Overproduction of a Metallo-β-Lactamase by a Strong Promoter Causes High-Level Imipenem Resistance in a Clinical Isolate of Pseudomonas aeruginosa.

Background: Metallo-β-lactamase is one of the feared resistance mechanisms inPseudomonas aeruginosa. Methods: β-Lactamase activity was determined using crude enzymes. Cloned plasmids were transformed in P. aeruginosa KG2505, PAO1 derivative without an AmpC β-lactamase and a MexAB-OprM efflux pump. Results:P. aeruginosa No. 20232 was highly resistant to imipenem (minimum inhibitory concentration >512 μg/ml). It possessed IMP-10 and the activity was 1.89 ± 0.42 μmol/min/mg of protein, which was 5–8 times higher than other tested isolates. The bla_IMP-10 promoter was strong (–35 region, TTGACA; –10 region, TAAACT); on the other hand, bla_IMP of other isolates had a hybrid promoter. Transformants with plasmid encoding bla_IMP-10 with a strong promoter had higher enzymatic activity and were less susceptible to imipenem than those encoding bla_IMP-10 with a hybrid promoter. Conclusions: The high metallo-β-lactamase activity caused by a strong promoter was a major determinant for high-level imipenem resistance of P. aeruginosa No. 20232. Copyright © 2008 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]