Pan-genome analysis of methicillin-resistant Staphylococcus aureus PSU20 from a hospital in Thailand reveals insights into virulence, antibiotic resistance, and genetic diversity.

Methicillin-resistant Staphylococcus aureus (MRSA) remains a major public health challenge due to its multidrug resistance and diverse virulence factors, which make it difficult to manage and represent a significant cause of hospital-associated infections. In this study, MRSA strain PSU20 was isolated from a patient at Songklanagarind Hospital. The genome analysis revealed multiple resistance genes, including those conferring resistance to aminoglycosides (ant(9)-Ia, ant(6)-Ia, aph(3')-III, aac(6')-aph(2″)), β-lactams (blaZ, mecA), and macrolide-lincosamide antibiotics (erm(A)). The virulence-associated genes identified were related to immune evasion (sak, scn, coa, femB), cytotoxicity (hlgA, hlgB, hlgC, lukD, lukE), enterotoxin production (sea, seg, sei, sem, sen, seo), and tissue invasion (aur, splA, splB), indicating the strain's capacity for immune evasion, systemic infection, and gastrointestinal pathogenicity. Moreover, several insertion sequences, transposons, and replicons were detected, particularly in contigs containing rep20 and rep21, along with qacA and cadA, which confer tolerance to quaternary ammonium compounds (QACs) and heavy metals commonly found in hospital disinfectants. The presence of oriC and oriT on the same contig (NODE_28) suggests the potential for horizontal gene transfer of plasmid-borne resistance determinants. Phylogenomic analysis identified PSU20 as sequence type ST228-SCCmec I-spa t001, a lineage predominantly reported in Germany and associated with early hospital-associated MRSA (HA-MRSA) outbreaks in Europe, showing close relatedness to HA-MRSA CC5 lineages such as N315 and USA100. These findings report the genomic characterization of PSU20, a multidrug-resistant strain isolated in Southern Thailand that is genotypically consistent with the classical HA-MRSA ST228 lineage, and support the role of ongoing genomic surveillance in tracking the evolutionary dynamics and dissemination of phylogenetically defined MRSA lineages in healthcare settings.