Tuberculosis ethambutol resistance: Concordance between phenotypic and genotypic test results

Plinke, Claudia; Cox, Helen; Kalon, Stobdan; Doshetov, Daribay; Rüsch-Gerdes, Sabine; Niemann, Stefan

doi:10.1016/j.tube.2009.09.001

Cited by 32 publications

(29 citation statements)

References 20 publications

(26 reference statements)

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“…In comparison with phenotypic DST, the MTBDRsl showed low specificity and sensitivity (55%), mainly due to embB mutations MIC values resolved the discrepancies between LiPA and DST but raised concerns on phenotypic EMB DST by MGIT. Our results support the findings of PLINKE et al [25] reporting that strains, phenotypically susceptible to EMB and carrying mutations at codon 306 of the embB gene, were found resistant after retesting. These findings raise concerns regarding the standardisation of phenotypic DST for EMB.…”

Section: Embsupporting

confidence: 92%

GenoType MTBDRslperformance on clinical samples with diverse genetic background

et al. 2012

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We evaluate the performance of the GenoType1 MTBDRsl (Hain Lifescience Nehren, Germany) for the detection of second-line resistant tuberculosis and we correlate the frequency of mutations to different Mycobacterium tuberculosis genotypes.We tested 175 strains and 59 clinical specimens interpreting the results according to the Standards for Reporting of Diagnostic Accuracy recommendations. All the strains were also investigated by spoligotyping and Mycobacterial Interspersed Repetitive Units-Variable Number of Tandem Repeats typing.The performances of the MTBDRsl in detecting resistance to fluoroquinolones (FQ), second-line injectable drugs (SLID), and ethambutol (EMB) on clinical isolates were similar (specificity ,99%, sensitivity ,70%, and positive predictive value (PPV) ,99%).Of the 59 respiratory specimens, three samples were classified as ''indeterminate''. The specificity in detecting resistances was similar for FQs and EMB 100% (95% CI 92.7-100%) and 100% (95% CI 83.9-100%), respectively with a PPV of 100% (95% CI 64.6-100%) and 100% (95% CI 87.9-100%), respectively. Detection of SLID showed a specificity of 89.1% (95% CI 77.0-95.3%) and a PPV of 58.3% (95% CI 32.0-80.7%). Sensitivity for FQ-resistance detection was 100% (95% CI 64.6-100%), whereas for SLID and EMB it was 89.1% (95% CI 77.0-95.3%) and 86.1% (95% CI 71.3-93.9%), respectively. We detected a significant association between mutations in the rrs gene and Beijing lineage.The MTBDRsl can be used to ''rule in'' extensively drug-resistant strains of tuberculosis in a high risk group; the low sensitivity and negative predicted value (NPV) make confirmation by conventional drug susceptibility testing mandatory when mutations are not identified. NPV for SLID is higher in Beijing strains, showing that the predictive values of the molecular tests are related to the genetic background.

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Section: Embsupporting

confidence: 92%

GenoType MTBDRslperformance on clinical samples with diverse genetic background

et al. 2012

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“…Because conventional culturebased phenotypic methods of EMB susceptibility testing are notoriously problematic, the presumably inaccurate conventional drug susceptibility results may be the major cause of the "EMBsusceptible" isolates that harbored embB mutations (13,14). Similarly, the problems of conventional proportion susceptibility were most likely responsible for the discrepancies between molecular and phenotypic EMB resistance test results (15). Here, our results demonstrate that ethambutol resistance determined by the broth microdilution MIC method revealed better correlation with embB mutations in MDR-TB isolates.…”

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confidence: 66%

Ethambutol Resistance as Determined by Broth Dilution Method Correlates Better than Sequencing Results with embB Mutations in Multidrug-Resistant Mycobacterium tuberculosis Isolates

Zhang

Wang²,

Kam

2014

J Clin Microbiol

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We evaluated the correlation of phenotypic ethambutol (EMB) susceptibility as determined by two drug susceptibility methods with embB mutations in multidrug-resistant (MDR) Mycobacterium tuberculosis strains. The concordance rate for EMB resistance between broth dilution method and sequencing results (83.6%) was significantly higher than between the proportion method and sequencing results (61.7%) (P ‫؍‬ 0.004). Of the embB mutants, 75.4% (46/61) possessed a mutation at embB306. Our results demonstrated that ethambutol resistance determined by broth dilution method reveals better correlation with embB mutations than the proportion method in MDR isolates. The emergence of multidrug-resistant (MDR) tuberculosis (TB), defined as tuberculosis that is resistant to at least isoniazid (INH) and rifampin (RFP), is a serious threat to global tuberculosis control (1). China is considered one of the global hotspots of MDR-TB, with an estimated 110,000 MDR-TB cases each year (2). There is an urgent demand for accurate and rapid drug susceptibility testing (DST) to help develop efficient anti-TB drug regimens for appropriate treatment of individual cases (3).Ethambutol (EMB), one of the key first-line antimicrobial agents for the treatment of tuberculosis (4), plays an important role in the chemotherapy of drug-resistant TB, including MDR-TB (5). EMB inhibits arabinosyl transferases, encoded by the embCAB operon, thereby inhibiting biosynthesis of the cell well components arabinogalactan and lipoarabinomannan (6). Previous studies showed that mutations in the embB gene are mainly observed in clinical EMB-resistant isolates (7,8). Of the various mutations of embB, mutations at codon 306 are the most commonly detected point mutations conferring EMB resistance, which have been suggested as important molecular indicators for rapid detection of EMB-resistant Mycobacterium tuberculosis isolates (9). In contrast, mutations in emb306 had also been observed among EMB-susceptible M. tuberculosis isolates (9). Previous studies have shown that a lack of consistency in conventional DST results for EMB is an inevitable problem in the tuberculosis laboratories (3, 10). It is therefore meaningful to investigate the concordance between phenotypic and genotypic EMB resistance testing. In this study, we screened for embB mutations among MDR strains isolated in China in order to assess and compare the correlation of phenotypic EMB susceptibilities determined by two DST methods with embB gene mutations among MDR strains.A total of 158 MDR isolates were collected from a national drug resistance survey of China. Drug susceptibility testing for EMB was performed by both the conventional proportion method recommended by World Health Organization and the broth dilution method according to previous reports (11,12). For the proportion method, the concentration of EMB in Lowenstein-Jensen (LJ) medium was 2 g/ml. For the broth dilution method, EMB concentrations were doubling dilutions from 0.125 to 32 g/ml, and the breakpoint MIC for EMB was taken as 5 ...

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“…Although the association between embB306 mutation and EMB resistance has been identified, the exact role of embB306 mutations in the development of ethambutol resistance and multidrug resistance in M. tuberculosis is not fully understood. Since the majority of EMB resistance occurs in MDR strains of M. tuberculosis, it is likely that embB306 substitutions were not directly associated with ethambutol resistance but rather with MDR-TB, and it is concluded that embB306 mutations can serve as a marker for development of drug resistance [20,21].…”

Section: Discussionmentioning

confidence: 99%

Frequency of mutational changes in the embB among the ethambutol-resistant strains of Mycobacterium tuberculosis in Iran

Rezaei

Haeili

Mohajeri

et al. 2016

J Infect Dev Ctries

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Introduction: Early detection of drug resistant tuberculosis is one of the main priorities of TB control program. Ethambutol (EMB) is a firstline anti-TB drug that is effective for preventing treatment failures caused by Mycobacterium tuberculosis strains that are resistant to other drugs. The aim of this study was to sequence the embB gene to characterize the mutations causing resistance to EMB and to analyze the relationship between bacterial genotype and EMB resistance among M. tuberculosis isolates in Iran. Methodology: A total of 20 M. tuberculosis isolates comprising 10 multidrug-resistant (MDR) and 10 non-MDR isolates, recovered from TB patients in four regions: Tehran, Isfahan, Zahedan, Khorasan, were analyzed. Mutational profiling was performed by amplifying and sequencing the embB gene. Spoligotyping was carried out to characterize the bacterial genotype. Results: Phenotypic EMB resistance was found in 13 strains. Mutations affecting ethambutol resistance-determining region (ERDR) of the embB were identified in 6 of 13 EMB-resistant isolates. The majority of these mutations resulted in amino acid substitution at position 306 (M306V). A novel mutation at codon 366 was identified (S366L) in one isolate. Ural was the most predominant genotype in the studied population. Beijing genotype was associated with both MDR and EMB resistance in which all mutations occurred at codon 306 of the embB gene. Conclusion: A significant association between Beijing genotype and EMB resistance was found, mainly due to mutations at embB306. Results of this study can be used as a basis to develop or improve rapid molecular tests to monitor drug-resistant strains in this country.

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Tuberculosis ethambutol resistance: Concordance between phenotypic and genotypic test results

Cited by 32 publications

References 20 publications

GenoType MTBDRslperformance on clinical samples with diverse genetic background

GenoType MTBDRslperformance on clinical samples with diverse genetic background

Ethambutol Resistance as Determined by Broth Dilution Method Correlates Better than Sequencing Results with embB Mutations in Multidrug-Resistant Mycobacterium tuberculosis Isolates

Frequency of mutational changes in the embB among the ethambutol-resistant strains of Mycobacterium tuberculosis in Iran

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