Tuberc Respir Dis > Accepted Articles
DOI:    [Accepted]
Published online February 23, 2022.
A rapid assessing method of drug susceptibility using flow cytometry for Mycobacterium tuberculosis isolates resistant to INH, RIF and EMB
Sun-Kyoung Lee1, Seung-Hun Baek2, Min-Sun Hong1, Jong-Seok Lee1, Eun-Jin Cho1, Ji-Im Lee1, Sang-Nae Cho1,2, Seok-Yong Eum1
1Division of Immunopathology and Cellular Immunology & Division of Microbiology, International Tuberculosis Research Center,Seoul, Republic of Korea
2ChangWon, Department of Microbiology, Yonsei University College of Medicine, Seoul, Republic of Korea
Correspondence:  Seok-Yong Eum, Tel: 82-55-246-1139, Fax: 82-55-246-1182, 
Received: 27 September 2021   • Revised: 26 November 2021   • Accepted: 22 February 2022
*Sun-Kyoung Lee and Seung-Hun Baek contributed equally to this study as co-first authors.
Current conventional drug susceptibility test (DST) for Mycobacterium tuberculosis (Mtb) takes several weeks of incubation for obtaining results. As a rapid method, molecular DST requires only a few days to get the results but does not fully cover the phenotypic resistance. A new rapid method based on the ability of viable Mtb bacilli to hydrolyze fluorescein diacetate (FDA) to free fluorescein with detection of fluorescent mycobacteria by flow cytometric analysis, has recently developed.
In this study, in order to evaluate this cytometric method, we have tested 39 clinical isolates which were susceptible or resistant to isoniazid (INH) or rifampin (RIF) or ethambutol (EMB) by phenotypic or molecular DST methods and compared the results.
The susceptibility was determined by measuring the viability rate of Mtb and all the isolates tested with INH, RIF and EMB showed the susceptibility results concordant with those by the phenotypic solid and liquid media methods. The isolates having no mutations in the molecular DST but resistance in the conventional phenotypic DST were also resistant in this cytometric method. These results suggest that the flow cytometric DST method is faster than conventional agar phenotypic DST and may complement the results of molecular DST.
In conclusion, the cytometric method could provide quick and useful information for the clinicians to choose more effective drugs.
Key Words: Mycobacterium tuberculosis, drug-susceptibility test, flow cytometry, clinical isolates

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