 Tract Microbiota of Monogamous Couples Through Subtle Nucleotide Variation. PLoS ONE 6(10): e26732. https://doi.org/10.1371/journal.pone.0026732
Editor: Jacques Ravel, Institute for Genome Sciences, University of Maryland School of Medicine, United States of America
Received: May 11, 2011; Accepted: October 3, 2011; Published: October 25, 2011
Copyright: © 2011 Eren et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: This work is supported by funding from the Research Institute for Children in New Orleans and NIH grant 5RO1AI79071-2. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing interests: The authors have declared that no competing interests exist.
As a group, bacteria are the most genetically diverse and abundant life form on Earth . In fact the human body is home to a diverse assemblage of bacteria that colonize the gastrointestinal tract, oral cavity, skin, airway passages and genitourinary system . Culture-independent surveys estimate that the human gut alone is home to 40,000 bacterial species  and it is estimated that the number of bacterial cells in the human body is ten-fold greater than the number of eukaryotic cells that comprise the human body , . Humans depend on a symbiotic relationship with bacteria to extract nutrients from food and for normal immune system development –. On the other hand, adverse medical conditions are also associated with changes in the composition and relative abundance of our bacterial microbiota.
One of the most well studied medical conditions associated with a change in the human microbiota is bacterial vaginosis (BV). BV is a common vaginal disorder and symptoms often include vaginal discharge, pruritis, and odor. The microbiology of BV is characterized by a drastic reduction in the concentration of Lactobacillus species in the vaginal environment and an increase in the concentration of G. vaginalis and many other bacterial genera . This shift in microbiota is reflected in quantifiable changes in vaginal smear Gram stains (GS) as measured by the Nugent Score (NS) . Women with Lactobacillus dominated microbiota have NS of 0–3 while women with BV have NS of 7–10. It is important to keep in mind that many women with BV as defined by NS are totally asymptomatic and for this reason some investigators in the field believe this represents a normal variant of the vaginal microbiota . Nevertheless, the microbiota associated with BV as defined by GS pattern is associated with a number of serious medical sequelae including preterm delivery , . A reduction in the concentration of Lactobacillus species leads to an increase in vaginal pH and a deterioration in immune response to sexually transmitted viral infections including HIV . Although the natural history of the microbial communities associated with BV is not yet fully understood , several studies suggest that the condition can be sexually transmitted ,  and that Gardnerella vaginalis may be the etiologic agent . In contrast to the latter assertion, G. vaginalis is also commonly detected in vaginal samples of women with GS-defined normal vaginal microbiota, albeit, at significantly lower concentrations than in GS-defined BV , , .
Phenotypic and genomic analyses of G. vaginalis isolates suggest that, in addition to low concentration, the conflicting observation of the presence of this species in both normal (or asymptomatic) and BV (or symptomatic) women may be rationalized by the existence of different strains of G. vaginalis, i.e. avirulent commensal strains colonize normal women while more-virulent strains may be infecting BV patients. This idea is supported by phenotypic analyses that show biofilm formation is a virulence trait of G. vaginalis isolates and the ability to form biofilms is associated with BV . In addition, a recent genomic study showed 