MICROBIOLOGICAL DIAGNOSIS OF TUBERCULOSIS

Abstract

  The most important criterion for the diagnosis of tuberculosis is the identification of Mycobacterium tuberculosis (M. tuberculosis) strains and their resistance to antituberculosis drugs. Proper sample collection, storage and transportation are of great importance for the successful isolation of mycobacteria from the test material. Microscopy cannot replace the culture method, but it is an effective and inexpensive way to identify infectious individuals dangerous to the public and to monitor the effectiveness of treatment. The fluorescent staining method is usually used as a selective method to determine RAB, all smears in which the glow is visible must be additionally stained by the modified Cylio-Nilsen method. Solid or liquid nutrient media are suitable for growing mycobacteria. In liquid nutritional media, mycobacteria grow better and faster – the growth of mycobacteria is usually seen within two weeks, while in solid nutritional media, it takes only 3–6 weeks. Nucleic acid amplification can detect M. tuberculosis complex and many atypical mycobacteria directly from prepared test material within hours, as can resistance to rifampicin and isoniazid caused by gene mutations. For the identification of mycobacteria from the culture, the liquid chromatography method is used, which is based on the analysis of the fatty acids of the mycobacterial cell wall. Although phenotypic methods for M. tuberculosis still remain the gold standard, genotyping methods or nucleic acid amplification and deoxyribonucleic acid (DNA) sequencing and restriction enzyme analysis are becoming increasingly popular. Determination of the resistance of mycobacteria of the M. tuberculosis complex to antituberculosis drugs and the interpretation of the results is carried out based on valid international standards.