Antibacterial activity of crude extracts of the leaves of Nauclea latifolia Smith (Rubiaceae) and some selected conventional antibiotics on clinical isolates of Salmonella typhi

Abstract

Background: Nauclea latifolia Smith (Rubiaceae) is a valuable medicinal plant used in folkloric medicine in the treatment of Typhoid fever. The public health significance of Salmonella typhi, the aetiologic agent in typhoid fever lies in the increasing resistance to antimicrobial agents. Objectives: To determine the antimicrobial potentials of the crude extracts of the leaves of Nauclea latifolia on clinical isolates of Salmonella typhi compared with some conventional antibiotics. Methods: Antibiogram was carried out on 25 biochemically confirmed clinical isolates of Salmonella typhi using disc diffusion method of Kirby Bauer. Nauclea latifolia leaves extracted with ethyl acetate and methanol in a Soxhlet apparatus were screened for secondary metabolites. The minimum inhibitory concentrations (MICs) of the extracts were determined by agar dilution method on the isolates. Results: The antibiogram of Samonella typhi showed the following resistance patterns: Augmentin® (24.0%), amoxicillin (44.0%), chloramphenicol (32.0%), gentamicin (20.0%), cloxacillin (96.0%), ciprofloxacin (8.0%), erythromycin (60.0%), tetracycline (32.0%) and cotrimoxazole (60.0%). The extracts showed good antibacterial activity on the clinical isolates including those resistant to antibiotics. The MIC of methanol extract ranged from1.56mg/ml to 6.25mg/ml and 3.13mg/ml to 25.0 mg/ml for ethyl acetate extract with exception of isolates 11, 12, 19 and 20 with high MIC values as 50mg/ml.  The methanol and ethyl acetate extracts gave a yield of 11.7% and 3.5% respectively. Bioactive secondary metabolites were detected from the extracts. Conclusion: The crude extracts of the leaves of Nauclea latifolia contained antimicrobial agents that were active on Salmonella typhi which could be used alone and in supportive with conventional antibiotics for therapeutic management of typhoid fever.