Emergence of resistance to amikacin during treatment of burn wounds: the role of antimicrobial susceptibility testing.

Amikacin has been used to treat Providencia stuarii infections on the Burn Service at Los Angeles County/University of Southern California Medical Center since March, 1973. The median minimal inhibitory concentration (MIC) of strains collected on this service prior to the introduction of amikacin was 3.13 mug. per milliliter, whereas the median MIC of strains collected during the last 4 months of the study was 12.5 mug per milliliter. High bactericidal concentrations (MBC) noted at the time of initial studies predicted the emergence of resistant clones, with MBV values rising to as great as 100 mu per milliliter. Further, isolates from burn patients during the initial 5 days of treatment with amikacin had a median MIC of 6925 mug per milliliter, in contrast to values of 25 mug per milliliter in strains isolated after 5 days of treatment. The epidemiologic significance of intensive treatment of gram-negative infections occurring in a close population with selected antibiotics is discussed. The performance of susceptibility tests which included determination of bactericidal concentrations was a major tool in the recognition of the potential for selection of resistant micro-organisms.