Molecular Characterisation of Bacterial Isolates Associated with Infested Dump Sites in Communities in Anambra State, Nigeria

Abstract

Microorganisms have long been known to support immunity, food webs, nutrient cycling, and the health of the mosquito biological niche. This study aimed to identify the bacteria associated with mosquito-infested dump sites. Based on phenotypic observations, the mosquitoes associated with the study were Aedes, Anopheles, and Culex mosquitoes. Six (6) water samples from two different mosquito-infested dump sites at Otoko and Umudioka in Awkuzu, Anambra East L.G.Aof Anambra state in Southeastern Nigeria were cultured using the pour plate method on MacConkey, cetrimide, and mannitol salt agars and subsequently identified using their morphological features, biochemical tests (catalase test, Kovacs citrate test, indole test, and oxidase test), and 16S rRNAgene sequencing. Antibiotic susceptibility testing (AST) was performed on Mueller-Hinton agar after standardising to 0.5 McFarland turbidity. The diameter of the zones of inhibition was measured in mm and interpreted using the European Committee on EUCAST breakpoint guidelines. Biofilm formation was determined in twenty (20) isolates, and the biofilm scoring was assigned as weak, moderate, and strong/high. A total of forty-five (45) isolates, comprising four bacterial species, namely Vagococcus fluvialis18 (40%), Serratia fonticola 12 (26.7%), Escherichia
coli 4(8.90%), and Pseudomonas aeruginosa 11 (24.4%), were isolated and identified. The antibiotic susceptibility test showed 95-100% resistance to imipenem, amoxicillin-clavulanate, nitrofurantoin, ampicillin, cefixime, cefuroxime, and ceftriaxone. The isolates were susceptible to levofloxacin, ofloxacin, and gentamicin. Biofilm evaluation showed 3.45% moderate and 46.6% strong biofilms from Vagococcus fluvialis, 3.45% moderate and 15.5% strong biofilms from Pseudomonas aeruginosa, and both 10.3% and 20.7% strong biofilms from E. coli and S. fonticola, respectively. This study identified bacteria associated with mosquito-infested dump sites and highlighted the importance of considering the environmental microbiome when studying mosquito biology and developing control strategies for these pests in relation to human health.