Identification of culturable fungi and bacteria in mosquito saliva and impact on arbovirus infection in vitro

Abstract

Mosquito saliva was shown to play a key role in arbovirus transmission and pathogenesis. In this study, we explored the presence of microbiota in mosquito saliva and their potential effect on mosquito-borne virus infection in vitro. Culturable fungal and bacterial colonies were isolated and identified from saliva harvested from Aedes aegypti (lab strain) and Culex pipiens (field-collected mosquitoes). For the first time, the fungal species Penicillium crustosum was identified in mosquitoes. Culturable bacteria detected in mosquito saliva included Serratia marcescens, Serratia nematodiphila, Enterobacter spp. and Klebsiella spp., which were previously identified as mosquito or insect endosymbionts in the midgut or other organs. Oral treatment of adult mosquitoes with antibiotics or an antifungal drug resulted in a significant reduction of bacteria or fungi in saliva. Saliva depleted from fungi or bacteria significantly decreased Semliki Forest virus infection in human skin fibroblasts compared to non-treated saliva when the virus was preincubated with saliva or when virus and saliva were added to the cells at the same time. These results suggest that the salivary microbiota may play an essential role in mosquito-borne viral replication in human skin cells. Nevertheless, the potential effect of salivary microbiota warrants further investigation in vivo.