Isolation of Lactococcus lactis subsp. cremoris from nature by colony hybridization with rRNA probes.

Lactococcus lactis subsp. cremoris is widely used in the manufacture of fermented milk products. Despite numerous attempts, efforts to isolate new strains by traditional plating and identification methods have not been successful. Previously, we described oligonucleotide probes for 16S rRNAs which could be used to discriminate L. lactis subsp. cremoris from related strains. These probes were used in colony hybridization experiments to screen large numbers of colonies obtained from enrichment cultures. A total of 170 strains of L. lactis were isolated from six milk samples, two colostrum samples, and one corn sample by using oligonucleotide probe 212RLa specific for the species L. lactis. Fifty-nine of these isolates also hybridized to L. lactis subsp. cremoris-specific probe 68RCa, and 26 of the strains which hybridized to the L. lactis subsp. cremoris-specific probe had the L. lactis subsp. cremoris phenotype.