Characterization of NPS-1, a novel plasmid-mediated beta-lactamase, from two Pseudomonas aeruginosa isolates

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Abstract
A novel .beta.-lactamase, which had a pI of 6.5 and a molecular weight of 25,000, was observed in two Pseudomonas aeruginosa isolates. The enzyme, designated NPS-1, was encoded by a plasmid of molecular weight 41 .times. 106 which also encoded resistance to streptomycin and sulfonamide. This plasmid, designated pMLH50, was freely transmissible to other P. aeruginosa strains, but not to Escherichia coli K-12. The enzyme was purified partially and shown to have activity against both penicillins and cephalosporins. Vmax rates for oxacillin and carbenicillin were less than 50% of the Vmax for benzylpenicillin, and the Vmax for cephaloridine was only 3% of the Vmax for benzylpenicillin. Imipenem, aztreonam, and several antipseudomonal cephalosporins were stable to the enzyme. Hydrolysis of most substrates obeyed Michaelis-menten kinetics, but cefsulodin induced a reversible reduction in the activity of the enzyme. Transconjugants of the .beta.-lactamase-producing isolates in P. aeruginosa PU21 acquired .beta.-lactam resistances which mirrored the hydrolytic activity of the enzyme.