria mellonella, with 90% mortality occurring within 48 h post-infection. Furthermore, whole genome sequencing identified 26 antibiotic resistance genes, including polymyxin resistance determinants (arnA and PmrF), beta-lactam resistance determinants (vatF and blaA), and 60 virulence genes such as yaxA and yaxB in Y. enterocolitica isolates. Notably, phylogenetic analysis revealed that Y. enterocolitica involved multilocus sequence types ST937 and ST631, which were clustered with strains isolated from a human in the United States or swine in China. The close relatedness to clinical isolates suggests that polymyxin-resistant Y. enterocolitica may pose considerable health risk to humans. Our findings provide evidence of the presence of polymyxin-resistant Y. enterocolitica in aquatic environments and raise concerns about health risks due to their potential high virulence.