Genotypic and phenotypic features of MRSA with an incomplete hemolysis phenotype in a tertiary teaching hospital in China

Staphylococcus aureus is a widespread bacterial pathogen responsible for hospital- and community-acquired infections, typically showing a β-hemolytic phenotype. An incomplete hemolytic phenotype (SIHP) in methicillin-resistant S. aureus (MRSA) has been rarely reported, and its genotypic and phenotypic traits remain unclear. This study analyzes the genotypic and phenotypic characteristics of MRSA clinical isolates with SIHP (SIHP-MRSA) collected from a tertiary teaching hospital in China and explores potential molecular mechanisms. MRSA isolates were obtained from patients admitted during 2010–2024, and hemolytic patterns were assessed on blood agar. MLST, spa, and SCCmec typing were used to characterize molecular genotypes, whereas virulence genes were detected using PCR. Mutations in the agrA gene were identified via Sanger sequencing. Biofilm formation was assessed using Congo red agar and crystal violet staining, and antimicrobial resistance profiles were determined using the VITEK-2 Compact system and broth
microdilution.This study provides the first report of a high prevalence of SIHP-MRSA in a tertiary teaching hospital in China, dominated by ST5-t2460-II and ST59-t437-IVa clones. SIHP-MRSA isolates showed enhanced biofilm formation and reduced susceptibility to daptomycin and teicoplanin, underscoring the need for surveillance to prevent spread in vulnerable populations. Furthermore, the widespread agrA-I238K mutation, identified mainly in ST5 and ST59 clones, emphasizes the influence of agr dysfunction on MRSA pathogenicity and antimicrobial resistance.