Antibiotic Susceptibility Pattern of Mycobacterium marinum

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Abstract
In vitro activities of 17 antibiotics against 53 clinical strains of Mycobacterium marinum , an atypical mycobacterium responsible for cutaneous infections, were determined using the reference agar dilution method. Rifampin and rifabutin were the most active drugs (MICs at which 90% of the isolates tested were inhibited [MIC 90 s], 0.5 and 0.6 μg/ml, respectively). MICs of minocycline (MIC 90 , 4 μg/ml), doxycycline (MIC 90 , 16 μg/ml), clarithromycin (MIC 90 , 4 μg/ml), sparfloxacin (MIC 90 , 2 μg/ml), moxifloxacin (MIC 90 , 1 μg/ml), imipenem (MIC 90 , 8 μg/ml), sulfamethoxazole (MIC 90 , 8 μg/ml) and amikacin (MIC 90 , 4 μg/ml) were close to the susceptibility breakpoints. MICs of isoniazid, ethambutol, trimethoprim, azithromycin, ciprofloxacin, ofloxacin, and levofloxacin were above the concentrations usually obtained in vivo. For each drug, the MIC 50 , geometric mean MIC, and modal MIC were very close, showing that all the strains had a similar susceptibility pattern. Percent agreement (within ±1 log 2 dilution) between MICs yielded by the Etest method and by the agar dilution method used as reference were 83, 59, 43, and 24% for minocycline, rifampin, clarithromycin, and sparfloxacin, respectively. Reproducibility with the Etest was low, in contrast to that with the agar dilution method. In conclusion, M. marinum is a naturally multidrug-resistant species for which the agar dilution method is more accurate than the Etest for antibiotic susceptibility testing.