Medicinal plant extracts modulate antibiotic activity against multidrug-resistant bacteria and Candida albicans

Microbial infections continue to pose significant challenges to global healthcare. Although the discovery of antimicrobial agents has revolutionized medicine and saved countless lives, the widespread misuse of antibiotics has led to the emergence of antimicrobial resistance (AMR), now a major global health threat. This study investigated the antimicrobial activities of methanolic extracts of the leaves of Azadirachta indica (AcE), Bidens pilosa (BpE), Psidium guajava (PgE), and the stem of Adenia cissampeloides (AcE) and their interactions with selected standard antibiotics against both normal and multidrug-resistant strains of Gram-negative bacteria (fluoroquinolone-resistant Escherichia coli and Klebsiella pneumoniae), Gram-positive bacteria (methicillin-resistant Staphylococcus aureus), and fungi (Candida albicans). The plant extracts exhibited antimicrobial activity across varying concentrations, with minimum inhibitory concentration (MIC) values ranging from 0.98 µg/ml to ≥ 500 µg/ml. The lowest MIC value (0.98 µg/ml) was observed for Azadirachta indica (AiE) and Adenia cissampeloides (AcE) extracts against Escherichia coli. Notably, these extracts also significantly enhanced the activity of ciprofloxacin against E. coli, reducing its MIC from 0.9 µg/ml to 0.12 µg/ml and 0.18 µg/ml, corresponding to 86% and 80% reductions, respectively. The plant-antibiotic combinations exhibited synergistic and additive effects against the tested microorganisms, suggesting their potential to enhance antibiotic efficacy and contribute to strategies aimed at mitigating antimicrobial resistance.