Antimicrobial susceptibility of Mycobacterium marinum determined by E-testand agar dilution

Mycobacterium marinum is recognized as a cutaneous pathogen requiring antib iotic treatment. We compared the E-test with a reference agar dilution meth od for susceptibility testing of M. marinum to amikacin, ciprofloxacin, cla rithromycin, doxycycline, rifampicin, trimethoprim-sulfamethoxazole and eth ambutol. MICs obtained after 6 d showed agreement between the E-test and ag ar dilution within +/- 2 dilutions in 95% of all cases for amikacin, ciprof loxacin, doxycycline and rifampicin. Inhibitory concentrations of trimethop rim-sulfamethoxazole were difficult to define using the E-test because of g radually decreased growth in the presence of increasing concentrations. For clarithromycin, results were generally 1-3 dilution steps lower with the E -test and for ethambutol they were often > 3 dilution steps lower. These di fferences always appeared in the low MIC range and did not affect the categ orization of the strains as susceptible to these 2 antimicrobial agents. Al l strains were interpreted as susceptible to all tested antibiotics, except for doxycycline, according to recommended breakpoints. Overall, our result s suggest that the E-test can be considered an alternative for susceptibili ty testing of certain antibacterial agents against M. marinum.