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

Background and aim The 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. Method Bioactive compounds were extracted from leaves of Leucanthemum vulgare, Cymbopogon citratus (DC.) Stapf, Moringa oleifera Lam and Vernonia amygdalina Delile; barks of Cinchona officinalis and Enantia chlorantha Oliv; barks and seeds of Garcinia lucida Vesque and leaves and seeds of Azadirachta indica (Neem) using distilled water and ethanol as solvents. The extracts were tested against Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 6538 and Candida albicans 10231 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 namely Achromobacter xylosoxidans 4892, Citrobacter freundii 426, Enterococcus avium 1669, Escherichia coli 1449, Klebsiella oxytoca 3003, Kocuria rizophilia. 1542, Moraxella catarrhalis 4222, Morganella morganii 1543, Pseudomonas aeruginosa 3057, Staphylococcus aureus 1449 and Streptococcus agalactiae 3984. Results We found that distilled water extracted a more important mass of phytochemical compounds (7.9-21.2%) compared to ethanol (5.8-12.4%). Except C. officinalis and G. lucida leaves, the rest of extracts were active with inhibition diameters (ID) ranging from 5 to 36 mm. Both ethanolic (EE) and aqueous extract (AE) of E. chloranta bark (ECB) were the most active against all pathogens with the mean ID of 17 and 36 mm vs S. aureus ATCC 6538, 23 and 14 mm vs E. coli ATCC 25922 and 36 and 19 mm vs C. albicans ATCC 10231. Only the EE of E. chloranta bark (ECB) had a strong activity against all the microorganisms tested (MIC <2 mg / ml); L. vulgare leaves (LVL) and G. lucida seed (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 against S. aureus and 0.250 against E. coli), nitrofurantoin (FIC = 0.250 against S. aureus and 0.188 against E. coli) and ampicillin (FIC = 0.125 against E. 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). Conclusion This 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.