Identification and evaluation of a new nucleic acid amplification test target for specific detection of Mycobacterium tuberculosis

Accuracy of TB-PCR using endobronchial ultrasound guided trans-bronchial needle aspiration (EBUS-TBNA) samples in mediastinal granulomatous lymphadenopathy

INTRODUCTION

Mediastinal granulomatous lymphadenopathies, such as tuberculous lymphadenitis, sarcoidosis, are frequently encountered by respiratory physicians, and their diagnosis is based on histological and microbiological tests. Endobronchial ultrasound-guided Trans bronchial needle aspiration (EBUS-TBNA) is widely used to perform mediastinal lymph node sampling. However, very limited data is available on the yield of polymerase chain reaction for Mycobacterium tuberculosis (TB-PCR) using EBUS-TBNA samples in patients with mediastinal granulomatous lymphadenopathy.

MATERIALS AND METHODS

A retrospective study using a prospectively collected database was performed from January 1, 2018 to December 31, 2018, to evaluate the efficacy of the TB-PCR test using EBUS-TBNA samples in patients with benign mediastinal lymphadenopathy which included both granulomatous lymphadenopathy and reactive lymphadenopathy. The cohort with reactive lymphadenopathy acted as the control group of the study population. The patients with mediastinal lymphadenopathy who were awaiting EBUS-TBNA either for diagnostic evaluation of primary disease or for staging of a known malignancy were included in the study. The patients were then followed up for 1 year post procedure with clinical and radiological evaluation.

RESULTS

Of the 310 patients with mediastinal lymphadenopathy who underwent EBUS-TBNA, 190 cases had a benign pathology with granulomatous lymphadenopathy in 120 and reactive lymphadenopathy in 70 patients. The sensitivity, specificity, the positive predictive value and the negative predictive value of TB-PCR was at 90%, 97.14%, 98.18%, and 85% respectively. The accuracy of TB-PCR is 92.63%.

CONCLUSION

TB-PCR using EBUS-TBNA samples is an effective tool for diagnosing mediastinal granulomatous lymphadenopathy. This technique can prevent further invasive interventions like mediastinoscopy in patients whose histological and microbiological tests are non-diagnostic. It should always be performed when tuberculosis is in the differential diagnosis of a patient with mediastinal lymphadenopathy.

Innovations in Molecular Identification of Mycobacterium tuberculosis

Tuberculosis (TB) continues to be a significant public health concern on a global scale. Quick and precise identification of Mycobacterium tuberculosis (MTB) in symptomatic patients is pivotal for worldwide TB eradication initiatives. As an infectious disorder induced by MTB, it remains a critical threat to public health, particularly in poor countries, due to an inadequate diagnostic research laboratory. There is a need for a persistent incentive to reduce response time for effective diagnosis and control of TB infection, which is a benefit that molecular techniques provide over traditional methods. Although there is a tremendous overall prevalence of TB and a relatively poor probability of case identification worldwide. Common screening techniques have focused on tests that have many fundamental shortcomings. Due to the development of antibiotic-resistant Mycobacterium strains, TB is one of the leading contributors to fatalities. It is now possible to examine TB using molecular detection techniques, which are faster and more cost-effective than previous methods, such as standard culture procedures to test and verify antibiotic resistance in patients with TB. Whole genome sequencing (WGS), faster nucleic acid amplification tests, has made it easier to diagnose and treat TB more quickly. This article addresses the genetic approaches for detecting Mycobacterium tuberculosis complex (MTBC) in clinical specimens as well as antibiotic resistance in mycobacterium and discusses the practical limitations of using these methods.

Molecular Diagnosis of Tuberculosis

Tuberculosis (TB) is one of the leading causes of adult death in the Asia-Pacific Region, including Indonesia. As an infectious disease caused by Mycobacterium tuberculosis (MTB), TB remains a major public health issue especially in developing nations due to the lack of adequate diagnostic testing facilities. Diagnosis of TB has entered an era of molecular detection that provides faster and more cost-effective methods to diagnose and confirm drug resistance in TB cases, meanwhile, diagnosis by conventional culture systems requires several weeks. New advances in the molecular detection of TB, including the faster and simpler nucleic acid amplification test (NAAT) and whole-genome sequencing (WGS), have resulted in a shorter time for diagnosis and, therefore, faster TB treatments. In this review, we explored the current findings on molecular diagnosis of TB and drug-resistant TB to see how this advancement could be integrated into public health systems in order to control TB.

The conservation and application of three hypothetical protein coding gene for direct detection of Mycobacterium tuberculosis in sputum specimens

Background

Accurate and early diagnosis of tuberculosis (TB) is of major importance in the control of TB. One of the most important technical advances in diagnosis of tuberculosis is the development of nucleic acid amplification (NAA) tests. However, the choice of the target sequence remains controversial in NAA tests. Recently, interesting alternatives have been found in hypothetical protein coding sequences from mycobacterial genome.

Methodology/Principal Findings

To obtain rational biomarker for TB diagnosis, the conservation of three hypothetical genes was firstly evaluated in 714 mycobacterial strains. The results showed that SCAR1 (Sequenced Characterized Amplified Region) based on Rv0264c coding gene showed the highest conservation (99.8%) and SCAR2 based on Rv1508c gene showed the secondary high conservation (99.7%) in M. tuberculosis (MTB) strains. SCAR3 based on Rv2135c gene (3.2%) and IS6110 (8%) showed relatively high deletion rate in MTB strains. Secondly, three SCAR markers were evaluated in 307 clinical sputum from patients in whom TB was suspected or patients with diseases other than TB. The amplification of IS6110 and 16SrRNA sequences together with both clinical and bacteriological identification was as a protocol to evaluate the efficacy of SCAR markers. The sensitivities and specificities, positive predictive value (PPV) and negative predictive value (NPV) of all NAA tests were higher than those of bacteriological detection. In four NAA tests, IS6110 and SCAR3 showed the highest PPV (100%) and low NPV (70% and 68.8%, respectively), and SCAR1 and SCAR2 showed the relatively high PPV and NPV (97% and 82.6%, 95.6% and 88.8%, respectively).

Conclusions/Significance

Our result indicated that SCAR1 and SCAR2 with a high degree of sequence conservation represent efficient and promising alternatives as NAA test targets in identification of MTB. Moreover, the targets developed from this study may provide more alternative targets for the development of a multisite system to effectively detect MTB in samples.

Brain tuberculoma (Mycobacterium africanum): high index of suspicion helps in avoiding biopsy/surgery

Partial seizures can be due to a growing cerebral lesion, which may be tumoral or inflammatory/infectious in nature. The differential diagnosis is obviously important; increasing immigration to Europe from Africa is leading to an increase of infectious disease involving also the central nervous system. The authors report imaging the a case of a brain tuberculoma due to Mycobacterium africanum mimicking brain tumor, in which diagnosis was possible by inoculum in guinea-pig of material obtained by mediastinal biopsy of enlarged lymph nodes. Specific treatment led to marked reduction in the size of the brain lesion.