Genetic characterization of some lactic acid bacteria occurring in an artisanal protected denomination origin (PDO) Italian cheese, the Toma piemontese

We studied the natural bacterial population used in the production of artisanal protected denomination origin (PDO) Toma piemontese cheese in order to obtain preliminary information on the lactic acid bacteria involved in the traditional fermentation of this cheese. A total of 116 coccal isolates and 11 mesophilic lactobacilli were collected from different curd and cheese samples, and were identified by the combined use of PCR 16S–23S rDNA spacer analyses, species-specific probes and 16S rDNA sequencing. The results obtained were supported by DNA/DNA hybridization studies and by reference cultures used as markers. Lactococci constituted 67% of the coccal isolates. They were identified as Lactococcus lactis and L. garvieae, with an incidence of this latter species higher than expected. The majority of these lactococcal isolates displayed an atypical phenotype of growing in the presence of 6.5% NaCl and at 101C. Enterococci were also isolated, principally from the cheese samples (16% of the coccal isolates), together with strains of Streptococcus macedonicus and S. thermophilus, the latter in a lower amount. Lactobacilli (principally Lactobacillus paracasei strains) were only detected in three samples and their incidence was very low ( 1, 3 and 7 cfu g–1, respectively). The presence of undesirable micro-organisms in some samples of curd emphasizes the necessity of improving the general hygienic conditions of cheese production. The results suggest the possibility of preserving the wild bacterial population in order to protect the typical organoleptic characteristics of this traditional raw milk cheese and to select new strains for the dairy industry.