Study and characterization of lactic acid bacteria as potential vaginal probiotics

  • Mélanie Isabel Esteves (Student)

Student thesis: Master's Thesis


Vaginal health is ensured by a vaginal microbiome which plays an essential role in preventing colonization and/or infection by pathogens. Conversely, when the vaginal microbiome is altered, the vaginal tract can be infected by several pathogenic microorganisms, which can cause diseases such as bacterial vaginosis, vulvovaginal candidiasis, among others. This study aimed to evaluate the antimicrobial activity of three lactic acid bacteria (Lactiplantibacillus plantarum R23, Lactiplantibacillus plantarum 299V and Pediococcus pentosaceus K34) against pathogens commonly found in the urogenital tract (Listeria monocytogenes, Escherichia coli and Candida albicans) in a simulated vaginal fluid at pH values of 4.2, 5.5 and 6.5. Additionally, lactic acid bacteria with the potential to inhibit vaginal pathogens were characterized as potential probiotic candidates. In simulated vaginal fluid, only L. monocytogenes was inhibited at pH 4.2 by Lb. plantarum R23 (until 48 h of contact) and P. pentosaceus k34 (after 2 h of contact), and at pH 5.5 by P. pentosaceus K34 (until 48 h of contact). Both strains produce bacteriocins active against L. monocytogenes, which could explain the results found. With the promising results on simulated vaginal fluid at two different pH values, P. pentosaceus K34 was selected for further characterization as a probiotic candidate. Several assays were performed since, for commercial purposes, potential probiotics should meet several requirements. Regarding their safety, any extracellular enzymes tested were produced by P. pentosaceus K34, and hemolytic activity or the ability to form the biogenic amines were also not found. However, despite being sensitive to most of the antibiotics tested, P. pentosaceus K34 was resistant to ampicillin, and the nature of such resistance requires further investigation. Pediococcus pentosaceus K34 also demonstrated a great capacity to adhere to Caco2 cells, but 24.1 ± 4.0% of cells were also able to invade the same cell culture line. These results need further confirmation to conclude about its possible form of administration since adherence to intestinal epithelium is another mandatory requirement for oral probiotics. Although more tests should be performed to validate and complete this preliminary study, P. pentosaceus K34 appears to be a potential probiotic candidate for the treatment of vaginal infections.
Date of Award18 Nov 2022
Original languageEnglish
Awarding Institution
  • Universidade Católica Portuguesa
SupervisorJoana Inês Bastos Barbosa (Supervisor) & Paula Teixeira (Co-Supervisor)


  • Probiotics
  • Pediococcus pentosaceus
  • Pathogens
  • Vaginal infections


  • Mestrado em Microbiologia Aplicada

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