Abstract: Objective To compare the difference of drug susceptibility of Mycobacterium tuberculosis（MTB） by using both absolute concentration method with different bacterium quantity and proportion method. Methods The 53 probable drug-susceptible or drug-resistant strains of MTB were selected.The bacterial suspensions of MTB were prepared using Mcfarland method.0.1 ml of bacterial suspensions(including 10^-4,10^-5,10^-6 mg/ml) was incubated for MTB CFU,respectively.0.1 ml of bacterial suspensions(including 10^-2,10^-3 mg/ml) was incubated for the drug susceptibility testing with absolute concentration method,respectively.0.1 ml of bacterial suspensions(including 10^-3,10^-5 mg/ml) was incubated for the drug susceptibility testing with proportion method,respectively. Results The number of MTB CFU was from 5×106 CFU/ml to 5×107 CFU/ml in Mcfarland method.The accordance rate of isoniazid and rifampicin drug susceptibility in 10^-2 and 10^-3 mg/ml of MTB was 98.1%,100.0% using absolute concentration method,respectively.The accordance rate of isoniazid and rifampicin drug susceptibility of MTB was from 90.6% to 100.0% with absolute concentration method and proportion method. Conclusion The result of drug susceptibility of MTB using absolute concentration method and proportion method is accordant.

Key words: Mycobacterium tuberculosis, CFU, Drug susceptibility testing