Evaluation of Antimicrobial Peptides Derived from Nigerian Medicinal Plant Extracts as Potential Alternatives to Conventional Antibiotics

Background: The global antibiotic resistance crisis has intensified interest in alternative antimicrobial agents, including plant-derived antimicrobial peptides and phytochemical fractions. Nigeria's rich biodiversity provides a largely untapped source of such compounds. This study evaluated the antimicrobial activity of peptide-rich fractions from selected Nigerian medicinal plants against multidrug-resistant bacterial isolates. Methods: Peptide-enriched fractions were prepared from the leaves of Ocimum gratissimum, Psidium guajava, and Senna alata, three plants used across multiple Nigerian geopolitical zones. Fractions were characterised by SDS-PAGE and tested in vitro against clinical MDR isolates of Staphylococcus aureus, Pseudomonas aeruginosa, and Klebsiella pneumoniae. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were determined by broth microdilution. Cytotoxicity was assessed against HeLa and Vero cell lines. Results: All three plant fractions demonstrated significant antimicrobial activity. O. gratissimum fraction had the lowest MIC against MRSA (62.5 ug/mL). P. guajava fraction showed broad-spectrum activity with MICs below 125 ug/mL for all tested organisms. Cytotoxicity indices were acceptable for O. gratissimum and P. guajava fractions at therapeutic concentrations. Conclusion: Plant-derived antimicrobial fractions from Nigerian species show promising activity against MDR pathogens with acceptable cytotoxicity profiles, supporting their development as antibiotic alternatives. Keywords: antimicrobial peptides, Nigerian plants, multidrug resistance, MIC, alternative antibiotics