Ubiquity and diversity of multidrug resistance genes in Lactococcus lactis strains isolated between 1936 and 1995

The presence and the nucleotide sequence of four multidrug resistance genes, lmrA, lmrP, lmrC, and lmrD, were investigated in 13 strains of Lactococcus lactis ssp. lactis, four strains of Lactococcus lactis ssp. cremoris, two strains of Lactococcus plantarum, and two strains of Lactococcus raffinolactis. Multidrug resistance genes were present in all L. lactis isolates tested. However, none of them could be detected in the strains belonging to the species L. raffinolactis and L. plantarum, suggesting a different set of multidrug resistance genes in these species. The analysis of the four deduced amino acid sequences established two different variants depending on the subspecies of L. lactis. Either lmrA, or lmrP, or both were found naturally disrupted in five strains, while full-length lmrD was present in all strains.