Work

Competitive dynamics of ST764 and ST5 MRSA in a new tertiary ICU: enhanced hospital adaptation via agrC mutations post-COVID-19

Year: 2025

Type: article

Abstract: BACKGROUND: Intensive care units (ICUs) face high risks of methicillin-resistant Staphylococcus aureus (MRSA) transmission, yet how accessory gene regulator (agr) dysfunction drives strain adaptation remains unclear. This study investigated MRSA epidemiology in a new ICU, focusing on post-COVID-19 clonal dynamics. METHODS: We conducted 6-month prospective surveillance (Oct 2022-Apr 2023) in a Chinese tertiary ICU. Biweekly environmental/patient sampling and admission/discharge screenings were performed. Isolates underwent whole-genome sequencing (WGS), core-genome multilocus sequence typing (cgMLST), antimicrobial susceptibility testing, and functional assays (CAMP/biofilm). RESULTS: MRSA colonization rates were 5.98% (environment) and 3.86% (patients), with 6.8% present on admission (POA) and 7.6% ICU-associated colonization. Dominant clonal complex (CC) 5 (65.33%) comprised sequence type (ST) 764 (pre-COVID-19) and ST5 (post-COVID-19). cgMLST identified 18 transmission clusters (cgSNP <15), revealing that CC5 isolates mainly originated from environmental reservoirs (beds, medical instruments). ST5 displaced ST764 post-COVID-19, mediated by an agrC mutation (agrC-T43I) that enhanced environmental fitness via increased biofilm formation and reduced antimicrobial susceptibility. ICU-associated colonization shifted toward CC5 (64% vs 30% POA), confirming nosocomial adaptation. CONCLUSIONS: Environmental contamination is the primary source of MRSA transmission in ICUs. The agrC-T43I mutation drives ST5 dominance post-pandemic by enhancing biofilm-dependent persistence, underscoring the need for genomic surveillance to guide infection control.

Source: International Journal of Infectious Diseases

DOI: 10.1016/j.ijid.2025.108186