The vaginal microbiota, host defence and reproductive physiology

Abstract

The interaction between the human host and the vaginal microbiota is highly dynamic. Major changes in the vaginal physiology and microbiota over a woman's lifetime are largely shaped by transitional periods such as puberty, menopause and pregnancy, while daily fluctuations in microbial composition observed through culture-independent studies are more likely to be the results of daily life activities and behaviours. The vaginal microbiota of reproductive-aged women is largely made up of at least five different community state types. Four of these community state types are dominated by lactic-acid producing Lactobacillus spp. while the fifth is commonly composed of anaerobes and strict anaerobes and is sometimes associated with vaginal symptoms. The production of lactic acid has been associated with contributing to the overall health of the vagina due to its direct and indirect effects on pathogens and host defence. Some species associated with non-Lactobacillus vaginal microbiota may trigger immune responses as well as degrade the host mucosa, processes that ultimately increase susceptibility to infections and contribute to negative reproductive outcomes such as infertility and preterm birth. Further studies are needed to better understand the functional underpinnings of how the vaginal microbiota affect host physiology but also how host physiology affects the vaginal microbiota. Understanding this fine-tuned interaction is key to maintaining women's reproductive health.

Associations of the vaginal microbiota with HIV infection, bacterial vaginosis, and demographic factors

“…To assign Lactobacillus sequences to the species level, sequences were compared to the 16S Lactobacillus type strains downloaded from Bacterio.net. As was seen in previous studies [3, 9, 11, 39, 40] , many samples showed high proportions of bacteria from the genus Lactobacillus (Figure 1D–E). A total of 99.3% of Lactobacillus sequences were classified to the species level (using BLAST with e-value threshold of 10 −5 and percent identity > 97%).…”

“…Diversity and pH were associated with Nugent score (Pearson’s correlation r=0.45 and r=0.44, p<0.001 and p<0.001 respectively, Supplemental Figure 2), paralleling several studies that have shown that BV is associated with low Lactobacillus , high diversity, and high pH [9, 11, 18, 39, 40] . The high diversity state was associated with increased representation of proinflammatory lineages (Figure 2G), including Mobiluncus .…”

“…This finding accounted for more frequent switching by the women sampled from the CC hospital. For some women, the vaginal microbiota has been reported to show longitudinal variation, in some cases associated with the menstrual cycle but also on other time scales as well [40, 44–46] . The factors driving longitudinal dynamics have not been fully clarified.…”

Metagenomic analysis with strain-level resolution reveals fine-scale variation in the human pregnancy microbiome

“…2011;DiGiulio et al 2015), an organism that has been associated with both health and disease (Macklaim et al 2011). Recent studies have shown that L. iners is associated with high diversity CSTs while L. crispatus (dominant species in CST I) is thought to be more protective against disease (Callahan et al 2017;Smith and Ravel 2017). We recovered 6 near complete L.…”

Influence of the microbiota on host physiology – moving beyond the gut

“…The five reviews that follow fall into two groups. Three address the nature and physiological effects of microbiota outside the alimentary tract – the skin, vaginal canal and the oral cavity (authored by Barnard & Li (), Smith & Ravel () and Kumar (), respectively). The remaining articles focus on the gut microbiota, but rather than asking how this extensive microbial community influences digestive health and disease, they summarize evidence to support a role for the gut microbiota in regulating either systemic metabolism (Janssen & Kersten, ) or brain function (Dinan & Cryan, ).…”