MRSA in Tibet: high prevalence driven by the epidemic clone CC59-ST59-SCCmec IV-t437 and insights from whole-genome...

Methicillin-resistant Staphylococcus aureus (MRSA) poses a serious public health burden in Tibet, where genome-informed epidemiological data remain limited. This study aimed to characterize the molecular epidemiology of MRSA among Tibetans and explore factors associated with its elevated prevalence.

We analyzed 115 non-duplicate MRSA isolates from Tibetans, comprising 51 hospital-associated MRSA (HA-MRSA) from clinical infections and 64 community-colonizing MRSA (CA-MRSA). CA-MRSA isolates were obtained from nasal swabs of hospitalized patients within 24 h of admission (to exclude nosocomial acquisition) and from their family members between June and December 2023. All isolates underwent antimicrobial susceptibility testing and whole-genome sequencing (WGS)-based typing [sequence type (ST), spa, SCCmec]. We performed core-genome single nucleotide polymorphism (cgSNP) phylogeny and profiled resistance and virulence determinants.

The MRSA nasal colonization rate was 10.53%. The clone CC59-ST59-SCCmec IV-t437 predominated, accounting for 59.4% of CA-MRSA and 39.2% of HA-MRSA. Phylogenetic analysis revealed a distinct Tibetan MRSA cluster with limited genetic relatedness to strains from other Chinese provinces. cgSNP analysis identified seven CA-MRSA transmission clusters defined by ≤25 cgSNP differences, approximating the ≤25 wgSNP threshold. a finding corroborated by epidemiological links to shared households or hospital exposure. While ST59 conserved core virulence determinants (capsule biosynthesis, iron acquisition), ST22 uniquely harbored the egc cluster and was uniformly positive for the lukS-PV/lukF-PVloci. No significant virulence differences were observed between HA-MRSA and CA-MRSA within the same ST. All isolates remained susceptible to vancomycin and linezolid, exhibiting concordant resistance profiles across both settings.

CC59-ST59-SCCmec IV-t437 is the predominant MRSA lineage in Tibet and shows substantial clonal overlap between HA-MRSA and CA-MRSA. These results support the use of whole-genome sequencing to guide empirical therapy and highlight the need for continued surveillance and targeted infection control in this high-burden region.