Acid production by vaginal flora in vitro is consistent with the rate and extent of vaginal acidification

Perinatally, and between menarche and menopause, increased levels of estrog en cause large amounts of glycogen to be deposited in the vaginal epitheliu m. During these times, the anaerobic metabolism of the glycogen, by the epi thelial cells themselves and/or by vaginal flora, causes the vagina to beco me acidic (pH similar to 4). This study was designed to test whether the ch aracteristics of acid production by vaginal flora in vitro can account for vaginal acidity. Eight vaginal Lactobacillus isolates from four species-L. gasseri, L. vaginalis, L. crispatus, and L. jensenii-acidified their growth medium to an asymptotic pH (3.2 to 4.8) that matches the range seen in the Lactobacillus-dominated human vagina (pH 3.6 to 4.5 in most women) (B. And ersch, L. Forssman, K, Lincoln, and P. Torstensson, Gynecol. Obstet. Invest ig. 21:19-25, 1986; L. Cohen, Br. J. Vener. Dis. 45:241-246, 1969; J. Paavo nen, Scand. J. Infect. Dis. Suppl. 40:31-35, 1983; C. Tevi-Benissan, L. Bel ec, M. Levy V. Schneider-Fauveau, A. Si Mohamed, M.-C. Hallouin, M. Matta, and G. Gresenguet, Clin. Diagn. Lab. Immunol. 4:367-374, 1997). During expo nential growth, all of these Lactobacillus species acidified their growth m edium at rates on the order of 10(6) protons/bacterium/s. Such rates, combi ned with an estimate of the total number of lactobacilli in the vagina, sug gest that vaginal lactobacilli could reacidify the vagina at the rate obser ved postcoitally following neutralization by the male ejaculate (W. H. Mast ers and V. E. Johnson, Human sexual response, p. 93, 1966). During bacteria l vaginosis (BV), there is a loss of vaginal acidity, and the vaginal pH ri ses to >4.5. This correlates with a loss of lactobacilli and an overgrowth of diverse bacteria. Three BV-associated bacteria, Gardnerella vaginalis, P revotella bivia, and Peptostreptococcus anaerobius, acidified their growth medium to an asymptotic pH (4.7 to 6.0) consistent with the characteristic elevated vaginal pH associated with BV. Together, these observations are co nsistent with vaginal Bore, rather than epithelial cells, playing a primary role in creating the acidity of the vagina.