Lactic acid and
short chain fatty acids (SCFAs) produced by vaginal microbiota have reported antimicrobial and immune modulatory activities indicating their potential as
biomarkers of disease and/or
disease susceptibility. In asymptomatic women of reproductive-age the vaginal microbiota is comprised of
lactic acid-producing bacteria that are primarily responsible for the production of
lactic acid present at ~110 mM and acidifying the vaginal milieu to pH ~3.5. In contrast,
bacterial vaginosis (BV), a
dysbiosis of the vaginal microbiota, is characterized by decreased
lactic acid-producing microbiota and increased diverse anaerobic bacteria accompanied by an elevated pH>4.5. BV is also characterized by a dramatic loss of
lactic acid and greater concentrations of mixed SCFAs including
acetate,
propionate,
butyrate, and
succinate. Notably women with
lactic acid-producing microbiota have more favorable reproductive and sexual health outcomes compared to women with BV. Regarding the latter, BV is associated with increased susceptibility to
sexually transmitted infections (
STIs) including HIV. In vitro studies demonstrate that
lactic acid produced by vaginal microbiota has microbicidal and virucidal activities that may protect against
STIs and endogenous opportunistic bacteria as well as immune modulatory properties that require further characterization with regard to their effects on the vaginal mucosa. In contrast, BV-associated SCFAs have far less antimicrobial activity with the potential to contribute to a pro-inflammatory vaginal environment. Here we review the composition of
lactic acid and SCFAs in respective states of eubiosis (non-BV) or
dysbiosis (BV), their effects on susceptibility to bacterial/viral
STIs and whether they have inherent microbicidal/virucidal and immune modulatory properties. We also explore their potential as
biomarkers for the presence and/or increased susceptibility to
STIs.