Djimefo, A. K. T. | bioRxiv Science

bioRxiv2026

Larvicidal Potential of Cola nitida Endophytic Bacteria Against Insecticide-Resistant Anopheles gambiae

BackgroundInnovative vector control strategies are urgently needed to combat malaria transmission by Anopheles gambiae, given the limitations of current insecticides--namely resistance, human toxicity, environmental damage, and high costs. This study evaluated the larvicidal efficacy of endophytic bacteria isolated from Cola nitida against third-instar larvae of Anopheles gambiae. MethodsEndophytic bacteria were isolated from nine Cola nitida plant parts (leaves, roots, stems, fruits, flowers, stem bark, branches, root bark, whole plant extracts) using standard surface sterilization and culturing protocols. Thirty-two morphologically distinct strains were purified and screened for larvicidal activity against third-instar An. gambiae larvae using the WHO-recommended turbidity method at McFarland 4 standard. Six active isolates underwent dose-response testing (McFarland 0.5-4) with mortality recorded at 24 and 48 hours. Environmental safety was assessed via Lemna minor growth inhibition, and molecular identification employed the API 20E biochemical gallery. ResultsScreening identified six strains with significant larvicidal activity (LC < McFarland 2). At McFarland 2 concentration, all six strains achieved >50% mortality within 24-48 hours, with Lemna minor EC >100% indicating minimal phytotoxicity. API 20E identification (96-99.99% similarity) revealed three strains (6164, 6211, 6501) matching Photobacterium damselae, two (6186-1, 6512-1) matching Salmonella enterica subsp. arizonae, and one (6600) matching Pseudomonas sp., confirmed by distinctive biochemical profiles. ConclusionThis study provides the first evidence of potent, environmentally safe larvicidal activity from Cola nitida endophytic bacteria against Anopheles gambiae. These strains represent promising biocontrol candidates to address insecticide resistance, offering a sustainable alternative for malaria vector management in endemic regions.

microbiology↗

bioRxiv2024

Chitosan nanocapsules with Alstonia boonei extract modulate the immune system in Wistar rats

The development of biosynthetic methods for nanoparticles using plants presents an exciting opportunity to better utilize our rich and diverse medicinal flora. We are particularly interested in creating nanocapsules using Alstonia boonei, a Cameroonian plant known for its immunomodulatory properties. Chitosan nanocapsules were synthesized from the methanol/dichloromethane extract of the powdered stem bark of A. boonei after harvest and drying. The encapsulation of the secondary metabolites was achieved using the ionic gelation method, which involved the agitation of a chitosan solution, extract, and tripolyphosphate. Subsequently, the encapsulation efficiency was calculated. Infrared spectroscopy identified the various functional groups present in the nanocapsules. The acute toxicological profile of these chitosan nanocapsules at a limit dose of 2000 mg/kg, along with their immunomodulatory activities, was evaluated in Wistar rats. The immunomodulatory potential was assessed in dexamethasone-induced immunosuppressed rats by measuring total blood count, delayed-type hypersensitivity response, and hemagglutinating antibody titre between groups of animals after 14 days of treatment. The data collected on the synthesis and characterization confirmed the formation of nanocapsules. This was evidenced by infrared spectroscopy and an entrapment efficiency of 69%. Powder X-ray diffraction confirmed the presence of chitosan in the polymer material. SEM imaging further confirmed the formation of nanocapsules. The toxicological profile of these nanocapsules was found to be satisfactory. Administration of chitosan nanocapsules containing Al. boonei methanol/dichloromethane extracts at doses of 100 mg/kg, 200 mg/kg, and 500 mg/kg body weight significantly prevented dexamethasone-induced immunosuppression in rats. This was achieved by increasing the parameters of total blood count (hematocrit, mean corpuscular volume, platelets, lymphocytes, and granulocyte counts), hemagglutinating antibody titre values, and delayed type hypersensitivity response induced by chicken red blood cells. However, doses of 500 mg/kg of crude A. boonei extract and 500 mg/kg body weight of empty chitosan nanocapsules did not show this effect. The nanocapsules generated from the extracts of chitosan and A. boonei are responsible for immunostimulatory activity and possess therapeutic potentials for the prevention of depressed immune depressed conditions with satisfactory safety at acute dose.

pharmacology and toxicology↗