Antibacterial properties of the extracts of Allexis obanensis and Allexis batangae (Violaceae) collected at Kribi (South Cameroon)

Abstract

The present work presents the antibacterial activities of organic and aqueous extracts of Allexis batangae and Allexis obanensis (violaceae). These plants were collected in the locality of Kribi (South Cameroon). The leaf powder of these plants was cold extracted with a (1:1) methanol/methylene chloride mixture and hot extracted successively with hexane, ethyl acetate, and ethanol. Bark powder was cold extracted with methanol and hot extracted successively with hexane, ethyl acetate, and ethanol. The root powder was hot extracted with hexane, ethyl acetate, and ethanol. For distilled water extraction, only the leaf powder was extracted by maceration. The best yield was of the aqueous extract of leaves (4.86%) and the lowest yield was obtained with the hexane extract of barks (0.35%) for Allexis obanensis, the best yield was of the organic extract of leaves with ethanol 8.31% and the lowest value of the yield was obtained with the hexane extract of barks 0.81% for Allexis batangae. These extracts were subsequently submitted to the phytochemical screening which revealed that this plant is rich of flavonoids, alkaloids, sugars, lipids, phenol glycosides and saponins. The antibacterial test was performed using micro dilution method on five species of bacteria such as Escherichia coli, Enterobacter aerogenes, Enterobacter cloacae, Providencia stuartii, Klebsiella pneumonia, subdivided into nine strains including three ATCC reference strains and six clinical isolates. It flows from these tests that the bark and the roots of Allexis batangae present a great activity against these strains unlike leaves. Among the organic extracts, EA extract of bark and roots strongly inhibited eight strains out of nine, including CM64, BM67, ATCC8739, K2, PS299645, ATCC13048, EA289, ATCC11296 with MIC ranging between 31,2μg/mL to 250μg/mL. However, the EA294 strain was only weakly sensitive to EA extracts of bark and roots and not sensitive to other extracts. The EA extracts exhibited bactericidal activities on the most strains. The aqueous extract of leaves was inactive on all strains tested. For Allexis obanensis, the EA extract of leaves, the ethanol extract of barks and roots and the water extract of roots inhibited the growth of the bacterial tested. This inhibition was performed with MIC equal to 1000, 250 and 125μg/mL. The most active extract was ethanol extract of roots. The sensibility of bacteria to these active extracts was below that of the reference drugCiprofloxacine. After determining the MBC of the extracts whose MIC were equal to 250 and 125μg/mL, the calculation of the ratio MIC to MBC discloses the bactericidal effect of the extracts. These results show that Allexis batangae and Allexis obanensis extracts can be used in therapy against bacterial infections