Selective inhibition of the Mycobacterium tuberculosis complex by p-nitro-alpha-acetylamino-beta-hydroxypropio phenone (NAP) and p-nitrobenzoic acid (PNB) used in 7H11 agar medium.

The potential of p-nitrobenzoic acid (PNB) and p-nitro-alpha-acetylamino-beta-hydroxypropiophenone (NAP) for discriminating the Mycobacterium tuberculosis (M.tb) complex from other mycobacteria was evaluated in cases of clinical isolates. For this purpose, 500 micrograms/ml of PNB and 5 or 10 micrograms/ml of NAP were incorporated in 7H11 agar medium, and appropriate dilutions corresponding to about 10(6) viable units were then plated on PNB- or NAP-containing media. Results were reported as growth or no growth as compared to a parallel control. Our data reconfirmed the potential of PNB to discriminate M.tb complex bacteria. This study also showed for the first time that the NAP test (used until now in 7H12a broth only) can also be successfully applied using 7H11 agar. Also, preliminary data with 5 micrograms/ml of NAP on a limited number of strains suggested that it may discriminate the M.tb complex bacilli from M. xenopi and M. gastri better than PNB in 7H11 agar.