Abstract
Purpose The purpose of this study was to examine the utility of gene analysis of Mycobacterium tuberculosis as a means of determining the current status of tuberculosis developing in patients long after primary infection and identifying the source of infection.
Methods We analyzed two outbreaks of tuberculosis involving chronic carriers in 2004 within Okayama prefecture. DNA was extracted from Mycobacterium tuberculosis stains isolated from the patients, and subjected to IS6110-RFLP and PGRS-RFLP analyses. The resulting IS6110-RFLP patterns were compared with a database (compiled since December 1999) of RFLP patterns of isolates from newly registered tuberculosis patients in the prefecture. Mutations in the rpoB gene for rifampicin resistance and the katG gene for isoniazid resistance of Mycobacterium tuberculosis were detected by real-time PCR followed by melting curve analysis. Bacterial isolates were tested for antimycobacterial susceptibility by the microdilution susceptibility method and the proportion method on Ogawa's medium.
Results In outbreak 1, an epidemiological survey suggested that two individuals contracted tuberculosis from the same patient after an interval of about 20 years. They differed from the suspected patient in the drug susceptibility patterns of bacterial isolates and mutations in the drug susceptibility-related genes, but the results of IS6110-RFLP and PGRS-RFLP analyses supported a conclusion of a common source of infection. In outbreak 2, a hospital employee developed primary multidrug-resistant tuberculosis of unknown origin. Comparison between the IS6110-RFLP patterns of the employee's bacterial isolate and the IS6110-RFLP database showed identity to a bacterial isolate from a chronic carrier who had died in the same hospital 4 years and 8 months earlier. Moreover, the two isolates were identical regarding drug susceptibility patterns and mutations in drug resistance-related genes, suggesting a nosocomial infection.
Conclusion These results indicates that tuberculosis gene analysis provides useful information for comprehension of the current status of tuberculosis developing in patients long after primary infection. Genotype database construction may allow detection of the source of infection, which cannot be identified by contact examination alone.
