Although sputum microscopy remains the most widely used diagnostic
method worldwide, given its low sensitivity (50-80%) and specificity (it does not
distinguish M. tuberculosis from nontuberculous mycobacteria), more rapid, sensitive,
and specific methods are required nowadays. Culture for mycobacteria continues to be
the gold standard due to its higher sensitivity and specificity, and because it also allows
the detection of strains resistant to antituberculosis drugs; however, even with liquid
culture media, at least one month of processing is required to obtain results. Therefore,
rapid genotyping methods (e.g., Xpert and line-probe assays known as LPAs) have
replaced phenotypic methods by allowing the identification of species and the presence
of mutations associated with resistance in less than 24 hours. The Xpert, an automated
real-time PCR system, can identify the presence of mutations associated with rifampin
resistance in less than two hours, with a sensitivity higher than 70% in patients with
negative microscopy. LPAs allow species identification and the presence of mutations
associated with resistance to isoniazid, rifampin, fluoroquinolones, and second-line
injectables in less than 24 hours. Progressively, the complete sequencing of the
Mycobacterium tuberculosis genome has been integrated into the diagnostic protocol,
allowing the identification of all mutations associated with resistance for all
antituberculosis drugs. Phenotypic methods (microscopy and cultures) continue to play
an essential role in the follow-up of patients who are already under treatment.
Keywords: Cultures, Diagnosis, Genome sequencing, LPA, MGIT, Microscopy,
Tuberculosis, Xpert.Cultures, Diagnosis, Genome sequencing, LPA, MGIT, Microscopy,
Tuberculosis, Xpert.
