Larvicidal and histopathological efficacy of inhabitant pathogenic bacterial strains to reduce the dengue vector competence.

Abstract

Aedes aegypti is a primary vector of dengue virus, and the causative agent of dengue is emerging globally as one of the most important arboviral diseases currently threatening human populations. Therefore, vector control is presently the primary intervention method of population reduction, in which natural A. aegypti populations would be reduced with inhabitant bacterial strains that are unable to transmit dengue virus. Based on the pathogenicity of strains, only four isolates effectively show larvicidal activity. The 16S rRNA gene sequences and the phylogeny depicted that the potential isolates were Bacillus firmus (MK791255), Bacillus paramycoides (MK788268), Bacillus siamensis (MK788212), and Bacillus licheniformis (MK791256). After 24 and 48 hours exposure, the B. licheniformis strain (cell mass of 2.2 × 107 CFU mL-1 ) showed potent larvicidal activity with LC50 of 16.22 μg mL-1 and 9.57 μg mL-1 and the B. paramycoides (cell mass of 3.1 × 107 CFU mL-1 ) strain inhibits the larval and pupal development with LC50 of 42.62 μg mL-1 and 26.97 μg mL-1 . Intermittent stages and causes of abscess in the gut and siphon regions were observed through histopathological studies. These two bacterial strains extend larval duration up to 15-16 days as well as reduce development. These studies demonstrate the challenge for dengue vector in reducing developmental and reproduction competence. © 2020 Society of Chemical Industry.