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.

OBJECTIVES: The aim of this study was to assess the in vitro activities of nemonoxacin against Gram-positive cocci with various resistance phenotypes.

METHODS: 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).

RESULTS: Nemonoxacin had potent activity against MSSA (MIC(90) of < or =0.03 mg/L), ciprofloxacin-susceptible MRSA (MIC(90) of < or =0.03 mg/L) and CA-MRSA (MIC(90) of 0.06 mg/L). For all invasive S. pneumoniae isolates, the activity of nemonoxacin (MIC(90) of 0.06 mg/L) was similar to that of gemifloxacin and much better than that of levofloxacin (MIC(90) of 2 mg/L) and moxifloxacin (MIC(90) 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 (MIC(90) of 1 mg/L), vancomycin-intermediate MRSA (MIC(90) of 2 mg/L), DNS-MRSA (MIC(90) of 1 mg/L), vancomycin-susceptible enterococci (MIC(90) of 2 mg/L for Enterococcus faecalis and 4 mg/L for Enterococcus faecium) and VRE (MIC(90) of 4 mg/L for E. faecalis and 16 mg/L for E. faecium).

CONCLUSIONS: 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.