PCR and RAPD identification of L. plantarum strains isolated from ovine milk and cheese. Geographical distribution of strains.

Lactobacilli, and specifically Lactobacillus plantarum, are an important group of microorganisms in ovine cheeses, even though they are not ordinarily included in the starter cultures added. The present study effected counts of lactobacilli in Roncal Protected Designation of Origin (PDO) milk and cheese samples and isolated a total of 1026 strains. The strains were identified to species level by polymerase chain reaction (PCR) using L. plantarum-specific oligonucleotide primers, and the strains belonging to this species were then characterized by randomly amplified polymorphic DNA (RAPD). The percentage of L. plantarum present in the cheeses depended on the plant where the cheese was manufactured. Cluster analysis of the RAPD profiles obtained revealed seven main clusters. On comparing the strains, most of the strains present in the cheese were found not to have come from the raw milk.