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Open Access Open Badges Research article

Cervicovaginal fluid and semen block the microbicidal activity of hydrogen peroxide produced by vaginal lactobacilli

Deirdre E O'Hanlon1*, Blair R Lanier1, Thomas R Moench2 and Richard A Cone12

Author Affiliations

1 Mucosal Protection Laboratory, Thomas C. Jenkins Department of Biophysics, Johns Hopkins University, Baltimore, MD 21218, USA

2 ReProtect, Inc., Baltimore, MD 21286, USA

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BMC Infectious Diseases 2010, 10:120  doi:10.1186/1471-2334-10-120

Published: 19 May 2010



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.


We measured the H2O2 concentration of CVF and the H2O2-blocking activity of CVF and semen using fluorescence and in vitro bacterial-exposure experiments.


The mean H2O2 measured in fully aerobic CVF was 23 ± 5 μM; however, 50 μM 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.


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.