Objectives: To determine critical concentrations of moxifloxacin and gatifloxacin for rapid evaluation of drug susceptibility of Mycobacterium tuberculosis in Middlebrook 7H9 broth using the automated system BACTEC™ MGIT™ 960.
Methods: In total we studied 152 strains. Critical concentrations of moxifloxacin and gatifloxacin in the BACTEC™ MGIT™ 960 and on Lowenstein-Jensen medium were determined using a panel of 68 strains. The proportion method on Middlebrook 7H10 medium was used as a reference method. Drug susceptibility testing against fluoroquinolones was done for the other 84 strains using the established critical concentrations. The gyrA and gyrB genes of all strains were studied by molecular tests.
Results: The critical concentrations determined for moxifloxacin and gatifloxacin were 0.25 mg/L in the BACTEC™ MGIT™ 960 system and 0.75 mg/L on Lowenstein-Jensen medium (absolute concentration method).
Conclusions: The moxifloxacin and gatifloxacin critical concentrations that we have established are reliable for rapid drug susceptibility testing in the BACTEC™ MGIT™ 960.
Keywords: drug resistance; fluoroquinolones; microbiology; rapid tuberculosis diagnostics.