Isolation and partial purification of a carbapenem-hydrolysing metallo-beta-lactamase from Pseudomonas cepacia

A metallo-beta-lactamase has been isolated from a clinical strain of Pseudomonas cepacia and partially purified using Cibacron blue F3GA coupled agarose. The resulting preparation showed a single band of beta-lactamase activity (pI 8.45) after analytical isoelectric focusing. The enzyme was particularly effective in the hydrolysis of imipenem. Meropenem, biapenem, cephaloridine, ceftazidime, benzylpenicillin, ampicillin and carbenicillin were also hydrolysed, although at a lower rate. An unusual inhibition profile was noted. Inhibition by the metal ion chelators ethylenediaminetetraacetic acid and o-phenanthroline was reversed by addition of zinc, indicating a metallo-enzyme, whilst > 90% inhibition was attainable with 0.1 mM concentrations of tazobactam and clavulanic acid. A study of 8 other clinical isolates showed the enzyme to be present and inducible by imipenem in each case. This enzyme was assigned PCM-I (Pseudomonas cepacia metalloenzyme I).