The Human Microbiome during Bacterial Vaginosis

Abstract

Bacterial vaginosis (BV) is the most commonly reported microbiological syndrome among women of childbearing age. BV is characterized by a shift in the vaginal flora from the dominant Lactobacillus to a polymicrobial flora. BV has been associated with a wide array of health issues, including preterm births, pelvic inflammatory disease, increased susceptibility to HIV infection, and other chronic health problems. A number of potential microbial pathogens, singly and in combinations, have been implicated in the disease process. The list of possible agents continues to expand and includes members of a number of genera, including Gardnerella, Atopobium, Prevotella, Peptostreptococcus, Mobiluncus, Sneathia, Leptotrichia, Mycoplasma, and BV-associated bacterium 1 (BVAB1) to BVAB3. Efforts to characterize BV using epidemiological, microscopic, microbiological culture, and sequenced-based methods have all failed to reveal an etiology that can be consistently documented in all women with BV. A careful analysis of the available data suggests that what we term BV is, in fact, a set of common clinical signs and symptoms that can be provoked by a plethora of bacterial species with proinflammatory characteristics, coupled to an immune response driven by variability in host immune function.

FIG 1

Schematic framework for syndromatic bacterial vaginosis (BV) presentation. The resident microbiome is shaped by host genetics, and in turn, the microbiome regulates host gene expression, while both vaginal and systemic exposures influence the vaginal microbiome-human genome encounter. The result of these interactions determines symptom severity and disparities within the syndrome known as BV.

FIG 2

Physiological in vitro model for the study of host-microbiome interactions in BV. Transmission electron microscopy illustrates human vaginal epithelial cells colonized with one of the signature bacterial species of BV, Atopobium vaginae. Epithelial cells show no signs of apoptosis. Bacteria appear as dense, dark, round bodies, intimately attached to the epithelial surface or taken up inside the epithelial cell cytosol. (Reprinted from reference with permission of the publisher.)