A rapid radiometric method for determining the sensitivity of clinical isolates of Mycobacterium tuberculosis to several chemotherapeutic agents.

Current methods of performing antibiotic susceptibility tests on M. tuberculosis require 4 to 6 weeks for completion and in some cases have a poor correlation with clinical results. We have developed a rapid radiometric method of sensitivity testing which utilizes the incorporation of 3H-uracil into ribonucleic acid (RNA) as a measure of mycobacterial growth. The radiometric method is sensitive and reproducible and the results are completed in 48 hours. An excellent correlation was found between the radiometric method of sensitivity testing and the traditional agar plate technique when the two were compared with respect to isoniazid, streptomycin, and rifampicin sensitivities. There was no correlation between the two methods when ethambutol was tested. These results have confirmed our previous experiments on the usefulness of the radiometric method for the rapid determination of antibiotic susceptibilities of mycobacteria.