Molecular diagnostics in tuberculosis: basis and implications for therapy.

The processing of clinical specimens in the mycobacterial diagnostic laboratory has undergone remarkable improvements during the last decade. While microscopy and culture are still the major backbone for laboratory diagnosis of tuberculosis on a worldwide basis, new methods including molecular diagnostic tests have evolved over the last two decades. The majority of molecular tests have been focused on (i) detection of nucleic acids, both DNA and RNA, that are specific to Mycobacterium tuberculosis, by amplification techniques such as polymerase chain reaction (PCR); and (ii) detection of mutations in the genes that are associated with resistance to antituberculosis drugs by sequencing or nucleic acid hybridization. Recent developments in direct and rapid detection of mycobacteria, with emphasis on M. tuberculosis species identification by 16S rRNA gene sequence analysis or oligohybridization and strain typing, as well as detection of drug susceptibility patterns, all contribute to these advances. Generally, the balance between genome instability and genome maintenance as the basis for evolutionary development, strain diversification and resistance development is important, because it cradles the resulting M. tuberculosis phenotype. At the same time, semi-automated culture systems have contributed greatly to the increased sensitivity and reduced turnaround time in the mycobacterial analysis of clinical specimens. Collectively, these advances are particularly important for establishing the diagnosis of tuberculosis in children. More basic and operational research to appraise the impact and cost effectiveness of new diagnostic technologies must, however, be carried out. Furthermore, the design and quality of clinical trials evaluating new diagnostics must be improved to allow clinical and laboratory services that would provide rapid response to test results. Thus, important work remains before the new diagnostic tools can be meaningfully integrated into national tuberculosis control programs of high-burden countries.