Frequency of β-lactamases that are markedly active against carbenicillin in the Pseudomonas aeruginosa strains isolated in a Medical School Hospital

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Abstract
During 1 yr 71 carbenicillin-resistant P. aeruginosa strains were isolated. The detection of the .beta.-lactamase activity in these strains was performed by the iodometric method. The .beta.-lactamases were found in 70% of the carbenicillin-resistant strains and were characterized by isoelectric focusing and by determination of substrate profiles. Of the .beta.-lactamases tested, 72% focused in the same way as the PSE-1 type from strain PU21(RPL11). The determination of the substrate profiles by the acidimetric method showed that these enzymes had a high activity towards carbenicillin and that they can vary in their hydrolysis of cephalosporins. Such PSE-1 type .beta.-lactamases were found in gentamicin-tobramycin-resistant strains; other types of enzymes (PSE-4 enzymes and enzymes with pI 7.7) were found in strains sensitive to these antibiotics.