In Vitro Activities of Tedizolid and Linezolid against Gram-Positive Cocci Associated with Acute Bacterial Skin and Skin Structure Infections and Pneumonia

Tedizolid is a novel, expanded-spectrum oxazolidinone with potent activity against a wide range of Gram-positive pathogens. A total of 425 isolates of Gram-positive bacteria were obtained consecutively from patients with acute bacterial skin and skin structure infections (ABSSSIs) or pneumonia. These isolates included methicillin-susceptible Staphylococcus aureus (MSSA) (n = 100), methicillin-resistant Staphylococcus aureus (MRSA) (n = 100), Streptococcus pyogenes (n = 50), Streptococcus agalactiae (n = 50), Streptococcus anginosus group (n = 75), Enterococcus faecalis (n = 50), and vancomycin-resistant enterococci (VRE) (Enterococcus faecium) (n = 50). The MICs of tedizolid and linezolid were determined by the agar dilution method. Tedizolid exhibited better in vitro activities than linezolid against MSSA (MIC90s, 0.5 versus 2 μg/ml), MRSA (MIC90s, 0.5 versus 2 μg/ml), S. pyogenes (MIC90s, 0.5 versus 2 μg/ml), S. agalactiae (MIC90s, 0.5 versus 2 μg/ml), Streptococcus anginosus group (MIC90s, 0.5 versus 2 μg/ml), E. faecalis (MIC90s, 0.5 versus 2 μg/ml), and VRE (MIC90s, 0.5 versus 2 μg/ml). The tedizolid MICs against E. faecalis (n = 3) and VRE (n = 2) intermediate to linezolid (MICs, 4 μg/ml) were 1 μg/ml and 0.5 μg/ml, respectively. The tedizolid MIC90s against S. anginosus, S. constellatus, and S. intermedius were 0.5, 1, and 0.5 μg/ml, respectively, and the rates of susceptibility based on the U.S. FDA MIC interpretive breakpoints to the isolates were 16%, 28%, and 72%, respectively. Tedizolid exhibited 2- to 4-fold better in vitro activities than linezolid against a variety of Gram-positive cocci associated with ABSSSIs and pneumonia. The lower susceptibilities of tedizolid against isolates of S. anginosus and S. constellatus than against those of S. intermedius in Taiwan were noted.