Correlation between polymerase chain reaction analysis of the histidine biosynthesis operon, randomly amplified polymorphic DNA analysis and phenotypic characterization of dairy Lactococcus isolates

A collection of 32 lactococcal strains isolated from raw milk in the Camemb ert RDO (registered designation of origin) area were phenotypically and gen otypically characterized. As expected for environmental isolates, all strai ns had a Lactococcus lactis subsp. lactis phenotype. The strains were then genotypically identified by the randomly amplified polymorphic DNA (RAPD) t echnique, using reference strains of lactococci. Two major clusters were id entified containing the two subspecies lactis and cremoris. The subspecies lactis cluster could be divided into five subgroups whereas there was a hig h coefficient of similarity between all strains in the subspecies cremoris cluster. This RAPD classification was then compared with that of a traditio nal PCR assay using L. lactis species-specific primers corresponding to par t of the histidine biosynthesis operon. The two subspecies were differentia ted by the size of the fragment amplified (about 200 bp longer for subspeci es cremoris). Unlike preliminary phenotypic assignments, the results of PCR experiments corroborated the genotypic identification of the lactococcal s trains by RAPD allowing the technique to be reconsidered on the basis of it s taxonomic efficiency.