Midgut microbial community plays a significant role in the vector competence of Phlebotomus duboscqi for Leishmania major

BACKGROUND AND PURPOSE: Phlebotomus sand flies (females) are blood sucking insects that vector Leishmania parasites causing leishmaniasis in humans and other vertebrates. A crucial step in Leishmania transmission is the development of the parasite in the sand fly midgut. This study investigated the significance of the midgut bacterial community in the vector competence of Phlebotomus duboscqi for Leishmania major. METHOD: Sand flies were fed heparinized mice blood inoculated with L. major parasites (~4x10⁶/ml). From day 4 post-infection, flies were given on a daily basis either penicillin/streptomycin (P/S) in sucrose (30% w/v) solution to reduce their gut microbiota (treatment group) or sucrose (30% w/v) without antibiotics (control group). Subsequently, sand flies from these groups were dissected at different time points to count the parasite numbers and to assess the concentration (colony forming unit counts) and diversity of the gut bacteria (culturing as well as culture independent approach). Additionally, the effect of P/S on the parasite survival in vitro was evaluated. RESULTS: P/S treated sand flies showed a significant (~1000x) reduction in the number of gut bacteria along with parasite numbers (>100x) compared to that of control flies. In vitro experiments revealed that P/S does not affect parasite survival directly. Ochrobactrum and Rahnella spp. were dominant in the gut of control flies and were replaced by Leifsonia spp. in the P/S treated flies. CONCLUSION: The bacterial community in the sand fly gut is essential for L. major development and might be used for manipulating the sand fly vector competence and for a paratransgenic approach to control Leishmania transmission.