Antibacterial and antibiotic-potentiating activities of Desmodium uncinatum, Neoboutonia glabrescens, Ternstroemia cameroonensis and eight other Cameroonian medicinal plants against multi-drug resistant bacteria expressing active efflux pumps

Abstract

Background: Infectious diseases remain a major public health problem in the world with a considerable impact in developing countries. Bacterial infections are of increasing concern due to the emergence and spread of bacteria resistant to antibiotics. Thus, it is necessary to develop methods and means to tackle drug resistance. The present study aimed at evaluating the antibacterial and antibiotic-potentiating activities of eleven Cameroonian medicinal plants: Sambucus nigra, Erigeron floribundus, Desmodium uncinatum, Neoboutonia glabrescens, Ficus exasperata, Sida rhombifolia, Echinaceae augustifolia, Centella asiatica, Tradescantia zebrina, Desmodium intortum and Ternstroemia cameroonensis against bacteria with multidrug-resistant (MDR) phenotypes.
Methods: The microdilution method was used to assess the antibacterial activities of the extracts as well as the effect of their combination with antibiotics. The phytochemical screening of the extracts was carried out according to qualitative described methods.
Results: The phytochemical screening revealed the presence of tannins, triterpenes, polyphenols, and flavonoids in almost all the extracts, with the other classes of secondary metabolites being selectively distributed. The tested extracts exhibited variable antibacterial activities, with minimum inhibitory concentrations (MICs) ranging between 512 and 1024 μg/mL. The Ficus exasperata leaves extract, Ternstroemia cameroonensis back extract, Erigeron floribundus whole plant extract, and Neoboutonia glabrescens leave extracts, presented the best spectra of inhibitions evaluated respectively at 60%, 60%, 70%, and 70% vis-à-vis all the bacterial strains tested. The whole plant extracts of Desmodium uncinatum and Centella asiatica, and of Ternstroemia cameroonensis have shown synergistic effects with more than 50% of the antibiotics (chloramphenicol, tetracycline, kanamycin, ciprofloxacin, ofloxacin, azithromycin and erythromycin) against more than 70% of the MDR bacteria tested.
Conclusion: The present study demonstrated that extracts from the bark of Ternstroemia cameroonensis, Neoboutonia glabrescens and Ficus exasperata leaves, Desmodium uncinatum, and Erigeron floribundus whole plants can be used alone or in combination with antibiotics against bacterial infections involving MDR bacteria.