Antimicrobial Activity of Acacia nilotica Stem Bark Extract against Bacterial Pathogens Associated with Wound Infections in Jos, Nigeria

Abstract

The study was carried out to evaluate the in vitro antimicrobial activity of crude extracts of Acacia nilotica against bacterial isolates from wound of out-patients’ at the Plateau Specialist Hospital, Jos, Nigeria using standard microbiological methods. Six bacterial isolates (Escherichia coli, Proteus mirabilis, Staphylococcus aureus, Streptococcus pyogenes, Pseudomonas aeruginosa and Klebsella pneumonia) were identified. Ethanol and aqueous extraction led to high percentage yields of 23.9% and 22.4% respectively. Phytochemical screening revealed the presence of tannins, saponins, flavonoids, carbohydrates, steroids, anthroquinines, terpenes and cardiac glycosides. The ethanol extract of A. nilotica stem bark was equally or more effective than the standard antibiotic (Gentamycin). Ethanol and aqueous stem back extracts of A. nilotica exhibited excellent antibacterial activity against all the isolates of wound infections tested, especially against Streptococcus pneumoniae which showed the maximum antibacterial activity with mean zones of inhibition (33 and 25mm) in ethanol and aqueous extracts respectively at 200 mg/ml concentration. Overall maximum inhibition zone (22mm) was caused by the ethanol extract against Streptococcus pneumoniae while the minimum zone of inhibition (12mm) was caused by the aqueous extract against Escherichia coli, Staphylococcus aureus had the lowest MIC (3.125mg/ml) for both aqueous and ethanol extracts. A. nilotica aqueous extracts exhibited the greatest antibacterial activities as determined by the MBC which ranged between 6.25 and 50 mg/ml. In the present study, the MIC value of the aqueous and ethanol extracts was lower than the MBC values, suggesting that A. nilotica aqueous extracts were bacteriostatic at lower concentrations but bactericidal at higher concentrations. Also, the bacterial zone of inhibition increased with increasing concentration of A. nilotica aqueous and ethanol extracts. All the bacterial isolates were susceptible to the plant extract used in this study. This supports the use of A. nilotica stem bark as a folklore remedy in the treatment of diseases caused by bacterial isolates in this study. Further research is needed to examine the extracts’ in-vivo mechanism of action, toxicity, and therapeutic effect.