IDENTIFICATION OF MULTIPLE CLONES OF EXTENDED-SPECTRUM CEPHALOSPORIN-RESISTANT STREPTOCOCCUS-PNEUMONIAE ISOLATES IN THE UNITED-STATES

We characterized 12 isolates of Streptococcas pneumoniae with various levels of susceptibility to penicillin and extended-spectrum cephalosp orins by antimicrobial susceptibility patterns, serotypes, ribotypes, chromosomal DNA restriction patterns by pulsed-field gel electrophores is, multilocus enzyme electrophoresis patterns, penicillin-binding pro tein (PBP) profiles, and DNA restriction endonuclease cleavage profile s of pbp1a, pbp2x, and pbp2b. Seven cefotaxime-resistant (MIC, greater than or equal to 2 mu g/ml) serotype 23F isolates were related on the basis of ribotyping, pulsed-field gel electrophoresis, and multilocus enzyme electrophoresis, but they had two slightly different PBP patte rns: one unique to strains for which the MIC of penicillin is high (4. 0 mu g/ml) and one unique to strains for which the MIC of penicillin i s low (0.12 to 1.0 mu g/ml). The pbp1a and pbp2x fingerprints were ide ntical for the seven isolates; however, the pbp2b fingerprints were di fferent. An eighth serotype 23F isolate with high-level resistance to cephalosporins was not related to the other seven isolates by typing d ata but was a variant of the widespread, multiresistant serotype 23F S panish clone. The PBP profiles and fingerprints of pbp1a, pbp2x, and p bp2b were identical to those of the Spanish clone isolate. An addition al serotype 6B isolate with high-level resistance to cephalosporins ha d unique typing profiles and was unrelated to the serotype 23F cephalo sporin-resistant isolates but was related on the basis of genetic typi ng methods to a second serotype 6B isolate that was cephalosporin susc eptible. The serotype 6B isolates had different PBP profiles and finge rprints for pbp1a, but the fingerprints for pbp2x and pbp2b were the s ame.