Chan, KS

Ho, PL

Leung, CC

Mok, TYW

Tam, CM

Yam, WC

Yew, WW

Hong Kong Medical Journal

HKU Scholars Hub

Title Molecular tests for rapid detection of rifampicin and isoniazidresistance in Mycobacterium tuberculosis.Author(s) Ho, PL; Yam, WC; Leung, CC; Yew, WW; Mok, TYW; Chan, KS;Tam, CMCitation Hong Kong Medical Journal, 2015, v. 21 n. 3, Suppl. 4, p. 4-7Issued Date 2015URL http://hdl.handle.net/10722/220172Rights Hong Kong Medical Journal. Copyright © Hong Kong Academyof Medicine Press.4 Hong Kong Med J  ⎥  Volume 21 Number 3 (Supplement 4)  ⎥  June 2015  ⎥  www.hkmj.org Hong Kong Med J  ⎥  Volume 21 Number 3 (Supplement 4)  ⎥  June 2015  ⎥  www.hkmj.orgK e y  M e s s a g e s 1. In patients suspected to have tuberculosis, a valid molecular test result was obtained in 94.3% and 88.3% of patients for the rpoB and katG loci, respectively, for prediction of drug susceptibility.2. Molecular testing based on katG and rpoB enabled rapid detection of Mycobacterium tuberculosis resistance in 46.8% and 87.5% of patients infected with isoniazid- and rifampicin-resistant strains, respectively. The same number of patients infected with resistant strains with mutations in katG and rpoB were detected using the MTBDRplus line probe assay. The combined use of katG and inhA regulatory region in the MTBDRplus line probe assay increased the proportion of patients identified with INH-resistant MTB strains to 72.3%.Molecular tests for rapid detection of rifampicin and isoniazid resistance in Mycobacterium tuberculosisIntroductionMultidrug-resistant tuberculosis (MDR-TB) often entails prolonged treatment and the use of more toxic drugs. It is also associated with higher rates of treatment failure and death. The World Health Organization category I regimens for the management of MDR-TB are inadequate. In British Medical Research Council studies, only three of the 11 patients with MDR-TB were cured when prescribed standard treatment. Early recognition of resistance and administration of two or more drugs have improved patient outcome. It is important to reduce the turn-around time for reporting anti-tuberculosis drug susceptibility. Cultures are the gold standard for susceptibility testing, but they are limited by the pre-requisite for a pure growth from clinical specimens. As the mechanisms for rifampicin (RIF) and isoniazid (INH) resistance in many isolates of Mycobacterium tuberculosis (MTB) are predictable, molecular methods are used for direct detection of RIF and INH resistance. This study evaluated genotypic tests to detect RIF and INH resistance in MTB in clinical specimens. The potential impact of implementing molecular tests to detect RIF and INH resistance in MTB was also assessed.MethodsThis study was conducted from April 2006 to June Hong Kong Med J 2015;21(Suppl 4):S4-7RFCID project number: 04050032PL Ho *, WC Yam, CC Leung, WW Yew, TYW Mok, KS Chan, CM Tam1 PL Ho *, 1 WC Yam, 2 CC Leung, 3 WW Yew, 4 TYW Mok, 5 KS Chan, 2 CM Tam1  Department of Microbiology, University of Hong Kong2 TB and Chest Service, Department of Health 3 TB and Chest Unit, Grantham Hospital 4 Respiratory Medical Department, Kowloon Hospital 5 Haven of Hope Hospital* Principal applicant and corresponding author: plho@hku.hk2009. Patients were prospectively identified from 15 participating centres at the tuberculosis and chest unit of the Department of Health, the Grantham Hospital, the Kowloon Hospital, and the Haven of Hope Hospital. Adult patients suspected to have active tuberculosis and were at risk of infection with INH- and/or RIF-resistant strains were enrolled. Clinical specimens (sputum or other appropriate samples) were tested by polymerase chain reaction (PCR) assays specific for IS6110, rpoB, and katG. The amplicons were sequenced to detect resistance mutations. PCR and sequencing were conducted on a weekly basis. Specimens with resistant strains were also tested by the MTBDRplus and the INNO-LiPA Rif.TB line probe assays. Acid-fast bacillus smear and mycobacterial culture were performed by conventional methods. ResultsPatient demographics and sensitivity of the PCR assaysA total of 820 specimens (>90% respiratory) were obtained from 720 patients. In 596 (82.7%) patients, the culture was positive for MTB. Using the culture and susceptibility testing result as reference, the overall sensitivity of the IS6110, rpoB, and katG PCR assays was 98.9%, 95.9%, and 88.7%, respectively (Table 1). 94.3% (562/596) and 88.3% (526/596) of RESEARCH FUND FOR THE CONTROL OF INFECTIOUS DISEASES3. The rapid tests improved patient management by enabling earlier admission, more timely use of World Health Organization category IV anti-tuberculosis regimens and discontinuation of ineffective drugs.Hong Kong Med J  ⎥  Volume 21 Number 3 (Supplement 4)  ⎥  June 2015  ⎥  www.hkmj.org#  Molecular tests for rapid detection of rifampicin and isoniazid resistance in Mycobacterium tuberculosis  # 5Hong Kong Med J  ⎥  Volume 21 Number 3 (Supplement 4)  ⎥  June 2015  ⎥  www.hkmj.orgpatients had valid molecular test results for the rpoB and katG loci, respectively. Susceptibility testing revealed that 50 patients were infected with strains resistant to INH and/or RIF, including MDR-TB (INH-R/RIF-R) [n=13], INH-R/RIF-S (n=34), and INH-S/RIF-R (n=3). The remaining 542 MTB isolates were susceptible to both INH and RIF. Correlation between susceptibility testing and rpoB mutationsAmong 562 valid molecular rpoB test results, the concordance rate with susceptibility testing was 99.5% (559/562). Mutations were found in codons 531, 533, 526, and 516 within the rpoB hotspot region. The discordant results involved three patients with RIF-susceptible isolates and one of two mutations (L533P and H526N). All rpoB mutations, including the three discordant results, were confirmed by testing the purified isolates. Fourteen (87.5%) of 16 patients infected with RIF-resistant strains were detected by the PCR-sequencing method. The detection rate for rpoB mutation was the same using the GenoType MTBDRplus test. Among 527 valid molecular katG test results, the concordance rate with susceptibility testing was 97.2% (512/527). Our katG PCR assay could rapidly detect resistance in only 22 (46.8%) of the 47 patients infected with INH-resistant strains. The same number (ie 22) of katG mutations was detected using the GenoType MTBDRplus test, which also detected an additional 12 patients with mutations in the promoter region of inhA. Therefore, INH resistance was correctly predicted by the GenoType MTBDRplus test in 34 (72.3%) of the 47 patients.Impact on patient managementOverall, 50 patients had a positive culture for MTB isolates resistant to INH and/or RIF. Susceptibility testing revealed that 34 isolates were resistant to INH alone, three to RIF alone, and 13 to both INH and RIF (ie MDR-TB). 92% and 80% of the 50 patients had a valid result for rpoB and katG mutations, respectively. The genotypic results according to PCR-sequencing correctly predicted rpoB resistance mutations in 15 specimens and katG resistance mutations in 22 specimens. These mutations involved 32 patients and the correlation with the susceptibility result is summarised in Table 2. The mean±standard deviation (SD) turnaround time was 10.2±5 days for rpoB and 9.5±4.8 days for katG. This was significantly shorter than the interval between first sputum specimen and susceptibility test reporting (15.4±5.4 weeks). This enables earlier * In 13 patients, the culture was positive for non-tuberculous mycobacteriaTABLE 1.  Comparative sensitivity of three polymerase chain reaction (PCR) assays for detection of Mycobacterium tuberculosis (MTB)Parameter No. (%) of patientsPositive results rpoB mutation katG Thr315IS6110 PCR rpoB PCR katG PCR Present Absent Indeterminate Present Absent IndeterminateMTB culture-positive (n=596) 590 (98.9) 572 (95.9) 529 (88.8) 17 545 10 21 505 3Smear-positive (n=538) 538 (100) 532 (98.8) 503 (93.5) 16 512 4 19 482 2Smear-negative (n=58) 52 (89.6) 40 (68.9) 26 (44.8) 1 33 6 2 23 1MTB culture-negative (n=124)* 66 54 41 0 53 1 0 41 0Total 656 (91.1) 626 (86.9) 570 (79.2) 17 598 11 21 546 3TABLE 2.  Correlation between polymerase chain reaction–sequencing for rpoB and katG mutations and susceptibility testing in 32 patients infected with Mycobacterium tuberculosis resistant to isoniazid and/or rifampicinGenotypic result obtained by testing of respiratory specimensNo. of phenotypic result obtained by susceptibility testingrpoB katG Isoniazid-resistant (n=17) Rifampicin-resistant (n=3) Multidrug-resistant (n=12)Mutated Mutated - - 4Mutated Wild type - 3 4Indeterminate Mutated - - 1Mutated Indeterminate - - 3Wild type Mutated 17 - -  #  Ho et al #6 Hong Kong Med J  ⎥  Volume 21 Number 3 (Supplement 4)  ⎥  June 2015  ⎥  www.hkmj.org Hong Kong Med J  ⎥  Volume 21 Number 3 (Supplement 4)  ⎥  June 2015  ⎥  www.hkmj.orgpatient isolation, admission for treatment, and discontinuation of inactive drugs (Table 3).DiscussionIn Hong Kong, diagnostic PCR is useful to detect MTB in clinical specimens.1 This study extended this by inclusion of two PCR assays specific for rpoB and katG genes to determine whether there were mutations associated with resistance to RIF and INH. Using culture and drug susceptibility results as reference, 94.3% and 88.3% of patients had valid molecular test results for the rpoB and katG loci, respectively. The result for both rpoB and katG was highly concordant with the conventional susceptibility result.2 As RIF and INH resistance could occur as a result of mutations in multiple gene loci, the specificity of molecular assays (as compared with susceptibility testing) would not be 100%. For RIF, a high degree of concordance between mutations in the rpoB hotspot region (codon 507-533) and phenotypic resistance was found. A rapid diagnosis was made for 87.5% of patients infected with RIF-resistant strains, as more than 96% of RIF-resistant strains have mutations in this region.3 In another three patients infected with phenotypic RIF-susceptible strains, the rapid test identified rpoB mutations (L533P or H526N), which were uncommon. The molecular assay results were reliable because identical mutations were confirmed by testing the isolates. These infrequent rpoB mutations may cause weak resistance to RIF and have the potential to cause highly discordant RIF susceptibility results, even when tested under proficiency evaluation settings by the Supra-National Tuberculosis Reference Laboratories.4 The MTBDRplus insert also indicated that the L533P mutation may be RIF-susceptible in susceptibility testing. Nonetheless, both L522P and H526N have been reported to cause high-level RIF resistance and to occur in MDR-TB strains.5 Further studies to assess the clinical significance of these low-level resistant isolates are necessary. Unlike RIF resistance, the katG PCR assay could provide rapid diagnosis in only 22 (46.8%) of the 47 patients infected with INH-resistant strains. The same number of katG mutations was detected by the MTBDRplus assay. The inhA promoter region was included in the MTBDRplus assay as an additional target. This enabled detection of an additional 12 patients with INH-resistant infection. Thus, the MTBDRplus assay could rapidly detect INH resistance in 34 (72.3%) of the 47 patients. 38 of the 47 INH-resistant isolates were found to have mutations in the katG gene and/or the inhA regulatory region. Thus, even if the PCR assay was 100% sensitive in detecting mutations in katG and the promoter of inhA in clinical specimens, direct testing would at best identify 80.9% (38/47) of INH-resistant infections. To improve the sensitivity further, it is necessary to include other gene target in molecular assays. A tuberculosis drug resistance TABLE 3.  Potential impact of molecular testing for Mycobacterium tuberculosis resistance mutations on patient management for seven representative casesCase No.Sex/age (years)History of tuber-culosisRisk factors for resistant tuberculosisGenotypic test on sputum Anti-tuberculosis treatmentRemarksIS6110 rpoB katG gyrA At testing After testing26 M/30 Yes Multiple treatment in ChinaPositive S531L S315T Mutated None Category IV Multidrug-resistant tuberculosis (MDR-TB); individualised category IV treatment started 1 week after patient presentation11 M/66 No Persistent smear positivity Positive WT S315T - Category I Stop isoniazidTest result contributed to individualised regimen decision14 F/48 Yes Previous treatment in ChinaPositive D516A S315N - Category II Category IV MDR-TB; test result contributed to individualised regimen decision28 F/50 No - Positive S531L WT - Category I Category IV Polydrug resistant tuberculosis; test result contributed to individualised regimen decision29 M/30 No Extensive disease Positive S531L Indeterminate - Category I Category IV MDR-TB; patient admitted for individualised treatment because of test result45 F/37 Yes Failed category I regimenPositive S531L WT Mutated Category IVCategory IV Extensively drug-resistant tuberculosis; test result contributed to individualised regimen decision50 M/70 Yes Failed category I regimenPositive D516V Indeterminate - Category I Category IV MDR-TB; culture and sensitivity testing was delayed because of mixed growth of M tuberculosis and M gordonae; test result contributed to individualised regimen decisionHong Kong Med J  ⎥  Volume 21 Number 3 (Supplement 4)  ⎥  June 2015  ⎥  www.hkmj.org#  Molecular tests for rapid detection of rifampicin and isoniazid resistance in Mycobacterium tuberculosis  # 7Hong Kong Med J  ⎥  Volume 21 Number 3 (Supplement 4)  ⎥  June 2015  ⎥  www.hkmj.orgdatabase has been established.5 The INH-resistant strains with wild type katG and promoter region in inhA may have mutations in the katG outside the fragment that was sequenced, within the inhA, intergenic region of oxyR-ahpC or other genes. ConclusionsThe molecular test result is valid in most patients with suspected and confirmed tuberculosis. The test result for rpoB and katG is reliable and highly concordant with results using culture isolates. Molecular testing enables better management of patients infected with drug-resistant tuberculosis.AcknowledgementsThis study was supported by the Research Fund for the Control of Infectious Diseases, Food and Health Bureau, Hong Kong SAR Government (#04050032). We thank the doctors, nurses, and clerical and laboratory staff at the participating centres for assistance with patient recruitment and data collection. We are grateful to Frankie Chow for excellent technical support, France Wong and Goretti Tse for dedicated secretarial assistance.References1. Cheng VC, Yam WC, Hung IF, et al. Clinical evaluation of the polymerase chain reaction for the rapid diagnosis of tuberculosis. J Clin Pathol 2004;57:281-5.2. Lau RW, Ho PL, Kao RY, et al. Rapid diagnosis of multidrug-resistant smear-positive pulmonary tuberculosis. Int J Antimicrob Agents 2010;35:202-3.3. Yam WC, Tam CM, Leung CC, et al. Direct detection of rifampin-resistant mycobacterium tuberculosis in respiratory specimens by PCR-DNA sequencing. J Clin Microbiol 2004;42:4438-43.4. Van Deun A, Barrera L, Bastian I, et al. Mycobacterium tuberculosis strains with highly discordant rifampin susceptibility test results. J Clin Microbiol 2009;47:3501-6.5. Sandgren A, Strong M, Muthukrishnan P, Weiner BK, Church GM, Murray MB. Tuberculosis drug resistance mutation database. PLoS Med 2009;6:e2.

Molecular tests for rapid detection of rifampicin and isoniazid resistance in Mycobacterium tuberculosis.

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Molecular tests for rapid detection of rifampicin and isoniazid resistance in Mycobacterium tuberculosis.

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