Antimicrobial activity of a new fluoroquinolone, DU-6859a, against quinolone-resistant clinical isolates of Neisseria gonorrhoeae with genetic alterations in the GyrA subunit of DNA gyrase and the ParC subunit of topoisomerase IV.

The in vitro antimicrobial activity of DU-6859a, a new fluoroquinolone, was tested against 22 clinical isolates ofPseudomonas aeruginosa, including strains with fluoroquinolone resistance-associated alterations in the GyrA subunit of DNA gyrase and the ParC subunit of topoisomerase IV. The MICs of DU-6859a for 10 isolates with both altered GyrA and ParC and for 7 isolates with altered GyrA alone ranged from 1.56 to 25 μg/mL and from 0.78 to 6.25 μg/mL, respectively. The MIC of DU-6859a at which 90% of the strains were inhibited (MIC90) of these 17 isolates was 12.5 μg/mL. However, there was no significant difference between DU-6859a and the other quinolones tested against 5 strains which did not have any alterations of either GyrA or ParC. Based on the MIC90s, DU-6859a exhibited 8- to 32-fold greater activity than the currently available fluoroquinolones against strains having alterations in DNA gyrase and topoisomerase IV.