📖 ABSTRACT/OVERVIEW
Pseudomonas aeruginosa biofilm-associated wound infections represent a major therapeutic challenge in Nigerian tertiary hospitals, where chronic wound prevalence is rising in line with increasing diabetes and trauma admissions. Quorum sensing (QS)-mediated biofilm formation is a central virulence mechanism of P. aeruginosa, and disrupting QS represents a novel anti-virulence strategy that bypasses conventional antibiotic resistance pathways. Azadirachta indica, distributed abundantly across North West Nigeria and used topically for wound infections, contains bioactive terpenoids and limonoids that may interfere with QS circuits. This PhD research investigates the anti-QS and antibiofilm activity of fractionated Azadirachta indica leaf extracts against clinical P. aeruginosa isolates from wound infections at Aminu Kano Teaching Hospital. QS inhibition was assessed using Chromobacterium violaceum CV026 violacein production reporter assay, elastase B activity, pyocyanin production, swimming and swarming motility assays, and las and rhl QS gene expression by RT-qPCR. Biofilm inhibition and eradication assays were performed using 96-well crystal violet and XTT reduction methods. SEM characterised biofilm ultrastructure. Terpenoid-enriched fractions significantly inhibited violacein production, pyocyanin, elastase, and motility without affecting planktonic growth, confirming anti-QS rather than bacteriostatic activity. RT-qPCR confirmed downregulation of lasI, lasR, rhlI, and rhlR genes. Biofilm inhibition of 72% was achieved at sub-MIC concentrations. Azadirachtin and nimbidin were identified as the principal active constituents. These findings establish a novel anti-virulence mechanism for Azadirachta indica and support its development as an adjunct wound care agent. Keywords: quorum sensing, biofilm, Azadirachta indica, Pseudomonas aeruginosa, wound infection
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