Recent advances in the diagnosis of Mycobacterium tuberculosis

PPE59 antibodies in tuberculous patients and potential use for diagnosis when assayed with other rapid biomarkers

BACKGROUND

PPE 59, which is absent from bacillus Calmette Guérin (BCG) strains, seems to induce a humoral immune response in patients with tuberculosis (TB). Additional studies are needed to better evaluate this protein in immune response to tuberculosis.

OBJECTIVES

To evaluate the response of antibodies to PPE59 in TB individuals, its combination with IgG response to other, previously tested mycobacterial antigens (Ag) and with sputum smear microbiology (SM) results.

METHODS

We have cloned and expressed the rv3429 gene that encodes PPE59, then IgG, IgM, and IgA against PPE59 antigens measured by enzyme-linked immunosorbent assay (ELISA) in 212 sera samples obtained from the following subject cohorts: TB residents from Italy (79) and in Brazil (52); and an all-Brazilian cohort of 55 patients with other respiratory disorders; 10 patients infected with non-tuberculous mycobacteria, and 16 asymptomatic subjects. Drawing on results from a previous study(17) of serum samples from Brazilian subjects tested for IgG by ELISA against mycobacterial antigens ESAT-6, 16kDa, MT10.3, MPT-64 and 38kDa, the results were analysed in combination with those of the PPE59 and SM tests.

FINDINGS

Keeping the specificity rate at 97%, the overall PPE59 IgA sensitivity was 42.7%, while IgG and IgM showed lower performance (p < 0.0001). Combining PPE59 IgA/16kDa IgG results increased sensitivity to 71%, and even higher rates when the results were combined with SM results (86.5%, p = 0.001), at 88.9% specificity. Positive IgA was associated with pulmonary image alterations of high TB probability (p < 0.05).

MAIN CONCLUSIONS

Tests with TB patients found a moderate frequency of positivity for PPE59 IgA. However, the higher level of sensitivity attained in combination with PPE59 IgA/16kDa IgG/SM results unheard of before, although imperfect, suggests that this may be a potential additional tool for rapid detection of TB in low-resource areas.

Molecular detection of Mycobacterium tuberculosis in pulmonary and extrapulmonary samples in a hospital-based study

OBJECTIVE

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb), remains a deadly infectious disease. India contributes to one-third of the global TB burden. However, no studies have been carried out in the Telangana (Hyderabad) population using real-time polymerase chain reaction (RT-PCR). Therefore, the current study evaluated the role of RT-PCR as a rapid and non-invasive test to diagnose TB by testing for pulmonary tuberculosis (PTB) and extrapulmonary tuberculosis (EPTB).

MATERIALS AND METHODS

This hospital-based study examined 1670 samples (900 EPTB; 770 PTB) comprising tissue (n = 537), peritoneal fluid (n = 420), sputum (n = 166), bronchial fluid (n = 126), cerebrospinal fluid (n = 145), ascetic fluid (n = 76), sputum pus (n = 78), urine (n = 79), and bronchoalveolar fluid (n = 43) samples. DNA from samples was separated using specific isolation kits and subjected to RT-PCR.

RESULTS

In this study, we enrolled 1670 subjects and categorized 54.4% as females and 45.6% as males. The collected samples were categorized as 48.5% of fluid samples, followed by tissue (32.2%), sputum (9.9%), urine (4.7%), and pus-swab (4.6%). RT-PCR analysis revealed that 4.7% patients were positive for Mtb. Our results revealed that 61% of the affected patients were male and 39% were female. Among the specimen types, tissue samples gave the highest proportion of positive results (36.3%).

CONCLUSION

The results showed that RT-PCR should be implemented and given top priority in TB diagnosis to save time and facilitate a definitive diagnosis. Tissue samples are highly recommended to screen the Mtb through the technique RTPCR. Future studies should extend the technique to the global population and exome sequencing analysis should be performed to identify TB risk markers.

The Diagnostic Value of Urine Lipoarabinomannan (LAM) Antigen in Childhood Tuberculosis

INTRODUCTION

Diagnosis of Tuberculosis (TB) in children is difficult because the clinical presentation is not specific, the chest X-ray interpretation has low accuracy and sputum sample is difficult to obtain. Antigen detection test such as rapid urine LAM is a non-invasive alternative for diagnosing TB . Lipoarabinomannan (LAM) is the main component of M.tuberculosis cell wall.

AIM

To determine the diagnostic value of urinary LAM antigen for diagnosis of childhood TB.

MATERIALS AND METHODS

In the present cross-sectional study, subjects were included using consecutive sampling method. All the children aged 0-14 years Suspected of pulmonary or extra pulmonary TB suffering from cough more than two weeks, fever without clear aetiology, loss of body weight or poor weight gain, fatigue, malaise, chronic lymph node enlargement, spine angulation, joint swelling and had history of contact with positive sputum smear adult TB patient were enrolled in the study. Pulmonary and extra pulmonary diagnosis was based on clinical presentation, Tuberculin Skin Test (TST), chest X-ray, Acid Fast Bacillus (AFB) staining and or sputum culture. Urinary LAM level was measured by using Enzyme-Linked Immunosorbent Assay (ELISA). Cut off value and Area Under the Curve (AUC) were determined using ROC statistical analysis (SPSS 21.0). Sensitivity and specificity was measured from 2x2 cross table.

RESULTS

Out of 61 subjects suspected as TB, 49 (80.3%) were eventually diagnosed with TB. Of those diagnosed with TB, 21 (42.9%) were microbiologically confirmed cases either by sputum microscopy (34.7%) or culture (8.2%), whereas 28 subjects were unconfirmed cases (57.1%). The urinary LAM level was higher in subjects with TB (1.80+1.02) mg/l compared to non-TB group (0.46+0.3) mg/l; p<0.001(independent t-test). Urine LAM had 83% sensitivity and 85% specificity with cut off value 0.98 mg/l using microbiological and clinical confirmation as standard reference and 33% sensitivity and 60% specificity with cut off value 1.69 mg/l using microbiological confirmation only.

CONCLUSION

Urinary LAM has good diagnostic value for childhood TB diagnosis.

Cytokine and Antibody Based Diagnostic Algorithms for Sputum Culture-Positive Pulmonary Tuberculosis

Background

Tuberculosis (TB) is one of the most serious infectious diseases globally and has high mortality rates. A variety of diagnostic tests are available, yet none are wholly reliable. Serum cytokines, although significantly and frequently induced by different diseases and thus good biomarkers for disease diagnosis and prognosis, are not sufficiently disease-specific. TB-specific antibody detection, on the other hand, has been reported to be highly specific but not sufficiently sensitive. In this study, our aim was to improve the sensitivity and specificity of TB diagnosis by combining detection of TB-related cytokines and TB-specific antibodies in peripheral blood samples.

Methods

TB-related serum cytokines were screened using a human cytokine array. TB-related cytokines and TB-specific antibodies were detected in parallel with microarray technology. The diagnostic performance of the new protocol for active TB was systematically compared with other traditional methods.

Results

Here, we show that cytokines I-309, IL-8 and MIG are capable of distinguishing patients with active TB from healthy controls, patients with latent TB infection, and those with a range of other pulmonary diseases, and that these cytokines, and their presence alongside antibodies for TB-specific antigens Ag14-16kDa, Ag32kDa, Ag38kDa and Ag85B, are specific markers for active TB. The diagnostic protocol for active TB developed here, which combines the detection of three TB-related cytokines and TB-specific antibodies, is highly sensitive (91.03%), specific (90.77%) and accurate (90.87%).

Conclusions

Our results show that combining detection of TB-related cytokines and TB-specific antibodies significantly enhances diagnostic accuracy for active TB, providing greater accuracy than conventional diagnostic methods such as interferon gamma release assays (IGRAs), TB antibody Colloidal Gold Assays and microbiological culture, and suggest that this diagnostic protocol has potential for clinical application.