In vitro evaluation of AZD2563, a new oxazolidinone, tested against unusual gram-positive species.

The recently introduced oxazolidinone, linezolid, has a spectrum and potency directed against Gram-positive organisms, including antimicrobial-resistant isolates. The newest agent in this class, AZD2563 was tested against uncommonly isolated Gram-positive species to establish the breadth of its spectrum. By reference broth microdilution methods, 120 strains were tested (48 Corynebacterium spp., 10 species; 27 Listeria spp., 2 species; 11 Micrococcus spp., 2 species; 23 Bacillus spp., 3 species; 6 Stomatococcus mucilaginosus and one strain each of 5 other species) against AZD2563 and compared to eight other agents. The AZD2563/linezolid MIC(50;) % inhibited at < or =4 microg/mL were: for corynebacteria (0.25/0.25 microg/mL; 100/100%), Listeria spp. (2/2 microg/mL; 100/100%), Micrococcus spp. (1/1 microg/mL; 100/100%), Bacillus spp. (0.5/1 microg/mL; 100/100%), and S mucilaginosus (0.5/1 microg/mL; 100/100%). Using the MIC(90) values, AZD2563 was slightly more potent than linezolid (two-fold). Only four genus- species groups had AZD2563 MICs of strains at 2 microg/mL (Aerococcus, Leuconostoc, Listeria, Rhodococcus), all other isolates were inhibited by < or = 1 microg/mL. The AZD2563 potency and spectrum versus these rarer species was at least equal to linezolid, including some strains resistant to penicillins, macrolides-lincosamides, and fluoroquinolones.