Antistaphylococcal Activity of Extracts, Fractions, and Compounds of Acacia polyacantha Wild (Fabaceae).

Acacia polyacantha is a medicinal plant traditionally used to treat livestock diseases and gastrointestinal infections; our study was undertaken to evaluate the antistaphylococcal activities of the methanolic leaf, bark, and root extracts, fractions, and compounds from Acacia polyacantha against a panel of 14 multidrug-resistant Staphylococcus bacterial strains overexpressing efflux pumps. The study was also extended to investigate two possible modes of action, that is, influence on bacterial growth kinetics and influence on proton-ATPase pumps, of the most active compound against a reference strain. Materials and Methods . The crude extracts after extraction were subjected to column chromatography. Antibacterial assays of extracts, fractions, and compounds alone and in the presence of efflux pump inhibitors were carried out using the broth microdilution method and the study of two mechanisms of action achieved by standard methods with the most active compound. Results . The phytochemical study of Acacia polyacantha leaves leads to the isolation of stigmasterol ( 1 ), β -amyrin ( 2 ), 3- O -methyl- _D -chiro-inositol ( 3 ), epicatechin ( 4 ), quercetin-3- O -galactoside ( 5 ), 3- O -[ β - _D -xylopyranosyl-(1 ⟶ 4)- β - _D -galactopyranosyl]-oleanolic acid ( 6 ), 3- O -[ β -galactopyranosyl-(1⟶ 4)- β - _D -galactopyranosyl]-oleanolic acid ( 7 ) and that of leaves lead to the isolation of lupeol ( 8 ) 2,3-dihydroxypropyltetracosanoate ( 9), and methyl-gallate ( 10 ). Leaf, root, and bark extracts inhibited 92.85% (13/14), 92.85% (13/14), and 71.43 % (10/14) of the tested bacteria strains, respectively, with minimum inhibitory concentration (MIC) varying between 16 and 1024  μ g/mL. Fractions exhibited better activities compared to those of their extracts of origin, as their MICs ranged from 16 to 512  μ g/mL, with fractions from leaves being more active than those obtained from barks. Compounds had varying activities; MICs varied from 16 to 512  μ g/mL with compound 4 presenting the best activity as MICs ≤100  μ g/mL were obtained against 11 of the tested bacteria. The activities of extracts, fractions, and compounds were improved in the presence of carbonyl cyanide m-chlorophenylhydrazone (CCCP) as an efflux pump inhibitor to as much as >128 folds. Meanwhile, in the presence of chlorpromazine as an efflux pump inhibitor, only the activity of compound 10 was improved on 10 of the tested bacteria strains. Compound 4 prolonged the lag phase of the growth kinetic in a concentration-dependent manner and equally inhibited the proton-ATPase pumps of the tested bacteria strains. Conclusion . The present study demonstrates the antistaphylococcal potential of Acacia polyacantha and its constituents to combat bacterial infections alone or in combination with efflux pump inhibitors.
Competing Interests: The authors declare that they have no conflicts of interest.
(Copyright © 2020 Fred A. Ashu et al.)