Clinical characteristics and whole-genome analysis of methicillin-resistant Staphylococcus aureus in ICU patients from a tertiary hospital in southern China

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OBJECTIVES: This study aimed to characterize the molecular epidemiology, antimicrobial resistance, virulence profiles, and clinical outcomes of Methicillin-resistant Staphylococcus aureus (MRSA) infections among intensive care unit (ICU) patients in southern China. METHODS: A total of 104 non-duplicate MRSA isolates were collected from ICU patients at a tertiary hospital between 2021 and 2024. Whole-genome sequencing was used to determine molecular characteristics. Antimicrobial susceptibility, biofilm formation, and hemolytic activity were conducted. Clinical data were analyzed to evaluate associations between MRSA lineages and patient outcomes. RESULTS: Eight clonal complexes and 16 sequence types were identified, with Clonal Complex (CC)5 (31.7 %), CC59 (20.2 %), and CC398 (18.3 %) being the most predominant. The dominant clones, namely CC5-ST5-SCCmec II-agr II, CC398-ST398-SCCmec V-agr I, and CC59-ST59-SCCmec IV-agr I, each exhibited distinct phylogenetic clustering patterns and resistance patterns. Notably, ST764, a variant of ST5, showed extensive multidrug resistance and robust biofilm-forming capacity, while ST59 isolates displayed the highest hemolytic activity. ST5 and ST764 exhibited the broadest resistance profiles. Virulence genes hla, psmα1-4 and psmβ1 present in all isolates, while tst was more frequent in CC5 and associated with higher 30-day death rate (P = 0.038). CC5 infections were linked to worse outcomes, with a death rate of 45.5 %. Renal insufficiency (P < 0.001) and malignancy (P = 0.011) were independent predictors of 30-day death rate. CONCLUSION: ICU-derived MRSA isolates in southern China display considerable molecular diversity and varying resistance and virulence profiles. CC5, especially ST764, is associated with multidrug resistance and poor clinical outcomes, highlighting the need for enhanced infection control in ICUs.

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