**4. Conclusions**

Rapid testing for tuberculosis, which includes the identification of resistance to tuberculosis drugs, is necessary to initiate effective treatment and halt disease transmission. A new generation of more sensitive, automated molecular diagnostic assays enables simultaneous detection of rifampicin and isoniazid resistance markers. An indubitable advantage of molecular assays is the short turnaround time and the possibility of starting the patient on the correct treatment. However, the results of numerous studies showed that drug resistance in *Mycobacterium tuberculosis* may be caused by other mutations in a region of the gene that is not analyzed by a given genetic test. Further research is therefore required to improve the molecular assays and to include new mutations responsible for resistance to tuberculosis drugs in commercial assays. Currently, in order to correctly determine the resistance of *Mycobacterium tuberculosis* strains to tuberculosis drugs, genetic testing must be supplemented with conventional drug resistance tests [14]. The presented case series illustrated the role of FluoroType® MTBDR VER. 2.0 in diagnosing the M. tuberculosis strain with isoniazid monoresistance as well as MDR-TB, directly from clinical samples.

**Author Contributions:** Conceptualization, E.A.-K. and A.Z.; data curation, D.F., A.Z., W.K., J.J. and Ł.O.; writing—original draft preparation, A.Z., D.F., M.S. and A.W.; writing—review and editing, E.A.-K. and M.S.; visualization, A.W., J.J. and W.K. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the National Science Center, gran<sup>t</sup> number 2019/35/B/NZ7/00942.

**Institutional Review Board Statement:** Ethical review and approval were waived for this case report due to the retrospective character of the published data.

**Informed Consent Statement:** Informed consent for publication has been obtained from the patients to publish this paper.

**Data Availability Statement:** The clinical data of the patients are available in the hospital database.

**Conflicts of Interest:** The authors declare no conflict of interest.
