Gatifloxacin (AM-1155, CG 5501) susceptibility testing interpretive criteria and quality control guidelines for dilution and disk (5-mu g) diffusion methods

Gatifloxacin (formerly AM-1155 and CG5501), a new 8-methoxy fluoroquinolone , has an expanded spectrum of activity against Gram-positive cocci and some anaerobic bacteria. This compound was tested against 600 recent clinical s trains of vapidly growing aerobic species to establish susceptibility resti ng interpretive criteria for the reference broth microdilu tion and standar dized disk (5-mu g) diffusion methods of the National Committee for Clinica l Laboratory Standards (NCCLS). These strains included 285 Enterobacteriace ae (17 species), 165 staphylococci, 49 enterococci, and 101 nonfermentative Gram-negative bacilli. Based on achievable serum levels with projected gat ifloxacin dosing regimens, MIC breakpoints of less than or equal to 2 mu g/ mL (greater than or equal to 18 mm) for susceptibility and greater than or equal to 8 mu g/mL (less than or equal to 14 mm) for resistance were select ed. The absolute agreement between tests was 94.3% with no very major false -resistant errors. The quality control ranges (MIC and zone diameters) for the NCCLS recommended strains were determined in a nine-laboratory NCCLS pr otocol as follows: Escherichia coli ATCC 25922 = 0.008-0.03 mu g/mL and 31- 37 mm; Enterococcus faecalis ATCC 29212 = 0.12-1 mu g/mL; Pseudomonas aerug inosa ATCC 27853 = 0.5-2 mu g/ml and 21-27 mm; Staphylococcus aureus ATCC 2 5923 = 27-33 mm and S. aureus ATCC 29213 = 0.03-0.22 mu g/mL. Gatifloxacin appears to be a promising new fluoroquinolone with acceptable susceptibilit y testing methods for routine clinical laboratory use. (C) 1999 Elsevier Sc ience Inc.