Validation of an immunochromatographic assay kit for the identification of the Mycobacterium tuberculosis complex

Rapid Identification of Mycobacterium tuberculosis Complex Using Mass Spectrometry: A Proof of Concept

Mycobacteria that form the Mycobacterium tuberculosis complex are responsible for deadly tuberculosis in animals and patients. Identification of these pathogens at the species level is of primary importance for treatment and source tracing and currently relies on DNA analysis, including whole genome sequencing (WGS), which requires a whole day. In this study, we report the unprecedented discrimination of M. tuberculosis complex species using matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF-MS), with WGS as the comparative reference standard. In the first step, optimized peptide extraction applied to 36 isolates otherwise identified in five of the 11 M. tuberculosis complex variants by WGS yielded 139 MALDI-TOF spectra, which were used to identify biomarkers of interest that facilitate differentiation between variants. In a second step, 70/80 (88%) other isolates were correctly classified by an algorithm based on specific peaks. This study is the first to report a MALDI-TOF-MS method for discriminating M. tuberculosis complex mycobacteria that is easily implemented in clinical microbiology laboratories.

Performance assessment of SD Bioline TB MPT64 assay for the diagnosis of Mycobacterium tuberculosis complex in Lagos, Nigeria

This study assessed the performance of SD Bioline MPT64 immunochromatographic test for the identification of Mycobacterium tuberculosis complex (MTBC) in Nigeria.A total of 157 mycobacterial isolates, comprising 120 (76.4%) MTBC (M. tuberculosis, 112; M. africanum, 5; M. bovis, 3) and 37 (23.6%) non-tuberculous mycobacteria (NTM) isolates from patients attending six DOTS centers in Lagos between June 2012 and July 2014 were analyzed. All the isolates were grown on Bactec MGIT960 liquid media and identified in parallel by the conventional method and MPT64 immunochromatographic test. Discrepant results were resolved using the line probe assay.The comorbid disease rates for HIV and type 2 diabetes were 20.9% and 8.2%, respectively. Compared to the conventional method, SD Bioline MPT64 identified 117 MTBC isolates correctly, producing a sensitivity of 97.5% (95% CI, 92.9-99.2) at a shorter growing median time of 11 days compared to 26 days by the conventional method. The three undetected MTBC were confirmed by the line probe assay to be M. tuberculosis strains. The test also identified all the NTM correctly producing a specificity of 100% (95% CI, 90.7-100).This study supports the integration of SD Bioline TB MPT64 antigen test into diagnostic workflow for rapid MTBC case identification in Nigeria.

MPT64 assays for the rapid detection of Mycobacterium tuberculosis

Background

Tuberculosis (TB) is a serious infectious disease caused by Mycobacterium tuberculosis (MTB). An estimated 1.7 billion people worldwide are infected with Mycobacterium tuberculosis (LTBI) during the incubation period without any obvious symptoms. Because of MTB’s high infection and mortality rates, there is an urgent need to develop a fast, portable, and sensitive diagnostic technology for its detection.

Methods

We included research from PubMed, Cochrane Library, Web of Science, and Embase and extracted the data. MetaDisc and STATA were used to build forest plots, Deek’s funnel plot, Fagan plot, and bivariate boxplot for analysis.

Results

Forty-six articles were analyzed, the results of which are as follows: sensitivity and specificity were 0.92 (0.91–0.93) and 0.95 (0.94–0.95) respectively. The NLR and PLR were 0.04 (95% CI 0.03–0.07) and 25.32 (95% CI 12.38–51.78) respectively. DOR was 639.60 (243.04–1683.18). The area under the SROC curve (AUC) was 0.99.

Conclusions

MPT64 exhibits good diagnostic efficiency for MTB. There is no obvious heterogeneity between the three commercial kits.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12879-021-06022-w.

Optimization of culture conditions for Mpt64 synthetic gene expression in Escherichia coli BL21 (DE3) using surface response methodology

MPT64 is a specific protein that is secreted by Mycobacterium tuberculosis complex (MTBC). The objective of this study was to obtain optimum culture conditions for MPT64 synthetic gene expression in Escherichia coli BL21 (DE3) by response surface methodology (RSM). The RSM was undertaken to optimize the culture conditions under different cultivation conditions (medium concentration, induction time and inducer concentration), designed by the factorial Box-Bhenken using Minitab 17 statistical software. From the randomized combination, 15 treatments and three center point repetitions were obtained. Furthermore, expression methods were carried out in the flask scale fermentation in accordance with the predetermined design. Then, the MPT64 protein in the cytoplasm of E. coli cell was isolated and characterized using sodium dodecyl sulfate polyacrilamide electrophoresis (SDS-PAGE) then quantified using the ImageJ program. The optimum conditions were two-fold medium concentration (tryptone 20 mg/mL, yeast extract 10 mg/mL, and sodium chloride 20 mg/mL), 5 h of induction time and 4 mM rhamnose. The average concentration of recombinant MPT64 at optimum conditions was 0.0392 mg/mL, higher than the predicted concentration of 0.0311 mg/mL. In conclusion, the relationship between the selected optimization parameters strongly influenced the level of MPT64 gene expression in E. coli BL21 (DE3).

Bacterial pili, with emphasis on Mycobacterium tuberculosis curli pili: potential biomarkers for point-of care tests and therapeutics

CONTEXT

Novel biomarkers are essential for developing rapid diagnostics and therapeutic interventions Objective: This review aimed to highlight biomarker characterisation and assessment of unique bacterial pili.

METHODS

A PubMed search for bacterial pili, diagnostics, vaccine and therapeutics was performed, with emphasis on the well characterised pili.

RESULTS

In total, 46 papers were identified and reviewed.

CONCLUSION

Extensive analyses of pili enabled by advanced nanotechnology and whole genome sequencing provide evidence that they are strong biomarker candidates. Mycobacterium tuberculosis curli pili are emphasised as important epitopes for the development of much needed point-of-care diagnostics and therapeutics.

Extra pulmonary tuberculosis: rapid identification of Mycobacterium tuberculosis grown in Mycobacterium growth indicator tube 960 and Lowenstein-Jensen media, employing Standard diagnostics Bioline Mycobacterium tuberculosis protein 64 antigen detection kit

BACKGROUND

Investigation of extra pulmonary tuberculosis (EPTB) in and around Pondicherry is being carried out since August 2011 in our tertiary care super specialty hospital.

OBJECTIVES

To compare the rapid Kit SD Bio-Line MPT 64 Ag with conventional and time consuming biochemical tests. Confirmation of Mycobacterium tuberculosis at a reasonable time frame is the main thrust.

MATERIALS AND METHODS

Thirty three Mycobacterium tuberculosis and four Non-Tuberculous Mycobacteria (NTM) grown in MGIT960 system/Lowenstein-Jensen media (LJ) were examined by the rapid MPT 64 antigen detection as well as a battery of conventional tests like niacin, nitrate reduction, paraminobenzoic acid susceptibility and cord formation.

RESULTS AND CONCLUSION

. Both the rapid kit and conventional tests correctly identified 33 M.tuberculosis isolates. Keeping conventional identification as reference, sensitivity and specificity for rapid kit was 100%. Rapid kit which takes only 15 minutes is accurate, cost effective, and facilitates early treatment for these EPTB patients, whose clinical specimens are paucibacillary.

Rapid Immunochromatographic Test for the Identification and Discrimination of Mycobacterium tuberculosis Complex Isolates from Non-tuberculous Mycobacteria

BACKGROUND

A new rapid Immunochromatographic test (ICT) kit (SDBioline TB Ag MPT64RAPID(®)) developed by Standard Diagnostics, South Korea was evaluated for rapid differentiation of M. tuberculosis from non tuberculous mycobacteria (NTM). It detects MPT 64 antigen in M. tuberculosis isolates using mouse monoclonal MPT 64 antibody. The kit was assessed for routine identification of the Acid Fast Bacilli(AFB) isolated in our laboratory.

MATERIALS AND METHODS

Two hundred eight culture isolates of Mycobacteria were tested using ICT test kit for detection of MPT 64 antigen from liquid and solid culture. H37Rv strain was employed as the positive reference control. Any negative result was referred for confirmation by Gen Probe Accu Probe assay for MTB Complex (Gen-Probe, San Diego, Calif.). Speciation of NTM was performed using genotypic Mycobacterium CM assay (Hain's life sciences, Germany).

RESULTS

Of the 208 culture positive isolates tested, 182 (87.5%) were found positive for Mycobacterium tuberculosis Complex and remaining 26 (12.5%) were considered as NTM. These results were further confirmed by Gen Probe Accu probe assay that served as the reference method for detection of MTBC. H37Rv reference strain was taken as a control for ICT test and molecular tests. The reference strain showed the presence of MPT64 antigen band in the ICT test. Similar bands were formed in all MTBC (182) isolates tested, proving 100 per cent sensitivity and no bands were detected in 48 (100%) NTM isolates tested, proving 100 per cent specificity of the ICT kit.

CONCLUSION

Tuberculosis is a global pandemic. Rapid identification of Mycobacteria as MTB complex or non-tuberculous Mycobacteria from culture is important for treatment of infected cases and drug susceptibility testing of the culture isolate. MPT 64 TB antgen detection using SD Bioline Immunochromatographic test is a simple and cost effective method for differentiation of Mycobacterial cultures as MTB complex from non- tuberculous Mycobacteria.

Mycobacterium tuberculosis pili (MTP), a putative biomarker for a tuberculosis diagnostic test

Novel biomarkers are urgently needed for point of care TB diagnostics. In this study, we investigated the potential of the pilin subunit protein encoded by the mtp gene as a diagnostic biomarker. BLAST analysis of the mtp gene on published genome databases, and amplicon sequencing were performed in Mycobacterium tuberculosis Complex (MTBC) strains and other organisms. The protein secondary structure of the amino acid sequences of non-tuberculous Mycobacteria that partially aligned with the mtp sequence was analysed with PredictProtein software. The mtp gene and corresponding amino acid sequence of MTBC were 100% homologous with H37Rv, in contrast to the partial alignment of the non-tuberculous Mycobacteria. The mtp gene was present in all 91 clinical isolates of MTBC. Except for 2 strains with point mutations, the sequence was 100% conserved among the clinical strains. The mtp gene could not be amplified in all non-tuberculous Mycobacteria and respiratory organisms. The predicted MTP protein structure of Mycobacterium avium, Mycobacterium ulcerans and Mycobacterium abscessus differed significantly from that of the M. tuberculosis, which was similar to Mycobacterium marinum. The absence of the mtp gene in non-tuberculous Mycobacteria and other respiratory bacteria suggests that its encoded product, the pilin subunit protein of M. tuberculosis may be a suitable marker for a point of care TB test.

Utility and diagnostic performance of Mycobacterium tuberculosis complex by two immunochromatographic assays as compared with the molecular Genotype assay in Nigeria

Among the disadvantages of smear microscopy for detection of tuberculosis cases is its inability to differentiate between Mycobacterium tuberculosis (MTB) and non-tuberculous mycobacteria (NTM). This study evaluated two, new immunochromatographic assays - Capilia TB-Neo and SD Bioline - on unheated and heated cultures at 80°C for 30min respectively for their ability to discriminate between MTB complex and NTM as compared with the molecular Genotype assay. Mycobacteria used in the study were obtained from smear-positive specimens collected from patients at four major hospitals in Cross River State, Nigeria. Capilia TB-Neo and SD Bioline showed sensitivities of 98.8% and 93.8% respectively and 100% specificity for both assays. Heating the isolates did not significantly impact the test performance. Both tests are recommended for use in rapid differentiation of strains isolated in Nigeria.

Immunochromatographic assays for detection of Mycobacterium tuberculosis: what is the perfect time to test?

In this study, we aimed to correlate the analytical performance of SD BIOLINE TB Ag MPT64 Rapid Test kit (MPT64 assay) with the mycobacterial growth unit (GU) reported by the BACTEC MGIT 960 (MGIT 960) instrument. A total of 394 culture isolates reported positive by MGIT 960 were processed daily (until 'day 4') with the MPT64 assay until a positive MPT64 result was obtained and their GU values were noted daily before MPT64 testing. Based on this correlation of MPT64 positivity and corresponding GU values, a GU cut-off was determined. In the validation phase, with the experimentally determined GU cut-off value, 99.1% (576/581) of culture isolates were correctly identified as MTB within 2 days from instrument positivity. All results were available using a single-MPT64 assay strip, making the assay cost-effective. Thus, systematic implementation of the MPT64 assay proved to be cost-effective in a high-throughput laboratory without any delay in patient reporting.