EVALUATION OF ETEST FOR RAPID SUSCEPTIBILITY TESTING OF MYCOBACTERIUM-CHELONAE AND M-FORTUITUM

Etest is a new concept for MIC determinations for antimicrobial agents that is based on a predefined antibiotic gradient on a plastic strip calibrated with a continuous logarithmic MIC scale covering 15 twofold dilutions. Etest was compared with a reference agar dilution method f or susceptibility testing of clinical isolates of Mycobacterium chelon ae and M. fortuitum. Results read after 3 days showed good agreement b etween MICs obtained with Etest and those obtained with the reference method within +/-2 dilutions for 90% of all test combinations. All but one of the strains were inhibited by low concentrations of ciprofloxa cin or amikacin. Susceptibility to clarithromycin, erythromycin, imipe nem, rifampin, doxycycline, and fusidic acid was variable, and all str ains were resistant to ceftazidime and trimethoprim. The results sugge st that Etest is well suited for studies of drug resistance in rapidly growing mycobacteria.