Evaluation of a rapid radiometric differentiation test for the Mycobacterium tuberculosis complex by selective inhibition with p-nitro-alpha-acetylamino-beta-hydroxypropiophenone

Abstract

A rapid technique for the differentiation of the M. tuberculosis complex from other mycobacteria, using p-nitro-.alpha.-acetylamino-.beta.-hydroxypropiophenone (NAP) as a selective inhibitory agent, was evaluated. Coded cultures, 234 cultures belonging to the M. tuberculosis complex and 182 cultures belonging to 35 other mycobacterial species, were tested in 2 laboratories for p-nitro-.alpha.-acetylamino-.beta.-hydroxypropiophenone inhibition to concentrations of 5 and 10 .mu.g of NAP/ml in Middlebrook 7H12 liquid medium. Two testing modes were compared: the indirect, in which a large bacterial inoculum was used from an isolated culture on a solid medium, and the direct, which used a small inoculum from 7H12 medium. A decrease or no increase in daily 14CO2 output as measured by a BACTEC system was considered evidence of inhibition. A concentration of 5 .mu.g of NAP/ml effectively separated the M. tuberculosis complex from other mycobacterial species in 4-6 days. The direct test data show that, unlike other conventional biochemical tests, it does not require a heavy inoculum of mycobacteria and can therefore be performed soon after growth is detected by the radiometric method.