COMPARISON OF ANTIMICROBIAL SUSCEPTIBILITY METHODS FOR DETECTION OF PENICILLIN-RESISTANT STREPTOCOCCUS-PNEUMONIAE

We sought to determine if commercially available susceptibility tests were accurate in detecting penicillin resistance and relative resistan ce in Streptococcus pneumoniae. We compared the reference MIC method w ith oxacillin disk screening and three commercial tests, E-test (AB Bi odisk), JustOne (Radiometer America), and MicroScan Pos MIC Panel Type 6 (Baxter Diagnostics), with 80 selected clinical isolates. Thirty-th ree additional isolates were tested by the reference method and the E- test to further validate the latter method. Oxacillin screening was ef fective in detecting all penicillin-resistant and relatively resistant strains of S. pneumoniae. The MicroScan method was not effective in d etecting penicillin resistance or relative resistance. The JustOne sys tem classified only 6 (35%) of 17 resistant strains correctly, with 11 resistant strains classified as relatively resistant. The E-test corr ectly classified 30 (83%) of 36 resistant isolates, with 6 resistant i solates interpreted as relatively resistant, For determining penicilli n MICs for S. pneumoniae, the E-test was the most accurate of the comm ercial systems that we studied.