Ebiloma, S.; Nwachuckwu, N. C.; Uchendu, N.; Okereke, H.

The increase threat of antimicrobial resistance, mainly among biofilm-forming pathogens, has prompted increased interest in plant-based alternatives with broad-spectrum antimicrobial properties. This study aimed to evaluate the antimicrobial activities of aqueous, ethanolic, and methanolic leaf extracts of Vernonia amygdalina against five biofilm-forming clinical isolates: Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Candida albicans. Plant extracts were obtained through maceration using respective solvents and tested at concentrations ranging from 100 to 500 mg/mL. The antimicrobial potential of each extract was assessed using the agar well diffusion method to determine the zone of inhibition, followed by minimum inhibitory concentration (MIC) and minimum bactericidal/fungicidal concentration (MBC/MFC) assays. Among the three extract types, the methanolic extract consistently showed the highest antimicrobial activity, with inhibition zones ranging from 20.0 {+/-} 0.38 mm to 24.0 {+/-} 0.60 mm. Ethanolic extracts showed moderate inhibition, while aqueous extracts were least effective, particularly at lower concentrations. MIC values for methanolic extracts ranged from 31.25 mg/mL for C. albicans to 500 mg/mL for S. aureus, with corresponding MBC values as low as 31.25 mg/mL for E. coli. One-way ANOVA indicated a statistically significant difference (p < 0.05) in mean inhibition zones across extract types. Post hoc Tukey test confirmed the superiority of methanol as an extraction solvent. These results validate the broad-spectrum antimicrobial properties of V. amygdalina and support its potential development as a natural therapeutic agent against resistant, biofilm-forming microbial infections.