Acute toxicity study and antibacterial activity of aqueous and methanol leaf extract of <i>Crotolaria retusa</i> Linn. against multidrug resistant bacterial isolates

Background: Dealing with drug-resistant pathogens is a serious health care challenge world-over, especially in developing countries. Effective first-line antibacterial agents are usually expensive, have side effects and are not readily available especially in most of Africa's rural areas where plant-based medicinal products such as Crotolaria retusa Linn. are commonly used for treatment of infectiousdiseases among others. Methods: The median lethal dose was investigated using Lorke's method. The antibacterial activity of the aqueous and methanol leaf extracts of C. retusa L. (rattle box) against some multidrug resistant (MDR) bacterial isolates were determined using the agar well diffusion method. Results: The acute oral toxicity studies of both the aqueous and methanol extracts of C. retusa revealed that the LD50 values were 2236.1 mg/kg and 1264.9 mg/kg, respectively. The aqueous and methanol leaf extracts demonstrated a concentration-dependent antibacterial activity against MDR clinical isolates of S. aureus, K.pneumonia, E. coli and P. aeruginosa. The results of minimum inhibitory concentration (MIC) of the extracts against the four MDR isolates ranged from 15.6 to 250 mg/ml while the minimum bactericidal concentration (MBC) ranged from 62.5 to 250 mg/ml.. Conclusion: The plant extracts used in this study significantly inhibited the selected microorganisms with MIC and MBC values comparable to ciprofloxacin and gentamicin. This suggests the plant has potential as a source of effective, relatively safer and affordable antibacterial agent.