Antibacterial activity and subchronic toxicity of Cassia fistula L. barks in rats

Increasing incidence of antibiotic resistance necessitates the development of more potent antibiotics. The aim of this work was to evaluate the antibacterial activity of Cassia fistula L. barks as an alternative agent for resistant pathogenic bacteria. The C. fistula barks were extracted with ethanol, followed by partition of the extract to give n-hexane, ethyl acetate and water fractions. An in vitro antibacterial assay was conducted to evaluate inhibitory activity of the extract and fractions against Salmonella typhosa and Shigella dysenteriae. An in vivo antibacterial activity was examined using S. typhosa-infected mouse models, in which the colony number of S. typhosa were counted from the infected rats’ feces. Assesment on safety of the extract was conducted by a subchronic toxicity test which mainly examined alteration occured in biochemical parameters and hystopatological conditions of livers and kidneys. The results showed that the ethanol extract inhibited the growth of both S. typhosa and S. dysenteriae with the MIC of 0.3125% w/v, and the ethyl acetate fraction with the MIC of 0.625% b/v. In the in vivo antibacterial assay, the extract at three doses decreased the colony number of S. typhosa significantly, and after the fourth to sixth days, the precentage of decrease reached more than 90% by 1000 mg/kg dose. The subchronic toxicity test revealed that after the extract exposured for 90 days, a dose of 1000 mg/kg induced liver and kidney damages histologically, however, it returned to normal condition after 30 days of recovery. The results of this study indicated that the extract of C. fistula L. barks had potent in vivo antibacterial activity against S. typhosa as sample of resistant bacteria, and is safe to be used as a herbal medicine, preferably at a dose lower than 1000 mg/kg.