Activity of ciprofloxacin against Mycobacteria in vitro: comparison of BACTEC and macrobroth dilution methods

Various clinical isolates of mycobacteria were tested for susceptibility to ciprofloxacin by a standard macrobroth dilution test and the radiometric BACTEC method. Agreement between the two test systems was species dependent: Mycobacterium tuberculosis (80%), M. kansasii with M. scrofulaceum (30%), M. avium-intracellulare (20%), and 0% for the rapidly growing mycobacteria. Most mycobacterial strains other than M. tuberculosis were susceptible to the breakpoint ciprofloxacin concentration of 2 mg/l as determined by BACTEC MICs, whereas none were susceptible by macrobroth testing. Seven of nine M. tuberculosis isolates were susceptible by either method. Ciprofloxacin merits further study as a potential antimycobacterial agent.