Antibacterial activity of four Cameroonian medicinal plants against MDR bacteria and study of mode of action

Abstract

Background: The increasing number of resistant bacteria to commonly used antibiotics makes the search for new active molecules a real challenge. The aim of this study is to evaluate the antibacterial activities of crude extracts and fractions from four Cameroonian medicinal plants against multi-resistant bacteria as well as their mechanisms of action.

Methods: The crude extracts were prepared by maceration in methanol. The fractionation was carried out by successive depletion in hexane and ethyl acetate. The qualitative phytochemical analysis of the extracts and fractions was performed using standard methods. The antibacterial activities of extracts alone and their synergistic effect with amoxicillin and serum were evaluated using the broth microdilution method. The effect of extracts on the red blood cells and bacterial cell membrane was determined by spectrophotometric method. The bacteriolytic activity was evaluated by the time-kill kinetic method.

Results: The results showed that all the crude extracts contain phenols, alkaloids, sterols, triterpenes and tannins. The extracts of Curcuma longa, Rubus idaeus, Centella asiatica and Taraxacum officinale displayed variable antibacterial activities (MIC= 64-2048 µg/mL) confirming their traditional use in the treatment of infectious diseases. The fractionation of methanol extracts of C. longa and R. idaeus has distributed the antibacterial activities in different fractions. Some synergistic effects between amoxicillin and methanol extracts of C. longa and R. idaeus were observed. The antibacterial activities of plant extracts and tetracycline increased under osmotic stress conditions (2.5% NaCl) while those of vancomycin decreased under these conditions. A loss of nucleic material and a decrease in the optical density from S. aureus suspension treated with the methanol extracts of C. longa and R. idaeus were observed. The serum resulted in a concentration-dependent increase in the antibacterial activity of the methanol extracts of C. longa and R. idaeus. The tested plant extracts showed less haemolytic activity, indicating their good selectivity to the bacterial cell.

Conclusions: Overall, the present results show that the studied plant extracts possess antibacterial activity that can justify their traditional use in the treatment of infected diseases. The antibacterial activity mechanism is due to cell lysis and disruption of the bacterial cytoplasmic membrane.