OXA-11, AN EXTENDED-SPECTRUM VARIANT OF OXA-10 (PSE-2) BETA-LACTAMASEFROM PSEUDOMONAS-AERUGINOSA

Pseudomonas aeruginosa ABD, which was isolated in October 1991 from bl ood cultures of a burn patient in Turkey, was resistant to cephalospor ins, particularly ceftazidime (MIC, 512 mug/ml), penicillins, aztreona m, and meropenem, but not to imipenem. Cephalosporin and penicillin re sistance transferred to P. aeruginosa PU21 and was associated with a b eta-lactamase with a pl of 6.4 encoded by a 100-MDa plasmid designated pMLH52. Like extended-spectrum TEM and SHV beta-lactamases, this enzy me hydrolyzed penicillins and newer cephalosporins but did not hydroly ze cefoxitin or carbapenems. However, it differed from TEM and SHV der ivatives in being a potent oxacillinase, and its encoding gene did not hybridize with probes to TEM and SHV genes. To characterize the enzym e, libraries of total DNA were cloned into plasmid pUC19 and were tran sformed into Escherichia coli DH5alpha. Recombinant plasmids that gave ceftazidime resistance all contained a 3.65-kb BamHI fragment. Deleti ons from this fragment allowed the beta-lactamase gene to be located o n a 1.4-kb section of DNA, which contained an open reading frame of 79 8 bases. This encoded a protein that was deduced to differ from PSE-2 beta-lactamase only in having serine instead of asparagine at position 143 and aspartate instead of glycine at position 157. It is concluded that the resistance of isolate ABD depended on an extended-spectrum v ariant of the PSE-2 enzyme. The ability of this enzyme to cause ceftaz idime resistance depended primarily on a low K(m) for the compound; V( max) remained low. It is proposed that PSE-2 should be transferred to the OXA group as OXA-10 and that the new enzyme be designated OXA-11.