[A study on the drug resistance to p-nitrobenzoic acid in Mycobacterium tuberculosis]

To investigate the resistance of Mycobacterium tuberculosis (MTB) to p-nitrobenzoic acid (PNB), in order to provide the scientific basis for reliable identification of laboratory strains of mycobacterium.

Strains of mycobacterium grown in PNB media were identified with additional traditional biochemical tests, according to the standard protocols of laboratory diagnostics for tuberculosis by the Chinese Antituberculosis Association. For mycobacteria grown in the PNB media but highly suspected as MTB by traditional biochemical tests, MPB64 monoclonal antibody was used for the differentiation between MTB and non-tuberculosis mycobacteria group (NTM). Minimal inhibitory concentrations (MIC) of PNB was further determined for culture-confirmed MTB, 10 strains of clinically isolated MTB (control), H(37)Rv standard strain, mycobacterium avium standard strain, and 5 strains of clinically isolated NTM.

A total of 1114 strains of MTB were confirmed, among which 58 PNB manifested resistance. The rate of resistance was 5.21% (58/1114), with an MIC ranging for 1.0 - 1.5 g/L. The MICs of control MTB and H(37)Rv standard strain were 0.25 - 0.5 g/L and 0.25 g/L, respectively. Both mycobacterium avium standard strain and clinically isolated NTM showed an MIC of > 2.0 g/L. Differences between groups were statistically significant (t = 4.87, 5.09, 6.68, respectively, P < 0.01).

In order to avoid laboratory misdiagnosis, for primary screening with NTB with PNB culture, the presence of MTB characteristics, including cream-colored broccoli-like colony morphologies, as well as clinical response to first-line anti-tuberculosis medications, despite PNB tolerance, warrants further investigations of traditional biochemical tests, differentiation with MPB64 monoclonal antibodies, or simply by the use of temperature manipulation or drug-sensitivity test results.