Free glycogen in vaginal fluids is associated with Lactobacillus colonization and low vaginal pH

Abstract

Objective: Lactobacillus dominates the lower genital tract microbiota of many women, producing a low vaginal pH, and is important for healthy pregnancy outcomes and protection against several sexually transmitted pathogens. Yet, factors that promote Lactobacillus remain poorly understood. We hypothesized that the amount of free glycogen in the lumen of the lower genital tract is an important determinant of Lactobacillus colonization and a low vaginal pH.

Methods: Free glycogen in lavage samples was quantified. Pyrosequencing of the 16S rRNA gene was used to identify microbiota from 21 African American women collected over 8-11 years.

Results: Free glycogen levels varied greatly between women and even in the same woman. Samples with the highest free glycogen had a corresponding median genital pH that was significantly lower (pH 4.4) than those with low glycogen (pH 5.8; p<0.001). The fraction of the microbiota consisting of Lactobacillus was highest in samples with high glycogen versus those with low glycogen (median = 0.97 vs. 0.05, p<0.001). In multivariable analysis, having 1 vs. 0 male sexual partner in the past 6 months was negatively associated, while BMI ≥30 was positively associated with glycogen. High concentrations of glycogen corresponded to higher levels of L. crispatus and L. jensenii, but not L. iners.

Conclusion: These findings show that free glycogen in genital fluid is associated with a genital microbiota dominated by Lactobacillus, suggesting glycogen is important for maintaining genital health. Treatments aimed at increasing genital free glycogen might impact Lactobacillus colonization.

Figure 1. Distribution of Relative Abundance of Lactobacillus by Glycogen Concentration.

Glycogen levels were measured in vaginal fluids collected annually from 21 women over 8–11 years. (A) The final analytic sample consisted of 177 observations with non-missing values for both glycogen and Lactobacillus. The distribution of Lactobacillus relative abundance is summarized by glycogen as a continuous variable. (B) The relative abundance of Lactobacillus and concentration of glycogen over time by participant. Left Y axis is relative abundance of Lactobacillus; right Y axis is glycogen concentration (µg/µl). X-axis is annual visit number.

Figure 2. High levels of free glycogen are associated with a vaginal microbiota dominated by Lactobacillus species and a low vaginal pH.

The final analytic sample consisted of 177 observations with non-missing values for both glycogen and Lactobacillus. Free glycogen was analyzed as a binary variable dichotomized about the median and categorically using cutpoints according quartiles of the distribution, as indicated. The distribution of Lactobacillus relative abundance (A) and vaginal pH (B) are summarized by glycogen as a continuous variable by glycogen quartiles. *p-value is estimated by extension of the Kruskal-Wallis test with adjustment for clustering among repeated measurements.

Figure 3. Relative Abundance of Lactobacillus Species by Category of Glycogen Concentration.

Free glycogen was analyzed as a binary variable dichotomized about the median and categorically using cutpoints according quartiles of the distribution, as indicated. The distribution of Lactobacillus species relative abundance is summarized by glycogen as a continuous variable by glycogen quartiles. Shaded portions represent interquartile range, horizontal bars represent medians, and whiskers represent 95% confidence intervals. *p<0.05 using extension of the Kruskal-Wallis test with adjustment for clustering among repeated measurements.