Abstract
Staphylococcus aureus causes severe bloodstream infections (BSIs), and methicillin-resistant S. aureus (MRSA) poses a major clinical threat due to strong antimicrobial resistance and limited therapeutic options. This retrospective study analyzed 96 S. aureus isolates from nosocomial BSIs in a tertiary hospital in central China from 2020 to 2024, to clarify the epidemiological characteristics of antimicrobial resistance and transmission mechanisms. Antimicrobial susceptibility testing, whole-genome sequencing and bioinformatics analysis were performed to identify antibiotics c resistance genes (ARGs), virulence factors (VFs), multilocus sequence typing (MLST), staphylococcal cassette chromosome mec (SCCmec) typing and phylogenetic features. MRSA accounted for 72.92% (70/96) of all strains. The total number of S. aureus isolates trended downward, while the MRSA proportion remained stable at 57.14-100.00%, with the Department of Nephrology showing the highest infection rate (36.46%). All strains were susceptible to linezolid and rifampicin; one vancomycin-resistant, one tigecycline-resistant and one phenotypically discordant MRSA strain were detected. Genomic analysis identified 29 resistance gene types, with frequent co-carriage of mec and bla family genes. Strains carried abundant VFs (average 74 genes per strain), including 45 core virulence genes and widely distributed lukF-PV/lukS-PV. MLST revealed 21 sequence types, dominated by ST59 (21.88%) and persistently epidemic ST22. SCCmec type IV (58.93%) was predominant, with no mecI in type IV/V strains and three pseudo-SCCmec carriers. Genomic epidemiology provides reliable evidence for precise medication, targeted prevention and control of MRSA BSIs, and references for understanding S. aureus antimicrobial resistance evolution.