Of yeasts, sandflies and leishmaniasis

The use of yeasts in biological control strategies is limited, probably due to the fact that yeasts have only been considered as organisms that can exert a positive effect on arthropod vectors. However, beyond the nutritional functions of yeasts, there are several roles that have been suggested but with limited experimental evidence: one of these is the protective/antagonist role. We have focused our research on the sandfly Phlebotomus perniciosus, the main vector of human and canine leishmaniasis in the Mediterranean area, with the aim at investigating if a yeast associated with this arthropod could exert inhibitory/killing activity against the pathogen Leishmania spp. First, we have investigated the mycobiota by culture-dependent approaches (microbiological analyses and the sequencing of the 26S rRNA), ITS rRNA metagenomic analysis, fluorescence in situ hybridisation (FISH) and phylogenomic analysis. Second, we have focused our attention on Wickerhamomyces anomalus, an ascomycete yeast well known for its antimicrobial properties; this yeast has been phylogenetically characterized and tested against sensible yeast strains, proving its killer phenotype. Finally, in order to explore their potential inhibitory/killing property against pathogens, we have tested the in vitro activity of W. anomalus strains against the pathogen Leishmania infantum. This study offers the basis for the development of an environment-friendly and safe method which may be included in the integrated approaches for the control of leishmaniasis, a worldwide re-emerging public health problem.