Glycogen in the vaginal epithelium (top layer of cells) is understood to support the growth of lactobacilli, but the glycogen must be broken down into smaller parts first.
The breakdown is performed by an enzyme found in saliva and the vagina, amylase. Amylase is the enzyme that breakdown carbohydrates.
Amylase is found naturally in the vaginal tract and plays a starring role in the survival of lactobacilli populations. Lactobacilli keep the vagina acidic, while other pathogens increase the pH, such as is found in bacterial vaginosis, aerobic vaginitis and other vaginal dysbioses.
How pH (vaginal acidity of alkalinity) affects the glycogen breaking-down process
The human vagina has a healthy pH range of between 3.8 and 4.5.
- pH 4 – α-amylase activity is low, but still present, and this (speculatively) keeps lactobacilli in check by not allowing their overgrowth.
- pH 5, 6 and 7 – α-amylase activity is increased, and glycogen is degraded faster than at pH 4. This (speculatively) helps promote lactobacilli, since not all microbes can use glycogen’s broken-up sugars as a food source.
One study examined the role of amylase under certain pH conditions in the growth rates of lactobacilli.
The researchers found, in two samples collected from the same woman at different times, that glycogen degradation was strikingly different, and that the carbohydrates produced from the glycogen were also different.
The sugars that glycogen degrades to are:
- Maltose
- Maltotriose
- Maltotetraose
In one of the samples, however, mostly maltose was found. One of the samples showed very high glycogen degradation at pH 4, more so than pH 7, which is contrary to the other findings.
This difference indicates that there are different patterns of pH sensitivity that lead to the determination of two profile types:
- Type I pattern
- Type II pattern
The researchers note that vaginal microbiota profiles were not consistently associated with either type I or type II pattern pH sensitivity. They checked L. iners, L.crispatus, L. jensenii, and Gardnerella vaginalis.
Interestingly, some women had non-amylase enzyme activity, which was more active at a lower pH. This enzyme has not been identified properly, and as yet does not have a name.
The researchers thereby suggest that vaginal pH by itself is not limiting to lactobacilli growth, but the activity of amylase is directly. Amylase is available in bountiful supply in saliva, but it is unclear how much amylase is in the vagina at any one time and where it comes from.
References
Effect of pH on Cleavage of Glycogen by Vaginal Enzymes, Greg T. Spear, Mary McKenna, Alan L. Landay, Hadijat Makinde, Bruce Hamaker, Audrey L. French, Byung-Hoo Lee, Published: July 14, 2015, DOI: 10.1371/journal.pone.0132646
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