FTIR Fingerprinting Unravels Solvent-Dependent Antibacterial Potentials of Vernonia amygdalina Leaf Extracts Against Selected Multidrug-Resistant ESKAPE Isolates

Plant-derived antimicrobials can potentially counteract the increasing ineffectiveness of conventional antibiotics against multidrug-resistant (MDR) ESKAPE pathogens. This study compared the extraction yield, phytochemical profile, functional-group signatures, and antibacterial activity of aqueous and n-hexane leaf extracts of Vernonia amygdalina against selected MDR ESKAPE pathogens from Katsina State, Nigeria. The fresh leaves were subjected to maceration, the obtained yield was calculated, and phytochemical constituents were screened using both standard qualitative assays and FTIR spectroscopy. Antibacterial activity was evaluated by agar well diffusion technique. Statistical significance was determined using the Welch test and two-way ANOVA. The n-hexane extract produced a significantly higher yield than the aqueous extract (28.81% vs. 9.87%; p < 0.0001). Conventional screening detected cardiac glycosides, saponins, steroids, and flavonoids, while FTIR analysis indicated bioactive functional groups consistent with terpenoids, steroids, polyacetylenes, cyanogenic glycosides, triglycerides, and lipophilic alkaloids. Both extracts inhibited the test pathogens, with no significant difference relative to the positive control (p = 0.066). These findings indicate solvent-dependent variation in bioactive metabolites present in V. amygdalina leaves. These compounds exhibited antibacterial activity against MDR ESKAPE pathogens and can hence be exploited as potential leads for discovering novel antibacterials to tackle these pathogens in the study area and beyond.