Penetration of beta-lactams through Pseudomonas aeruginosa porin channels.

Diminished permeation of beta-lactam antibiotics in a mutant (PCC23) of Pseudomonas aeruginosa, PAO503, was investigated. Resistance to beta-lactam antibiotics could not be correlated to a change in the beta-lactamase or target proteins in strain PCC23 but was correlated with decreased permeability. In liposome swelling assays, the permeability defect was associated with strain PCC23 porin. Amino acid analysis did not show significant difference of the porin of the mutant (PCC23) from that of the parent (PAO503). Changes in the behavior of isolated porin from PCC23 in migration in sodium dodecyl sulfate-polyacrylamide gels and in response to trypsin digestion as well as preferential labeling of PCC23 by a monoclonal antibody with a preference for the modified form of porin F (F) indicate that a structural alteration had occurred in this strain and correlated with the change in permeability.