Extracts of Ansellia africana and Platycarpha glomerata exhibit antibacterial activities against some respiratory tract, skin and soft tissue infections implicated bacteria

Infectious diseases such as respiratory tract, skin and soft tissue infections are a cause of high morbidity rates worldwide due to the emergence of antibiotic resistant bacteria. Medicinal plants such as Ansellia africana and Platycarpha glomerata which have been reported traditionally to be useful in treating these infections may be key to finding alternative treatment options. Antibacterial activities of different solvent crude extracts (each at 10 mg/mL) of A. africana (root and stem) and P. glomerata (leaf and rhizome) were screened against respective test bacteria using the agar well diffusion method. The MIC and the MBC values of the extracts were determined using the broth micro-dilution assay, while the checker board method was used to assess the extracts' interactions with ciprofloxacin. The membrane damaging potentials of the extracts against selected bacteria was determined by measuring the percentage cytosolic lactate dehydrogenase released. Zones of inhibition of the dichloromethane and acetone extracts of A. africana ranged from 8.33 ± 1.53 to 19.3 ± 4.93 mm, while P. glomerata extracts had zones of inhibition ranging from 9.67 ± 2.52 to 15.7 ± 0.58 mm. The MIC values of A. africana extracts were found to range from 2.5-10 mg/mL and their bactericidal activity was observed against Mycobacterium smegmatis (ATCC 14468) and Staphylococcus aureus (ATCC 25925) only. The MIC values of P. glomerata extracts ranged from 5 to 10 mg/mL, with bactericidal activity being observed against S. aureus (ATCC 25925) only by all the extracts except the DCM leaf extracts. Significant membrane damaging potentials of 79 ± 1.21% were exhibited by the acetone stem extract of A. africana against S. aureus (ATCC 25925). Synergistic interactions between the acetone stem and root extracts of A. africana were observed against M. smegmatis (ATCC 14468), while, all the interactions of the extracts with ciprofloxacin were indifferent. However, interactions of the DCM (rhizome and leaf) and acetone (rhizome and leaf) extracts of P. glomerata with ciprofloxacin showed synergism. The results of this study therefore, indicate that P. glomerata could be a potential source of new antibacterial compounds for the treatment of skin and soft tissue bacterial infections, while A. africana could be a potential source of antibacterial compounds for the treatment of respiratory tract bacterial infections especially those caused by S. aureus species.