Emergence and genomic characterization of mcr-8.2-positive Klebsiella pneumoniae from layer chickens in Xinjiang, China

Klebsiella pneumoniae as a conditional pathogen has become a worldwide public health issue. It can colonize animals and is capable of transmitting to humans through the food chain, raising serious concerns about antimicrobial resistance (AMR). In this study, the prevalence, phenotypes, genomic characteristics of K. pneumoniae in layer chicken feces were investigated across five regions of Xinjiang, China. From 1115 samples collected, 408 (36.6%) K. pneumoniae were isolated. Antimicrobial susceptibility testing revealed the highest resistance rates to colistin (55.0%) and florfenicol (50.0%). PCR results revealed high detection rate of plasmid-mediated quinolone resistance (PMQR) genes, with oqxA (97.8%) and oqxB (90.4%) being the most prevalent. Among β-lactam-resistance genes, bla_SHV was predominant (97.8%), while bla_CTX-M (10.3%) and bla_TEM (10.5%) showed lower prevalence. The overall detection rate of mcr genes (mcr-1 to mcr-9) was low (0.5%). ESBL-producing isolates were identified in 9.8% (n = 40) of the total strains, indicating the presence of extended-spectrum β-lactamase-mediated resistance mechanisms. Importantly, two mcr-8.2 positive isolates were detected, one of which belonged to the ST147 clone. The backbone structure of the mcr-8.2 positive IncFII plasmid (pCD19-mcr8) identified in this study shared high structural similarity with known mcr-8.2-positive plasmids from chicken, human, and environmental sources. The mcr-8.2 core genetic environment (IS903B-dgkA-baeS-copR-ISEcl1-mcr-8.2-ISKpn26) also found in these plasmids. In addition, transfer of the IncFII plasmid pCD19-mcr8 into E. coli did not result in a significant fitness cost. To our knowledge, this is the first report of mcr-8.2-positive K. pneumoniae in layer chickens in Xinjiang, China. These findings highlight the contribution by mobile genetic elements (MGEs) to cross-species dissemination of colistin resistance and emphasize the necessity of a One Health strategy for monitoring and controlling such pathogens and AMR.