Relationship between the molecular diversity of plasmids, antibiotic resistance and virulence genes of Staphylococcus aureus isolates from private hospitals in Gauteng, South Africa

Abstract

Objectives: Replication initiation (rep) genes found in plasmids have been linked to antibiotic resistance in bacteria. This study aimed to explore the relationship between plasmid diversity, antibiotic resistance profiles and the presence of virulence genes in S. aureus isolates from private hospitals in Gauteng, South Africa.

Methods: Automated antibiotic susceptibility testing was done on 100 taphylococcus aureus isolates. Plasmid DNA extraction and polymerase chain reaction (PCR)-based replicon typing were done on all isolates. Multiplex-PCR was used to screen for virulence genes in plasmid positive isolates. Whole genome sequencing (WGS) was conducted on 10 representative isolates to assess genetic diversity.

Results: The most common phenotypic antibiotic resistances observed were erythromycin 29% (29/100), clindamycin 26% (26/100) and ciprofloxacin 15% (15/100). Plasmids were found in 60% (60/100) of the isolates. Associations were observed between: rep7a (pS0385p1) with tetracycline (tetK) and rep7a (pTZ4) with chloramphenicol (cat) resistance, rep10a (pDLK1) with macrolide, lincosamide and streptogramin (ermC) resistance and rep5 (pN315) and rep16 (pSaaS6159) with penicillin (blaZ) resistance. No specific virulence gene could be associated with a particular rep gene. Sequence types (ST) associated with epidemics (ST22 and ST36), foodborne outbreaks (ST6) and zoonosis (ST1 and ST152) were identified by WGS. The ST1, ST6, ST22 and ST36 were identified in one isolate each, while ST152 was identified in two isolates.

Conclusions: These findings highlighted an association between certain plasmids (pS0385p1, pTZ4, pDLK1, pN315, and pSaaS6159) and ARG. Enhanced surveillance and antibiotic stewardship programs in South Africa focusing on these plasmids could help better understand the spread of antibiotic resistance in healthcare settings.