[Phenotypic characterization of pyrazinamide-resistant Mycobacterium tuberculosis isolated in Poland]

Pyrazinamide (PZA) is an important first-line antituberculous drug, which is applied together with INH, RMP, EMB and SM. This drug plays a unique role in the first phase of TB therapy because it is active within macrophages and kills tubercule bacilli. Testing of the resistibility of Mycobacterium tuberculosis to PZA is technically difficult because PZA is active only at acid pH. Therefore routine drug resistibility testing of M. tuberculosis for PZA is not performed in many laboratories. The objective of our study was to estimate the resistibility for PZA among M. tuberculosis isolates from polish patients in 2000-2008 years.

We analyzed M. tuberculosis strains with different resistibility to first-line antituberculous drugs. The strains were isolated from 1909 patients with tuberculosis. The strains were examined for PZA resistibility by the radiometric Bactec 460-TB method. The PZA-resistant strains were examined for following MIC PZA for drug concentration: 100, 300, 600, 900 microg/mL.

PZA resistance among M. tuberculosis strains was found in 6.7% untreated patients and in 22.2% previously treated patients (p < 0.001). In both groups resistance to PZA was correlated with drug resistance for INH + RMP + SM + EMB in 32.7% untreated patients and in 34.5% previously treated ones (p < 0.8). The PZA-monoresistant strains were observed in 20.8% untreated patients groups. Among resistant strains: in 3.4% MIC for PZA was > 100 microg/mL, in 11.6% >or= 300 microg/mL, in 8.9% >or= 600 microg/mL and in 76% >or= 900 microg /mL.

Among M. tuberculosis strains PZA resistance was found in 6.7% of untreated patients and in 22.2% of previously treated patients. Among the PZA-resistant strains very high MIC value for PZA (>or= 900 microg/mL) was revealed for 76% M. tuberculosis strains.