Detection of penicillin and extended-spectrum cephalosporin resistance among Streptococcus pneumoniae clinical isolates by use of the E test.
Increasing penicillin resistance and the initial recognition of resistance to extended-spectrum cephalosporins among Streptococcus pneumoniae isolates have placed greater emphasis on accurate methods for susceptibility testing of clinical isolates. This study has evaluated the use of the E test (AB Biodisk NA, Piscataway, N.J.) for the detection of penicillin and cefotaxime resistance among 147 pneumococcal clinical isolates in three geographically separate laboratories. These included 42 penicillin-resistant (MIC, > or = 2 micrograms/ml) and 14 cefotaxime-resistant (defined here as an MIC of > or = 2 micrograms/ml) isolates. E test strips were applied to the surface of Mueller-Hinton sheep blood agar plates and incubated at 35 degrees C in 5% CO2 for 20 to 24 h. E test MICs were compared with MICs determined with lysed horse blood-supplemented Mueller-Hinton broth in a microdilution format as recommended by the National Committee for Clinical Laboratory Standards. Penicillin MICs agreed within one log2 dilution for 136 of 147 (92.5%) isolates, and cefotaxime MICs agreed within one log2 dilution for 142 of 147 (96.6%) isolates. No very major or major interpretive errors occurred with either penicillin or cefotaxime E test MIC results. There were 9.5 and 5.4% minor interpretive category errors with penicillin and cefotaxime E test MICs, respectively. These data indicate that the E test represents a convenient and reliable method for the detection of penicillin or cephalosporin resistance in pneumococci.
Jorgensen
J H
JH
Department of Pathology, University of Texas Health Science Center, San Antonio 78284-7750.
Ferraro
M J
MJ
McElmeel
M L
ML
Spargo
J
J
Swenson
J M
JM
Tenover
F C
FC
D000388:Air; D002245:Carbon Dioxide; D002439:Cefotaxime / Q000494:pharmacology*; D004352:Drug Resistance, Microbial; D005069:Evaluation Studies as Topic; D008826:Microbial Sensitivity Tests / Q000379:methods* / Q000592:standards; D010403:Penicillin Resistance; D011933:Reagent Kits, Diagnostic; D015203:Reproducibility of Results; D013296:Streptococcus pneumoniae / Q000187:drug effects*
D011933:Reagent Kits, Diagnostic; D002245:Carbon Dioxide; D002439:Cefotaxime