Analysis of gene mutations associated with isoniazid, rifampicin and ethambutol resistance among Mycobacterium tuberculosisisolates from Ethiopia

Belay Tessema,Arne C Rodloff,Joerg Beer,Frank Emmrich,Ulrich Sack

doi:10.1186/1471-2334-12-37

Abstract

BackgroundThe emergence of drug resistance is one of the most important threats to tuberculosis control programs. This study was aimed to analyze the frequency of gene mutations associated with resistance to isoniazid (INH), rifampicin (RMP) and ethambutol (EMB) among Mycobacterium tuberculosis isolates from Northwest Ethiopia, and to assess the performance of the GenoType® MTBDRplus and GenoType® MTBDRsl assays as compared to the BacT/ALERT 3D system.MethodsTwo hundred sixty Mycobacterium tuberculosis isolates from smear positive tuberculosis patients diagnosed between March 2009 and July 2009 were included in this study. Drug susceptibility tests were performed in the Institute of Medical Microbiology and Epidemiology of Infectious Diseases, University Hospital of Leipzig, Germany.ResultsOf 260 isolates, mutations conferring resistance to INH, RMP, or EMB were detected in 35, 15, and 8 isolates, respectively, while multidrug resistance (MDR) was present in 13 of the isolates. Of 35 INH resistant strains, 33 had mutations in the katG gene at Ser315Thr 1 and two strains had mutation in the inhA gene at C15T. Among 15 RMP resistant isolates, 11 had rpoB gene mutation at Ser531Leu, one at His526Asp, and three strains had mutations only at the wild type probes. Of 8 EMB resistant strains, two had mutations in the embB gene at Met306Ile, one at Met306Val, and five strains had mutations only at the wild type probes. The GenoType® MTBDRplus assay had a sensitivity of 92% and specificity of 99% for INH resistance, and 100% sensitivity and specificity to detect RMP resistance and MDR. The GenoType® MTBDRsl assay had a sensitivity of 42% and specificity of 100% for EMB resistance.ConclusionThe dominance of single gene mutations associated with the resistance to INH and RMP was observed in the codon 315 of the katG gene and codon 531 of the rpoB gene, respectively. The GenoType® MTBDRplus assay is a sensitive and specific tool for diagnosis of resistance to INH, RMP and MDR. However, the GenoType® MTBDRsl assay shows limitations in detecting resistance to EMB.

Highlights

The emergence of drug resistance is one of the most important threats to tuberculosis control programs
According to the World Health Organization (WHO) report, the proportion of multidrug resistant tuberculosis (MDR-TB), resistant to at least isoniazid and rifampicin among new and previously treated TB cases globally ranges from 0% to 28.3% and from 0% to 61.6%
History of previous treatment for tuberculosis was significantly associated with gene mutations conferring resistance to INH (P = 0.001), RMP (P = 0.002) and multidrug resistance (MDR) (P = 0.044)

Summary

Introduction

The emergence of drug resistance is one of the most important threats to tuberculosis control programs. For proper treatment and control of tuberculosis, WHO is recommending countries to expand their capacity for culture based drug-susceptibility testing (DST) and consider new, molecular-based assays for diagnosing drug resistance [7,8]. The gold-standard of TB diagnosis by culture takes weeks to become positive, and even with the up-to date automated fluid culture methods it takes an average of 14 days. Another 14 days for additional testing are required to get the information on drug susceptibility [9,10,11]. Molecular methods of drug resistance testing, based on the identification of mutations in genes associated with drug resistance, like GeneXpert MTB/RIF assay, offer an effective tool for determining drug resistance because of their high sensitivity, specificity and speed [12]

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