Identification of a Culturable Fungal Species and Endosymbiotic Bacteria in Saliva of Aedes aegypti and Culex pipiens and Their Impact on Arbovirus Infection in Vitro

Mosquito saliva plays a key role in arbovirus transmission and pathogenesis. This study isolated and identified culturable fungal and bacterial colonies from saliva harvested from Aedes aegypti (lab strain) and Culex pipiens (field-collected) mosquitoes. For the first time, Penicillium crustosum was identified in mosquito saliva. 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. Analysis with 16S metagenomics showed that the bacterial community in saliva appeared more diverse than the bacterial communities in midguts. Blood feeding did not affect the fungal or bacterial load in mosquito saliva. Oral treatment of adult mosquitoes with antibiotics or an antifungal drug resulted in a significant reduction of resp. bacteria or fungi present in the mosquito saliva. Co-incubation of Semliki Forest virus with saliva from antibiotic or antifungal treated mosquitoes triggered a decrease in viral infection in human skin fibroblasts compared to non-treated saliva. This work lays the foundation for further exploration of the impact of fungi and bacteria in mosquito saliva on both vector competence and arbovirus infection in the mammalian host.