Abstract

Glycogen expressed by the lower genital tract epithelium is believed to support Lactobacillus growth in vivo, although most genital isolates of Lactobacillus are not able to use glycogen as an energy source in vitro. We recently reported that α-amylase is present in the genital fluid of women and that it breaks down glycogen into small carbohydrates that support growth of lactobacilli. Since the pH of the lower genital tract can be very low, we determined how low pH affects glycogen processing by α-amylase. α-amylase in saliva degraded glycogen similarly at pH 6 and 7, but activity was reduced by 52% at pH 4. The glycogen degrading activity in nine genital samples from seven women showed a similar profile with an average reduction of more than 50% at pH 4. However, two samples collected from one woman at different times had a strikingly different pH profile with increased glycogen degradation at pH 4, 5 and 6 compared to pH 7. This second pH profile did not correlate with levels of human α-acid glucosidase or human intestinal maltase glucoamylase. High-performance anion-exchange chromatography showed that mostly maltose was produced from glycogen by samples with the second pH profile in contrast to genital α-amylase that yielded maltose, maltotriose and maltotetraose. These studies show that at low pH, α-amylase activity is reduced to low but detectable levels, which we speculate helps maintain Lactobacillus growth at a limited but sustained rate. Additionally, some women have a genital enzyme distinct from α-amylase with higher activity at low pH. Further studies are needed to determine the identity and distribution of this second enzyme, and whether its presence influences the makeup of genital microbiota.

Highlights

  • The lower genital tract microbiota of many women is dominated by bacteria of the genus Lactobacillus

  • We recently reported that α-amylase is present in the genital fluid of women and that it breaks down glycogen into small carbohydrates that support growth of lactobacilli

  • High-performance anion-exchange chromatography showed that mostly maltose was produced from glycogen by samples with the second pH profile in contrast to genital α-amylase that yielded maltose, maltotriose and maltotetraose

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Summary

Introduction

The lower genital tract microbiota of many women is dominated by bacteria of the genus Lactobacillus. In those women, production of lactic acid by Lactobacillus acidifies the vaginal. In a study that compared genital pH with microbiota identified by high throughput sequencing, Ravel et al [3] found that in women whose lower genital tract microbiota was dominated by Lactobacillus, the pH was typically 4–4.5 while in most of the women whose microbiota was not dominated by Lactobacillus, the pH was >5.5. The low pH created by Lactobacillus is thought to be the main mechanism by which colonization by this bacterium reduces susceptibility of women to acquiring sexually transmitted infections [4,5,6]

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