Origin and diversity of mesophilic lactobacilli in Comté cheese, as revealed by PCR with repetitive and species-specific primers

Abstract The objectives of this work were to describe the diversity of mesophilic lactobacilli in Comte cheese at the strain and species levels, to determine the origin(s) of this non-starter microflora, and to get a collection of well characterised strains from Comte cheeses. Strains were isolated from milks, starter cultures and eight cheeses from two factories, with four cheeses made from the same vat in each factory. Strain and species assignations were performed with a combination of two PCR-based methods, amplification with the pairs of repetitive primers ERIC1/ERIC2 and REP–1R-Dt/REP2-D, and amplification with specific primers for Lactobacillus zeae , Lactobacillus paracasei and Lactobacillus rhamnosus . The reliability and reproducibility of these methods were assessed using 49 collection strains of mesophilic lactobacilli commonly detected in cheeses. A total of 488 isolates of mesophilic lactobacilli was collected and was assigned to 44 different strains and three different species. Lactobacillus paracasei and Lactobacillus rhamnosus were the predominant species in milks, starter cultures and cheeses, and constituted 98.7% of the isolates. Strain diversity was found at both individual cheese and factory levels. Thirteen and fifteen different strains were detected throughout cheesemaking and ripening in two individual cheeses made in different factories; only 11 different strains were detected in the two corresponding mature cheeses. The data strongly suggest that most mesophilic lactobacilli strains originate from raw milk.