RESUMEN
The study of the conditions which affect the pharmacological activity of medicinal plants is the basis for the development of phytomedicine. This study aimed at identifying some optimal conditions for antibacterial activity of extracts of Harungana madagascariensis. The leaves, bark, and roots were harvested in Douala, Littoral Region of Cameroon, in August 2019 at three times of the day: early in the morning (6 a.m.), at midday (12 p.m.), and in the afternoon (6 p.m.). They were dried at room temperature and ground to give a fine powder. Each powder was macerated in methanol for 72 h and boiled in distilled water and palm wine. The obtained extracts were evaluated for their antibacterial activity by broth microdilution method on 31 clinical and 4 reference bacterial strains. The results show that the best extraction yield was obtained using the bark extracted from palm wine by decoction. The methanol bark extract was found to be more active than other solvents (8 and 512 µg/mL). In fact, the activity of the 6 a.m. extract was significant on 4 of the 35 strains tested (MIC< 100 µg/mL) and moderate on 27 of the 35 strains tested (100≤ MIC≤ 625 µg/mL). The activity of the noon extract was significant on 8 strains and moderate on 23 strains and, finally, the activity of the extract of 6 p.m. was significant on 9 strains and moderate on 25 strains. The extract harvested at 6 p.m. inhibited the growth of the 35 strains tested and revealed significant activity (MIC <100 µg/mL) on Staphylococcus aureus, Escherichia coli, Citrobacter freundii, Serratia marcescens, Salmonella enterica serovar typhi, and Yersinia enterocolitica, making this hour the best harvesting time. This study further confirms that the bark of H. madagascariensis is a potent antibacterial agent, being better still when harvested at 6 p.m. and extracted with methanol.
RESUMEN
Infectious diseases caused by bacteria constitute the main cause of morbidity and mortality throughout the world and mainly in developing countries. In this work, the influence of fractioning and the mode of action of stem barks methanol extract of Enantia chlorantha were investigated. The aim was to optimize the antibacterial activity of the methanol extract. The extract was prepared by maceration of barks powder in methanol. Fractioning was done using increasing solvents polarity. Standard phytochemical methods were used for phytochemical screening. Minimum Inhibitory Concentrations (MIC) and Minimum Bactericidal Concentration (MBC) of the methanol extract and fractions were determined using broth microdilution method. The studied mode of action of both methanol extract and n-butanol fraction included antibiofilm activity, H+-ATPase-mediated proton pumping assay, salt tolerance, and cells cycle. The methanol extract of E. chlorantha stem barks was found to be active on all the bacteria tested (32 ≤ MIC ≤ 512 µg/mL), its activity being significant (MIC < 100 µg/ml) out of 5 of the 28 clinical isolates used. Salmonella enterica serovar paratyphi A was the most sensitive (32 µg/mL). Compared to the extract and other fractions, the n-butanol fraction was found to be more active (32 ≤ MIC ≤ 256). Significant antibacterial activity of this fraction was observed out of 10 of the 28 bacterial isolates and 3 out of 7 bacterial strains. Lowest MIC values (32 µg/ml) of this fraction were obtained with Escherichia coli (136), Pseudomonas aeruginosa (CIP 76110), and Salmonella enterica serovar typhi 9. The methanol extract of E. chlorantha and its n-butanol fraction revealed several modes of action including the prolongation of the latency phase of the bacterial growth, the inhibition of the pump with protons H+ - ATPases bacterial, the loss of the salt tolerance of the Staphylococcus aureus, and inhibition of the formation of the bacterial biofilm. The present results showed that the n-butanol fraction of the methanol stem barks extract of E. chlorantha possess the essential antibacterial components and could best be used to fight against bacterial infections as compared to methanol extract.
