Incidence of strains producing plasmid determined β-lactamases among carbenicillin resistant pseudomonas aeruginosa

A total of 1056 strains of Pseudomonas aeruginosa isolated from human clinical specimens from patients was collected from eight laboratories in order to study the frequency of plasmid-determined β-lactamase producers and the different enzymes represented. The strains from each laboratory comprised consecutive, non-repeated, clinical isolates.In the 166 strains selected because they were carbenicillin resistant, the isoelectric points of the β-lactamases were studied by means of analytical isoelectric focusing and the different types of plasmid-determined β-lactamases identified. Seventy-five of the strains (45.18%) were plasmid-mediated β-lactamase producers; the frequency varied among laboratories from 0% to 100%. Overall the most frequently identified β-lactamase type was PSE-1 (49.34%) followed by TEM-1 (37.34%). The remaining carbenicillin-resistant strains did not produce plasmid-determined B-lactamases. © 1986, by The British Society for Antimicrobial Chemotherapy.