Differences in the Enterococcus faecalis lsa Locus That Influence Susceptibility to Quinupristin-Dalfopristin and Clindamycin

摘要

We have previously shown that the Enterococcus faecalis lsa gene, encoding the putative ABC protein Lsa, influences resistance to quinupristin-dalfopristin (Q-D) and clindamycin (CLI). We have now found that, while cloned lsa from E. faecalis strain V583 (lsaV) fully restored resistance to Q-D, CLI, and dalfopristin (DAL) lost by the OG1 lsa disruption mutant TX5332 and also caused increased MICs for Lactococcus lactis LM2301, cloned lsa from OG1 (lsaOG) did not cause any increase in MICs for either species. Sequencing of ca. 2 kb of these two lsa alleles found differences between lsaOG and lsaV in the upstream region as well as in the 5′ and 3′ halves of the lsa gene. To investigate the reason for the phenotypic differences expressed by the two cloned loci, 5′ half plus 3′ half hybrid constructs were created. When introduced into both TX5332 and L. lactis, cloned lsaV5′OG3′ conferred increases in MICs of Q-D, CLI, and DAL similar to those of cloned lsaV while cloned lsaOG5′V3′ showed a moderate increase in MICs relative to those of lsaOG, indicating that both halves of the locus can influence resistance expression. After site-directed mutagenesis of the cloned lsa alleles at positions −131 and −133 (relative to the putative Lsa start codon ATG), which converted two A's of lsaV to the G and T of lsaOG and vice versa, MIC testing showed that mutagenized lsaOG (lsaOG-M) was strongly influenced by these changes in terms of conferring increased MICs of Q-D, CLI, and DAL relative to lsaOG while the phenotype of mutagenized lsaV (lsaV-M) was less influenced, with moderately decreased MICs, primarily to CLI, relative to lsaV. In conclusion, this study found that changes in different regions of the E. faecalis lsa locus influence the ability of cloned lsa to confer resistance to Q-D, CLI, and DAL.