High-level amikacin resistance in Pseudomonas aeruginosa associated with a3 '-phosphotransferase with high affinity for amikacin

This work describes the characterization of the phosphotransferase enzymati c activity responsible for amikacin resistance in two clinical Pseudomona a eruginosa strains, isolated from a hospital that used amikacin as first-lin e aminoglycoside. Amikacin-resistant P. aeruginosa PA40 and PA43 (MIC: 118 mg/l) were shown to have APH activity with a substrate profile similar to t hat of APH(3')-VI. The enzyme from P. aeruginosa PA40 was purified to > 70% homogeneity. The K-m of amikacin for this enzyme was 1.4 mu M, the V-max/K -m ratio for amikacin was higher than for the other aminoglycosides tested and PCR and DNA sequencing ruled out the presence of aph(3')-Hps. Amikacin resistance in this strain was, therefore, associated with APH(3')-VI and th e high affinity of this enzyme for amikacin could explain the high-level re sistance that we observed. (C) 2000 Elsevier Science B.V. and International Society of Chemotherapy, All rights reserved.