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    Vaginal pH measured in vivo: lactobacilli determine pH and lactic acid concentration

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    Author
    O’Hanlon, D.E.
    Come, R.A.
    Moench, T.R.
    Date
    2019
    Journal
    BMC Microbiology
    Publisher
    BioMed Central Ltd.
    Type
    Article
    
    Metadata
    Show full item record
    See at
    https://dx.doi.org/10.1186/s12866-019-1388-8
    Abstract
    Background: Lactic acid (protonated lactate) has broad antimicrobial activity. Vaginal lactobacilli produce lactic acid, and are known to confer protection against reproductive tract infections when they are predominant in the vaginal microbiota. Using novel ex vivo methods, we showed that cervicovaginal fluid (CVF) from women with a predominantly lactobacilli-morphotype microbiota contains significantly more lactic acid than previously thought, sufficient to inactivate reproductive tract pathogens. Here, we measured vaginal pH in vivo in 20 women with a predominantly lactobacilli-morphotype (low Nugent score) microbiota. We also investigated the in vitro production of protons (as hydrogen ions) and lactate by vaginal lactobacilli. Results: The average vaginal pH in these women was 3.80 ± 0.20, and the average lactate concentration was 0.79% ± 0.22% w/v, with pH and lactate concentration tightly correlated for each sample. In vitro, lactobacilli cultured from these CVF samples reached an average pH of 3.92 ± 0.22, but the average lactate concentration was only 0.14% ± 0.06% w/v, approximately five-fold less than in the corresponding CVF samples. When the pH of the cultures was raised, lactate and hydrogen ion production resumed, indicating that production of lactate and hydrogen ions by vaginal lactobacilli is limited primarily by their sensitivity to hydrogen ion concentration (low pH) not lactate concentration. Conclusions: Some vaginal lactobacilli cultures have a lower limiting pH than others, and limiting pHs in vitro showed good correlation with pHs measured in vivo. The limiting pH of the lactobacilli predominant in a woman's vaginal microbiota seems critical in determining the concentration of antimicrobial lactic acid protecting her. © 2019 The Author(s).
    Keyword
    bacterial vaginosis
    Lactobacilli
    pH
    vaginal
    Bacteria
    Lactic Acid
    Microbiota
    Vaginosis, Bacterial
    Identifier to cite or link to this item
    https://www.scopus.com/inward/record.uri?eid=2-s2.0-85059934425&doi=10.1186%2fs12866-019-1388-8&partnerID=40&md5=bcfe6ecd36522ef22b71fd1863db3729; http://hdl.handle.net/10713/8551
    ae974a485f413a2113503eed53cd6c53
    10.1186/s12866-019-1388-8
    Scopus Count
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    UMB Open Access Articles 2019

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