Different Combretum molle (Combretaceae) leaf extracts contain several different antifungal and antibacterial compounds

Abstract

Combretum molle occurs widely in Africa and is used traditionally to treat many different ailments including microbial infections. Some work has been done on the antimicrobial activity of bark extracts, but not on leaf extracts, a sustainable resource.Dried ground leaves were extracted with methanol, butanol, acetone, ethyl acetate, chloroform, dichloromethane and n-hexane. The antibacterial and antifungal activities were determined by using a serial microplate dilution method and the number of antimicrobial compounds were determined by bioautography. Both animal (Candida albicans, Cryptococcus neoformans, Aspergillus fumigatus) and plant (Penicillium janthinellum, Aspergillus niger, Aspergillus parasiticus, Fusarium oxysporum, Rhizoctonia solani) pathogenic fungal species were examined. Four important nosocomial bacterial species (Staphylococcus aureus, Escherichia coli, Enterococcus faecalis and Pseudomonas aeruginosa) were also examined.Butanol extracted the highest mass of plant material (41 mg) and hexane and dichloromethane extracted the lowest masses, 8 and 9 mgl, respectively. In bioautograms developed with BEA sprayed with Aspergillus fumigatus, all the extracts had clear zones of inhibition at R values of c. 0.12, 0.23, and 0.40 for the different fungi.The MIC values of the extracts ranged from 0.04 to 0.77 mg/ml after 12 h incubation. The acetone leaf extract was the most active with an MIC of 0.04 mg/ml against P. janthinellum, an important plant fungal pathogen. The total activity of 775 ml/g (indicating that the extract obtained from 1 g of leaves can be diluted to 775 ml and will still inhibit the growth) means that the acetone leaf extract could be used to control P. janthinellum infections on plants.