Detecting Ethambutol Resistance in Mycobacterium tuberculosis Isolates in China: A Comparison Between Phenotypic Drug Susceptibility Testing Methods and DNA Sequencing of embAB

Ma-Chao Li,Hai-Can Liu,Kang-Lin Wan,Rong Chen,Shi-Qiang Lin,Li-Li Zhao,Gui-Lian Li,Zhi-Guang Liu,Xiu-Qin Zhao,Yao Lu

doi:10.3389/fmicb.2020.00781

Abstract

With the increasing incidence of drug-resistant tuberculosis (DR-TB), determining a rapid and accurate drug susceptibility testing (DST) method to identify ethambutol (EMB) resistance in Mycobacterium tuberculosis has become essential for patient management in China. Herein, we evaluated the correlation between three phenotypic DST methods, namely, proportion method (PM), MGIT 960 system, and microplate alamar Blue assay (MABA), and DNA sequencing of embAB in 118 M. tuberculosis isolates from China. When the results of the phenotypic DST methods were compared with those of DNA sequencing, the overall agreement and kappa values of the PM, MGIT 960 system, and MABA were 81.4% and 0.61, 77.1% and 0.55, and 84.7% and 0.67, respectively. The agreement for EMB resistance between MABA and PM was significantly higher than that between the MGIT 960 system and PM (P = 0.02). Moreover, among the isolates with detectable embAB mutations, 97.2% (70/72 isolates) harbored mutations in embB. The analysis of embB mutations predicted EMB resistance with 81.3% sensitivity, 86.8% specificity, and 83.1% accuracy. Thus, MABA may be a better phenotypic DST method for detecting EMB resistance. DNA sequencing of embB may be useful for the early identification of EMB resistance and the consequent optimization of the treatment regimen.

Highlights

Despite a decreasing trend in the incidence of tuberculosis (TB) in recent years, TB remains a major public health threat in China; in 2018, the World Health Organization (WHO) estimated 900,000 new cases and 37,000 deaths (World Health Organization [WHO], 2018)
drug susceptibility testing (DST) of TB isolates to antitubercular drugs isoniazid (INH), rifampin (RIF), streptomycin (SM), and EMB was performed on Lowenstein–Jensen (L-J) proportion method (PM) according to the WHO guideline, with the critical concentrations being 0.2 μg/ml for INH, 40 μg/ml for RIF, 4.0 μg/ml for SM, and 2.0 μg/ml for EMB (World Health Organization [WHO], 2009)
In China, phenotypic DST based on L-J solid media and the liquid culture system MGIT 960 is routinely performed with all M. tuberculosis isolates

Summary

Introduction

Despite a decreasing trend in the incidence of tuberculosis (TB) in recent years, TB remains a major public health threat in China; in 2018, the World Health Organization (WHO) estimated 900,000 new cases and 37,000 deaths (World Health Organization [WHO], 2018). Rapid and accurate detection of drug resistance is crucial for timely optimizing treatment regimens and reducing treatment failure to prevent the transmission of DR-TB and the development of MDR-TB. Ethambutol (EMB) is an essential first-line anti-TB drug that is routinely recommended in combination with other drugs for treating TB and DR-TB It serves as a key drug in second-line regimens for MDR-TB when drug susceptibility testing (DST) results are available. Certain mutations within the upstream region (UR) of embA are associated with EMB resistance (Cui et al, 2014; Brossier et al, 2015; Zhao et al, 2015). We compared the correlation between three phenotypic EMB susceptibility testing methods and DNA sequencing of embAB mutations in 118 Mycobacterium tuberculosis (M. tuberculosis) isolates from China

Methods

Results

Conclusion