CRITICAL-APPRAISAL OF E-TEST FOR THE DETECTION OF FLUOROQUINOLONE RESISTANCE

The ability of E test to accurately detect fluoroquinolone resistance was compared with an agar dilution reference method. Nearly 300 isolat es belonging to 26 different species (62.5% with documented ciprofloxa cin resistance) were tested with ciprofloxacin, fleroxacin, levofloxac in, norfloxacin, ofloxacin, and sparfloxacin. In contrast to earlier r eports, E test MIC values for: pneumococci and all rapid growing aerob es were routinely higher (approximately 0.5 log(2) dilution step) than agar dilution results. The E test stable-gradient method also efficie ntly indentified fluoroquinolone-resistant subpopulations which were n ot detected by the reference procedure with the standard inoculum. Cat egorical agreement for 1710 test comparisons was approximately 90% wit h no very major, false-susceptible errors. We found the E test to be a valid, reproducible method for fluoroquinolone susceptibility testing that provided quantitative results and produced a conservative (1.6% false-resistant results) assessment of susceptibility of bacteria incl uding isolates of Streptococcus pneumoniae and Pseudomonas aeruginosa to compounds in this antimicrobial class.