Distribution of Penicillium commune isolates in cheese dairies mapped using secondary metabolite profiles, morphotypes, RAPD and AFLP fingerprinting

Abstract

In an 8-year study of the diversity and distribution of Penicillium commune contaminants in two different cheese dairies, swab and air samples were taken from the production plants, the processing environment and contaminated cheeses. A total of 321 Penicillium commune isolates were characterized using morphotypes (colony morphology and colours) and secondary metabolite profiles. Based on production of secondary metabolites the P. commune isolates were classified into 6 groups. The genetic diversity of the P. commune isolates was assessed using randomly amplified polymorphic DNA (RAPD) and amplified fragment length polymorphism (AFLP). For a sub-set of 272 P. commune isolates RAPD analysis generated 33 RAPD groups whereas AFLP profiling revealed 55 AFLP groups. This study conclusively showed that the discriminatory power of AFLP was high compared to RAPD and that AFLP fingerprinting matched morphotyping. P. commune isolates with identical profiles using all four typing techniques were interpreted as closely related isolates with a common origin and the distribution of these isolates in the processing environment indicated possible contamination points in the cheese dairies. The coating process and unpacking of cheeses with growth of P. commune seemed to cause the contamination problems. Several identical P. commune isolates remained present in the processing environment for more than 7 years in both dairies.