Penicillin-Binding Protein Families: Evidence For the Clonal Nature of Penicillin Resistance in Clinical Isolates of Pneumococci

In view of the worldwide emergence of penicillin-resistant pneumococci among clinical isolates it was of importance to examine a large number of strains to test the uniformity of the resistance mechanism. Among 160 clinical isolates of pneumococci (minimum inhibitory concentration [MIC], 0.005-16 ng/mL), susceptible strains showed a common pattern of five penicillin-binding proteins (PBPs) with high penicillin affinities (PBP 3 > 1A ≥ 2A > IB > 2B). PBPs 1A, 2A, and 2B (but not PBP 3) each showed distinct stepwise decreases in penicillin affinities parallel with increasing levels of antibiotic resistance. The number and molecular sizes of PBPs became variable in strains with MIC values >1.0 Hg/mL; among 39 strains with a MIC of ≥ 1.0 μg/mL, 11 distinct and stable PBP patterns could be identified. Using PBP profiles, serotypes, and antibiotic resistance patterns, as well as data on isolation dates and sites, we identified at least three groups of resistant strains that showed clear indication of clonal origin.