Investigating the role of Lactobacillus isolates from South African young women in the control of bacterial vaginosis (BV) - associated Gardnerella vaginalis and Candida.

Abstract

Background: Lactobacillus (L.) strains offer a promising approach for preventing and treating viral, bacterial, and fungal infections, serving as alternatives or complements to traditional antibacterial and antifungal therapies. Current treatments for bacterial vaginosis (BV) often entail side effects such as gastrointestinal disturbances, antibiotic resistance, and high recurrence rates, while antifungal treatments may lead to skin irritation and gut health issues, particularly in pregnant women. These challenges underscore the urgent need for alternative strategies to manage vaginal infections. This study investigated the probiotic characteristics of Lactobacillus species isolated from healthy African women and assessed their effects on pathogenic microbes, specifically Gardnerella (G.) vaginalis and Candida (C.) albicans, alongside their production of antimicrobial substances, including lactic acid and H₂O₂. Methods: Thirteen strains of vaginal Lactobacillus species (L. crispatus, L. gasseri, L. jensenii, L. mucosae, and L. vaginalis) were pre-isolated from HIV-negative young women from South Africa. The cell morphology of the bacterial strains was confirmed with the Gram staining technique. The ability of Lactobacillus strains to acidify culture media was measured by monitoring the pH changes over time during incubation using a calibrated pH meter. The production of antimicrobial compounds, specifically D- and L-lactate and hydrogen peroxide (H₂O₂), were quantified using colorimetric assay kits. The inhibitory activity of the isolated Lactobacillus strains against G. vaginalis and C. albicans was assessed using standardised in vitro assays, which typically involved co-culturing the Lactobacillus culture supernatants (LCS) with the pathogens and measuring growth inhibition by optical density (OD600nm) over time. The study compared differences in inhibitory effects, lactic acid, H₂O₂ production, and pH reduction among the Lactobacillus species and strains. The Mann-Whitney non-parametric t-test was used to analyse the data for two groups, while the Kruskal-Wallis one-way ANOVA unpaired test was used with the unadjusted Dunn’s multiple comparisons tests. Results: The growth kinetics of the Lactobacillus isolates were comparable, with their optimum growth reached at 48 to 72 hours. The pH of MRS cultures decreased over time from 6 to 3.5 by all the vaginal isolates. The isolates produced relatively low but measurable H₂O₂, D- and L-lactic acid concentrations ranging from 253 to 440 μMol/L, 1.05 to 2.9 ng/μL, and 0.09 to 0.13 mM, respectively. Lactobacillus crispatus (70.7pa and 94.79pa) showed better production of metabolites, followed by L. gasseri and L. jensenii (95.1pa). Lactobacillus gasseri and L. crispatus demonstrated vigorous antibacterial activity against G. vaginalis, decreasing its growth to about 50%. Candida albicans grew to approximately 70% in the v presence of L. crispatus (70.7pa and 94.79pa) and L. vaginalis 88.5b, showing better inhibitory activity than the other tested Lactobacillus strains. Conclusion: This study highlights the significant potential of African-derived vaginal Lactobacillus species as probiotics for preventing and treating vaginal infections, with L. gasseri and L. crispatus showing the most potent properties. These strains effectively inhibited pathogenic microbes and produced higher amounts of lactic acid and H₂O₂, essential for maintaining a healthy vaginal environment. The results indicate that probiotic efficacy is both species- and strain-dependent, underscoring the need for alternative treatments given the limitations of current therapies.