EVALUATION OF A NEW METHOD FOR RAPID DRUG SUSCEPTIBILITY TESTING OF MYCOBACTERIUM-AVIUM COMPLEX ISOLATES BY USING THE MYCOBACTERIA GROWTH INDICATOR TUBE

The reliability of the Mycobacteria Growth Indicator Tube (MGIT [BBL]) for rapid drug susceptibility testing of Mycobacterium avium complex (MAC) isolates was evaluated, MICs of amikacin, clarithromycin, clofaz imine, ethambutol, and rifabutin were determined by the MGIT system fo r 16 MAC strains, The results were compared with those obtained by the BACTEC broth macrodilution method, The turnaround times were 6 to 8 d ays (median, 7 days) for the MCIT and 5 to 7 days (median, 6 days) for the BACTEC system, Agreements with BACTEC system-determined MICs, wit hin +/-1 log(2) dilution, were 100, 100, 88, 63, and 44% for amikacin, clofazimine, rifabutin, clarithromycin, and ethambutol, respectively, Within +/-2 log(2) dilutions, agreement with BACTEC system-determined MICs increased to 100% for all the tested drugs, In addition, if MGIT -determined MICs were evaluated according to the thresholds adopted fo r the interpretation of BACTEC system-determined ones, ethambutol was the only drug for which susceptible strains were frequently misclassif ied as resistant, It is concluded that the MGIT system is a promising, nonradiometric alternative to the BACTEC method for rapid susceptibil ity testing of MAC isolates; however, additional studies are required to confirm our results and to determine the optimal criteria for the i nterpretation of ethambutol MICs.