ABSTRACT
Background: Early diagnosis of drug resistance (DR) to ethambutol (EMB) in tuberculosis (TB) remains a challenge. Simple and reliable method (s) are needed for rapid detection of DR Mycobacterium tuberculosis (MTB) in clinical specimens. Objectives: The aim of this study was to design fluorescence resonance energy transfer hybridisation probe-based real-time polymerase chain reaction (PCR) method for the early detection of EMB-resistant MTB direct from clinical sputa. Materials and Methods: Primers and probes were designed against 306 codon of embB gene which is commonly associated with EMB resistance. A comparative study was done between Lowenstein–Jenson (L–J) proportion and hybridisation probe-based real-time PCR method for susceptibility testing. DNA sequencing was used in nine representative isolates to validate the efficiency of real-time PCR method to detect emb306 mutation of MTB. Results: A total of 52 clinical sputum samples and corresponding culture isolates (from category II pulmonary TB cases) were included in this study. Out of 52 MTB isolates, 32 and 20 were resistant and susceptible to EMB, respectively, as determined by L–J proportion method. Real-time PCR showed 95% specificity, 75% sensitivity and 82.69% accuracy when compared with L–J proportion method. A 100% of concordance was observed by validating the real-time PCR results with DNA sequencing. Conclusions: Our real-time PCR hybridisation probe method promises for rapid detection of EMB-resistant MTB directly from clinical specimens. However, future studies and modifications of method by incorporating other potential loci along with targeted mutation (emb306) are still required to increase the sensitivity of method.
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OBJECTIVE To design molecular beacon detecting embB330 codon of ethambutol-resistant Mycobacterium tuberculosis(MTB),meanwhile,and try to detect fluorescence of mutation site of embB330 codon in liquid by fluorescence microscope by compareing the mutation strains and standard strains.METHODS The software,Beacon designer,was used to design molecular beacon detecting embB330codon and detecting fluorescence signal from hybridization between the amplified product and probe by fluorescence microscope,and to confer to the sequencing results.RESULTS The difference between PCR products from standard strain and ethambutol-resistant one was obvious in detecting the fluorescent light by use of fluorescence microscope.We detected fluorescent light signal between the 33 ethambutol-resistant strains and 10 H37RV standard strains.The rate of ethambutol-resistant strains was about 3%,and the rate of sequencing was about 3%.CONCLUSIONS The technology of molecular beacon effectually can detect mutation single base site of embB330codon.Fluorescence microscope owns characteristics such as high sensitiveness to detect the fluorescent light.
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Background & objectives: Ethambutol (EMB) resistance, thought to be occurring due to mutations in embB gene of Mycobacterium tuberculosis on the rise is a cause of grave concern. The present study was planned to investigate the presence of EMB resistance in M. tuberculosis isolates and to look for prevalent mutations in embB gene. Methods: A total of 591(283 from new and 308 from previously treated cases) sputum samples from the same number of pulmonary tuberculosis cases were cultured. Isolates were tested by 1 per cent proportion method for resistance to isoniazid, rifampicin streptomycin and ethambutol. Minimum inhibitory concentration (MIC) of EMB was measured by absolute concentration method. Ten randomly selected isolates were subjected to single strand conformational polymorphism (SSCP) and direct DNA sequencing to look for mutation in 364 bp segments of embB gene. Results: Of 353 isolates of M. tuberculosis from 591 sputum samples, 62 (17.58%) were resistant to EMB, of which, 16 (25.8%) showed initial resistance and 46 (74.2%) acquired. Mono resistance to EMB was rare. Only two isolates showed resistance to EMB alone. From 62 EMB resistant isolates, 88.7 per cent (55) were resistant to INH, 82.2 per cent (51) to rifampicin and 61.2 per cent (38) were resistant to streptomycin. Co-resistance to isoniazid and rifampicin (multidrug resistant, MDR-TB) with EMB resistance was seen in 41(66.1%) isolates. High level of EMB resistance was seen in 16.5 per cent isolates. SSCP showed altered mobility in 8 of 10 isolates tested. Among the 8 mutants, 4 had known mutations at codon Met 306 being replaced by Val/ Leu. The second most frequent mutation encountered was at codon Phe 287 being replaced by Val, Cys or Leu (novel mutations). Sequence analysis revealed 10 novel mutations in codon 221, 225, 227, 271, 272, 281, 282, 287, 293 and 294 within embB gene. Interpretation & conclusions: Presence of high frequency of EMB resistance, occurrence of high level EMB resistance, co-existence of MDR-TB with EMB resistance and novel mutations in emb B gene of M. tuberculosis clinical isolates reported highlight the need to work on larger samples to identify the diagnostic marker of EMB resistance in mycobacteria.
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BACKGROUND: Ethambutol(EMB) is one of the first-line drugs included in short-course anti-tuberculosis therapy. The point mutations in embB gene have been speculated to be associated EMB resistance. However, detection of embB mutations at these positions have been observed in both EMB-susceptible isolates; thus, it remains controversial whether these mutations are associated with EMB resistance METHODS: The 36 M. tuberculosis isolates were selected from clinical isolates which tested susceptible to EMB and resistant to at least one drug. DNA extracted from the isolates was analyzed by amplifying embB gene. The PCR products were purified and directly sequenced. We reviewed the history of past drug susceptibility test results. RESULTS: Out of 36 EMB-susceptible strains, 3 strains (8.3%) had a mutation in codon 306 or 406 of the embB gene. These three strains had at least isoniazid resistance. They grew at 1.0 mcg/ml of EMB in Lowenstein-Jensen media. The patients of the strains were continuously smear-positive for over 3 years despite taking TB therapy. One strain had been EMB-resistant in past drug susceptibility tests. CONCLUSION: EMB-susceptible strains containing embB mutation may be caused by decreased viability in vitro test not by itself.
Subject(s)
Humans , Codon , DNA , Drug Resistance , Ethambutol , Isoniazid , Korea , Mycobacterium tuberculosis , Mycobacterium , Point Mutation , Polymerase Chain Reaction , TuberculosisABSTRACT
Objective:To design hair clamp probe and the probes with single extending arm detecting embB306codon of Ethambutol resis-tant Mycobacterium tuberculosis bacterium(MTB),meanwhile,to design fair clamp probe chip and detecting fluorescence signal from hy-bridization between the amplified product and probe by fluorescence microscope.Methods:The software,Beacon designer,was used to de-sign fair clamp probe and the probes with single extending arm detecting embB303codon and detecting fluorescence signal from hybridiza-tion between the amplified product and probe,and confer to the sequencing results.Results:The difference between PCR products from standard strain and ethambutol resistant one was obvious in detecting the fluorescent light with fluorescence microscope.We detected fluo-rescent light signal between the 33 ethambutol resistant strains and 10 H37RV standard strains.The rate of resistant ethambutol detected with hair clamp probe was about 66%,and the rate of sequencing was about 69%.Conclusions:The mutation site of embB306codon of MTB is the main reason of ethambutol resistant MTB.The technology of fair clamp DNA probe chip can effectively detect mutation of single base site.Fluorescence microscope can sensitivily detect the site of hybridization on fluorescence chip.