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Lebeer S.
University Antwerpen, Belgium

Because of the increased occurrence of antibiotic resistance and the side effects of antibiotic (mis)use, probiotic bacteria with strong antimicrobial capacity form an interesting alternative for antibiotics. Topically applied probiotics hold especially potential in niches outside the gastro-intestinal tract, because these niches are generally less densely populated with a diverse microbiota and are more accessible. However, such applications require other activities and other formulation and administration strategies. Therefore, we developed a screening platform for the screening and formulation of probiotics for non-intestinal applications. Especially Lactobacillus strains from original niches were screened, because of their GRAS (generally recognized as safe)/QPS (qualified presumption of safety) state and their well-known strong antimicrobial potential.

Various Lactobacillus strains are isolated from original niches, including fermented vegetables (carrots), human vagina, human nasopharynx and human skin and characterized at species level by 16S rRNA gene sequencing. Subsequently, their antipathogenic potential is screened against non-intestinal pathogens, mainly urogenital pathogens (incl. Candida albicans, uropathogenic E. coli, Gardnerella vaginalis), nasopharyngeal pathogens (incl. Haemophilus influenza, Streptococcus pneumoniae, Staphylococcus aureus, Moraxella catarrhalis), and skin pathogens (incl. Propionibacterium acnes, dermatophytes and Candida) via radial diffusion, spot and streak line assays as well as time course analyses of antmicrobial activity in suspension and antibiofilm activities. Lactobacillus rhamnosus GG is included as reference probiotic strain with strong antimicrobial potential. The bio-active antimicrobial molecules of the lactobacilli are characterized by genetic and biochemical approaches.

In addition to the well-known antimicrobial potential of Lactobacillus strains against gastro-intestinal pathogens, we observed that many of our Lactobacillus isolates can also inhibit pathogens from other niches including vaginal, nasopharyngeal and skin pathogens. L- and D- lactic acid are key antipathogenic compounds, but also other bioactive molecules such as exopolysaccharides, lectins and bacteriocines were explored. For instance, we found Lactobacillus lectins with a strong antibiofilm activity against uropathogenic E. coli.

The Lactobacillus isolates with the strongest antimicrobial activity are further explored for topical applications, depending on their antipathogenic spectrum and strongest activity. Together with specialists from the pharmaceutical department, suitable formulations with live probiotics for the specific niche(s) of application are explored. In addition, (pre)clinical studies for vaginal and skin applications are ongoing in which the impact of the probiotics on the full microbiome (including pathogenic and commensal microbes) is investigated via 16S rRNA metagenetics (Illumina Miseq). We believe such an integrated approach is important to fully assess the potential of topically applied probiotics as alternative for antibiotics.

Keywords: Antipathogenic, Effector molecules, Exopolysaccharides, Probiotics, Lectins

Lebeer S. (2016). Lactobacilli as alternative for antibiotics in non-intestinal applications. Conference Proceedings of IPC2016. Paper presented at the International Scientific Conference on Probiotics and Prebiotics, Budapest (p. 42.). IPC2016

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