Method for identifying selective growth inhibitors

Selective growth inhibitors are identified by (i) providing a semi-solid nutrient medium (e.g., an agar plate) co-seeded with a strain of cells (e.g., bacteria or fungi) that is sensitive to growth inhibitors having a particular mode of action and with a strain that is essentially the same as the sensitive strain except that it is resistant to said growth inhibitors, wherein the sensitive strain is co-seeded in the nutrient medium in an amount substantially in excess of that of the resistant strain; (ii) treating the medium with a test substance; (iii) incubating the treated medium under conditions suitable for the growth of both the sensitive and the resistant strains; and (iv) examining the incubated treated medium for growth inhibition. The observation in (iv) of a zone of no growth except for isolated colonies of the resistant strain is an indication that the test substance is a selective growth inhibitor having the mode of action of interest.