Major Related Sets of Antibiotic‐Resistant Pneumococci in the United States as Determined by Pulsed‐Field Gel Electrophoresis andpbp1a‐pbp2b‐pbp2x‐dhfRestriction Profiles

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Abstract
To assess the genetic diversity of pneumococci causing serious disease within the United States, restriction profiles of 3 penicillin-binding protein (PBP)-gene amplicons and the dhf amplicon were examined in 241 recent sterile-site isolates from 7 population centers. This analysis provided markers useful for epidemiologic studies and was generally predictive of resistances to β-lactam antibiotics and trimethoprim-sulfamethoxazole. Eight pulsed-field gel electrophoresis (PFGE) types, each representing 3–40 isolates, accounted for 134 of the 144 β-lactam-resistant pneumococci (MICs ⩾1 μ g/mL for penicillin, cefotaxime, or both). Five of these PFGE types contained subtypes highly related to subtypes of previously characterized pneumococcal clones. Within 4 of these PFGE types, the major composite PBP gene-dhf profile was highly related to the composite profile from the previously characterized related clone. Eight capsular serotypes were found among the 144 β-lactam-resistant pneumococci. Divergent capsular types among isolates with identical PBP gene-dhf profiles and related PFGE types indicated several instances of capsular serotype switching.

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