Prevalence and characterization of Staphylococcus aureus isolated from patients with aerobic vaginitis in Shenzhen, Southern China

Aerobic vaginitis (AV), characterized by vaginal inflammation and elevated pH, is associated with severe complications such as preterm delivery. Staphylococcus aureus (S. aureus) is a predominant pathogen in AV, but its molecular epidemiology, virulence profiles, and antimicrobial resistance in vaginal infections remain poorly defined. Between August 2023 and August 2024, 38 S. aureus isolates from AV patients were analyzed for antimicrobial susceptibility, multilocus sequence typing (MLST), spa typing, accessory gene regulator (Agr) typing, PCR-based detection of virulence, hemolysin, and efflux pump genes, as well as their biofilm formation potential. A total of 38 S. aureus isolates were obtained from the vaginal samples of 38 AV patients, including 14 aged 20–30 years and 24 aged ≥ 31 years, of whom 13 were parturients. Penicillin resistance was highest (68.4%), followed by erythromycin and clindamycin (15.8% each); two MRSA strains carried mecA and pvl but lacked tsst. Resistance genes were frequent, with sepA (97.4%), norA (71.1%), and mepA (63.2%), and norA/mepA and mdeA/mepA combinations were linked to Fuyan Jie (FJ) resistance (P < 0.05). Detergent resistance rates were 55.3% (FJ), 44.7% (Metronidazole Chlorhexidine Detergent, MCD), and 31.6% (Honghe Fuyan Jie, HFJ). Virulence factors included sea (57.9%), tsst (47.4%), and hld (100%). Biofilm assays using the 96-well microtiter plate method showed strong biofilm formation in 72.2% of isolates, particularly among clonal complex (CC) 55 and AgrⅢ strains. MLST identified 12 STs, with ST188 predominant (21.1%) and four novel STs (ST9745, ST9746, ST9747, ST9749); CC1 was most common (42.1%), spa type t189 (26.3%) was dominant, and AgrⅠ (60.5%) prevailed. These findings highlight S. aureus genetic diversity, hemolysin and virulence gene prevalence, and resistance phenotypes in AV, providing insights for targeted therapy.