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Background: Heteroresistance is the coexistence of susceptible and resistant strains in the same individual, considered the preliminary step for total resistance, and can stem from mixed infection or clonal heterogeneity. The aim of this study was to evaluate the heteroresistance of Mycobacterium tuberculosis to rifampicin and isoniazid and its characterization. Method: GenoType MTBDRplus®; Sanger sequencing of the rpoB, katG, and inhA genes; and Mycobacterial Interspersed Repetitive Unit – Variable Number Tandem Repeat (MIRU-VNTR) were performed. Results: In a total of 654 isolates, 530 were resistant, 124 were susceptible, and 29 were heteroresistant to a first-line drug. GenoType MTBDRplus® detected heteroresistance in the rpoB gene in 26/29 (89.6%), as compared to 5/29 (17.2%) in the katG gene and 2/29 (6.8%) in the inhA gene. Four isolates showed heteroresistance in these genes. The Sanger sequencing detected heteroresistance in the rpoB gene in 7/29 (24.1%), as compared to 3/29 (10.3%) in the katG gene. In one isolate, heteroresistance was concomitant in both the rpoB and katG genes. MIRU-VNTR detected mixed infection in three heteroresistant isolates, while four isolates showed clonal heterogeneity. Conclusions: GenoType MTBDRplus® detected more cases of heteroresistance when compared to sequencing. It was also possible to characterize mixed infection and clonal heterogeneity by MIRU-VNTR.

Background: Drug-resistant tuberculosis (TB) is an ongoing health threat, and the greatest challenge to adequate control of TB in many countries lies in the lack of proper laboratory drug-susceptibility test. The aim of this study was to evaluate the activity-based costs (ABC) of Kit SIRE Nitratase® (Kit SIRE) and compare its values with the conventional drug-susceptibility test. Methods: The ABC was calculated for three different approaches: Kit SIRE (clinical samples and cultures), proportion methods in Lowenstein Jensen (PM-LJ), and the Bactec™ MGIT™ 960 system based on Mycobacterial Research Laboratory's routine. Results: The ABC of Kit SIRE from cultures was US$ 148.54, while from clinical samples was US$ 136.12. In the case of conventional tests, the ABC of Bactec™ MGIT™ 960 was US$ 227.63 and of the PM-LJ was US$ 132.64. The Kit SIRE has a lower ABC when clinical samples are used instead of cultures. Compared to conventional tests, the ABC is similar to the PM-LJ and lower the Bactec™ MGIT™ 960. Conclusion: The Kit SIRE should be used as a screening method in clinical specimens and in culture for laboratories that do not have Bactec™ MGIT™ 960. Therefore, it can be incorporated into the routine of laboratories in countries with low resources and a high burden of TB and drug-resistant TB.