The aim of this study was to investigate the genomic epidemiology of MRSA in China to identify predominant lineages and their associated genomic and phenotypic characteristics. In this study, we conducted whole-genome sequencing on 565 MRSA isolates from 7 provinces and municipalities of China between 2014 and 2020. MRSA isolates were subjected to MLST, spa typing, SCC mec typing, analysis of virulence determinants and antimicrobial susceptibility testing. Among 565 MRSA isolates tested, clonal complex (CC) 59 (31.2%), CC5 (23.4%) and CC8 (13.63%) were the major lineages, and the clonal structure was dominated by ST59-t437-IV (14.9%), ST239-t030-III (6.4%) and ST5-t2460-II (6.0%), respectively. Of note, CC8, the predominant lineage in 2014–2015, was replaced by CC59 after 2016. Interestingly, the extension and unstable structure of the CC5 population was observed, with ST5-t311-II, ST764-t1084-II, ST5-t2460-II and ST764-t002-II existing complex competition. Further analysis revealed that virulence determinant profiles and antibiograms were closely associated with the clonal lineage. The CC59 MRSA was less resistant to most tested antimicrobials and carried fewer resistance determinants. But rifampicin resistance and mupirocin resistance were closely linked with CC8 and CC5, respectively. MRSA isolates conservatively carried multiple virulence genes involved in various functions. PVL encoding genes were more common in ST338, CC30, CC398, ST8 and CC22, while tsst -1 was associated with ST5. In conclusion, the community-associated CC59-ST59-t437-IV lineage was predominant in China, with diverse clonal isolates alternately circulating in various geographical locations. Our study highlights the need for MRSA surveillance in China to monitor changes in MRSA epidemiology.

Objectives: Ongoing acquisition of antimicrobial resistance genes has made Morganella morganii a new clinical treatment challenge. Understanding the molecular epidemiology of M. morganii will contribute to clinical treatment and prevention.Methods: We undertook a 6-year clinical molecular epidemiological investigation of M. morganii from three tertiary hospitals in China since 2014. Antimicrobial susceptibility testing was performed using a VITEK-2 system. All isolates were screened for β-lactam and plasmid-mediated quinolone resistance genes by PCR. Isolates carrying carbapenem-resistant genes were subjected to whole-genome sequencing (WGS). The variation and evolution of these mobile genetic elements (MGEs) were then systematically analyzed.Results: Among all M. morganii isolates (n = 335), forty (11.9%) were recognized as multidrug resistant strains. qnrD1, aac(6′)-Ib-cr, blaTEM–104, and blaCTX–M–162 were the top four most prevalent resistance genes. Notably, phylogenomic and population structure analysis suggested clade 1 (rhierBAPS SC3 and SC5) associated with multiple resistance genes seemed to be widely spread. WGS showed a blaOXA–181-carrying IncX3 plasmid and a Proteus genomic island 2 variant carrying blaCTX–M–3, aac(6′)-Ib-cr coexisted in the same multidrug resistant strain zy_m28. Additionally, a blaIMP–1-carrying IncP-1β type plasmid was found in the strain nx_m63.Conclusion: This study indicates a clade of M. morganii is prone to acquire resistance genes, and multidrug resistant M. morganii are increasing by harboring a variety of MGEs including two newly discovered ones in the species. We should be vigilant that M. morganii may bring more extensive and challenging antimicrobial resistance issue.

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