Antimicrobial resistance profiles and genomic diversity of vaginal Prevotella bivia isolates from South African women, including the first report of nimK in South African vaginal P. bivia isolates

Objectives To characterise the phenotypic and genotypic antimicrobial resistance (AMR) profiles and genomic diversity of vaginal Prevotella bivia isolates obtained from South African women and to compare them with publicly available genomes. Methods P. bivia isolates were recovered from lateral vaginal wall swabs and identified by polymerase chain reaction (PCR) and 16S rRNA gene sequencing. Antimicrobial susceptibility testing against metronidazole, clindamycin, azithromycin, amoxicillin and doxycycline was performed using MIC test strips (MTS). Whole-genome sequencing was undertaken using the Illumina MiSeq platform to investigate genomic diversity, AMR gene carriage and mobile genetic elements. Results Thirty-five P. bivia isolates from 30 vaginal samples underwent phenotypic characterisation, and 33 high-quality genomes were included in genomic analyses. Resistance to metronidazole and clindamycin was low (11.4% and 8.6%, respectively). The tetQ and cfxA genes were the most frequently detected AMR determinants (90.9% and 72.7% of genomes, respectively), whereas ermF and nimK were rare (3.0% each). Comparative genomic analysis revealed generally low within-sample diversity, although one participant harboured genetically distinct strains, and strain persistence was observed in another participant over a 16-week interval. South African isolates clustered separately from most publicly available isolates originating from the United States. One isolate harboured nimK within a previously described Tn6456-like mobile element, representing, to our knowledge, the first identification of nimK in a South African vaginal P. bivia isolate. Conclusions Vaginal P. bivia isolates from South African women exhibited low genomic diversity, evidence of strain persistence and occasional co-colonisation with multiple P. bivia strains. Although resistance to standard bacterial vaginosis therapies remained low, the presence of mobile AMR determinants highlights the importance of continued genomic and phenotypic surveillance of vaginal P. bivia populations.