Variation in penicillin-binding protein patterns of penicillin-resistant clinical isolates of pneumococci

Abstract

A large number of pneumococcal isolates (over 80 strains) from a variety of geographic locales and representing a spectrum of resistance levels from a penicillin MIC of 0.003 microgram/ml up to an MIC of 16 micrograms/ml were analyzed for their penicillin-binding protein (PBP) patterns. With a few exceptions, the great majority of strains with penicillin MICs up to about 0.05 microgram/ml contained the same set of five PBPs with molecular sizes typical of those of susceptible pneumococci. In strains with penicillin MICs of about 0.1 microgram/ml and up, virtually all isolates showed two common features: (i) all isolates showed loss of PBP 1A (98 kilodaltons) with or without a parallel appearance of a "new" PBP that ranged in molecular size between 96 and 97 kilodaltons; and (ii) in strains with penicillin MICs of 0.5 microgram/ml or more, PBP 2B could not be detected on the fluorograms even with very high concentrations of radioactive penicillin. Beyond these two common features, resistant strains with similar penicillin MICs showed a surprising variety of PBP profiles (i.e., in the number and molecular sizes of PBPs), each characteristic of a given isolate. We suggest that in pneumococci remodeling of critical PBPs in more than one way may result in comparable levels of penicillin resistance.