Lactobacillus acidophilus has been reported to be the predominant vaginal species. Vaginal lactobacilli isolated from 215 sexually active women were identified using whole-chromosomal DNA probes to 20 American Type Culture Collection Lactobacillus strains. Most women were colonized by L. crispatus (32%), followed by L. jensenii (23%), a previously undescribed species designated L. 1086V (15%), L. gasseri (5%), L. fermentum (0.3%), L. oris (0.3%), L. reuteri (0.3%), L. ruminis (0.3%), and L. vaginalis (0.3%). H2O2 was produced by 95% of L. crispatus and 94% of L. jensenii isolates, compared with only 9% of L. 1086V. Colonization by L. crispatus or L. jensenii was positively associated with being white (P<.001), age >/=20 years (P=.05), barrier contraceptive usage (P=.008), and lower frequency of bacterial vaginosis (P<.001) and gonorrhea (P=.03). L. crispatus and L. jensenii, not L. acidophilus, are the most common species of vaginal lactobacilli.

Lactobacilli colonizing the rectum may be a reservoir for vaginal lactobacilli. In a cross-sectional study of 531 females, vaginal and rectal colonization by lactobacilli were assessed by culture methods. A subset of isolates was identified to the species level by use of whole-chromosomal DNA probes. Lactobacillus crispatus (16%), L. jensenii (10%), and L. gasseri (10%) were the prevalent lactobacilli colonizing the rectums of 290 females. Only 13 (9%) of 147 females colonized by L. crispatus or L. jensenii vaginally and/or rectally had bacterial vaginosis (BV), compared with 12 (44%) of 27 females colonized by other H(2)O(2)-producing lactobacilli (P < .001). Cocolonization of the vagina and rectum by H(2)O(2)-producing lactobacilli was associated with the lowest prevalence of BV (5%), whereas females colonized only vaginally, only rectally, or at neither site had a successively increased risk of BV (P < .001). Lactobacillus species in the rectum may contribute to the maintenance of vaginal microflora.

To identify factors that predict sustained colonization by vaginal lactobacilli, microbiologic, behavioral, and demographic data were obtained from 101 nonpregnant women at baseline and at 4 and 8 months. A total of 272 isolates of lactobacilli were identified to the species level by use of whole chromosomal DNA homology to type strains. The predominant lactobacilli were the species Lactobacillus crispatus (38%) and L. jensenii (41%). Of 57 women initially colonized by H(2)O(2)-producing L. crispatus or L. jensenii, 23 (40%) remained colonized over 8 months, compared with 1 (5%) of 21 women colonized by other H(2)O(2)-producing species or by H(2)O(2)-negative strains (P=.01). Frequency of sexual intercourse (> or =1 sex act per week) was associated with loss of colonization with H(2)O(2)-producing lactobacilli (P=.018), as was antibiotic use (P< or =.0001). Other behavioral and demographic characteristics did not predict sustained colonization. The production of H(2)O(2) is closely linked with species and is a predictor for sustained long-term colonization of the vagina.

These data suggest that the factors that predict failure to become colonized by probiotic lactobacilli include exposure to semen, vaginal intercourse, and the presence of lactobacilli of the same species at enrollment.