In the present narrative review, the probiotic effects of vaginal Lactobacillus spp. are described in detail, covering the importance of the differential production of
lactic acid, the
lactic acid D/L
isoforms, the questionable in vivo effect of
hydrogen peroxide, as well as
bacteriocins and other core
proteins produced by vaginal Lactobacillus spp. Moreover, the microbe-host interaction is explained with emphasis on the vaginal mucosa. To understand the crucial role of Lactobacillus spp. dominance in the vaginal microbiota, different dysbiotic states of the vagina are explained including
bacterial vaginosis and aerobic
vaginitis. Finally, this review takes on the therapeutic aspect of live lactobacilli in the context of
bacterial vaginosis. Until recently, there was very low-quality evidence to suggest that any probiotic might aid in reducing vaginal
infections or
dysbiosis. Therefore, clinical usage or over the counter usage of probiotics was not recommended. However, recent progress has been made, moving from probiotics that are typically regulated as food supplements to so-called live biotherapeutic products that are regulated as medical drugs. Thus, recently, a phase 2b trial using a Lactobacillus crispatus strain as a therapeutic add-on to standard
metronidazole showed significant reduction in the recurrence of
bacterial vaginosis by 12 weeks compared to placebo. This may constitute evidence for a brighter future where the
therapeutic use of lactobacilli can be harnessed to improve women's health.