Evaluation of several tree species for activity against the animal fungal pathogen Aspergillus fumigatus

Abstract

Aspergillus fumigatus causes severe problems in poultry production systems. Seven South African tree species were selected from the database of the Phytomedicine Programme based on its antifungal activity against the fungus Cryptococcus neoformans. The acetone leaf extracts of the selected species hadminimum inhibitory concentrations (MICs) of 0.16 mg/ml and lower in the preliminary screening. The antibacterial and antifungal activities of hexane, dichloromethane, acetone and methanol extracts of the leaves were determined using a two-fold serial microdilution method against a range of commonly encountered animal pathogenic fungi (A. fumigatus, Candida albicans, C. neoformans, Microsporum canis and Sporothrix schenckii) and four nosocomial bacteria (Staphylococcus aureus, Enterococcus faecalis, Escherichia coli and Pseudomonas aeruginosa). The plant species investigated were Combretum vendae (A.E. vanWyk) (Combretaceae), Commiphora harveyi (Engl.) Engl. (Burseraceae), Khaya anthotheca (Welm.) C.DC (Meliaceae), Kirkia wilmsii Engl. (Kirkiaceae), Loxostylis alata A. Spreng. ex Rchb. (Anacardiaceae), Ochna natalitia (Meisn.)Walp. (Ochnaceae) and Protorhus longifolia (Bernh.) Engl. (Anacardiaceae). All the extracts had activity against at least one of the test organisms over an incubation period of 24 or 48 h. TheMIC values of the non-polar and intermediate polarity extracts of O. natalitia, K. anthotheca, C. vendae, C. harveyi, and P. longifolia hadMICs as low as 0.08 mg/ml against at least one of the tested bacteria. Furthermore, the acetone extracts of L. alata, K. wilmsii, O. natalitia and C. vendae had antifungal activities with MIC values ranging from 0.04 to 0.08 mg/ml against at least one of the tested fungi. The average MIC values of the plant extracts against the different bacteria ranged from 0.17 to 2.11 mg/ml, while the range was 0.23–1.98 mg/ml for fungi. The Gram-positive bacteria (S. aureus and E. faecalis) were more susceptible to the plant extracts than the Gram-negative bacteria (E. coli and P. aeruginosa). E. faecalis was the most susceptible microbe and C. vendae extracts were themost active against nearly all the bacteria tested. The acetone extract of L. alata was the most active against fungal pathogens,with activity against at least 3 fungal organisms. L. alata was selected for further work to isolate compounds active against A. fumigatus and other fungal pathogens.