Methods of isolating biologically active molecules from an organism, for example from a fungus, are described. The methods involve isolating an active molecule which possesses a specific biological activity on, in or against wild-type yeast cells, but not on, in or against yeast cells that express a given ABC transporter from a given organism, including but not limited to Magnaporthe species such as Magnaporthe grisea. In preferred embodiments, the biological activity is antifungal activity. In most preferred embodiments, the antifungal activity is against a human pathogen, including but not limited to Candida albicans. The biologically active molecules can be formulated as pharmaceutical compositions and used to treat fungal infections in a subject, including a human subject.
