PT - JOURNAL ARTICLE AU - Yu Zhang AU - Shengyi Min AU - Yuxuan Sun AU - Jiaquan Ye AU - Zhemin Zhou AU - Heng Li TI - Genomic analysis of population structure, antimicrobial resistance, and virulent factors of methicillin-resistant <em>Macrococcus caseolyticus</em> in global lineages AID - 10.1101/2022.04.12.488041 DP - 2022 Jan 01 TA - bioRxiv PG - 2022.04.12.488041 4099 - http://biorxiv.org/content/early/2022/04/13/2022.04.12.488041.short 4100 - http://biorxiv.org/content/early/2022/04/13/2022.04.12.488041.full AB - Macrococcus caseolyticus is an opportunistic pathogen frequently detected in dairy products as well as veterinary infections. The present study examined the population structure, antimicrobial resistance, and virulent factors of methicillin-resistant M. caseolyticus isolates in retail meat from Shanghai (n=10) and global isolates from GenBank (n=87). All strains were divided into five lineages that distributed in Europe (82.4%, n = 80), Asia (11.3%, n = 11), North America (4.1%, n = 4), Oceania (1%, n = 1) and Africa (1%, n = 1). MLST typing revealed novel alleles in Chinese M. caseolyticus strains. Furthermore, a total of 24 AMR genes associated with 10 classes of antimicrobial agents were identified in the isolates from global lineages, carried by dominant plasmids such as rep7a, rep22 and repUS56. Comparing to other lineages, genomes from the Chinese lineage carried significantly more AMR genes (p&lt;0.005) and less virulent factors (p&lt;0.001), which may be explained by the local evolution of M. caseolyticus in China. Finally, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were enrolled for morphology comparison between M. caseolyticus and S. aureus, showing that M. caseolyticus has a larger diameter and thicker cell wall. The present study showed geographical variation with regards to MLST profiles, antimicrobial resistance, and virulent factors in global M. caseolyticus lineages. This study suggests that such local evolution of foodborne or livestock origin M. caseolyticus may serve as vehicles for domestic transmission of methicillin resistance in retail meat in China.HighlightsGlobal M. caseolyticus strains were divided into five lineages from A to E.MLST typing revealed novel alleles in Chinese M. caseolyticus strains.Chinese lineage carried significantly more AMR genes and less virulent factors.Macrococcus caseolyticus has a larger diameter and thicker cell wall compared with S.aureus.Macrococcus caseolyticus may enhance the domestic transmission of methicillin resistance in China.Competing Interest StatementThe authors have declared no competing interest.