Integrated polymerase chain reaction-based procedures for the detection and identification of species and subspecies of the Gram-positive bacterial genus Lactococcus

Aims: Five species of the Gram-positive bacterial genus Lactococcus (Lactococcus lactis , L. garvieae , L. plantarum , L. piscium and L. raffinolactis ) are currently recognized. The aim of this work was to develop a simple approach for the identification of these species, as well as to differentiate the industrially important dairy subspecies L. lactis subsp. lactis and L. lactis subsp. cremoris. Methods and Results: Methods were devised based on specific polymerase chain reaction (PCR) amplifications that exploit differences in the sequences of the 16S ribosomal RNA genes of each species, followed by restriction enzyme cleavage of the PCR products. The techniques developed were used to characterize industrial cheese starter strains of L. lactis and the results were compared with biochemical phenotype and DNA sequence data. Conclusions: The PCR primers designed can be used simultaneously, providing a simple scheme for screening unknown isolates. Strains of L. lactis show heterogeneity in the 16S ribosomal RNA gene sequence. Significance and Impact of the Study: This work provides an integrated set of methods for differentiation and identification of lactococcal species associated with agricultural, veterinary, medical and processed food industries.