Publications (16) View all
-
Article: Genetic environment and stability of cfr in methicillin-resistant Staphylococcus aureus CM05.
[show abstract] [hide abstract]
ABSTRACT: The Cfr methyltransferase confers resistance to many 50S ribosomal subunit-targeted antibiotics, including linezolid (LZD), via methylation of the 23S rRNA base A2503 in the peptidyl transferase center. Methicillin-resistant Staphylococcus aureus strain CM05 is the first clinical isolate documented to carry cfr. While cfr is typically plasmid borne, in CM05 it is located on the chromosome and is coexpressed with ermB as part of the mlr operon. Here we evaluated the chromosomal locus, association with mobile genetic elements, and stability of the cfr insertion region in CM05. The cfr-containing mlr operon is located within a 15.5-kb plasmid-like insertion into 23S rRNA allele 4. The region surrounding the cfr gene has a high degree of sequence similarity to the broad-host-range toxin/antitoxin multidrug resistance plasmid pSM19035, including a second ermB gene downstream of the mlr locus and istAS-istBS. Analysis of several individual CM05 colonies revealed two distinct populations for which LZD MICs were either 8 or 2 μg/ml. In the LZD(s) colonies (designated CM05Δ), a recombination event involving the two ermB genes had occurred, resulting in the deletion of cfr and the 3' flanking region (cfr-istAS-istBS-ermB). The fitness advantage of CM05Δ over CM05 (though not likely due to the cfr deletion itself) results in the predominance of CM05Δ in the absence of selective pressure. Minicircles resulting from the ermB recombination event and the novel association of cfr with the pSM19035 plasmid system support the potential for the continued dissemination of cfr.Antimicrobial Agents and Chemotherapy 01/2012; 56(1):332-40. · 4.84 Impact Factor -
Article: The oxazolidinones: past, present, and future.
[show abstract] [hide abstract]
ABSTRACT: The success of linezolid stimulated significant efforts to discover new agents in the oxazolidinone class. Over a dozen oxazolidinones have reached the clinic, but many were discontinued due to lack of differentiated potency, inadequate pharmacokinetics, and safety risks that included myelosuppression. Four oxazolidinones are currently undergoing clinical evaluation. The Trius Therapeutics compound tedizolid phosphate (formerly known as torezolid phosphate, TR-701, DA-7218), the most advanced, is in phase 3 clinical trials for acute bacterial skin and skin structure infections. Rib-X completed two phase 2 studies for radezolid (Rx-01_667, RX-1741) in uncomplicated skin and skin structure infections and community-acquired pneumonia. Pfizer and AstraZeneca have each identified antitubercular compounds that have completed phase 1 studies: sutezolid (PNU-100480, PF-02341272) and AZD5847 (AZD2563), respectively. The oxazolidinones share a relatively low frequency of resistance largely due to the requirement of mutations in 23S ribosomal RNA genes. However, maintaining potency against strains carrying the mobile cfr gene poses a challenge for the oxazolidinone class, as well as other 50S ribosome inhibitors that target the peptidyl transferase center.Annals of the New York Academy of Sciences 12/2011; 1241:48-70. · 3.15 Impact Factor -
Article: Elevated linezolid resistance in clinical cfr-positive Staphylococcus aureus isolates is associated with co-occurring mutations in ribosomal protein L3.
[show abstract] [hide abstract]
ABSTRACT: Resistance to linezolid (LZD) occurs through mutations in 23S rRNA and ribosomal proteins L3 and L4 or through methylation of 23S rRNA by Cfr. Here we report novel L3 mutations, ΔSer145/His146Tyr and ΔMet169-Gly174, co-occurring with cfr in LZD-resistant Staphylococcus aureus isolates recovered from a hospital outbreak in Madrid, Spain. LZD MIC values (16, 32, or 64 μg/ml) correlated with the presence and severity of the L3 mutation. All isolates had TR-700 (torezolid) MIC values of ≤ 2 μg/ml.Antimicrobial Agents and Chemotherapy 12/2010; 54(12):5352-5. · 4.84 Impact Factor -
Article: Structure-activity relationships of diverse oxazolidinones for linezolid-resistant Staphylococcus aureus strains possessing the cfr methyltransferase gene or ribosomal mutations.
[show abstract] [hide abstract]
ABSTRACT: Staphylococcal resistance to linezolid (LZD) is mediated through ribosomal mutations (23S rRNA or ribosomal proteins L3 and L4) or through methylation of 23S rRNA by the horizontally transferred Cfr methyltransferase. To investigate the structural basis for oxazolidinone activity against LZD-resistant (LZD(r)) strains, we compared structurally diverse, clinically relevant oxazolidinones, including LZD, radezolid (RX-1741), TR-700 (torezolid), and a set of TR-700 analogs (including novel CD-rings and various A-ring C-5 substituents), against a panel of laboratory-derived and clinical LZD(r) Staphylococcus aureus strains possessing a variety of resistance mechanisms. Potency against all strains was correlated with optimization of C- and D-rings, which interact with more highly conserved regions of the peptidyl transferase center binding site. Activity against cfr strains was retained with either hydroxymethyl or 1,2,3-triazole C-5 groups but was reduced by 2- to 8-fold in compounds with acetamide substituents. LZD, which possesses a C-5 acetamide group and lacks a D-ring substituent, demonstrated the lowest potency against all strains tested, particularly against cfr strains. These data reveal key features contributing to oxazolidinone activity and highlight structural tradeoffs between potency against susceptible strains and potency against strains with various resistance mechanisms.Antimicrobial Agents and Chemotherapy 12/2010; 54(12):5337-43. · 4.84 Impact Factor -
Article: Mutations in ribosomal protein L3 are associated with oxazolidinone resistance in staphylococci of clinical origin.
[show abstract] [hide abstract]
ABSTRACT: Following recent reports of ribosomal protein L3 mutations in laboratory-derived linezolid-resistant (LZD(r)) Staphylococcus aureus, we investigated whether similar mutations were present in LZD(r) staphylococci of clinical origin. Sequence analysis of a variety of LZD(r) isolates revealed two L3 mutations, DeltaSer145 (S. aureus NRS127) and Ala157Arg (Staphylococcus epidermidis 1653059), both occurring proximal to the oxazolidinone binding site in the peptidyl transferase center. The oxazolidinone torezolid maintained a >or=8-fold potency advantage over linezolid for both strains.Antimicrobial Agents and Chemotherapy 10/2009; 53(12):5275-8. · 4.84 Impact Factor
