Patterns and mechanisms of emergence of resistance to amikacin.

Emergence of gram-negative bacilli resistant to amikacin occurred in five of 96 patients treated. Three of the five instances were associated with clinical failure and arose during therapy for an infection caused by a pathogen also susceptible to gentamicin. The other two episodes were associated with colonization. The enzyme aminoglycoside-6'-acetyltransferase, which inactivates amikacin, was found in Serratia marcescens. Decreased permeability to amikacin was shown in four isolates of Pseudomonas aeruginosa. The emergence and existence of these organisms is of great epidemiologic importance. Judicious use of amikacin and adherence to general principles of infection control are advised.