title: Novel ribosomal mutations in Staphylococcus aureus strains identified through selection with the oxazolidinones linezolid and torezolid (TR-700).
abstract: TR-700 (torezolid), the active moiety of the novel oxazolidinone phosphate prodrug TR-701, is highly potent against gram-positive pathogens, including strains resistant to linezolid (LZD). Here we investigated the potential of Staphylococcus aureus strains ATCC 29213 (methicillin-susceptible S. aureus [MSSA]) and ATCC 33591 (methicillin-resistant S. aureus [MRSA]) to develop resistance to TR-700. The spontaneous frequencies of mutation of MSSA 29213 and MRSA 33591 resulting in reduced susceptibility to TR-700 at 2 x the MIC were 1.1 x 10(-10) and 1.9 x 10(-10), respectively. These values are approximately 16-fold lower than the corresponding LZD spontaneous mutation frequencies of both strains. Following 30 serial passages in the presence of TR-700, the MIC for MSSA 29213 remained constant (0.5 microg/ml) while increasing eightfold (0.25 to 2.0 microg/ml) for MRSA 33591. Serial passage of MSSA 29213 and MRSA 33591 in LZD resulted in 64- and 32-fold increases in LZD resistance (2 to 128 microg/ml and 1 to 32 microg/ml, respectively). Domain V 23S rRNA gene mutations (Escherichia coli numbering) found in TR-700-selected mutants included T2500A and a novel coupled T2571C/G2576T mutation, while LZD-selected mutants included G2447T, T2500A, and G2576T. We also identified mutations correlating with decreased susceptibility to TR-700 and LZD in the rplC and rplD genes, encoding the 50S ribosomal proteins L3 and L4, respectively. L3 mutations included Gly152Asp, Gly155Arg, Gly155Arg/Met169Leu, and DeltaPhe127-His146. The only L4 mutation detected was Lys68Gln. TR-700 maintained a fourfold or greater potency advantage over LZD against all strains with ribosomal mutations. These data bring to light a variety of novel and less-characterized mutations associated with S. aureus resistance to oxazolidinones and demonstrate the low resistance potential of torezolid.
authors.affiliation: Trius Therapeutics, Inc., San Diego, CA 92121, USA.
authors.forename: Jeffrey B
authors.initials: JB
authors.lastname: Locke
authors.forename: Mark
authors.initials: M
authors.lastname: Hilgers
authors.forename: Karen Joy
authors.initials: KJ
authors.lastname: Shaw
mesh_terms: D000081:Acetamides / Q000737:chemistry / Q000494:pharmacology*; D000900:Anti-Bacterial Agents / Q000737:chemistry / Q000494:pharmacology*; D000069349:Linezolid; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects / Q000235:genetics; D008826:Microbial Sensitivity Tests; D015394:Molecular Structure; D009154:Mutation; D023303:Oxazolidinones / Q000737:chemistry / Q000494:pharmacology*; D012338:RNA, Ribosomal, 23S / Q000235:genetics*; D000090822:Ribosomal Protein L3; D012269:Ribosomal Proteins / Q000235:genetics*; D013211:Staphylococcus aureus / Q000187:drug effects / Q000235:genetics; D013777:Tetrazoles / Q000737:chemistry / Q000494:pharmacology*
chemical_list: D000081:Acetamides; D000900:Anti-Bacterial Agents; D023303:Oxazolidinones; D012338:RNA, Ribosomal, 23S; D000090822:Ribosomal Protein L3; D012269:Ribosomal Proteins; D013777:Tetrazoles; C056368:ribosomal protein L4; C546016:tedizolid; D000069349:Linezolid