Lactobacillus species as biomarkers and agents that can promote various aspects of vaginal health

Abstract

The human body is colonized by a vast number of microorganisms collectively referred to as the human microbiota. One of the main microbiota body sites is the female genital tract, commonly dominated by Lactobacillus spp., in approximately 70% of women. Each individual species can constitute approximately 99% of the ribotypes observed in any individual woman. The most frequently isolated species are Lactobacillus crispatus, Lactobacillus gasseri, Lactobacillus jensenii and Lactobacillus iners. Residing at the port of entry of bacterial and viral pathogens, the vaginal Lactobacillus species can create a barrier against pathogen invasion since mainly products of their metabolism secreted in the cervicovaginal fluid can play an important role in the inhibition of bacterial and viral infections. Therefore, a Lactobacillus-dominated microbiota appears to be a good biomarker for a healthy vaginal ecosystem. This balance can be rapidly altered during processes such as menstruation, sexual activity, pregnancy and various infections. An abnormal vaginal microbiota is characterized by an increased diversity of microbial species, leading to a condition known as bacterial vaginosis. Information on the vaginal microbiota can be gathered from the analysis of cervicovaginal fluid, by using the Nugent scoring or the Amsel's criteria, or at the molecular level by investigating the number and type of Lactobacillus species. However, when translating this to the clinical setting, it should be noted that the absence of a Lactobacillus-dominated microbiota does not appear to directly imply a diseased condition or dysbiosis. Nevertheless, the widely documented beneficial role of vaginal Lactobacillus species demonstrates the potential of data on the composition and activity of lactobacilli as biomarkers for vaginal health. The substantiation and further validation of such biomarkers will allow the design of better targeted probiotic strategies.

Keywords: STIs; bacterial vaginosis; lactobacilli; probiotics; vaginal microbiota.

Figure 1

Composition of VMB during healthy and dysbiotic states. The vaginal microbiota in healthy adult premenopausal women can be divided into different community groups. The exact number and type of community groups is still under debate (Verhelst et al., ; Ravel et al., ; Gajer et al., ; Santiago et al., 2012). The most commonly isolated dominating species belong to L. crispatus, L. gasseri, L. iners and L. jensenii. The vaginal community group dominated by L. iners is also often isolated during menstruation and in the transitional microbiota between healthy and BV state or vice-versa. Because this species is often isolated during BV, L. iners may not be able to effectively protect against pathogens. Additionally, a non-Lactobacillus dominated VMB is also documented in various healthy individuals (Zhou et al., ; Ravel et al., ; Santiago et al., 2012). For each compositional state, we have added an example of their abundance based on the study of Ravel et al. (2011). However, these numbers are only exemplary and should be considered with caution, as they clearly depend on the study population (size and characteristics) and they certainly need to be substantiated in further studies.