Antibacterial Activity of Three Cameroonian Medicinal Plants Traditionally Used for the Treatment of Urinary Tract Infections and Their Synergistic Effects with Amoxicillin and Serum

Background: Urinary tract infections (UTIs) are the second most common form of infectious diseases that affect humans after respiratory diseases. It is predicted that 20% of the adult female population is exposed to development of an UTI. The emergence of UTIs is promoted by the development of the resistance to antibiotics, highlighting the research of new antibiotics that can be used to fight effectively and at affordable cost against these infections.

Aim: The present study was designated to evaluate the antibacterial activity of three Cameroonian medicinal plants traditionally used for the treatment of UTIs and their synergistic effects with amoxicillin and serum.

Methods: The plant extracts were prepared by maceration in methanol. The methanol extract was partitioned into hexane, ethyl acetate and residual fractions and phytochemical analysis was carried out using standard methods. The antibacterial activities of the extracts alone and their combinations with amoxicillin and serum were evaluated using the broth microdilution method.

Results: Phytochemical analysis showed the presence of alkaloids, flavonoids, anthraquinones, tannins and polyphenols in the methanol extracts of Calystegia sepium (L.) R. Br. (Convolvulaceae), Dacryodes edulis (G. Don) H. J. Lam (Burseraceae) and Carica papaya L. (Caricaceae). The other classes of compounds (anthocyanines, triterpenes, steroids and saponines) were selectively distributed in the extracts. All the extracts exhibited antibacterial activities (MIC = 256 - 2048 μg/ml) that varied according to the bacterium and extract, confirming the traditional use of these plants in the treatment of UTIs. The fractionation of the methanol extract of D. edulis leaves did not enhance its activity and unequally distributed the antibacterial activities in different fractions. The interaction of extracts with serum resulted in a concentration-dependent-increase in the antibacterial activity of the different extracts, suggesting that the chemical constituents of the tested extracts weakly bind to the serum proteins. As a function of tested bacterial species, synergistic, additive and indifference effects between amoxicillin and the MeOH extract of D. edulis were observed.

Conclusion: The overall results of this study indicate that the extracts and fractions from the studied plants can be used to treat the UTIs caused by the tested bacteria subject to further toxicological and pre-clinical studies.