Abstract

In the present study, an endophytic fungus with a considerable antimicrobial activity was isolated from the medicinal plant Mentha Pulegium L. The morphological and molecular identification revealed that this fungus is a Penicillium griseofulvum. A preliminary screening was done to choose the suitable culture medium for a maximum production of the bioactive compounds using the dual-culture agar diffusion assay. The malt extract agar (MEA) and potato dextrose agar (PDA) media were the suitable, and the MEA was selected for the further study. Extraction was done with three solvents, n-Hexane, dichloromethane and ethyl acetate, and the crude extracts were tested against Gram-positive and negative bacteria. A high activity was found with ethyl acetate and dichloromethane crude extracts against all bacteria with a maximal inhibition zones of 45.5 and 41 mm respectively obtained against Escherichia coli. The minimum inhibitory and bactericidal concentrations (MIC, MBC) of ethyl acetate crude extract were evaluated using the broth micro-dilution method. A MIC of 50 µg / ml on Gram-negative bacteria and of 100 µg / ml on Gram-positive bacteria was found. The MBC_S ranged from 50 and 200 µg/ml. The time kill study has revealed a bactericidal activity of the Penicillium griseofulvum crude extract. At 10 h and for all concentrations (MIC, MIC× 2 and MIC× 4), 99.9% killing of the bacterial cells was achieved. These results prove that the extract of Penicillium griseofulvum can be a promising source of important bioactive molecules.

Keys words: Antibacterial activity, endophytic fungi, Mentha pulegium L., Penicillium griseofulvum.