Introduction We tested the hypothesis that vaginal microbiota influence women’s susceptibility to T. vaginalis (TV) acquisition.
Methods We conducted a nested case-control study of 25 episodes of TV infection using vaginal samples collected 30–60 days prior to infection in 18 HIV-negative women and 50 incidence-density matched controls. Broad-range 16S rRNA gene PCR was used to measure total vaginal bacterial load. Deep sequencing was applied to 18 first episodes of TV infection and 36 matched controls to measure bacterial diversity (Shannon index) and species richness (Chao-1 index). Bacterium-specific quantitative PCR was performed for Lactobacillus crispatus, Prevotella amnii, Sneathia sanguinegens, Dialister species Type 2, Bacterial Vaginosis Associated Bacterium 1 (BVAB-1), and Mageeibacillus indolicus for all TV infection cases and controls. The associations between Shannon and Chao-1 indices and TV acquisition were evaluated using logistic regression. Generalised estimating equations with logit link were used to evaluate associations between TV acquisition, detection of bacterial species, and total vaginal bacterial load.
Results There was no association between total vaginal bacterial load, species diversity, or richness, and likelihood of TV acquisition. Detection of S. sanguinegens (odds ratio [OR] 4.00, 95% CI 1.19–13.50) and P. amnii (OR 3.45, 95% CI 1.29–9.24) were both associated with TV acquisition. M. indolicus was also associated with TV acquisition (OR 2.47, 95% CI 0.88–6.93), although not significantly. Compared to women with none of these species, women with all three bacterial species had substantially higher likelihood of TV acquisition (none-reference category; one-OR 1.57, 95% CI 0.21–11.86; two-OR 4.50, 95% CI 0.93–21.76; three-OR 5.50, 95% CI 1.15–26.40). There was no association with the other three bacterial species.
Conclusion The presence of three bacterial species commonly associated with BV may increase susceptibility to TV infection. Elimination of these bacteria could be explored as an approach to decrease women’s risk of trichomoniasis.
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