title: Antibacterial activity of PD 131628 and proposed disc diffusion susceptibility test criteria.
abstract: The antibacterial activity of PD 131628 was compared with that of ciprofloxacin against 401 clinical isolates. The two drugs had comparable MICs for most Gram-negative species. PD 131628 was two to eight times more active against Gram-positive species and against Xanthomonas maltophilia. Both drugs were bactericidal, Among Gram-positive isolates, resistant mutants were not detected in vitro. Among Gram-negative bacilli, spontaneously occurring mutants resistant to PD 131628 were readily demonstrated more frequently than for ciprofloxacin. Resistance to PD 131628 was more readily induced by serially transferring the Gram-negative species, and resistant organisms emerged more rapidly on prolonged incubation in time-kill studies. Correlating the PD 131628 5 micrograms disc diffusion zone diameters with PD 131628 MICs, the following breakpoints are tentatively proposed: susceptible, MIC < or = 1 mg/L or zone > or = 19 mm; intermediate, MIC 2.0 mg/L or zones 16-18 mm; and resistant, MIC > or = 4.0 mg/L or zones < or = 15 mm.
authors.affiliation: St. Vincent Hospital & Medical Center, Portland, OR 97225.
authors.forename: P C
authors.initials: PC
authors.lastname: Fuchs
authors.forename: A L
authors.initials: AL
authors.lastname: Barry
authors.forename: M A
authors.initials: MA
authors.lastname: Pfaller
mesh_terms: D000890:Anti-Infective Agents / Q000494:pharmacology*; D002939:Ciprofloxacin / Q000494:pharmacology; D004352:Drug Resistance, Microbial; D024841:Fluoroquinolones; D006090:Gram-Negative Bacteria / Q000187:drug effects / Q000235:genetics; D006094:Gram-Positive Bacteria / Q000187:drug effects / Q000235:genetics; D008826:Microbial Sensitivity Tests; D009154:Mutation; D009287:Naphthyridines / Q000494:pharmacology*
chemical_list: D000890:Anti-Infective Agents; D024841:Fluoroquinolones; D009287:Naphthyridines; C068217:PD 131628; D002939:Ciprofloxacin