[Microbiological aspects of identification of patients with drug-resistant tuberculosis].
This review discusses controversial issues, such as definitions of drug resistance, the conditions laboratory drug-susceptibility testing in all new patients is justified, and the requirements for the optimum turnaround time of laboratory reports. It also analyses the advantages and disadvantages of different methods for drug susceptibility testing, including those based on cultivation in the solid and liquid media, as well as molecular phenotypic and genotypic methods. While molecular genotypic methods represent the most promising direction for future development, their application in the clinical laboratory setting today is limited to the initial preliminary screening for rifampicin resistance as a marker for possible MDR and as an indicator for the need for subsequent testing with other drugs. The direct susceptibility test in the solid media (at least that with rifampicin and isoniazid) represents the most affordable method that allows timely adjustment in the treatment regimen if drug resistance is detected. The total turnaround time can be as short as three weeks for 85-90% of smear-positive specimens when the agar plate technique is used for a direct test. Introduction of a liquid media system is the next step to achieving the expected results in all patients.