Phytochemical analysis and antibiotic-modulating activity of Cocos nucifera, Glycine max and Musa sapientum methanol extracts against multidrug resistant Gram-negative bacteria

Abstract

Background: The rapid emergence of multidrug resistant (MDR) bacteria is occurring worldwide, endangering the efficacy of antibiotics, which have transformed medicine and saved millions of lives. Antibiotic-resistant infections are already widespread in the Sub-Saharan Africa and across the globe. To extend the search for new and more efficient antimicrobial drugs from natural sources, this work has been carried out to study the phytochemical composition and the antibacterial activities of some Cameroonian dietary plants (Cocos nucifera, Glycine max and Musa sapientum) against several MDR Gram-negative strains including Escherichia coli, Enterobacter aerogenes, Providencia stuartii, Klebsiella pneumoniae, Pseudomonas aeruginosa species expressing efflux pumps. Methods: Phytochemical screening of plant extracts was performed using qualitative standard methods and the antimicrobial assays of these extracts alone and in combination with antibiotics were done using serial 96-wells microplate dilution essays. Results: Each plant extract contained at least three mean classes of secondary metabolites. Glycine max, epicarps, leaves and bark of C. nucifera as well as mesocarps of M. sapientum contained each alkaloids, polyphenols, flavonoids, and triterpenes. Moreover, steroids were also found in G. max, steroids and saponins in epicarps and saponins in bark of C. nucifera. Meanwhile epicarps from M. sapientum contained only polyphenols, flavonoids and saponins. Antibacterial assays showed that different parts of C. nucifera were more active than other extracts. Their minimal inhibitory concentrations (MICs) varied from 128 to 2048 µg/mL. The bark part presented the highest antibacterial potential inhibiting the growth of 90% of strains with significant activity (100≤MIC≤512 µg/mL) against 50% of them (three E. coli, four E. aerogenes and three K. pneumoniae). It showed bactericidal effects (MBC/MIC≤4) on 45% of the same bacterial species. It was followed by epicarps and leaves parts which exhibited an inhibitory power against 75% and 60% of bacteria with significant activity on 40% and 20% of them respectively. They also showed bactericidal effects on E. coli ATCC8739 for epicarps extract and E. coli ATCC8739 and P. stuartii NEA16 for leaves extract. Extracts from G. max were less active and those from mesocarps and epicarps of M. sapientum did not showed any activity on all studied bacteria. Bark and epicarps extracts of C. nucifera potentiated the activities of all used antibiotics against at least 70% of bacteria while leaves extract exhibited this effect improving the activities of 67% of antibiotics with improvement activity factors (IAF) ranging from 2 to 256 suggesting that they contain bioactive compounds which could be considered as efflux pumps inhibitors. Extracts from G. max, epicarps and mesocarps of M. sapientum enhanced the inhibitory potential of 56%, 34% and 23% of antibiotics respectively against at least 70% of studied bacteria. These increases of activities also characterize synergistic effects between antibiotics and bioactive compounds of plants. Conclusion: The findings of this work suggest that infections by resistant bacteria can be treated using different parts of C. nucifera as an alternative to commonly used antibiotics.