Current issues on molecular and immunological diagnosis of tuberculosis

Comparison of Diagnostic Yield of Tuberculosis Loop-Mediated Isothermal Amplification Assay With Cartridge-Based Nucleic Acid Amplification Test, Acid-Fast Bacilli Microscopy, and Mycobacteria Growth Indicator Tube Culture in Children With Pulmonary Tuberculosis

BACKGROUND

Cartridge-based nucleic acid amplification test (CB-NAAT) has been recommended for diagnosis of tuberculosis (TB) in children, but its wide use is limited by high cost and the need for well-equipped laboratories. This study was conducted in children with pulmonary TB to compare the diagnostic yield of TB-LAMP (loop-mediated isothermal amplification test) with CB-NAAT and other conventional methods.

METHODS

Patients ≤ 14 years of age diagnosed with probable pulmonary TB were included in the study. Induced sputum/gastric aspirate was obtained and subjected to acid-fast bacilli (AFB) microscopy, mycobacteria growth indicator tube (MGIT) culture, CB-NAAT, and TB-LAMP. The TB-LAMP assay was performed using 2 different primers, IS6110 and mpb64, for detection of Mycobacterium tuberculosis (MTB). TB-LAMP assays were compared to other assays using appropriate statistical tests.

RESULTS

One hundred fourteen subjects were recruited in the study. AFB microscopy, MGIT culture, CB-NAAT, TB-LAMP IS6110, and TB-LAMP mpb64 showed positivity of 32 (28.1%), 59 (51.7%), 66 (57.9%), 75 (65.8%), and 81 (71%), respectively. TB-LAMP IS6110 showed significantly higher MTB detection in comparison to AFB microscopy and MGIT culture (P = .0001 and P = .03, respectively), and showed no significant difference in MTB detection in comparison with CB-NAAT (P = .219). TB-LAMP mpb64 showed significantly higher MTB detection as compared to AFB microscopy, MGIT culture, and CB-NAAT (P = .0001, P = .003, and P = .037, respectively). TB-LAMP mpb64 and IS6110 showed sensitivity of 94.9% (95% confidence interval [CI], 85.9%-98.9%) and 89.8% (95% CI, 79.7%-96.2%), respectively, in reference to MGIT culture. The degree of agreement between TB-LAMP (mpb64 and IS6110) with CB-NAAT showed κ values of 0.718 and 0.834, respectively.

CONCLUSIONS

TB-LAMP assay can be a useful alternative test in diagnosis of pulmonary TB in children.

Production of MPT-64 recombinant protein from virulent strain of Mycobacterium bovis

Tuberculosis (TB) is a zoonotic infectious disease common to humans and animals which has been caused by a rod shaped, acid fast bacterium, called Mycobacterium bovis. The rapid and sensitive detection is a great challenge for TB diagnosis. The virulent strains of Mycobacterium tuberculosis complex (MTBC) have 16 different regions of difference (RD) in their genome which encode some important antigens. The major protein of M. bovis 64 (MPT-64) is one of the main immune-stimulating antigens which are encode by RD-2 region. The aim of the present study was cloning, expression and purification of MPT-64 as a protein antigen of M. bovis in a prokaryotic system for the usage in the future diagnostic studies. In this experimental study, the mpt-64 gene with 687 bp has been proliferated from M. bovis whole genome by polymerase chain reaction (PCR) method. The PCR product has been digested by BamHI and HindIII restriction enzymes and cloned into pQE-30 plasmid. The recombinant protein has been expressed in the Escherichia coli M15 with induction by isopropyl-β-D-thiogalactopyranoside (IPTG). The expressed protein was analyzed on SDS-PAGE, and purified with Nitrilotriacetic acid (Ni-NTA) column. Finally, its biological properties were confirmed in Western blotting method using specific antibodies. Data showed the successful cloning of mpt-64 gene (as a 687 bp segment) in expression vector. The MPT-64 recombinant protein was ideally expressed and purified as a 24 kDa protein. The result of this study indicated that MPT-64 recombinant protein (24 kDa) has been successfully expressed and purified in a prokaryotic system, so this protein could be used for differential diagnosis of pathogenic and non-pathogenic Mycobacterium, in suspected BTB cases.

Accuracy of the QuantiFERON-TB Gold in Tube for diagnosing tuberculosis in a young pediatric population previously vaccinated with Bacille Calmette-Guérin

Objective:

To evaluate the accuracy of an interferongamma release assay (QuantiFERON-TB Gold in Tube) for diagnosing Mycobacterium tuberculosis infection in a young pediatric population.

Methods:

195 children previously vaccinated with BCG were evaluated, being 184 healthy individuals with no clinical or epidemiological evidence of mycobacterial infection, and 11 with Mycobacterium tuberculosis infection, according to clinical, radiological, and laboratory parameters. A blood sample was obtained from each child and processed according to the manufacturer's instructions. The assay performance was evaluated by a Receiver Operating Characteristic (ROC) curve.

Results:

In the group of 184 non-infected children, 130 (70.6%) were under the age of four years (mean age of 35 months). In this group, 177 children (96.2%) had negative test results, six (3.2%) had indeterminate results, and one (0.5%) had a positive result. In the group of 11 infected children, the mean age was 58.5 months, and two of them (18%) had negative results. The ROC curve had an area under the curve of 0.88 (95%CI 0.82-0.92; p<0.001), disclosing a predictive positive value of 81.8% for the test (95%CI 46.3-97.4). The assay sensitivity was 81.8% (95%CI 48.2-97.2) and the specificity was 98.8% (95%CI 96-99.8).

Conclusions:

In the present study, the QuantiFERON-TB Gold in Tube performance for diagnosing M. tuberculosis infection was appropriate in a young pediatric population.

Evaluation of the GenoType MTBDR assay for detection of rifampicin and isoniazid resistance in Mycobacterium tuberculosis complex isolates

Detection of drug resistance plays a critical role in tuberculosis treatment. The aim of this study was to evaluate the performance of GenoType Mycobacteria Drug Resistance (MTBDR) assay (Hain Lifescience, Germany) and to compare it with radiometric BACTEC 460 TB system (Becton Dickinson, USA) for the detection of rifampicin (RIF) and isoniazid (INH) resistance in 84 Mycobacterium tuberculosis complex (MTBC) isolates. RIF resistance was identified in 6 of 7 (85.7%) isolates and INH resistance was identified in 8 of 14 (57.1%) isolates by the GenoType MTBDR assay. Compared with BACTEC system, the sensitivity, specificity, positive predictive value and negative predictive values were 85.7%, 98.7%, 85.7% and 98.7% for RIF resistance; and 57.1%, 100%, 100% and 92.1% for INH resistance, respectively. GenoType MTBDR assay is reliable when tested specimen is resistant to the tested drugs. Although test was more successful in the detection of RIF resistance, it exhibited low sensitivity for the detection of INH resistance.

Evaluation of real-time loop-mediated isothermal amplification (RealAmp) for rapid detection of Mycobacterium tuberculosis from sputum samples

Tuberculosis (TB) caused by Mycobacterium tuberculosis (MTB) leads to serious health problems as a chronic respiratory infectious disease. Here we established a real-time fluorescence loop-mediated isothermal amplification assay (RealAmp) using a portable ESE Quant tube scanner as a convenient rapid detection method for MTB. The method efficacy from sputum samples was further investigated, and the reaction time was only 20min with the detection limit low to 10(2)CFU/ml concentration of MTB. We assessed a total of 1067 samples by the RealAmp assay, comparing the results with smear microscopy and conventional culture methods. To examine whether the failure to detect TB by culturing is due to low sensitivity or true absence, we examined the culture negative samples by commercial real time PCR MTB detection kit, and the results were compared with RealAmp. The data showed that RealAmp assay had a higher positive rate than that of sputum smear and culture methods. RealAmp had a sensitivity of 96.70% and a specificity of 91.55% when compared with culture. In addition, its sensitivity and specificity were 95.29% and 86.88% respectively compared with examination of smear samples using light microscopy. The sensitivity of RealAmp in comparison to real time PCR was 98.25% and specificity was 99.11% in validation of culture negative samples. The present study revealed the newly established RealAmp assay as a convenient, efficient, sensitive and specific method that could be an alternative for rapid detection of MTB and a tool to validate culture and smear negative samples. Furthermore, the portability of the ESE Quant tube scanner also contributed to the promising application for grassroots and field detection of MTB.

Evaluation of immunological parameters in purified protein derivative positive tuberculin workers

OBJECTIVE(S)

According to the occupationally risk of infection in staff workers who have direct contact with mycobacterium species, we investigated their immunological parameters and compared with healthy purified protein derivative (PPD) negative volunteers. Materials and Methods : We investigated 20 PPD positive volunteers working at Tuberculin Unit of Razi Vaccine and Serum Research Institute and PPD negative healthy controls with no exposure or history of active tuberculosis. The percentages of circulating lymphocyte subpopulations were detected by flowcytometry. IL-4 and IFN-γ production levels were measured by ELISA in supernatants of PPD-stimulated peripheral blood mononuclear cells (PBMCs) culture. Results : Tuberculin workers showed an increase in IFN-γ level and significant decrease of CD4+ T cells percentage and CD4/CD8 ratio compared to PPD negative normal individuals. However the IL-4 production and percentage of other lymphocyte population has been unchanged.

DISCUSSION

These observations suggest that the immunological parameters of tuberculin workers with PPD positive reaction, who are occupationally exposed to mycobacterium antigens, could be changed. Future studies will be directed towards cytokine networking and regulatory lymphocytes, which will help us validate the significant data presented in this study.

Systematic review and meta-analysis of antigen detection tests for the diagnosis of tuberculosis

Tests that detect Mycobacterium tuberculosis antigens in clinical specimens could provide rapid direct evidence of active disease. We performed a systematic review to assess the diagnostic accuracy of antigen detection tests for active tuberculosis (TB) according to standard methods and summarized test performance using bivariate random effects meta-analysis. Overall, study quality was a concern. For pulmonary TB (47 studies, 5,036 participants), sensitivity estimates ranged from 2% to 100% and specificity from 33% to 100%. Lipoarabinomannan (LAM) was the antigen most frequently targeted (23 studies, 49%). The pooled sensitivity of urine LAM was higher in HIV-infected than HIV-uninfected individuals (47%; 95% confidence interval [CI], 26 to 68% versus 14%; 95% CI, 4 to 38%); pooled specificity estimates were similar: 96%; 95% CI, 81 to 100% and 97%; 95% CI, 86 to 100%, respectively. For extrapulmonary TB (21 studies, 1,616 participants), sensitivity estimates ranged from 0% to 100% and specificity estimates from 62% to 100%. Five studies targeting LAM, ESAT-6, Ag85 complex, and the 65-kDa antigen in cerebrospinal fluid, when pooled, yielded the highest sensitivity (87%; 95% CI, 61 to 98%), but low specificity (84%; 95% CI, 60 to 95%). Because of the limited number of studies targeting any specific antigen other than LAM, we could not draw firm conclusions about the overall clinical usefulness of these tests. Further studies are warranted to determine the value of LAM detection for TB meningitis in high-HIV-prevalence settings. Considering that antigen detection tests could be translated into rapid point-of-care tests, research to improve their performance is urgently needed.

QuantiFERON-TB GOLD ELISA assay for the detection of Mycobacterium tuberculosis-specific antigens in blood specimens of HIV-positive patients in a high-burden country

Tuberculosis is a life-threatening infection worldwide. Despite improvements in therapy, it results in 2 million deaths and 9 million new cases annually. This study evaluated the use of the QuantiFERON-TB GOLD enzyme-linked immunosorbent assay in a high HIV/TB burden setting in an ARV clinic at the Tshwane District Hospital, South Africa. The sensitivity and specificity of the QF assay in the clinic were 30% (9/30) and 63% (19/30), respectively, when compared with the gold standard culture results. Analysis also suggested that the sensitivity of the QuantiFERON assay is determined by a limiting patient CD4 value between 150 and 200.

Molecular findings and approaches spotlighting Mycobacterium bovis persistence in cattle

Mycobacterium tuberculosis (Mtb) and Mycobacterium bovis (M. bovis) are the etiological agents of human and bovine tuberculosis (TB, bTB) respectively, and share genetic identity over 99% at the whole genome level. Progress has been made towards explaining how mycobacteria and their infected hosts remain in balance without producing clinical symptoms of disease, a phenomenon referred to as latency or persistence, which can be mimicked by certain in vitro conditions. Latency/persistence has mainly been studied using Mtb, where the two-component signalling system, dosRS, has been assigned an instrumental role, and even constitutes the current basis for development of new diagnostic methods and treatment addressing this particular stage of TB. M. bovis conserves homolog genes that in Mtb play a role in human latent TB infection and that, by analogy, would allow it to enter a persistent state in infected cattle; nevertheless, little attention has been paid to this stage in bovine hosts. We suggest that many of the advances acquired through the study of Mtb can and should be taken into consideration by research groups and veterinary professionals dealing with bTB. The study of the infection in bovines, paying particular attention to defining the molecular and cellular markers of a M. bovis persistent infection in cattle, presents great opportunities for the development and trial of new diagnostic tests and vaccines, tools that will surely help in promoting eradication of bTB in high-burden settings.

Expression and evaluation of Chikungunya virus E1 and E2 envelope proteins for serodiagnosis of Chikungunya virus infection

PURPOSE

Chikungunya virus (CHIKV) causes endemic or epidemic outbreaks of CHIKV fever, which is a mosquitoe- transmitted viral disease in Africa, India, South-East Asia, and recently Southern Europe. Currently, serological diagnostic tests such as hemagglutination inhibition test (HI test), in-house IgM capture enzyme-linked immunosorbent assays (ELISA), and indirect immunofluorescence test were used for diagnosis of chikungunya fever, which are based on whole virus antigens.

MATERIALS AND METHODS

CHIKV E1, and E2 envelope proteins for the CHIKV-specific serodiagnostic reagents for chikungunya fever were expressed in baculovirus expression system. The seroreactivity of recombinant CHIKV E1 and E2 envelope proteins were evaluated using sera panels of patients from Laboratoire Marcel Merieux by indirect IgM capture ELISA.

RESULTS

The recombinant CHIKV E1 and E2 envelope protein showed sensitivity of 77.5% and 90%, respectively. The specificities of both CHIKV E1 and E2 envelope proteins were 100%.

CONCLUSION

The recombinant CHIKV E1 and E2 envelope proteins could be a useful diagnostic reagent for CHIKV infection.

Evaluation of reverse transcription loop-mediated isothermal amplification in conjunction with ELISA-hybridization assay for molecular detection of Mycobacterium tuberculosis

Traditional culture, followed by a panel of biochemical tests for the diagnosis of tuberculosis (TB), is time-consuming, and rapid identification of Mycobacterium tuberculosis is crucial for the early administration of appropriate therapy. In this study, the reverse transcription loop-mediated isothermal amplification combined with enzyme-linked immunosorbent hybridization (RT-LAMP-ELISA-hybridization) assay has been designed for the rapid detection of 16S rRNA in clinical isolates of M. tuberculosis. This assay reproducibly detected a single copy, as opposed to 2000 copies of MTB 16S rRNA detected by conventional gel electrophoresis. Among the 150 specimens of sputum analysed, RT-LAMP-ELISA-hybridization assay had a sensitivity of 94.1% in the culture method, compared to the Amplified M. tuberculosis Direct Test (AMTD), 91.1% and the 88.2% sensitivity of acid-fast staining. Furthermore, RT-LAMP-ELISA-hybridization assay is more cost-effective when compared to the real-time TaqMan RT-PCR and AMTD assays. In conclusion, our results suggest that the RT-LAMP-ELISA-hybridization assay is a highly sensitive, low cost diagnostic tool useful for the rapid and accurate direct diagnosis of sputum specimens, and is suitable for routine clinical use.

Pulmonary tuberculosis in a young pregnant female: challenges in diagnosis and management

Background. With the world becoming a global village, tuberculosis is no longer limited to endemic areas. Our case emphasizes the impact of immigration on infectious disease epidemiology and challenges associated with diagnosis and treatment in pregnancy. Case. A 21-year-old Hispanic female presented in preterm labor and was found to be hypoxic. Chest X-ray revealed a paratracheal mass which a CT scan confirmed. PPD test was positive. Bronchoalveolar lavage did not reveal acid-fast bacilli and biopsy revealed caseating granulomas. Diagnosis and treatment were challenging due to constraints in radiological investigations, lack of initial evidence of acid-fast bacilli, and toxic profile of medications. Due to her high risk, she was started on antituberculosis regimen. The diagnosis was confirmed on Day 26 when Mycobacterium tuberculosis was isolated by DNA probe. Conclusion. A high index of suspicion is required to recognize the changing face and disease spectrum of tuberculosis and initiate treatment for better outcomes.