In vitro activity of nemonoxacin (TG-873870), a novel non-fluorinated quinolone, against clinical isolates of Staphylococcus aureus, enterococci and Streptococcus pneumoniae with various resistance phenotypes in Taiwan

The aim of this study was to assess the in vitro activities of nemonoxacin against Gram-positive cocci with various resistance phenotypes. MICs of nemonoxacin were determined for 798 recently collected (2005-07) and non-duplicate isolates of Gram-positive cocci by the agar dilution method. These isolates included: methicillin-susceptible Staphylococcus aureus (MSSA; n = 100); methicillin-resistant S. aureus (MRSA), including ciprofloxacin-susceptible (n = 50), ciprofloxacin-resistant (n = 100), vancomycin-intermediate (n = 50) and daptomycin-non-susceptible (DNS-MRSA; n = 5) isolates, and community-acquired MRSA (CA-MRSA; n = 101); invasive Streptococcus pneumoniae isolates (n = 150); levofloxacin-non-susceptible (MICs of 4-64 mg/L) S. pneumoniae isolates (n = 30); and enterococci (n = 212), including vancomycin-resistant enterococci (VRE; n = 112). Nemonoxacin had potent activity against MSSA (MIC90 of < 0.03 mg/L), ciprofloxacin-susceptible MRSA (MIC90 of < 0.03 mg/L) and CA-MRSA (MIC90 of 0.06 mg/L). For all invasive S. pneumoniae isolates, the activity of nemonoxacin (MIC90 of 0.06 mg/L) was similar to that of gemifloxacin and much better than that of levofloxacin (MIC90 of 2 mg/L) and moxifloxacin (MIC90 of 0.25 mg/L). Nemonoxacin had a 32- to 64-fold higher activity than levofloxacin against levofloxacin-non-susceptible isolates. Nemonoxacin exerted limited activity against ciprofloxacin-resistant MRSA (MIC90 of 1 mg/L), vancomycin-intermediate MRSA (MIC90 of 2 mg/L), DNS-MRSA (MIC90 of 1 mg/L), vancomycin-susceptible enterococci (MIC90 of 2 mg/L for Enterococcus faecalis and 4 mg/L for Enterococcus faecium) and VRE (MIC90 of 4 mg/L for E. faecalis and 16 mg/L for E. faecium). Our findings point to a potentially useful role for nemonoxacin in the treatment of infections caused by MSSA, ciprofloxacin-susceptible MRSA and S. pneumoniae with various resistance phenotypes.