Antibacterial Activity of Hibiscus Acid Alone and Combined with Chloramphenicol in CD-1 Mice Infected with Multidrug-Resistant Enterohemorrhagic <i>Escherichia coli</i> and <i>Salmonella</i> Typhimurium

The antibacterial effect of chloramphenicol, hibiscus acid, and a mixture of hibiscus acid and chloramphenicol against antibiotic-resistant enterohemorrhagic <i>Escherichia coli</i> (EHEC) and <i>Salmonella</i> Typhimurium (ST) was determined in Caesarean-Derived (CD)-1 mice. Hibiscus acid was isolated from <i>Hibiscus sabdariffa</i> calyces. The minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) of chloramphenicol (CH), hibiscus acid (HA), and mixtures of HA/CH were determined for EHEC and ST. 11 groups of six mice each were formed. Four groups were inoculated orally with 4 log₁₀ Colony forming units (CFU) of ST, four groups were inoculated with 4 log₁₀ CFU of EHEC, and the remaining three groups were not inoculated. Six hours post inoculation, the mice in some groups received, via the oral route, solutions of hibiscus acid (7 mg/mL), chloramphenicol (82 µg/mL), a mixture of HA/CH (5.7 mg/mL HA and 4 µg/mL CH), or isotonic saline solution. The MIC and MBC values were between 7 and 5 mg/mL for hibiscus acid, between 17.6 and 82 µg/mL for chloramphenicol, and between 4.2 mg/mL/0.3 µg/mL and 5.7 mg/mL/0.4 µg/mL (concentration of hibiscus acid/concentration of chloramphenicol) or HA/CH. EHEC and ST were not detected in the feces of mice that were administered hibiscus acid alone or in mixture with chloramphenicol. By contrast, pathogens were isolated from the feces of untreated mice and those treated with chloramphenicol alone throughout the study.