Screening of antimicrobial activity of aqueous and ethanolic extracts of some medicinal plants from Cameroon and assessment of their synergy with common antibiotics against multidrug-resistant uropathogenic bacteria

AbstractBackground and aimThe Cameroonian flora abounds in plants with multidimensional therapeutic virtues which can play an important role in the fight against resistance to antibiotics and the search for new antimicrobials. This study aimed to screen the antimicrobial potential of aqueous and ethanolic extracts of thirteen (13) samples (Bark, leaf, seed) of eight (8) plants from Cameroon against 3 reference pathogens and to evaluate their synergy with conventional antibiotics against eleven (11) multiresistant uropathogenic (MRU) bacteria.MethodBioactive compounds were extracted from leaves ofLeucanthemum vulgare, Cymbopogon citratus(DC.) Stapf,Moringa oleiferaLam andVernonia amygdalinaDelile; barks ofCinchona officinalisandEnantia chloranthaOliv; barks and seeds ofGarcinia lucidaVesque and leaves and seeds ofAzadirachta indica(Neem) using distilled water and ethanol as solvents. The extracts were tested againstEscherichia coliATCC 25922,Staphylococcus aureusATCC 6538 andCandida albicans10231 using the well diffusion method and the microdilution method. The synergistic effect was assessed (using disc diffusion method and the checkerboard method) against MRU bacteria namelyAchromobacter xylosoxidans4892,Citrobacter freundii426,Enterococcus avium1669,Escherichia coli1449,Klebsiella oxytoca3003,Kocuria rizophilia. 1542,Moraxella catarrhalis4222,Morganella morganii1543,Pseudomonas aeruginosa3057,Staphylococcus aureus1449 andStreptococcus agalactiae3984.ResultsWe found that distilled water extracted a more important mass of phytochemical compounds (7.9-21.2%) compared to ethanol (5.8-12.4%). ExceptC. officinalisandG. lucidaleaves, the rest of extracts were active with inhibition diameters (ID) ranging from 5 to 36 mm. Both ethanolic (EE) and aqueous extract (AE) ofE. chlorantabark (ECB) were the most active against all pathogens with the mean ID of 17 and 36 mm vsS. aureusATCC 6538, 23 and 14 mm vsE. coliATCC 25922 and 36 and 19 mm vsC. albicansATCC 10231. Only the EE ofE. chlorantabark (ECB) had a strong activity against all the microorganisms tested (MIC <2 mg / ml);L. vulgareleaves (LVL) andG. lucidaseed (GLS) had moderate (average MIC of 8 mg/ml) while all other extracts showed very weak antimicrobial activity. In addition, the fractional inhibitory concentration (FIC) ranged from 0.125 to 0.750. No antagonism (FIC> 4) or indifference (1≤ FIC≤4) was noted between the extracts and the antibiotics, but the best synergies were found with ECB which well-modulated Kanamycin (FIC = 0.125 againstS. aureusand 0.250 againstE. coli), nitrofurantoin (FIC = 0.250 againstS. aureusand 0.188 againstE. coli) and ampicillin (FIC = 0.125 againstE. coli). Similarly, compared to other extracts, ECB, LVL and GLS also well-modulated ampicillin, ceftazidime, tetracycline, nitrofurantoin, and trimethoprim against all the above-mentioned resistant uropathogenic bacteria with important increase in fold area (IFA).ConclusionThis study show that E. chlorantha bark, L. vulgare leaves G. lucida seed, have good antimicrobial activity against both bacteria (Gram positive and Gram negative) and fungi (C. albicans); and should be more investigated for their possible use to the fight against MDR and MRU microorganisms.