The human vaginal bacterial biota and bacterial vaginosis

Abstract

The bacterial biota of the human vagina can have a profound impact on the health of women and their neonates. Changes in the vaginal microbiota have been associated with several adverse health outcomes including premature birth, pelvic inflammatory disease, and acquisition of HIV infection. Cultivation-independent molecular methods have provided new insights regarding bacterial diversity in this important niche, particularly in women with the common condition bacterial vaginosis (BV). PCR methods have shown that women with BV have complex communities of vaginal bacteria that include many fastidious species, particularly from the phyla Bacteroidetes and Actinobacteria. Healthy women are mostly colonized with lactobacilli such as Lactobacillus crispatus, Lactobacillus jensenii, and Lactobacillus iners, though a variety of other bacteria may be present. The microbiology of BV is heterogeneous. The presence of Gardnerella vaginalis and Atopobium vaginae coating the vaginal epithelium in some subjects with BV suggests that biofilms may contribute to this condition.

Figure 1

Competing models for the pathogenesis of BV. At least 2 models exist to explain the pathogenesis of BV. The lactobacillus depletion model suggests that there is a decrease in hydrogen peroxide producing lactobacilli as the primary event that allows for the overgrowth of facultative anaerobes resulting in BV. The primary pathogen model suggests that the entry of facultative anaerobes causes the displacement of lactobacilli thereby resulting in BV.

Figure 2

Comparison of vaginal bacterial species detected by broad range 16S rRNA gene PCR using two different forward primers and the same reverse primer in one sample. The pie charts show the percentages of clones in each library corresponding to specific bacterial 16S rRNA gene sequences obtained using broad range PCR followed by cloning and sequencing in a vaginal sample from a subject diagnosed with bacterial vaginosis. Data obtained using the 338f (a) primer shows a balanced representation of clones while the data obtained using the 27f (b) primer is skewed toward Atopobium vaginae. Note the absence of Gardnerella vaginalis clones in the clone library created with the 27f primer. BVAB denotes bacterial vaginosis associated bacterium.

Figure 3

The microbiology of BV is heterogeneous. Comparison of rank abundance plots from 2 subjects diagnosed with BV. The charts show the percentages of clones in each library corresponding to specific bacterial 16S rRNA gene sequences obtained using broad range PCR followed by cloning and sequencing. The most prevalent bacterial clones in Subject A include those matching Gardnerella vaginalis, Prevotella sp. type 1, BVAB2, Prevotella sp. type 2, and Leptotrichia amnionii. In contrast, the most prevalent clones in Subject B include BVAB1, Sneathia sanguinegens, Prevotella sp. type 1, candidate division TM7, and Prevotella sp. type 2.

Figure 4

Fluorescence image of vaginal fluid from a subject with BV. Bacteria are shown hybridizing with probes targeting BVAB1 (green) and Mobiluncus (red) and visualized by fluorescence in situ hybridization (FISH). Other bacteria (blue) are seen with 4′,6-diamidine-2-phenylindole, dihydrochloride, (DAPI), which stains DNA. The inset shows that Mobiluncus (green) is larger than BVAB1 (red) but has the same curved morphology. (With permission from D. N. Fredricks, T. L. Fiedler, and J. M. Marrazzo, “Molecular identification of bacteria associated with bacterial vaginosis,” New England Journal of Medicine, vol. 353, pp. 1899–1911, 2005.)

Figure 5

Transmission electron micrographs. (a) Electron micrograph of vaginal fluid from a woman with bacterial vaginosis and high concentrations of bacterial vaginosis associated bacterium 1 (BVAB1) shows many curved rods with an electron translucent zone at the outer edge of the cell. (b) These cells are different from the larger, wider, and more electron dense curved rods observed in a pure culture of Mobiluncus curtisii. Both images are at 20 000x magnification.

Figure 6

Summary data of rank abundance plots depicting the bacterial species detected in clone libraries from subjects without BV (A) and with BV (B) in our studies. Broad range PCR using primers 338f and 1407r along with clone library analysis of 1327 clones from 13 subjects without BV resulted in 16 phylotypes being detected. Similar analysis of 2577 clones from 23 clone libraries from 17 subjects with BV resulted in the detection of 44 different bacterial species. Vaginal bacterial species are indicated on the x-axis and the numbers of clones are indicated on the y-axis and above every bar. Subjects without BV have bacterial biotas dominated by lactobacilli while subjects with BV have a diverse bacterial biota. BVAB denotes bacterial vaginosis associated bacterium.

Figure 7

Vaginal biopsy from a subject with BV. A Gardnerella vaginalis biofilm (yellow) is detected at the edge of the vaginal epithelium (bottom) by fluorescence in situ hybridization (FISH). The yellow color is the result of using a combination of probes targeting G. vaginalis (Red), all bacteria (Eub338, green), and 4′,6-diamidine-2-phenylindole, dihydrochloride (DAPI, blue) which stains DNA. Note human cell nuclei in blue. The image on the right shows a vaginal epithelial cell with a cluster of G. vaginalis breaking off the epithelium and likely forming a clue cell.