Major related sets of antibiotic-resistant pneumococci in the United States as determined by pulsed-field gel electrophoresis and pbp1a-pbp2b-pbp2x-dhf restriction profiles

To assess the genetic diversity of pneumococci causing serious disease with in the United States, restriction profiles of 3 penicillin-binding protein (PBP)-gene amplicons and the dhf amplicon were examined in 241 recent steri le-site isolates from 7 population centers, This analysis provided markers useful for epidemiologic studies and was generally predictive of resistance s to beta-lactam antibiotics and trimethoprim-sulfamethoxazole. Eight pulse d-field gel electrophoresis (PFGE) types, each representing 3-40 isolates, accounted for 134 of the 144 beta-lactam-resistant pneumococci (MICs greate r than or equal to 1 mu g/mL for penicillin, cefotaxime, or both). Five of these PFGE types contained subtypes highly related to subtypes of previousl y characterized pneumococcal clones. Within 4 of these PFGE types, the majo r composite PBP gene-dhf profile was highly related to the composite profil e from the previously characterized related clone. Eight capsular serotypes were found among the 144 beta-lactam-resistant pneumococci, Divergent caps ular types among isolates with identical PBP gene-dhf profiles and related PFGE types indicated several instances of capsular serotype switching.