Bacterial communities forming the vaginal micro-ecosystem in norm and in bacterial vaginosis

Background. Bacterial vaginosis (BV) is disturbance of the vaginal microbiota, characterized by displacement of lactobacilli with anaerobic bacteria and capable of adversely affecting women’s reproductive health. In the development of BV, a wide spectrum of bacteria substantially differing in their properties is involved. Grouping vaginal bacterial communities into clusters, or types of microbiocenosis, might contribute to understanding of pathogenic mechanisms and elaboration of effective tools for diagnostics and therapy of the disease.

Aim. Determination and comparative analysis of clusters of vaginal bacterial communities in norm and in BV.

Materials and methods. Women of reproductive age were enrolled in the study. For the diagnosis of BV, the Nugent score was used. Vaginal swab samples from all women were analyzed with the test Femoflor-16, intended for evaluation of the vaginal microbiocenosis using multiplex quantitative real-time PCR. Two-step cluster analysis was applied for grouping bacterial communities. Differences between the clusters were evaluated using pairwise comparisons.

Results. Of 280 women enrolled in the study, 172 had normal microflora, 27 – intermediate microflora, 81 – BV. In cluster analysis, 270 samples valid in PCR testing were included. All the vaginal bacterial communities were grouped into 4 clusters. Cluster 1 (n = 171) included cases when the vaginal microflora consisted mostly of lactobacilli. Cluster 2 (n = 11) encompassed cases of domination of aerobic microflora: Enterobacteriaceae, Streptococcus and Staphylococcus. Clusters 3 (n = 57) and 4 (n = 31) were connected with BV and included cases of prevailing of facultative anaerobes (Gardnerella vaginalis, Atopobium vaginae) and obligate anaerobes (Sneathia/Leptotrichia/Fusobacterium, Megasphaera/Veillonella/Dialister, Lachnobacterium/Clostridium), respectively. Nearly all cases of cluster 1 belonged to the category of normal microflora of the Nugent score. The majority of bacterial communities of cluster 2 matched intermediate microflora, cluster 3 – BV category with a score of 7 or 8, cluster 4 – BV category with a score of 9 or 10. The clusters differed significantly in vaginal рН, with the highest values observed for cluster 4.

Conclusions. Vaginal bacterial communities are grouped into 4 main clusters, characterized by domination of lactobacilli, aerobes, facultative anaerobes or obligate anaerobes. The clusters belong to different categories of the Nugent score and differ significantly in vaginal pH.