Comparison of growth and susceptibility testing of pyrazinamide in different Bactec media using strains of the M. tuberculosis complex.

The aim of this study was to evaluate and compare growth and susceptibility testing of pyrazinamide (pza) in different Bactec media using 85 strains of the M. tuberculosis complex. Fifty-four were clinical isolates of M. tuberculosis, of which 34 strains were selected as they failed to grow in primary pza susceptibility testing. Fourteen were strains of M. bovis, 10 were different strains of M. bovis BCG, five were strains of M. africanum, and two were strains of M. microti. The following Bactec media were evaluated: (1) Bactec PZA test medium, (2) acidified Bactec 12B medium with pH reduced to 5.6, (3) acidified 12B medium supplemented with fresh egg yolk, (4) acidified 12B medium supplemented with a commercial egg yolk enrichment. Demonstration of pyrazinamidase activity was included for comparison. All strains of M. tuberculosis, M. microti and M. africanum were inhibited by pza at 100 micrograms/ml, and all strains of M. bovis and M. bovis BCG were found to be resistant to pza at 100 micrograms/ml. Bactec PZA test medium supported growth for all 85 strains tested. The two egg yolk-supplemented media supported growth in all strains except one strain of M. microti, and acidified but otherwise unsupplemented Bactec 12B medium supported growth in 64 strains (75%). A pza sensitivity test result could be obtained within one week in > 79% of strains. An overall correlation of 89% between susceptibility to pza and demonstration of pyrazinamidase activity was demonstrated.