A normal vaginal microbiota is characterized by the predominance of bacteria of the genus Lactobacillus. Their reduction can lead to dysbiosis, which is often associated with two clinically important infections: vulvovaginal candidiasis, caused by the fungus Candida albicans, and bacterial vaginosis, associated with the bacterium Gardnerella vaginalis. Standard treatment is based on the use of antifungals and antibiotics; however, increasing attention has recently been directed toward the use of probiotics. The aim of this master’s thesis was to identify, among isolated strains of different Lactobacillus species, the most suitable probiotic candidates to support the restoration of the vaginal microbiota and reduce the risk of recurrent infections.
In this master’s thesis, we evaluated the antimicrobial activity of selected strains of Lactobacillus crispatus, Lactobacillus gasseri, Lactobacillus jensenii, and Limosilactobacillus vaginalis, isolated from healthy volunteers, against C. albicans and G. vaginalis. In addition, we assessed their hemolytic activity and antibiotic susceptibility using the Etest method and investigated the role of two key antimicrobial mechanisms.
As a favorable safety parameter, the absence of hemolytic activity was confirmed, as none of the strains showed hemolysis on medium supplemented with human blood. All lactobacilli were resistant to metronidazole, while strains of L. gasseri were also resistant to clindamycin. Antimicrobial activity against C. albicans was evaluated by co-cultivation on solid de Man–Rogosa–Sharpe medium, whereas activity against G. vaginalis was tested using a microdilution method with lactobacillus culture supernatants. In both cases, six strains of L. crispatus exhibited the strongest antimicrobial effect. To determine the mechanism of action (low pH and/or H₂O₂ production), the supernatants were additionally neutralized and treated with catalase. Both C. albicans and G. vaginalis were sensitive to low pH. A difference in sensitivity to H₂O₂ between the microorganisms was observed: G. vaginalis was sensitive at lower concentrations (MIC 0.005%), whereas the MIC for C. albicans was 0.03%. We found that reduction in pH due to lactic acid production is a more important factor in antimicrobial activity than H₂O₂ production.
The pronounced antimicrobial activity of six L. crispatus strains against C. albicans and G. vaginalis, together with favorable safety results, indicates that they are promising candidates for further testing and probiotic application.
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