Genotypic and Phenotypic Methods in the Detection of MDR-TB and Evolution to XDR-TB

Background : Accurate and rapid diagnosis of drug-resistant tuberculosis is essential for initiating appropriate treatment and preventing the transmission of these strains. This study compares phenotypic and genotypic methods of drug susceptibility testing for Mycobacterium tuberculosis (M. tuberculosis) . Methods : Resistance to first-line drugs, as well as resistance to second-line drugs (fluoroquinolones and aminoglycosides), was assessed using the Löwenstein-Jensen medium phenotypic method and the GenoType MTBDR plus genotypic method and analyzed. Results : The phenotypic resistance rate was 84.85% for INH ( n = 56), 46.97% for RIF ( n = 31), 48.48% for STR ( n = 32), and 30.30% for EMB ( n = 20). Of the MDR-TB isolates ( n = 29), 41.37% were resistant to fluoroquinolones ( n = 12) and 31.03% were resistant to both fluoroquinolones and injectable aminoglycosides, being classified as XDR-TB ( n = 9). In addition, 22.73% of the MDR-TB isolates were resistant to all four first-line drugs ( n = 15). The overall concordance between the line probe assay method and phenotypic testing was 94.74% for RIF and 95.16% for INH. Discordances were identified in three cases for RIF and two cases for INH, where isolates were reported as susceptible by GenoType MTBDR plus , but phenotypically resistant. Conclusions : Genotypic testing using GenoType MTBDR plus provides rapid and accurate results, but some cases of phenotypic resistance are not detected by this method. The results highlight the importance of using combined phenotypic and genotypic methods for accurate diagnosis of MDR-TB, as well as the need to integrate genomic sequencing to improve diagnostic accuracy.