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Differences in the Enterococcus faecalis lsa locus that influence susceptibility to quinupristin-dalfopristin and clindamycin.

ABSTRACT: 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 (lsa(V)) 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 (lsa(OG)) did not cause any increase in MICs for either species. Sequencing of ca. 2 kb of these two lsa alleles found differences between lsa(OG) and lsa(V) 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 lsa(V5)(')(OG3)(') conferred increases in MICs of Q-D, CLI, and DAL similar to those of cloned lsa(V) while cloned lsa(OG5)(')(V3)(') showed a moderate increase in MICs relative to those of lsa(OG), 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 lsa(V) to the G and T of lsa(OG) and vice versa, MIC testing showed that mutagenized lsa(OG) (lsa(OG-M)) was strongly influenced by these changes in terms of conferring increased MICs of Q-D, CLI, and DAL relative to lsa(OG) while the phenotype of mutagenized lsa(V) (lsa(V-M)) was less influenced, with moderately decreased MICs, primarily to CLI, relative to lsa(V). 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.

SUBMITTER: Singh KV

PROVIDER: S-EPMC538898 | biostudies-literature | 2005 Jan

REPOSITORIES: biostudies-literature

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Differences in the Enterococcus faecalis lsa locus that influence susceptibility to quinupristin-dalfopristin and clindamycin.

Singh Kavindra V KV Murray Barbara E BE

Antimicrobial agents and chemotherapy 20050101 1

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 (lsa(V)) 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 (lsa(OG)) did not cause any increase in MICs fo ...[more]

PMID: 15616272

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Project description:BACKGROUND:The bacterial ribosome is a primary target of several classes of antibiotics. Investigation of the structure of the ribosomal subunits in complex with different antibiotics can reveal the mode of inhibition of ribosomal protein synthesis. Analysis of the interactions between antibiotics and the ribosome permits investigation of the specific effect of modifications leading to antimicrobial resistances. Streptogramins are unique among the ribosome-targeting antibiotics because they consist of two components, streptogramins A and B, which act synergistically. Each compound alone exhibits a weak bacteriostatic activity, whereas the combination can act bactericidal. The streptogramins A display a prolonged activity that even persists after removal of the drug. However, the mode of activity of the streptogramins has not yet been fully elucidated, despite a plethora of biochemical and structural data. RESULTS:The investigation of the crystal structure of the 50S ribosomal subunit from Deinococcus radiodurans in complex with the clinically relevant streptogramins quinupristin and dalfopristin reveals their unique inhibitory mechanism. Quinupristin, a streptogramin B compound, binds in the ribosomal exit tunnel in a similar manner and position as the macrolides, suggesting a similar inhibitory mechanism, namely blockage of the ribosomal tunnel. Dalfopristin, the corresponding streptogramin A compound, binds close to quinupristin directly within the peptidyl transferase centre affecting both A- and P-site occupation by tRNA molecules. CONCLUSIONS:The crystal structure indicates that the synergistic effect derives from direct interaction between both compounds and shared contacts with a single nucleotide, A2062. Upon binding of the streptogramins, the peptidyl transferase centre undergoes a significant conformational transition, which leads to a stable, non-productive orientation of the universally conserved U2585. Mutations of this rRNA base are known to yield dominant lethal phenotypes. It seems, therefore, plausible to conclude that the conformational change within the peptidyl transferase centre is mainly responsible for the bactericidal activity of the streptogramins and the post-antibiotic inhibition of protein synthesis.

Dataset Information

Differences in the Enterococcus faecalis lsa locus that influence susceptibility to quinupristin-dalfopristin and clindamycin.

Publications

Differences in the Enterococcus faecalis lsa locus that influence susceptibility to quinupristin-dalfopristin and clindamycin.

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