Vaginal microbiota were shown to be primarily dominated by Lactobacillus crispatus and L iners, the latter of which was associated with an increased risk for Chlamydia trachomatis infection, according to the results of a recent study published in Sexually Transmitted Infections.
In this nested case-control study, data from yearly population-based screening for C trachomatis were used to compare vaginal microbiota from Dutch women who tested negative at one screening and positive at the following screening with controls who tested negative at 2 yearly screenings in a row. Vaginal swabs from the first visit were analyzed using 16s rRNA sequencing.
Of the 5 vaginal community state types identified, 4 were predominated by Lactobacillus species: L crispatus (37%), L iners (33%), L gasseri (3%), and L jensenii (2%). The fifth community state type (25%) was comprised of various strict and facultative anaerobic bacteria, including Gardnerella vaginalis, Megasphaera spp., Atopobium vaginae, and Prevotella spp.
A vaginal community state type dominated by L iners was associated with an increased risk for C trachomatis infection within one year of sampling (odds ratio [OR] 2.58; 95% CI, 1.01-6.61). Another factor associated with acquisition of C trachomatis was being in a sexual relationship but living apart (OR 14.51; 95% CI, 1.45-145.3).
In a linear discriminant analysis effect size algorithm, C trachomatis infection acquisition was strongly associated with the presence of L iners and P amnii. In contrast, not acquiring C trachomatis was associated with the presence of L crispatus.
The study authors explained that “vaginal microbiota dominated by Lactobacillus spp. does not necessarily protect against the acquisition of [sexually transmitted infections] like C trachomatis.” Based on these results, the authors suggested that “the composition of the vaginal microbiota is indicative of increased host predisposition to acquiring [sexually transmitted infections]. The exact mechanism behind this still needs to be unraveled.”
van Houdt R, Ma B, Bruisten SM, Speksnijder AGCL, Ravel J, de Vries HJC. Lactobacillus iners-dominated vaginal microbiota is associated with increased susceptibility to Chlamydia trachomatis infection in Dutch women: a case-control study [published online September 25, 2017]. Sex Transm Infect. doi: 10.1136/sextrans-2017-053133