TRANSFERABLE PRODUCTION OF PER-1 BETA-LACTAMASE IN PSEUDOMONAS-AERUGINOSA

PER-I, an extended-spectrum class A beta-lactamase, has been described only from Pseudomonas aeruginosa RNL-1, which was obtained in France in 1991. During studies on ceftazidime-resistant P. aeruginosa collect ed from December 1991 to July 1993 in Ankara, Turkey, we found 14 furt her isolates with PER-1 enzyme, as recognised by isoelectric point (pI 5.4), hydrolytic activity, gene hybridization and DNA sequence. Five of these isolates also had OXA-10 (PSE-2)-related enzymes and one hype r-produced ampC beta-lactamase, whereas eight had PER-1 enzyme alone. The last group, from four wards, appeared to be identical, giving the same DNA restriction patterns and carrying the PER-1 gene on an 8.5 kb HincII fragment. Two more producers were related but the other four w ere unique. In several representatives of the group of eight replicate s, the PER-1 gene was shown to be encoded on a plasmid, larger than 15 4 kb in size, which transferred to P. aeruginosa PU21. A further isola te had the gene on an even larger conjugative plasmid. By contrast, th e PER-1 gene reportedly was chromosomally-inserted in strain RNL-1. Th e PER-1 producers and their transconjugants were highly resistant to c eftazidime and aztreonam (MIG greater than or equal to 128 mgl/L) but not to carbapenems or latamoxet. Piperacillin insusceptibility was mar ginal (MIG 8 mg/L). Clavulanate 4 mg/L, but not tazobactam 4 mg/L, rev ersed resistance to ceftazidime and carbenicillin. Purification of the enzyme to homogeneity wits achieved by three ion exchanges and one ge l filtration. We found much lower V-max rates for aminothiazolyl cepha losporins than reported previously for PER-1 enzyme. This reflected th e present assays being in 0.1 M phosphate butter pH 7.0, whereas the p revious were pH-stat-regulated; concentrated phosphate reduced enzyme activity against ceftazidime, but not against cephaloridine.