Description
The dilution plate count of P. verrucosum is obtained by a surface plating technique. After homogenizing a specified quantity (40 g), a serial dilution is carried out. Of each dilution 0.1 ml is spread plated onto the culture medium in duplicate. After incubation at 20.0 +/-1.0 C for 7 days, the colonies with a characteristic appearance are counted. The number of cfu of P. verrucosum per gram of food is calculated. The direct plating of P. verrucosum is performed by placing 100 food pieces (often kernels) on the medium, 5-10 on each 9 cm Petri dish (this procedure may be repeated with surface disinfected food pieces). The number of food pieces from which at least one colony of P. verrucosum grows out is recorded and the percentage infestation (or infection) is calculated.