Linezolid-resistant methicillin-resistant Staphylococcus aureus isolated after long-term, repeated use of linezolid

Linezolid (LZD)-resistant. However, seven different variants were identified by spa typing. According to the Escherichia coli numbering system, seven LRSA isolates contained a G2576T mutation (G2603T, S. aureus numbering) in one to four of the five copies of domain V of the 23S rRNA genes. One strain also contained a mutation (C2461T, E. coli numbering) not previously reported. Two strains, including one without domain V mutations, possessed single amino acid substitutions (Gly152Asp or Gly139Arg) in the ribosomal protein L3 of the peptidyltransferase center, substitutions not previously reported in clinical isolates. Emergence of LRSA is a serious concern for CF patients who undergo prolonged courses of LZD therapy.

Section: Vol 55 2011 Linezolid-resistant S Aureus In Cf Patients 1685supporting

confidence: 92%

mentioning

confidence: 99%

Emergence of Linezolid-Resistant Staphylococcus aureus after Prolonged Treatment of Cystic Fibrosis Patients in Cleveland, Ohio

Endimiani

Blackford²,

Dasenbrook

et al. 2011

“…Analysis of 23S rRNA encoding DNA sequences showed that linezolid-resistant S. aureus had a G-to-T mutation at position 2576 (Escherichia coli numbering). The same point mutations also were observed in S. aureus isolated in other clinical studies (7)(8)(9)(10)(11)(12)(13)(14). Later, amino acid substitutions in ribosomal protein L3 (50S large-subunit ribosomal protein) were associated with oxazolidinone resistance (linezolid MIC, 8 g/ml) in a clinical S. aureus strain (15).…”

supporting

confidence: 64%

In Vitro Resistance Studies with Bacteria That Exhibit Low Mutation Frequencies: Prediction of “Antimutant” Linezolid Concentrations Using a Mixed Inoculum Containing both Susceptible and Resistant Staphylococcus aureus

Firsov

Golikova

Strukova

et al. 2015

Bacterial resistance studies using in vitro dynamic models are highly dependent on the starting inoculum that might or might not contain spontaneously resistant mutants (RMs). To delineate concentration-resistance relationships with linezolid-exposed Staphylococcus aureus, a mixed inoculum containing both susceptible cells and RMs was used. An RM selected after the 9th passage of the parent strain (MIC, 2 g/ml) on antibiotic-containing media (RM9; MIC, 8 g/ml) was chosen for the pharmacodynamic studies, because the mutant prevention concentration (MPC) of linezolid against the parent strain in the presence of RM9 at 10 2 (but not at 10 4 ) CFU/ml did not differ from the MPC value determined in the absence of the RMs. Five-day treatments with twice-daily linezolid doses were simulated at concentrations either between the MIC and MPC or above the MPC. A specific mechanism of oxazolidinone action blocks functional initiation complexes in bacterial translation systems. Given the lack of analogues among available antimicrobials, a low probability of preexisting, naturally occurring resistance mechanisms has been hypothesized (1, 2). For example, resistance of Staphylococcus aureus rarely occurred through spontaneous mutations at frequencies of only 10 Ϫ9 to 10 Ϫ11 (3-5). However, the first report on the detection of a clinical isolate of S. aureus with a linezolid MIC of Ͼ32 g/ml was published as early as 2001 (6). Analysis of 23S rRNA encoding DNA sequences showed that linezolid-resistant S. aureus had a G-to-T mutation at position 2576 (Escherichia coli numbering). The same point mutations also were observed in S. aureus isolated in other clinical studies (7-14). Later, amino acid substitutions in ribosomal protein L3 (50S large-subunit ribosomal protein) were associated with oxazolidinone resistance (linezolid MIC, 8 g/ml) in a clinical S. aureus strain (15). Thus, clinical data indicate that resistance to linezolid mediated by mutations in ribosomal genes may emerge more readily than was initially predicted by routine in vitro studies performed early in the development of oxazolidinones, because they were not specifically designed to simulate antibiotic exposures that would allow the enrichment of resistant mutants.The resistance studies with linezolid cited above were not supported by concomitant pharmacokinetic studies to relate antibiotic concentrations to the selection of resistant mutants. To be sure, some in vitro model studies of the enrichment of resistant S. aureus simulated linezolid pharmacokinetics (16, 17).However, these attempts were unsuccessful because resistant mutants were not enriched, at least in simulations of oscillating antibiotic concentrations that mimic the usual linezolid dosing in humans. Linezolid-resistant staphylococci also were not enriched in other in vitro studies that were not designed to establish concentration-resistance relationships (18)(19)(20), probably because of the lack of spontaneous mutants in the starting inocula.To more clearly delineate concentration-resistance rel...

“…This mutation has been reported in both staphylococci and enterococci (6,15,34,40,59,61,70,71,87,97,101), and a clear correlation between the number of mutated rRNA operons and the linezolid MIC has been found (2,35,59). Most reports of the G2576U mutation in clinical isolates are associated with some form of increased or prolonged linezolid treatment or with high linezolid usage at the local hospital (29,84), underscoring the importance of judicious use of linezolid in clinical settings.…”

Section: Resistance Caused By 23s Rrna Mutationsmentioning

confidence: 96%

Resistance to Linezolid Caused by Modifications at Its Binding Site on the Ribosome

Long

Vester

2012

306

204

Linezolid is an oxazolidinone antibiotic in clinical use for the treatment of serious infections of resistant Gram-positive bacteria. It inhibits protein synthesis by binding to the peptidyl transferase center on the ribosome. Almost all known resistance mechanisms involve small alterations to the linezolid binding site, so this review will therefore focus on the various changes that can adversely affect drug binding and confer resistance. High-resolution structures of linezolid bound to the 50S ribosomal subunit show that it binds in a deep cleft that is surrounded by 23S rRNA nucleotides. Mutation of 23S rRNA has for some time been established as a linezolid resistance mechanism. Although ribosomal proteins L3 and L4 are located further away from the bound drug, mutations in specific regions of these proteins are increasingly being associated with linezolid resistance. However, very little evidence has been presented to confirm this. Furthermore, recent findings on the Cfr methyltransferase underscore the modification of 23S rRNA as a highly effective and transferable form of linezolid resistance. On a positive note, detailed knowledge of the linezolid binding site has facilitated the design of a new generation of oxazolidinones that show improved properties against the known resistance mechanisms. LINEZOLID