An Appraisal of Identification Methods for Penicillium Species: Novel Taxonomic Criteria Based on Temperature and Water Relations

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Abstract
Examination of media and methods currently used in Penicillium taxonomy led to the conclusion that by using only two media, Czapek yeast autolysate agar and malt extract agar, and by incubating cultures at 25 C for 7 days, one could obtain classical taxonomic data with optimal efficiency. The effect of reduced water activity and reduced and elevated temperatures on the growth of Penicillium spp. accepted in the Raper and Thom A Manual of the Penicillia was studied. On a glycerol-nitrate salts agar of 0.93 water activity, and on Czapek yeast autolysate agar at 5 C and 37 C, extent of growth after 7 days provided taxonomically valuable data; within-species variation was low, while between-species variation was sufficiently marked to assist in determinative classification. Moreover, water relations, as assessed by the above technique, showed a very high correlation with penicillus type in some Sections of the genus.