Resistance
Mutations in the pncA gene of M. tuberculosis, which encodes a pyrazinamidase and converts pyrazinamide to its active form pyrazinoic acid, are responsible for the majority of pyrazinamide resistance in M. tuberculosis strains. A few pyrazinamide-resistant strains with mutations in the rpsA gene have also been identified. However, a direct association between these rpsA mutations and pyrazinamide resistance has not been established. The pyrazinamide-resistant M. tuberculosis strain DHMH444, which harbors a mutation in the carboxy terminal coding region of rpsA, is fully susceptible to pyrazinoic acid and pyrazinamide resistance of this strain was previously associated with decreased pyrazinamidase activity. Further, this strain was found to be susceptible to pyrazinamide in a mouse model of tuberculosis. Thus, current data indicate that rpsA mutations are not likely to be associated with pyrazinamide resistance. Currently, three main methods of testing are used for pyrazinamide resistance: 1) phenotypic tests where a tuberculosis strain is grown in the presence of increasing concentrations of pyrazinamide, 2) measuring levels of pyrazinamidase enzyme produced by the tuberculosis strain, or 3) looking for mutations in the pncA gene of tuberculosis. Concerns exist that the most widely used method for phenotypic resistance testing may overestimate the number of resistant strains.Global resistance of tuberculosis to pyrazinamide has been estimated to be in 16% of all cases, and 60% of people with multidrug-resistant tuberculosis. Abbreviations
The abbreviations PZA and Z are standard, and used commonly in the medical literature, although best practice discourages the abbreviating of drug names to prevent mistakes.
Hereditary benign intraepithelial dyskeratosis is a rare autosomal dominant disease of the conjunctiva and the oral mucosa caused by a duplication of chromosome 4q35. In the mouth it appears similar to white sponge nevus, with painless, diffuse, folded and spongy white plaques. In the eye it appears as gelatinous plaques on bulbar perilimbal conjunctiva. == References ==