Mitigation of chytrid infection on tadpoles with the antimicrobial metabolites of Xenorhabdus szentirmaii

Survival of amphibian assemblages is threatened by many factors. Among them, chytridiomycosis, the disease caused by the chytrid fungus Batrachochytrium dendrobatidis (Bd) has great importance, also threatening the populations of the yellow-bellied toad (Bombina variegata), which has a scattered, isolated distribution in Hungary. Treatment with secondary metabolites of the entomopathogenic bacterium, Xenorhabdus szentirmaii is a promising method in the mitigation of chytridiomycosis, as recently demonstrated. To assess whether it may also be effective for lowering infection intensities in B. variegata tadpoles, we extracted cell-free culture media (CFCM) from liquid cultures of X. szentirmaii and tested their antifungal efficacy at a dilution of 0.1 % (v/v), while also measuring possible short-term malign effects on tadpoles experimentally infected with Bd or sham infection. According to our results, CFCM treatment alone did not compromise tadpoles survival probability, nor reduced the body mass and developmental speed of the individuals. At the same time, the treatment reduced the intensity and prevalence of Bd infection, but this effect was affected by the population of origin. The antimicrobial metabolites produced by X. szentirmaii may therefore be suitable for the safe mitigation of chytridiomycosis in B. variegata tadpoles, but further studies are needed, aiming to monitor and increase the efficacy of this method.