Plasmid diversity, antibiotic resistance and virulence genes associated with Staphylococcus aureus isolates from private hospitals in Gauteng, South Africa.

This study investigated the association between plasmid diversity, antibiotic resistance and virulence genes of Staphylococcus aureus (S. aureus) isolates from private hospitals in Gauteng, South Africa. Automated antibiotic susceptibility testing was done on 100 S. aureus isolates. Plasmid extraction and polymerase chain reaction (PCR)-based replicon typing were done on all isolates, followed by a multiplex-PCR assay screening for virulence genes in plasmid-positive isolates. Whole genome sequencing (WGS) was conducted on ten representative isolates selected based on the presence and number of plasmids, replicon gene profiles and antibiotic susceptibility patterns. Resistance to erythromycin (29%; 29/100), clindamycin (26%; 26/100) and ciprofloxacin (15%; 15/100) was observed. Plasmids were detected in 60% (60/100) of isolates, with pN315 (70%; 7/10) and pSaaS6159 (50%; 5/10) predominating among representative isolates and carrying antibiotic resistance genes (ARGs). Specific rep–ARG associations included rep7a (pS0385p1) with tetK, rep7a (pTZ4) with cat, rep10a (pDLK1) with ermC and rep5a (pN315) and rep16 (pSaaS6159) with blaZ. No virulence gene was specifically linked to any rep gene. Sequence types identified by WGS included ST22, ST35 and ST5 among MRSA isolates and ST152, ST5, ST6, ST1 and ST45 among MSSA isolates. These findings highlight an association between specific plasmids (pS0385p1, pTZ4, pDLK1, pN315 and pSaaS6159) and ARGs. The lack of association between replicon type and virulence gene carriage suggests that plasmid-borne traits in S. aureus are more strongly driven by antimicrobial selection than by virulence factors, with most virulence genes residing on the chromosome. Enhanced surveillance programs targeting these plasmids may improve understanding of ARG dissemination in healthcare settings.