High-level amikacin resistance in Pseudomonas aeruginosa associated with a 3′-phosphotransferase with high affinity for amikacin

This work describes the characterization of the phosphotransferase enzymatic activity responsible for amikacin resistance in two clinical Pseudomona aeruginosa strains, isolated from a hospital that used amikacin as first-line aminoglycoside. Amikacin-resistant P. aeruginosa PA40 and PA43 (MIC: 118 mg/l) were shown to have APH activity with a substrate profile similar to that 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 the high affinity of this enzyme for amikacin could explain the high-level resistance that we observed. (C) 2000 Elsevier Science B.V. and International Society of Chemotherapy, All rights reserved.