Bacterial Vaginosis-Vaginal Polymicrobial Biofilms and Dysbiosis

Abstract

Background: Bacterial vaginosis (BV) is the most common genital disease worldwide in women of sexually active age, with a prevalence of 23-29%. Its traditional definition as dysbiosis, i.e., a disruption of the normal balance of the vaginal microbiota, with a massive increase of facultative and obligate anaerobic bacteria (mainly Gardnerella spp.) and a loss of lactobacilli, accurately describes the change in the vaginal microbiota, but does not explain the underlying pathophysiology.

Methods: This review is based on information in pertinent articles retrieved by a selective literature search and on the authors' own research findings.

Results: Fluorescent in situ hybridization (FISH) has revealed Gardnerella spp.-dominated polymicrobial vaginal biofilm as a cause of ascending gynecologic and pregnancy-related infections, preterm birth, and infertility in patients with BV. The biofilm-induced disturbance of epithelial homeostasis favors co-infection with pathogens of sexually transmitted infection (STI). Standard antibiotic therapy is ineffective against biofilms, and there is thus a recurrence rate above 50%. The characteristic biofilm can be followed as a diagnostic marker and is considered evidence of sexual transmission when heterosexual couples and ejaculate samples are examined. FISH studies have shown that, in addition to biofilm-related vaginosis, there are other dysbiotic changes in the vaginal microbiota that have not yet been characterized in detail. It is therefore justified to speak of a "bacterial vaginosis syndrome."

Conclusion: The simplistic view of BV as dysbiosis, characterizable by microscopic reference methods, has so far led to inadequate therapeutic success. An evaluation of molecular genetic testing methods that would be suitable for routine use and the development of therapeutic agents that are effective against biofilms are urgently needed if the "bacterial vaginosis syndrome" is to be effectively treated.

Figure 1

a) Confluent Gardnerella spp.-dominated biofilm on the vaginal epithelium of a patient with bacterial vaginosis (Gardnerella spp. Cy5 probe [red fluorescence] × 400). One can discern the formation of clue cells through desquamation of vaginal epithelial cells with adherent biofilm. b) Gram stain of a vaginal biopsy showing the formation of clue cells × 1000. The Gram stain also reveals how the clue cells are coated with the entire biofilm, thereby becoming a vector of infection transmission.

Figure 2

a) Healthy premenopausal woman Main image: Vaginal epithelial cells and isolated lactobacilli, Lactobacillus Cy3 probe (yellow fluorescence) × 400 Inset: Same microscopic field—clear contours of epithelial cells visible, stained with DAPI (nonspecific DNA stain, blue fluorescence) ×400 b) Biofilm vaginosis: clue cells Main image: Biofilm-coated vaginal epithelial cells (clue cells), Gardnerella spp. Cy3 probe (yellow fluorescence) × 400 Inset: Clue cells with low bacterial density in a different patient with bacterial vaginosis (BV), Gardnerella spp. Cy3 probe (yellow fluorescence) and DAPI counterstain (blue fluorescence) × 400. Despite lower bacterial density, the biofilm on the epithelial cells can be clearly seen. c) Dysbiotic change in the vaginal microbiota: pseudo clue cells Main image: diffusely distributed bacteria (pseudo clue cells) and epithelial cells with surfaces free of bacteria, enterobacteria Cy5 probe (red fluorescence) × 1 000 Inset: massive accumulation of enterobacteria not adhering to epithelial cells in a different field of view of the same specimen (pseudo clue cells) d) Dysbiotic changes in the vaginal microbiota: pseudo clue cells Islands of growth/clusters of bacteria without adherence to epithelial cells (pseudo clue cells), Lactobacillus iners Cy3 probe (yellow fluorescence), DAPI counterstain (blue fluorescence) × 400

eFigure 1

Polymicrobial composition of the biofilm, illustrated using the example of Fannyhessia vaginae bacterial cells integrated in the Gardnerella spp. biofilm (Fannyhessia vaginae probe, Cy3 [yellow fluorescence] and Gardnerella spp. probe, Cy5 [red fluorescence] × 1000)

eFigure 2

Gardnerella spp. biofilm in the endometrium (luteal); (Gardnerella spp. Cy3 probe, yellow fluorescence × 1000)

eFigure 3

Proliferating Gardnerella spp.-dominated polymicrobial biofilm on the vaginal epithelium at day 35 following completion of standard metronidazole therapy (Gardnerella spp. Cy5 probe, red fluorescence, Fannyhessia vaginae Cy3 probe, yellow fluorescence × 400)