Killer yeasts exert anti-plasmodial activities against the malaria parasite Plasmodium berghei in the vector mosquito Anopheles stephensi and in mice

Background Wickerhamomyces anomalus is a yeast associated with different insects including mosquitoes, where it is proposed to be involved in symbiotic relationships with hosts. Different symbiotic strains of W. anomalus display a killer phenotype mediated by protein toxins with broad-spectrum antimicrobial activities. In particular, a killer toxin purified from a W. anomalus strain ( Wa F17.12), previously isolated from the malaria vector mosquito Anopheles stephensi , has shown strong in vitro anti-plasmodial activity against early sporogonic stages of the murine malaria parasite Plasmodium berghei . Results Here, we provide evidence that Wa F17.12 cultures, properly stimulated to induce the expression of the killer toxin, can directly affect in vitro P. berghei early sporogonic stages, causing membrane damage and parasite death. Moreover, we demonstrated by in vivo studies that mosquito dietary supplementation with activated Wa F17.12 cells interfere with ookinete development in the midgut of An. stephensi . Besides the anti-sporogonic action of Wa F17.12, an inhibitory effect of purified Wa F17.12-killer toxin was observed on erythrocytic stages of P. berghei , with a consequent reduction of parasitaemia in mice. The preliminary safety tests on murine cell lines showed no side effects. Conclusions Our findings demonstrate the anti-plasmodial activity of Wa F17.12 against different developmental stages of P. berghei . New studies on P. falciparum are needed to evaluate the use of killer yeasts as innovative tools in the symbiotic control of malaria. Electronic supplementary material The online version of this article (10.1186/s13071-019-3587-4) contains supplementary material, which is available to authorized users.