Antibacterial Activity against Clinical Isolates of Salmonella enterica Serovar Paratyphi and Brine Shrimp Lethality Assay of Trichilia megalanthaHarms and Trichilia welwitschii C. DC

Abstract

Increasing resistance of typhoidal Salmonella enterica to conventional antibiotics has caused more cases of typhoid, therapeutic failure, morbidity and mortality; creating the need to search for new and effective antimicrobial agents from medicinal plants. The present study aimed to detect antisalmonella activity and cytotoxicity (safety) status of the stem bark and leaves of two Nigerian medicinal plants, Trichilia megalantha and Trichilia welwitschii. Nine clinical isolates of Salmonella paratyphi, whose antibiogram were determined by Kirby-Bauer disc diffusion method were used. Antibacterial activity, minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of the extracts on the clinical isolates were done by agar cup diffusion and agar dilution methods, respectively. Acute toxicity of the extracts was determined using brine shrimp lethality assay (BSLA). All the nine isolates of Salmonella paratyphi were resistant to β-lactam antibiotics (augmentin, cefuroxime, ceftazidime and ampicillin) but susceptible to fluoroquinolones (ciprofloxacin, ofloxacin), nitrofurantoin and gentamicin. The crude extracts of the two plants elicited activity against the nine clinical isolates with the bark extracts being more active than the leaf extracts. T. welwitschii was slightly less active than T. megalantha. The MIC and MBC ranged 1.25 - 5.0 mg/ ml and 2.5 - 10 mg/ml, respectively for the plants. The antisalmonella activity of methanolic extracts of both plants were found to be less than that of ciprofloxacin and ofloxacin. With modal cytotoxicity values of 400 - 500 μg/ml, the plant parts were considered nontoxic. Therefore, T. megalantha and T. welwitschii could provide a potential source of antibacterial agent(s) for the treatment of Salmonella paratyphoid infections.

Keywords: Trichilia megalantha; Trichilia welwitschii, antisalmonella; cytotoxicity; Salmonella paratyphi