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Journal of Clinical Microbiology, 08 1997, 2083-2086, Vol 35, No. 8
CM Flynn, CM Kelley, MS Barrett and RN Jones
Mycobacterium marinum, a well-recognized cutaneous pathogen, is usually
treated by chemotherapy without available standardized in vitro
susceptibility testing information. In this study, we have attempted to
apply the stable-gradient method (Etest; AB Biodisk, Solna, Sweden) to
susceptibility testing of M. marinum in order to assess the activities of
eight antimicrobial agents against 60 recent clinical strains of M. marinum
collected from 10 geographic sites within the United States. Two plated
media (5% sheep blood Mueller-Hinton agar and Middlebrook 7H11 agar) were
compared, and 7H11 agar was found to be superior in supporting the growth
of all strains. Four reference strains of M. marinum were tested on five
occasions with eight drugs (160 tests) in order to evaluate Etest
reproducibility. Results were observed to be within 1 log2 dilution of the
all-test median MIC for 97.5% of the Etests. Our MIC results for the 60
strains clearly demonstrate the best in vitro potency against M. marinum
isolates to be as follows (rank order): trimethoprim-sulfamethoxazole (MIC
at which 90% of the isolates are inhibited [MIC90], 0.25 and 4.25
microg/ml, respectively) = ethambutol > clarithromycin (MIC90, 1
microg/ml) > minocycline = doycycline (MIC90, 4 microg/ml) > amikacin
(MIC90, 8 microg/ml). Rifampin was only marginally active against the M.
marinum strains tested (MIC90, at the National Committee for Clinical
Laboratory Standards) breakpoint of 1 microg/ml), and ciprofloxacin was not
active (MIC90, 8 microg/ml). These data should enhance the empiric drug
selection for contemporary M. marinum infections and also provide evidence
that the Etest can be utilized to guide chemotherapy with alternative
agents.
Copyright © 1997 by the American Society for Microbiology. All rights reserved.
Application of the Etest to the antimicrobial susceptibility testing of Mycobacterium marinum clinical isolates
Department of Pathology, University of Iowa College of Medicine, Iowa City 52242, USA.
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