Er. Boskey et al., Acid production by vaginal flora in vitro is consistent with the rate and extent of vaginal acidification, INFEC IMMUN, 67(10), 1999, pp. 5170-5175
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.