Introduction:

Tuberculosis continues to be a public health problem that is now aggravated by drug-resistant Mycobacterium tuberculosis. More than 95% of rifampicin (RIF)-resistant strains of M. tuberculosis have mutations in a region of the rpoB gene. Xpert™ MTB/RIF is a molecular biology system that allows identifying mutations in the RIF-resistance determining region of this gen using 5 probes (A, B, C, D, E) that make up the rpoB gene sequences.

Objective:

To describe the distribution and frequency of potential mutations associated with RIF resistance in the rpoB gene of M. tuberculosis detected in pulmonary and extrapulmonary samples using the Xpert® MTB/RIF method.

Materials and methods:

Retrospective study in which 66 samples positive for RIF-resistant M. tuberculosis, processed using the GeneXpert MTB/RIF system between January 2011 and July 2019 at a university hospital in Medellín, Colombia, were analyzed. According to the Dx System software of the GenXpert instrument, a potential mutation and RIF resistance were established if the probes did not bind to their natural complementary beacon or if there was a delay in binding (delta CT>4) in relation the other probes due to the presence of an abnormal beacon. Data were analyzed using descriptive statistics.

Results:

Of the 66 samples (48 pulmonary and 18 extrapulmonary), 63.64% were from men and participants' mean age was 39.60 ± 17.69 years. The frequency and distribution of mutations was as follows: probe E: 38 mutations (57.58%), B: 16 mutations (24.24%), D: 8 mutations (12.12%), A: 3 mutations (4.54%) and D&E: 1 mutation (1.52%). No mutation was detected in probe C.

Conclusions:

Mutations associated with RIF resistance in the rpoB gene of M. tuberculosis detected by the Xpert® MTB/RIF method were mainly found in probe E (codons 529-533). On the other hand, no mutation was detected in probe C.

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