Penicillin-binding proteins of Pseudomonas aeruginosa. Comparison of two strains differing in their resistance to β-lactam antibiotics

Abstract
The contributions of inducible β-lactamase, penicillin-binding protein (PBP) affinity and envelope permeability to the resistance phenotype of two strains of Pseudomonas aeruginosa. which differ markedly in their sensitivities to β-lactam antibiotics, have been investigated. The isolation of β-lactamase non-inducible mutants of the two Ps. aeruginosa strains indicated that the enzyme provided protection against antibiotics sensitive to it. Furthermore, one of the strains, but not the other, still possessed significant resistance levels in the absence of its inducible β-lactamase. Comparison of the affinities of selected β-lactam antibiotics for the PBPs of the two non-inducible mutants with their antibacterial activities indicated that the two Ps. aeruginosa strains owed their differences in non-β-lactamase-mediated resistance primarily to differences in their ability to exclude the compounds by their respective permeability barriers rather than to variations in PBP target affinity or to the stability of PBP-inhibitor complexes.

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