The means by which vaginal microbiomes help prevent urogenital diseases in women and maintain health are poorly understood. To gain insight into this, the vaginal bacterial communities of 396 asymptomatic North American women who represented four ethnic groups (white, black, Hispanic, and Asian) were sampled and the species composition characterized by pyrosequencing of barcoded 16S rRNA genes. The communities clustered into five groups: four were dominated by Lactobacillus iners, L. crispatus, L. gasseri, or L. jensenii, whereas the fifth had lower proportions of lactic acid bacteria and higher proportions of strictly anaerobic organisms, indicating that a potential key ecological function, the production of lactic acid, seems to be conserved in all communities. The proportions of each community group varied among the four ethnic groups, and these differences were statistically significant [χ 2 (10) = 36.8, P < 0.0001]. Moreover, the vaginal pH of women in different ethnic groups also differed and was higher in Hispanic (pH 5.0 ± 0.59) and black (pH 4.7 ± 1.04) women as compared with Asian (pH 4.4 ± 0.59) and white (pH 4.2 ± 0.3) women. Phylotypes with correlated relative abundances were found in all communities, and these patterns were associated with either high or low Nugent scores, which are used as a factor for the diagnosis of bacterial vaginosis. The inherent differences within and between women in different ethnic groups strongly argues for a more refined definition of the kinds of bacterial communities normally found in healthy women and the need to appreciate differences between individuals so they can be taken into account in risk assessment and disease diagnosis. T he human body harbors microorganisms that inhabit surfaces and cavities exposed or connected to the external environment. Each body site includes ecological communities of microbial species that exist in a mutualistic relationship with the host. The kinds of organisms present are highly dependent on the prevailing environmental conditions and host factors and hence vary from site to site. Moreover, they vary between individuals and over time (1). The human vaginal microbiota seem to play a key role in preventing a number of urogenital diseases, such as bacterial vaginosis, yeast infections, sexually transmitted infections, urinary tract infections (2-9), and HIV infection (10, 11). Common wisdom attributes this to lactic acid-producing bacteria, mainly Lactobacillus sp., that commonly inhabit the vagina. These species are thought to play key protective roles by lowering the environmental pH through lactic acid production (12, 13), by producing various bacteriostatic and bacteriocidal compounds, or through competitive exclusion (13-16). The advent of culture-independent molecular approaches based on the cloning and sequencing of 16S rRNA genes has furthered our understanding of the vaginal microbiota by identifying taxa that had not been cultured (17-24). However, this technique is limited by high cost and low throughput, hence only small ...

Elucidating the factors that impinge on the stability of bacterial communities in the vagina may help in predicting the risk of diseases that affect women’s health. Here, we describe the temporal dynamics of the composition of vaginal bacterial communities in 32 reproductive age women over a 16-week period. The analysis revealed the dynamics of five major classes of bacterial communities and showed that some communities change markedly over short time periods, whereas others are relatively stable. Modeling community stability using new quantitative measures indicates that deviation from stability correlates with time in the menstrual cycle, bacterial community composition and sexual activity. The women studied are healthy, thus it appears that neither variation in community composition per se, nor higher levels of observed diversity (co-dominance) are necessarily indicative of dysbiosis, in which there is microbial imbalance accompanied by symptoms.

Recent investigations have demonstrated that human milk contains a variety of bacterial genera; however, as of yet very little work has been done to characterize the full diversity of these milk bacterial communities and their relative stability over time. To more thoroughly investigate the human milk microbiome, we utilized microbial identification techniques based on pyrosequencing of the 16S ribosomal RNA gene. Specifically, we characterized the bacterial communities present in milk samples collected from 16 women at three time-points over four weeks. Results indicated that milk bacterial communities were generally complex; several genera represented greater than 5% of the relative community abundance, and the community was often, yet not always, stable over time within an individual. These results support the conclusion that human milk, which is recommended as the optimal nutrition source for almost all healthy infants, contains a collection of bacteria more diverse than previously reported. This finding begs the question as to what role this community plays in colonization of the infant gastrointestinal tract and maintaining mammary health.

The maintenance of a low pH in the vagina through the microbial production of lactic acid is known to be an important defense against infectious disease in reproductive age women. Previous studies have shown that this is largely accomplished through the metabolism of lactic acid bacteria, primarily species of Lactobacillus. Despite the importance of this defense mechanism to women's health, differences in the species composition of vaginal bacterial communities among women have not been well defined, nor is it known if and how these differences might be linked to differences in the risk of infection. In this study, we defined and compared the species composition of vaginal bacterial communities in 144 Caucasian and black women in North America. This was carried out based on the profiles of terminal restriction fragments of 16S rRNA genes, and phylogenetic analysis of 16S rRNA gene sequences of the numerically dominant microbial populations. Among all the women sampled, there were eight major kinds of vaginal communities ('supergroups') that occurred in the general populace at a frequency of at least 0.05 (P ¼ 0.99). From the distribution of these supergroups among women, it was possible to draw several conclusions. First, there were striking, statistically significant differences (P ¼ 0.0) in the rank abundance of community types among women in these racial groups. Second, the incidence of vaginal communities in which lactobacilli were not dominant was higher in black women (33%) as compared to Caucasian women (7%). Communities not dominated by lactobacilli had Atopobium and a diverse array of phylotypes from the order Clostridiales. Third, communities dominated by roughly equal numbers of more than one species of Lactobacillus were rare in black women, but common in Caucasian women. We postulate that because of these differences in composition, not all vaginal communities are equally resilient, and that differences in the vaginal microbiota of Caucasian and black women may at least partly account for known disparities in the susceptibility of women in these racial groups to bacterial vaginosis and sexually transmitted diseases.

Background DNA extraction is an essential step in all cultivation-independent approaches to characterize microbial diversity, including that associated with the human body. A fundamental challenge in using these approaches has been to isolate DNA that is representative of the microbial community sampled. Methodology/Principal Findings In this study, we statistically evaluated six commonly used DNA extraction procedures using eleven human-associated bacterial species and a mock community that contained equal numbers of those eleven species. These methods were compared on the basis of DNA yield, DNA shearing, reproducibility, and most importantly representation of microbial diversity. The analysis of 16S rRNA gene sequences from a mock community showed that the observed species abundances were significantly different from the expected species abundances for all six DNA extraction methods used. Conclusions/Significance Protocols that included bead beating and/or mutanolysin produced significantly better bacterial community structure representation than methods without both of them. The reproducibility of all six methods was similar, and results from different experimenters and different times were in good agreement. Based on the evaluations done it appears that DNA extraction procedures for bacterial community analysis of human associated samples should include bead beating and/or mutanolysin to effectively lyse cells.