Early detection of drug resistance constitutes one of the priorities of TB control programs. It allows initiation of the appropriate treatment in patients and also surveillance of drug resistance. Detection of drug resistance has been performed in the past by so-called ‘conventional methods’ based on detection of growth of M. tuberculosis in the presence of the antibiotics. However, due to the laboriousness of some of these methods, and most of all, the long period of time necessary to obtain results, in recent years new technologies and approaches have been proposed.
These include both phenotypic and genotypic methods. In many cases, the genotypic methods in particular have been directed towards detection of RIF resistance, since it is considered a good surrogate marker for MDR-TB, especially in settings with a high prevalence of MDR-TB. Genotypic methods have the advantage of a shorter turnaround time, no need for growth of the organism, the possibility of direct application in clinical samples, lower biohazard risks, and the feasibility of automation; however, not all molecular mechanisms of drug resistance are known.
Phenotypic methods, on the other hand, are in general simpler to perform and might be closer to implementation on a routine basis in clinical mycobacteriology laboratories. The following section describes the conventional phenotypic methodologies proposed for drug resistance detection in TB.
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