Predominance of the ST22-MRSA-IV-t32 Clone and Molecular Epidemiology of Methicillin-Resistant Staphylococcus aureus in a Tertiary Hospital in Thailand

Objective: This study aimed to determine the molecular characteristics of Methicillin-resistant Staphylococcus aureus (MRSA) strains in a tertiary hospital in Bangkok, Thailand.Material and Methods: Twenty-one MRSA isolates were collected from clinical specimens; between December 2022 and May 2023. These isolates were characterized by determining their antimicrobial susceptibility profiles, Staphylococcal Cassette Chromosome mec and staphylococcal protein A types, multilocus sequence types, biofilm-forming abilities and whole-genome sequences from six representative strains.Results: ST22-MRSA-IV-t032 was the most common clone (57.1%), followed by ST22-MRSA-IV-t628, ST22-MRSA-IV-t1467, ST5-MRSA-II-t21248, ST3976-MRSA-IV-t32, ST764-MRSA-II-t045, ST8502-MRSA-V-t21247; ST1-MRSA-IV-t1784, ST188-MRSA-IV-t189 and ST8-MRSA-IV-t008 (4.8% each).Most (66.6%) MRSA strains produced a strong biofilm: 28.6% produced a moderate biofilm and 14.8% produced a weak biofilm. When the strains were divided into two groups (ST22 and non-ST22), ST22 strains had a greater ability to produce biofilm than non-ST22 strains. All six genomes carried the exoenzyme aureolysin gene, hemolysin-associated hlgA, hlgB, and hlgC genes, and host-immune system modulator genes; including a staphylokinase and staphylococcal complement inhibitor. Conclusion: This study revealed that ST22-MRSA-IV-t32 was the dominant clone related to the ST22 EMRSA-15 epidemic in Europe. These results emphasize the necessity of continuous surveillance for effective management and control measures to understand microbial infections and their patterns of antibiotic resistance, as well as to identify the emergence of new clones.