Abstract
Human microbiota plays an indispensable role in physiology, nutrition and most significantly, in imparting immunity. The role of microbiota has remained cryptic for years, until recently meticulous studies revealed the interaction and dynamics of these microbial communities. This diversified state is governed by hormonal, behavioral and physio-chemical changes in the genital tract. Many inclusive studies have revealed “Lactobacillus” to be the most dominant member of vaginal flora in most of the healthy, reproductive age group and pregnant females. A total of five community state types have been described, out of which four are dominated by Lactobacillus while the fifth one by facultative or strict anaerobic species. A variation between species stability and gestational age has also been revealed. Studies have divulged a significant higher stability of vaginal microbiota in early stages of pregnancy and the same increased subsequently. Inter-species and racial variation has shown women belonging to White, Asian, and Caucasian race to harbor more of the anaerobic flora. The vaginal microbiome in pregnancy play a significant role in preterm and spontaneous labor. This Lactobacillus-rich microbiome falls tremendously, becoming more diverse in post-partum period. Apart from these known bacterial communities in human vagina, other microbial communities have also been traced. The major fragment is constituted by vaginal viral virome and very little information exists in relation to vaginal mycobiome. Studies have revealed the abundance of ds DNA viruses in vaginal microbiome, followed by ssDNA, and few unidentified viruses. The eukaryotic viruses detected were very few, with Herpesvirales, and Papillomaviridae being the only pathogenic ones. This flora is transmitted to infants either via maternal gut, vagina or breast milk. Recent studies have given an insight for vaginal microbiome, dissociating the old concept of “healthy” and “diseased.” However, more extensive studies are required to study evolution of virome and mycobiome in relation to their association with bacterial communities; to establish and decode full array of vaginal virome under the influence of genotypic and environmental factors, using novel bioinformatic, multi-omic, statistical model, and CRISPR/Cas approaches.
Highlights
Human microbiota is an array of microbes, including archaea, protista, bacteria, fungi, and viruses that exist on and within the human tissues, fluids and body cavities, along with varied anatomical sites; whereas microbiome is an aggregate of the genetic materials of resident microbiota [1, 2]
The microbiota in pregnant vagina is less rich and less diverse as compared to non-pregnant vagina, with a predominance of Lactobacillus species. This microbiome was characterized in 182 pregnant females of 11–16 weeks gestation and 310 non-pregnant females, via pyrosequencing of cpn60 region and revealed six different community state types profiles [73]
Similar to the ones described earlier by Ravel et al [32], along with interstate variations in vagina were noted. These variations were represented as a Markov chain and a significant correlation was observed for Gardenella and Ureaplasma, when tested independently while association with Gardenella remained significant on non-independent analysis. This highlights the importance of Gardenella in a setting of low Lactobacilli burden, as a potential contributor to preterm labor (PTL)
Summary
Human microbiota is an array of microbes, including archaea, protista, bacteria, fungi, and viruses that exist on and within the human tissues, fluids and body cavities, along with varied anatomical sites; whereas microbiome is an aggregate of the genetic materials of resident microbiota [1, 2]. Pregnant women of European lineage showed only a lower prevalence of L. crispatus accompanied by a richer prevalence of L. iners [51] In all these females, the microbiome shifted more toward a stable, Lactobacillus-dominant profile with a major shift in early stages of pregnancy, significantly in women of African or Hispanic lineage. The microbiota in pregnant vagina is less rich and less diverse as compared to non-pregnant vagina, with a predominance of Lactobacillus species This microbiome was characterized in 182 pregnant females of 11–16 weeks gestation and 310 non-pregnant females, via pyrosequencing of cpn region and revealed six different community state types profiles [73]. There is a need for further studies to discover the basis of this “steady-state immune-bacterial crosstalk” and the interaction between bacterial microbiome and oncogenic virome
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