Methicillin-resistant Staphylococcus aureus (MRSA) infection in hospitalized patients is dominated by community-acquired strains: genomic epidemiological evidence

OBJECTIVE: This study aimed to systematically investigate the molecular epidemiological characteristics of methicillin-resistant Staphylococcus aureus (MRSA) in Ningxia hospitals, to elucidate their genetic evolutionary relationships, and to delineate the genomic and phenotypic profiles of the dominant lineages. METHODS: Clinical isolates of MRSA strains collected between 01/01/2024 and 30/06/2024 were analyzed, employing second-generation gene sequencing technology, combined with MLST and SCCmec typing, along with evaluation of drug resistance and virulence genes. A phylogenetic tree was constructed to analyze strain homology. RESULTS: A total of 74 non-duplicate Staphylococcus aureus strains (67 MRSA and 7 MSSA) were collected. The most common clonal strain was ST59-IVa, accounting for 46.27%. This strain exhibited a high prevalence of resistance genes mecA and blaZ, at 91.04%. All five ST22-IVa strains were found to lack mecA and erm genes but showed β-lactam resistance, while possessing both lukS/F-PV (PVL) and tsst-1 virulence genes, indicating a significant toxicity risk. Genetic evolution analysis revealed that ST3355, ST4513, and ST59 were closely related, all belonging to SCCmec types IVa; the other ST types exhibited mutations at various loci, with ST5 as the central node, resulting in a wider array of ST and SCCmec typing. CONCLUSION: The ST59-IVa clone is the predominant MRSA strain in Ningxia hospitals, exhibiting multidrug resistance and virulence gene profiles consistent with national trends. However, the emergence of hypervirulent ST22-IVa strains with atypical resistance mechanisms warrants increased vigilance. We recommend enhancing the rational use of antibiotics in hospitals and implementing molecular surveillance for these highly virulent strains.