Tuberc Respir Dis.  2022 Jul;85(3):264-272. 10.4046/trd.2021.0134.

A Rapid Assessing Method of Drug Susceptibility Using Flow Cytometry for Mycobacterium tuberculosis Isolates Resistant to Isoniazid, Rifampin, and Ethambutol

• Lee SK
• Baek SH
• Hong MS
• Lee JS
• Cho EJ
• Lee JI
• Cho SN
• Eum SY

• KMID: 2531455
• DOI: http://doi.org/10.4046/trd.2021.0134

Abstract

Background
The current conventional drug susceptibility test (DST) for Mycobacterium tuberculosis (Mtb) takes several weeks of incubation to obtain 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 to free fluorescein with detection of fluorescent mycobacteria by flow cytometric analysis, was recently developed.
Methods
To evaluate this cytometric method, we 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.
Results
The susceptibility was determined by measuring the viability rate of Mtb and all the isolates which were tested with INH, RIF, and EMB showed 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.
Conclusion
In conclusion, the cytometric method could provide quick and more accurate information that would help clinicians to choose more effective drugs.

Keyword

Drug Susceptibility Test; Flow Cytometry; Clinical Isolates