Genomic Landscape and Antimicrobial Resistance of Listeria monocytogenes in Retail Chicken in Qingdao, China.

Listeria monocytogenes (L. monocytogenes) is an important foodborne pathogen that poses great risks to food safety and public health, and knowledge about its presence and diversity in potential sources is crucial for effectively tracking and controlling it in the food chain. In this study, we investigated the prevalence, antimicrobial susceptibility, and genomic characteristics of Listeria monocytogenes (L. monocytogenes) collected from retail chicken meat samples in Qingdao, China, in 2022. A total of 38 (10.6%, 38/360) L. monocytogenes isolates were recovered from 360 retail chickens. All 38 isolates were classified into two lineages (I and II), three serogroups (IIa, IIb, IIc), eight sequence types (STs), eight clonal complexes (CCs), eight Sublineages (SLs) and nine cgMLSTs (CTs). ST121 and ST9 were the most prevalent STs in this study. The ST121 strains from China had heterogeneity with those from other countries, while the Chinese ST9 strains had homogeneity with those from other countries. One resistance cassette tet(M)-entS-msr(D) was identified in eight L2-SL121-ST121-CT13265 isolates, the genetic structure of which was identical to that of three reference genomes. All isolates carried the L. monocytogenes pathogenic island (LIPI)-1, with only one carrying LIPI-3 and three carrying LIPI-4. In addition, 11 isolates subtyped as L2-SL121-ST121-CT13265 were found to have a premature stop codon (PMSC) in the inlA gene in this study. Our data revealed the antimicrobial susceptibility, genomic characteristics and evolutionary relationships of L. monocytogenes in retail chicken in Qingdao, China. The characterization of genotypes, virulence, stress and antimicrobial markers of strains circulating in retail chicken in Qingdao, as described in this study, provides the opportunity to improve risk assessments of L. monocytogenes exposure.