Bactericidal effects of sugar-fed antibiotics on resident midgut bacteria of newly emerged anopheline mosquitoes (Diptera : Culicidae)

A protocol was developed for significantly reducing resident midgut bacteri a in newly emerged anopheline mosquitoes using a combination of antibiotics . Pupa harvested from colony-reared Anopheles gambiae s.l. Giles and Anophe les stephensi (Liston) were placed in cages wiped previously with 70% alcoh ol and kept under UV light for 24 h. Emerging adult mosquitoes were fed for 3 consecutive days on antibiotic solution, consisting of 0.4% gentamicin s ulfate and 1% penicillin-streptomycin solution in a 10% sterile sucrose sol ution. Bacterial suspensions of Escherichia coli, Klebsiella pneumoniae (Sc hroeter, 1886), and Pseudomonas stutzeri (Lehmann & Neumann, 1896) isolated from wild-caught anophelines were fed to antibiotic-treated mosquitoes sta rved for 24 h via either sugar or membrane-feeding. Mosquitoes dissected 1 and 24 h after blood-feeding or sugar-feeding, and plated on trypticase soy agar plates, yielded the some type of bacteria fed originally without evid ence of contaminants. There was no residual effect of the antibiotics on in troduced single bacteria strains as judged by the presence of bacteria in a ntibiotic-treated mosquitoes. This experimental reduction of resident midgu t bacteria and their replacement with single strains in newly emerged anoph eline mosquitoes should facilitate further investigations of the interactio ns between malaria parasites and bacteria found in the midguts of mosquitoe s.