Vector microbiota and parasite infection: bacteria-mediated effects on Leishmania in Phlebotomus papatasi and culture.

AIM: Microbes are increasingly being explored as tools to control leishmaniasis and sandfly populations. This study investigated the interactions between sandflies, Leishmania, and their microbiota. METHODS: The in vitro and in vivo survival and development of Leishmania major in the presence of seven bacterial species were assessed. In vitro experiments included Leishmania co-cultures with bacteria applied at different concentrations (102-108 CFU/ml), monitoring parasite survival/development at early (30-120 min) and late (12-240 h) time points. In vivo experiments in Phlebotomus papatasi examined Leishmania infection rate and intensity on days 2, 6, and 8 post co-infection with the same bacterial species (108 CFU/ml). RESULTS: All bacteria demonstrated negative effects on Leishmania survival and development. Under in vitro conditions, the speed of Leishmania ablation (48-216 h) depended on the bacterial species and concentration, impacting Leishmania motility and viability, and halting the development of metacyclic forms. In vivo studies demonstrated that bacterial overgrowth negatively impacted the intensity of Leishmania infection and percentage of stomodeal valve colonization (27.58-82.14%). CONCLUSIONS: The observed effect of bacteria on Leishmania under in vitro and in vivo conditions points out toward the potentially greater role of microbes in Leishmania survival in vectors, highlighting the need for deeper investigations of sandfly-Leishmania-microbiota interactions.