Phytochemistry, Antibacterial Properties, and FT-IR Spectra of Khaya senegalensis Stem Bark Extracts against Escherichia coli 0157:H7 and Salmonella typhimurium

Abstract

The increasing prevalence of multidrug-resistant bacterial pathogens has intensified the search for alternative antimicrobial agents derived from medicinal plants. This study investigated the phytochemical composition, antibacterial activity, and Fourier-transform infrared (FTIR) spectra of methanolic and n-hexane extracts of Khaya senegalensis stem bark against Escherichia coli O157:H7 and Salmonella typhimurium. The extracts were obtained by reflux extraction, and their phytochemical constituents were quantified. Minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations were determined using broth microdilution and subculture methods, respectively, while functional groups were characterized using a PerkinElmer 100-series FTIR spectrometer. The methanolic extract contained higher concentrations of phenols, flavonoids, alkaloids, and tannins, whereas the n-hexane extract contained higher concentrations of saponins and steroids. The methanolic extract exhibited greater antibacterial activity, with E. coli O157:H7 showing the highest susceptibility (MIC = 3.12 mg/mL), followed by S. typhimurium (MIC = 12.5 mg/mL). By comparison, the n-hexane extract produced an MIC of 25 mg/mL against both bacterial isolates. The FTIR spectrum of the methanolic extract displayed five absorption peaks, including bands at 3271.86 and 1604.91 cm⁻¹ associated with terminal alkyne C–H and aromatic C=C stretching, respectively, and bands at 1031.28, 562.00, and 552.94 cm⁻¹ within the fingerprint region. The n-hexane extract exhibited bands corresponding to O–H stretching, aromatic C=C stretching, N–O stretching, alkane C–H bending, C–O–C stretching, and C–O stretching. These findings demonstrate that the antibacterial activity of K. senegalensis stem bark varies according to solvent polarity and phytochemical composition, with the methanolic extract showing superior efficacy against the tested organisms. The study provides preliminary scientific support for the traditional use of K. senegalensis stem bark in managing diarrhoea, dysentery, and other gastrointestinal ailments, while further toxicological and in vivo investigations are required to establish its therapeutic applicability.