title: Comparison of agar dilution, microdilution, E-test, and disk diffusion methods for testing activity of cefditoren against Streptococcus pneumoniae.
abstract: This study evaluated the susceptibility of pneumococci to cefditoren by agar dilution and microdilution methods (both in air) and by E-test (AB Biodisk, Solna, Sweden) and disk diffusion methods (both in CO(2)). By the three MIC tests, the MICs at which 50 and 90% of isolates were inhibited (MIC(50)s and MIC(90)s) were, respectively, as follows (in micrograms per milliliter): for the 65 penicillin-susceptible strains tested, 0.016 and 0.03 (by agar dilution), 0.016 and 0.03 (by microdilution), and 0.016 and 0.03 (by E test); for the 68 penicillin-intermediate strains tested, 0.125 and 0.5 (by agar dilution), 0.125 and 0.5 (by microdilution), and 0. 25 and 0.5 (by E test); and for the 67 penicillin-resistant strains tested, 1.0 and 1.0 (by agar dilution), 0.5 and 1.0 (by microdilution), and 1.0 and 1.0 (by E test). With tentative cefditoren breakpoints (in micrograms per milliliter) of </=2.0 (susceptible), 4.0 (intermediate), and >/=8.0 (resistant), all strains were susceptible to cefditoren by agar, microdilution, and E-test results; with breakpoints of </=1.0, 2.0, and >/=4.0 microg/ml, 97% of strains were cefditoren susceptible by agar dilution results, 98% were susceptible by microdilution results, and 99% were susceptible by E-test results. When microdilution and E-test results were compared to those from the reference agar dilution method, 191 (95.5%) and 183 (91.5%) of strains gave essential agreement (+/-1 log(2) dilution); 8 (2.7%) minor discrepancies were found for both methods with a breakpoint of </=1. 0 microg/ml, and no discrepancies were found with a breakpoint of </=2.0 microg/ml. Disk test results (breakpoint, </=1.0 microg/ml) produced 2 major and 30 minor errors, with corresponding zone diameters (in millimeters) of >/=20 (susceptible), 17 to 19 (intermediate), and </=16 (resistant); a </=2.0-microg/ml breakpoint yielded zone diameters of >/=16 mm (susceptible). All three methods for testing the MIC of cefditoren showed excellent correlation.
authors.affiliation: Department of Pathology (Clinical Microbiology), Hershey Medical Center, Hershey, Pennsylvania 17033, USA.
authors.forename: L M
authors.initials: LM
authors.lastname: Kelly
authors.forename: M R
authors.initials: MR
authors.lastname: Jacobs
authors.forename: P C
authors.initials: PC
authors.lastname: Appelbaum
mesh_terms: D002511:Cephalosporins / Q000494:pharmacology*; D004058:Diffusion; D008826:Microbial Sensitivity Tests / Q000379:methods*; D013296:Streptococcus pneumoniae / Q000187:drug effects*
chemical_list: D002511:Cephalosporins; C073460:cefditoren