Culturable microbial composition in the midgut of Aedes aegypti strains with different susceptibility to dengue-2 virus infection

Dengue is the widest spread vector-borne viral disease around the world and is transmitted mainly by the urban mosquito, Aedes aegypti. At present, vector control is the most widely used strategy to decrease disease incidence. However, it has demonstrated limited success. A new control strategy, associated with the manipulation of vector competence (VC) using endosymbiotic microorganisms, may be more sustainable because these microorganisms can influence mosquito development, the vector immune response, and vectorial capacity for infection with dengue virus (DENV). Hence, we explored the diversity of culturable midgut microbiota from two field-derived Aedes aegypti strains that are either susceptible or refractory to DENV infection and evaluated how strain-level dissection of the gut microbiome modulates VC. Microbial identification was carried out by mass spectrometry using MALDI-TOF, Vitek-2, BD Phoenix, and 16 s rRNA sequencing. There were differences in the composition and density of midgut microbiota in both mosquito strains. The refractory strain showed the highest microbial diversity and density with the highest prevalence of Gram-negative bacteria including Pseudomonas, Serratia, Stenotrophomonas, and Escherichia genera. In the susceptible strain, only Gram-positive bacteria of the Bacillus genus and Candida yeast were observed in the midgut. To evaluate the effect of midgut microbiota on DENV-2 infectivity in both Aedes aegypti strains, mosquitoes were treated with sugar and an antibiotic/antimycotic cocktail or sugar alone (the control) and were subsequently challenged with a mixture of blood and DENV-2. DENV-2 infection in the mosquitos' heads (salivary glands) and midguts was evaluated after an extrinsic period of ten days with indirect immunofluorescence. A significant increase in DENV-2 susceptibility was observed in the treated refractory strain from 51.22% to 86.64% (Chi-square = 9.747, p < 0.05), while no changes were observed in the susceptible strain. These results confirm that susceptible and refractory mosquito strains may influence or are influenced by the presence of different gut microorganisms that affect virus infection susceptibility.