Gardnerella Species and Their Association With Bacterial Vaginosis

Abstract

Background: Bacterial vaginosis (BV) is a condition marked by high vaginal bacterial diversity. Gardnerella vaginalis has been implicated in BV but is also detected in healthy women. The Gardnerella genus has been expanded to encompass 6 validly named species and several genomospecies. We hypothesized that particular Gardnerella species may be more associated with BV.

Methods: Quantitative polymerase chain reaction (PCR) assays were developed targeting the cpn60 gene of species groups including G. vaginalis, G. piotii/pickettii, G. swidsinskii/greenwoodii, and G. leopoldii. These assays were applied to vaginal swabs from individuals with (n = 101) and without BV (n = 150) attending a sexual health clinic in Seattle, Washington. Weekly swabs were collected from 42 participants for up to 12 weeks.

Results: Concentrations and prevalence of each Gardnerella species group were significantly higher in participants with BV; 91.1% of BV-positive participants had 3 or more Gardnerella species groups detected compared to 32.0% of BV-negative participants (P < .0001). BV-negative participants with 3 or more species groups detected were more likely to develop BV within 100 days versus those with fewer (60.5% vs 3.7%, P < .0001).

Conclusions: These results suggest that BV reflects a state of high Gardnerella species diversity. No Gardnerella species group was a specific marker for BV.

Keywords: Gardnerella; cpn60; bacterial vaginosis; microbiome.

Figure 1.

Gardnerella cpn60 gene concentrations in participants with and without symptomatic BV. Log transformed baseline Gardnerella cpn60 gene concentrations as measured by qPCR in BV-negative (n = 150) and BV-positive (n = 101) participants by Amsel criteria. Each datapoint represents a participant at baseline and is colored and shaped according to BV diagnosis by Nugent score. Boxes show lower quartile, median, and upper quartile with whiskers extended to 1.5 times the interquartile range. Median Gardnerella species group cpn60 concentrations were significantly higher in BV-positive participants. ****P < .0001, Mann-Whitney test. Abbreviations: BV, bacterial vaginosis; qPCR, quantitative polymerase chain reaction.

Figure 2.

Gardnerella cpn60 concentrations in participants with Amsel and Nugent score concordant and discordant BV diagnoses. Log transformed baseline Gardnerella cpn60 gene concentrations in participants with concordant BV-negative diagnosis (Amsel negative, Nugent score 0–3, n = 110), asymptomatic BV/intermediate microbiota (Amsel negative, Nugent score 4–10, n = 39), and concordant BV-positive diagnosis (Amsel positive, Nugent score 4–10, n = 96). Each datapoint represents a participant at baseline and is colored and shaped according to BV diagnosis by Nugent score. Boxes show lower quartile, median, and upper quartile with whiskers extended to 1.5 times the interquartile range. Median Gardnerella species group cpn60 concentrations were significantly higher in participants with concordant BV and asymptomatic BV/intermediate microbiota compared to concordant BV-negative participants. *P < .05, ****P < .0001, Mann-Whitney test. Abbreviations: BV, bacterial vaginosis; ns, not significant.

Figure 3.

Gardnerella cooccurrence and correlation. A, Cooccurrence heatmaps of Gardnerella species groups in BV-negative (n = 150) and BV-positive (n = 101) participants by Amsel criteria. Percentage of BV-negative or BV-positive participants with cooccurrence of Gardnerella species group pairs by qPCR is shown with darker color indicating higher rate of cooccurrence. B, Spearman correlation values based on concentrations of each Gardnerella species group by qPCR in BV-negative (n = 150) and BV-positive (n = 101) participants by Amsel criteria. Correlation values are shown for each Gardnerella species group pair and colored according to correlation strength; solid color is positive correlation and hatch pattern is negative, with asterisks indicating statistical significance (P < .001). Abbreviations: BV, bacterial vaginosis; qPCR, quantitative polymerase chain reaction.

Figure 4.

Gardnerella cpn60 DNA concentrations in BV-negative participants at baseline and subsequent BV development. Log transformed baseline Gardnerella cpn60 gene concentrations as measured by qPCR in BV-negative participants (Amsel criteria) with detection of each Gardnerella species group. Each point represents an individual participant and is colored and shaped based on Nugent score at baseline. Boxes show lower quartile, median, and upper quartile with whiskers extended to 1.5 times the interquartile range. Significance calculated using Mann-Whitney test. ***P < .001. Abbreviations: BV, bacterial vaginosis; ns, not significant; qPCR, quantitative polymerase chain reaction.

Figure 5.

Changes in Gardnerella concentration in response to antibiotic treatment for symptomatic BV. Log transformed Gardnerella species group cpn60 gene concentrations at antibiotic prescription (day 0), week 1 (days 1–7), week 2 (days 8–14), and week 3 (days 15–21). There were 44 episodes of BV and subsequent antibiotic prescription in 26 participants in the 12-week period examined. Only episodes with detection of each Gardnerella species group at prescription are shown in each plot. Boxes show lower quartile, median, and upper quartile with whiskers extended to 1.5 times the interquartile range. Mann-Whitney test was used to calculate significance. ***P < .001, ****P < .0001. Abbreviations: BV, bacterial vaginosis; ns, not significant.