In Vitro Antibacterial Evaluation of Leaf Extracts of Medicinal Plants in the Treatment of <em>Escherichia coli</em>, <em>Klebsiella pneumoniae</em>, and Salmonella Calve Diarrhea

This study employed the disc diffusion and broth microdilution tests to evaluate the antibacterial activities of the methanolic leaf extract of five medicinal plants (Vernonia amygdalina, Cordia africana, Calpurnia aurea, Croton macrostachyus, and Melia azedarach) against Salmonella, Escherichia coli, and Klebsiella pneumoniae. The extracts of Calpurnia aurea, Melia azedarach, and Vernonia amygdaline showed comparable effects (P &gt; 0.05) with gentamicin. The isolates and laboratory strains were most susceptible to the original concentration (1000 mg/ml) of Vernonia amygdaline on Salmonella (19.33 to 20.00 mm) and E. coli (21.33 mm). Vernonia amygdaline (1000 mg/ml) showed significantly (P &lt; 0.05) superior activity on clinical isolates of Salmonella and E. coli. At 1000 mg/ml, Melia azedarach had significant (P &lt; 0.05) superiority over other plants against K. pneumoniae. The minimum inhibitory concentration (MIC) ranged from 6.09 mg/ml (E. coli) to 48.75 mg/ml (Salmonella), and the minimum bactericidal concentration (MBC) value ranged from 12.18 mg/ml (E. coli) to 97.5 mg/ml (Salmonella). Calpurnia aurea and Vernonia amygdalina had all the tested secondary metabolites, except for cardiac glycosides. The yield percentage ranged from 7.9 % (C. macrostachyus) to 11.9 % (Calpurnia aurea and Cordia africana). These results support the potential of plant-based extracts as alternative antimicrobial agents.