Background: Gardnerella vaginalis is an organism associated with bacterial vaginosis and spontaneous preterm birth (sPTB) outcomes. Categorised into four clades (1-4), G. vaginalis colonisation and clade type is likely to influence the vaginal microbiota and subsequent disease state, however, there are limited studies describing colonisation at the clade level.
Methods: This study identified the distribution of G. vaginalis, and clades 1-4, between term and sPTB groups in a pregnant population via real-time qPCR. Vaginal swabs were randomly selected based on delivery outcome from the Preterm Birth Prevention Study clinical trial where participants were recruited at 14-20 weeks gestation. A total of 104 vaginal swabs were analysed, half from term pregnancies and half from sPTB cases. Swabs positive for G. vaginalis were cultured for additional phenotypic and genotypic characterisation.
Results: Overall, no significant difference in G. vaginalis colonisation was observed between term and sPTB groups (p=0.64), with qPCR detection in 42.3% and 51% of vaginal samples, respectively. History of sPTB was associated with G. vaginalis presence and bacterial load, and logistic regression revealed a 2.76-fold higher likelihood of G. vaginalis colonisation in women with prior sPTB. Of the positive samples (n=53), 31 women were colonised by a single clade, with clades 1 (20.8%), 2 (17%) and 4 (17%) predominating over clade 3 (3.8%). Clade 4 was distinctly more prevalent among sPTB (n=8) cases compared to term deliveries (n=1). Co-colonisation was observed across 22 women, with multiple clade combinations of G. vaginalis; two in the sPTB group contained all four clades.
Conclusion: This study highlights the importance of characterisation beyond the species to understand the intricacies between clade dynamics. While no significant difference in G. vaginalis colonisation rates was observed between groups, the participant birth history and clades present a different view. Our research aims to improve our understanding of these bacteria through additional sequencing to determine genetic differences, including potential virulence genes, between sPTB and term isolates, while also improving publicly available genomic data.