Activity of gatifloxacin against strains resistant to ofloxacin and ciprofloxacin and its ability to select for less susceptible bacterial variants

Gatifloxacin is an 8-methoxy fluoroquinolone. On quinolones, this side chai n imparts increased activity against Gram-positive bacteria and enhanced ki lling. Gatifloxacin was tested against ofloxacin non-susceptible (ofloxacin MIC > 2 mg/l) strains of Streptococcus pneumoniae (gatifloxacin MIC90 1 mg /l) and methicillin-resistant Staphylococcus aureus (MRSA, gatifloxacin MIC 90, 4 mg/l), and to ciprofloxacin non-susceptible (ciprofloxacin MIC > 1 mg /l) strains of Escherichia coli (gatifloxacin MIC90 > 16 mg/l) and ciproflo xacin non-susceptible (ciprofloxacin MIC > 0.06 mg/l) Neisseria gonorrhoeae (gatifloxacin MIC50 0.12 mg/l and MIC90 0.5 mg/l). Though gatifloxacin sho wed some reduced susceptibility to these populations, the MIC50 and MIC50 v alues suggest that gatifloxacin may be useful against pneumococci and some gonococcal strains not susceptible to other fluoroquinolones. Gatifloxacin did not select for less susceptible variants of MRSA and pneumococci, in co ntrast to the 10- to 100-fold higher selection frequencies with ciprofloxac in and ofloxacin. The single-step E. coli mutants selected by gatifloxacin and the comparator quinolones had quinolone MICs within the susceptible ran ge. These data suggest that gatifloxacin use may hinder the development of quinolone-resistance, particularly in Gram-positive bacteria. (C) 2001 Else vier Science BN. and International Society of Chemotherapy. All rights rese rved.