Abstract
We examined the antibacterial efficacy of streptomycin, hibiscus acid, and their combination against multidrug-resistant Shiga-toxin-producing Escherichia coli (STEC) and Salmonella Typhimurium in mice. We determined the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) for streptomycin, hibiscus acid, and their combination against STEC and Salmonella. Fifteen sets of six mice in each set were utilised: six groups were orally exposed to 4 log(10) colony forming units (CFUs) of S. Typhimurium and another six to STEC, and three acted as the controls. Six hours post-inoculation, specific groups of mice received either oral solutions containing hibiscus acid at 5 and 7 mg/ml; streptomycin at 50 and 450 μg/ml; hibiscus acid/streptomycin (5 mg/ml hibiscus acid and 50 μg/ml streptomycin); or isotonic saline. The study determined the MIC and MBC of 7 mg/ml of hibiscus acid; 300 and 450 μg/ml of streptomycin; and two concentrations of hibiscus/streptomycin (3 mg/ml / 20 μg/ml and 5 mg/ml / 50 μg/ml). Interestingly, the mice that were infected and subsequently treated with hibiscus acid at 7 mg/ml alone or in conjunction with streptomycin did not have either STEC or Salmonella in their faecal samples, and none of the mice died. In contrast, the untreated mice and those exclusively treated with streptomycin had the pathogens present in their stool, leading to the mortality of all the subjects.