Evaluation of various methods of susceptibility to ofloxacin in strains of Mycobacterium tuberculosis.

A comparison of three methods of susceptibility testing was undertaken on 30 susceptible and 25 resistant strains of Mycobacterium tuberculosis to determine an acceptable in vitro definition of resistance of ofloxacin. The strains were tested by the proportion method on Lowenstein Jensen (L-J) and 7H11 media and also by the BACTEC radiometric method. Using a criterion of 1 per cent or more growth at a concentration of 2 mg/1, there was a 100 per cent agreement with the conventional MIC method by the proportion tests on L-J as well as on 7H11 media. The BACTEC radiometric method, at the same concentration, yielded 98 per cent agreement. Thus, any of these methods could be used depending upon the infrastructure available.