Analysis of genes encoding D-alanine:D-alanine ligase-related enzymes in Leuconostoc mesenteroides and Lactobacillus spp.

Degenerate oligodeoxyribonucleotides complementary to sequences encoding conserved amino acid (aa) motifs in D-alanine:D-alanine ligases (Ddl) were used to amplify approx. 600-bp fragments from glycopeptide-resistant strains of Leuconostoc mesenteroides (Lm), Lactobacillus plantarum, La. salivarius and La. confusus, and from a susceptible strain of La. leichmannii. Comparison of the deduced aa sequences of the PCR products revealed that the Ddl-related enzymes of resistant Lm and Lactobacillus spp. are more akin to each other (47-63% aa identity) than to that of susceptible La. leichmannii (33-37% aa identity), indicating that the Ddl-related enzymes in these intrinsically resistant species of Gram+ bacteria exhibit structural differences with those in susceptible species. The Ddl-related enzymes, VanA and VanB, implicated in acquired resistance to glycopeptides in enterococci, were not closely related to their counterparts in Lm and Lactobacillus spp., as they displayed only 26-32% aa identity.