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Updated: Jun 12, 2026

A Murine Model of Group B Streptococcus Vaginal Colonization
Published on: November 16, 2016
Cervicovaginal fluid and semen block the microbicidal activity of hydrogen peroxide produced by vaginal lactobacilli
Deirdre E O'Hanlon1, Blair R Lanier, Thomas R Moench
1Mucosal Protection Laboratory, Thomas C, Jenkins Department of Biophysics, Johns Hopkins University, Baltimore, MD 21218, USA. eohanlon@jhu.edu
Background:
H2O2 produced by vaginal lactobacilli is believed to protect against infection, and H2O2-producing lactobacilli inactivate pathogens in vitro in protein-free salt solution. However, cervicovaginal fluid (CVF) and semen have significant H2O2-blocking activity.
Methods:
We measured the H2O2 concentration of CVF and the H2O2-blocking activity of CVF and semen using fluorescence and in vitro bacterial-exposure experiments.
Results:
The mean H2O2 measured in fully aerobic CVF was 23 +/- 5 microM; however, 50 microM H2O2 in salt solution showed no in vitro inactivation of HSV-2, Neisseria gonorrhoeae, Hemophilus ducreyii, or any of six BV-associated bacteria. CVF reduced 1 mM added H2O2 to an undetectable level, while semen reduced 10 mM added H2O2 to undetectable. Moreover, the addition of just 1% CVF supernatant abolished in vitro pathogen-inactivation by H2O2-producing lactobacilli.
Conclusions:
Given the H2O2-blocking activity of CVF and semen, it is implausible that H2O2-production by vaginal lactobacilli is a significant mechanism of protection in vivo.
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