Twenty‐nine Lactococcus lactis isolates from one traditional 24 h‐old Pecorino Sardo cheese were characterized phenotypically, technologically and genotypically in order to assess the biodiversity within this wild microbial population. Two DNA‐based techniques, plasmid profiling and PFGE, were used for the genetic typing of the isolates. All 29 isolates were characterized at strain level and eight different genotypes were recognized. In addition, by combining the results from plasmid profile analysis and PFGE, it was possible to identify closely related isolates probably belonging to the same clonal lineage. The dominant biotype was identified in the 24 h‐old cheese, as were the strains believed to act as starters for the curd. Atypical lactococci, able to grow in 6·5% NaCl, were isolated. The results suggest that wild bacterial populations should be preserved in order to protect the traditional raw milk cheeses, and to select new starter strains for the dairy industry.
Aims: To assess the intraspeci®c genetic diversity of lactococci and enterococci isolated from 24-h, 1-and 2-month-old home-made Pecorino Sardo ewes' milk cheese. Methods and Results: Two molecular techniques, plasmid pro®ling and pulsed-®eld gel electrophoresis, were used in order to type the isolates at strain level. The present study revealed that the lactococcal and enterococcal microbial populations of home-made Pecorino Sardo cheese were complex, not only 24 h after manufacture, but also after 1 and 2 months of ripening. The genetic diversity at subspecies level ranged from 58 to 80% during the three periods examined. The study also showed that the strains that dominated in the ®rst stage of ripening were not necessarily predominant in the later periods. A high number of strains isolated at 24 h were still present in the mature cheese, but many of the genotypes were only found in the cheese after 1 or 2 months.
Conclusions:The results showed a high intraspeci®c genetic diversity in the natural microbial population colonizing home-made Pecorino Sardo cheese. Two molecular techniques are necessary for a thorough and precise typing at strain level in order to better distinguish between closely related isolates and between isolates that probably belong to the same clonal lineage. Signi®cance and Impact of the Study: The genetic complexity observed in the present study is of particular relevance in the preservation of the natural micro¯ora of traditional Protected Designation of Origin raw milk cheeses, as well as in the selection of new starter strains for the dairy industry.
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