Differentiating Penicillium species by detection of indole metabolites using a filter paper method

The indole secondary metabolites chaetoglobosin C, cyclopiazonic acid, isofumigaclavine A and rugulovasine A and B produced by several Penicillium species growing on Czapek yeast autolysate agar were detected directly in the culture using filter paper wetted with Ehrlich reagent dissolved in ethanol. The filter paper was placed on the mycelial side of an agar plug and the metabolites were visualized as a violet zone on the paper within 10 min. It was shown that the combined characters of the violet reaction on filter paper and the ability to grow on creatine sucrose agar occurred in 5 out of 16 species of Penicillium examined. A few additional simple morphological and physiological criteria were then sufficient for identification of P. camemberti, P. commune, P. discolor, P. expansum and P. roqueforti var. roqueforti.