Antibacterial activity of methanol leaf extract of Sterculia tragacantha against selected multidrug- resistant clinical bacterial isolates

antimicrobial agents. Sterculia tragacantha is a medicinal plant with reported phytochemical constituents and ethnomedicinal uses. This study evaluated Sterculia tragacantha against selected multidrug-resistant clinical bacterial isolates. The leaves of S. tragacantha were collected, oven-dried, pulverized and extracted with Analar Grade (99%) methanol by batch maceration method. One thousand grams of powdered leaves were macerated in 2000 mL methanol, yielding 70.1 g (7.01% w/w) crude extract. The stock extract (100 mg/mL) and its 50, 25 and 12.5 mg/mL dilutions were tested by agar-well diffusion against pre-existing clinical isolates of Klebsiella pneumoniae, Staphylococcus aureus, Pseudomonas aeruginosa, and Escherischia coli. Meropenem was used as the standard antibiotic/positive control. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were determined by broth dilution. The extract produced the greatest activity against S. aureus, with zones of inhibition of 13 mm, 11 mm, 10 mm, and 10 mm at 100, 50, 25 and 12.5 mg/ml, respectively. P. aeruginosa showed zones of 12 mm, 8 mm, 6 mm, and 6 mm, while K. pneumoniae and E. coli showed 12–13 mm only at the stock concentration. These antibacterial sensitivity results were statistically significant among the four clinical bacterial isolates (F = 103.332, p < 0.001). The extract showed statistically significant activity against S. aureus with the lowest MIC (12.5 mg/ml) (χ²=18.147, p<0.001) and MBC (25 mg/ml) (χ²=37.44, p<0.001) when compared with the other isolates. Conclusion: Methanol leaf extract of S. tragacantha demonstrated measurable, concentration-dependent antibacterial activity, particularly against S. aureus, and warrants further investigation as a source of antibacterial compounds.