Evaluation of in vitro susceptibility of Gram-positive pathogens from a tertiary care hospital in Singapore to a novel oxazolidinone, tedizolid, by a gradient diffusion method and broth microdilution.

We compared the in vitro antimicrobial activities of tedizolid and linezolid on the Sensititre broth microdilution system for Gram-positive cocci isolates (n=146) from skin and skin structure infections and bloodstream infections, bronchoalveolar lavage and sputum. These pathogens included 40 methicillin-resistant Staphylococcus aureus, 38 coagulase-negative staphylococci, 20 Enterococcus faecalis and 48 beta-haemolytic Streptococcus spp. Susceptibility was simultaneously determined for 48 vanA vancomycin-resistant enterococci isolates 2013-2016 from rectal swabs (23 E. faecalis and 25 E. faecium, of which 4 were linezolid-non-susceptible). MIC90s for tedizolid were fourfold to eightfold lower than linezolid on the Sensititre and ranged from 0.12 to 0.5 µg/mL for the different pathogen groups. All isolates were susceptible to tedizolid except two vanA E. faecium strains (MICs of 1 and 2 µg/mL, respectively). Categorical and essential agreement for tedizolid were 99.48% and 92%, respectively, between Liofilchem gradient diffusion and Sensititre methods. Overall, the drug exhibited excellent activity against the surveyed Gram-positive pathogens.