Resolution and characterization of subgroups of Gardnerella vaginalis and description of the vaginal microbiota of women with preterm premature rupture of membranes
The vaginal microbial community is critical to a woman’s health and the health of her family. Bacterial vaginosis (BV) is a polymicrobial syndrome characterized by a shift of the vaginal microbiota from a Lactobacillus dominated community to a dense biofilm containing a complex mixture of organisms. Although BV is an important risk factor for poor reproductive health outcomes, the etiology of BV is poorly understood. Gardnerella vaginalis is a hallmark species of BV. Phylogenetic analysis of cpn60 universal target sequences from metagenomic studies of the vaginal microbiome and from G. vaginalis isolates resolved four subgroups within the species. This subdivision, supported by whole genome similarity comparisons, demonstrated that these subgroups might represent different species. Among a group of African women, only G. vaginalis subgroup B was significantly more abundant in women with BV relative to women with Nugent scores not consistent with BV. To characterize the subgroups further, several phenotypic and molecular factors of G. vaginalis subgroups were assessed. Proteomic profiles of isolates within each subgroup formed unambiguous clusters. Sialidase gene sequences were detected in all subgroups, however enzymatic activity was detected only in subgroup B. Two isolates of subgroup B isolates (N153 and N101) were incapable of growth in 7% CO2. Given the well-known relationship between an anaerobic microbiota and BV, anaerobic isolates of G. vaginalis are potentially important players in the vaginal microbial community. To determine genome content differences that could account for the phenotypic difference, whole genome sequences of four G. vaginalis subgroup B isolates representing facultative and anaerobic phenotypes were determined. Comparison of genomes led to the identification of genes predicted to encode proteins involved in cell wall biogenesis and protection from oxidative damage that might account for the observed phenotypes. The cpn60 universal target based methodology that improved resolution of the vaginal microbiota including G. vaginalis was applied in a prospective study of the vaginal microbiome of women with preterm premature rupture of membranes (PPROM). The objectives were to characterize the vaginal microbiota of women following PPROM, and to determine if microbiome composition at the time of rupture predicts latency duration and perinatal outcomes. Only 13/70 samples collected from 36 women were dominated by Lactobacillus spp., the expected profile for healthy women, while Megasphaera type 1 and Prevotella spp. were detected in all samples. Microbiome profiles at the time of membrane rupture did not cluster by gestational age at PPROM, or latency duration. Microbial profiles were unstable over the latency period, with dramatic shifts in composition between weekly samples, and an overall decrease in Lactobacillus abundance. Mollicutes were detected by PCR in 81% (29/36) of women, and these women had significantly lower gestational age at delivery and correspondingly lower birth weight infants than Mollicutes negative women. Taken together, the results presented in this thesis demonstrate the value of high resolution profiling of the vaginal microbiome using cpn60 UT sequences. The resolution of subgroups within G. vaginalis has potentially significant implications for women's health diagnostics, requiring a shift away from considering G. vaginalis as a single entity. The PPROM study provides foundational information that may lead to the identification of informative sequence patterns, providing clinicians with better tools for expectant management following PPROM.
BV, bacterial vaginosis, PPROM, preterm premature rupture of membranes, Gardnerella vaginalis, vaginal microbiome, cpn60, pyrosequencing, genome sequencing
Doctor of Philosophy (Ph.D.)