| Summary: | <p>Abstract</p> <p>Background</p> <p>Pyrazinamide (PZA) is among the first-line drugs for the treatment of tuberculosis. In vitro, it kills semidormant mycobacteria only at low pH. The purpose of this study was to compare PZA resistance with pyrazinamidase (PZase) activity and the genotype to better understand the molecular basis of PZA resistance and to expand the profile of <it>pncA</it> mutations worldwide.</p> <p>Results</p> <p>Of the 28 tested strains of <it>Mycobacterium tuberculosis</it>, 6 were susceptible to PZA and positive for PZase activity and had no <it>pncA</it> mutations. Twenty-one strains were resistant to PZA and negative for PZase activity and had mutations in the <it>pncA</it> gene, including 15 point mutations, 5 insertions, and 2 deletions. One strain had no mutation in the <it>pncA</it> gene, even though it was resistant to PZA and negative for PZase activity. Three isolates had adenine to guanine point mutations in the -11 upstream region, making this the most common type of <it>pncA</it> mutations in this study, with at least two different RFLP patterns.</p> <p>Conclusion</p> <p>These data help in the understanding of the molecular basis of PZA resistance. An adenine to guanine point mutation in the -11 upstream region was the most common type of <it>pncA</it> mutation in our isolates. The results of <it>pncA</it> mutation analyses should be carefully interpreted for epidemiologic purposes.</p>
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