Comparative study of diagnostic accuracy of established PCR assays and in-house developed sdaA PCR method for detection of Mycobacterium tuberculosis in symptomatic patients with pulmonary tuberculosis

Development and clinical evaluation of a real-time multiple cross displacement amplification assay for rapid and sensitive detection of Mycobacterium tuberculosis

Molecular techniques of nucleic acid testing recommended by the World Health Organization (WHO) for the Mycobacterium tuberculosis (MTB) detection were considered to have the potential access to the accurate tuberculosis (TB) notifications. In this study, a new method, which coupled real-time (rt) fluorescence technique with multiple cross displacement amplification (MCDA), was developed for the rapid, sensitive and specific detection of MTB (termed MTB-rt-MCDA). According to the principle of the rt-MCDA test, a set of ten primers were designed for the MCDA reaction, of which one was engineered with a restrictive endonuclease recognition site, a fluorophore and a quencher for achieving the real-time fluorescence detection. MTB-rt-MCDA test was conducted under the optimized conditions (67 °C, 40 min) on the real-time fluorescence platform. The MTB-rt-MCDA assay accurately identified the MTB strains with no cross reaction with other bacteria. The lowest detectable genomic DNA concentration of the MTB-rt-MCDA assay was 25 fg/μl. We employed the genomic DNA templates extracted from sputum of clinical cases for validating the practical applicability of this assay, and the detection power of the MTB-rt-MCDA assay was comparable to that of the Xpert method and MCDA-based biosensor detection and superior to smear microscope method. The complete process of the MTB-rt-MCDA assay, including rapid extraction of DNA and rt-MCDA test, takes less than 1 h. In conclusion, the presented MTB-rt-MCDA assay provided an effective and simple option for the rapid screening of MTB infection.

Molecular diagnosis of Tuberculous meningitis: sdaA-based multi-targeted LAMP and GeneXpert Ultra

SETTING

Nucleic acid amplification techniques like GeneXpert and GeneXpert Ultra (Xpert Ultra), the first-line tests for diagnosing Tuberculous meningitis (TBM), are expensive and depend on sophisticated equipment.

OBJECTIVE

The diagnostic potential of multitargeted loop-mediated isothermal assay (MLAMP), a low-cost simple test using novel gene combination, was evaluated for TBM.

DESIGN

300 CSF specimen (200 TBM patients, 100 controls) processed between January 2017 and December 2021 were subjected to MLAMP (using sdaA, IS1081 and IS6110 gene targets), sdaA PCR and Xpert Ultra. The performance was evaluated against uniform case definition as per Marais criteria, and against culture.

RESULTS

Uniform case definition classified 50 as definite TBM and 150 as probable or definite TBM. Against this uniform case definition, the sensitivity and specificity of MLAMP was 88% and 100%, respectively. The sensitivity was 96% against culture-positive cases and 85.3% against culture-negative cases. The sensitivity of sdaA-LAMP, IS1081-LAMP, IS6110-LAMP, Xpert Ultra and sdaA-PCR was 82.5%, 80.5%, 85.3%, 67% and 71%, respectively against uniform case definition. sdaA-LAMP detected additional two cases and IS1081-LAMP detected nine. 11 of 134 (8.2%) cases were reported rifampicin resistant by Xpert Ultra.

CONCLUSION

MLAMP, incorporating sdaA and IS1081, is a cheap, easy and accurate first-line diagnostic test for TBM.

Detection of Mycobacterium tuberculosis Complex in Sputum Samples Using Droplet Digital PCR Targeting mpt64

Tuberculosis (TB) is one of the top 10 causes of death worldwide. It is challenging to find methods of diagnosis of active pulmonary TB that are sensitive enough to detect cases for proper treatment before unintentional transmission. Droplet digital PCR (ddPCR) is a highly sensitive method to detect genetic material of pathogens, but it has rarely been used for diagnosis of TB. This study compared the sensitivity of ddPCR with that of GeneXpert and AFB smear microscopy in 180 leftover sputum samples from patients suspected of having TB on the basis of clinical symptoms and radiography. Absolute quantification of copy numbers of MTB-specific genes was possible using ddPCR targeting the mpt64 gene. Among the 180 samples, 41.1% were diagnosed as having TB using ddPCR. The sensitivities of AFB smear microscopy, GeneXpert and ddPCR were 41.9%, 82.4% and 100%, respectively. AFB smear microscopy and GeneXpert both had a specificity of 100%, and the specificity of ddPCR was 95.3%. The accuracy of ddPCR (97.2%) is higher than that of GeneXpert (92.7%). This robust ddPCR system could potentially be used as a method for early diagnosis of TB.

Truenat MTB assays for pulmonary tuberculosis and rifampicin resistance in adults

This is a protocol for a Cochrane Review (diagnostic). The objectives are as follows:

To determine the diagnostic accuracy of Truenat assays (MTB, MTB Plus, and MTB RIF Dx) for detecting pulmonary tuberculosis and rifampicin resistance in adults with presumptive pulmonary tuberculosis.

Modified genome comparison method: a new approach for identification of specific targets in molecular diagnostic tests using Mycobacterium tuberculosis complex as an example

BACKGROUND

The first step of designing any genome-based molecular diagnostic test is to find a specific target sequence. The modified genome comparison method is one of the easiest and most comprehensive ways to achieve this goal. In this study, we aimed to explain this method with the example of Mycobacterium tuberculosis complex and investigate its efficacy in a diagnostic test.

METHODS

A specific target was identified using modified genome comparison method and an in-house PCR test was designed. To determine the analytical sensitivity and specificity, 10 standard specimens were used. Also, 230 specimens were used to determine the clinical sensitivity and specificity.

RESULTS

The identity and query cover of our new diagnostic target (5KST) were ≥ 90% with M. tuberculosis complex. The 5KST-PCR sensitivity was 100% for smear-positive, culture-positive and 85.7% for smear-negative, culture-positive specimens. All of 100 smear-negative, culture-negative specimens were negative in 5KST-PCR (100% clinical specificity). Analytical sensitivity of 5KST-PCR was approximately 1 copy of genomic DNA per microliter.

CONCLUSIONS

Modified genome comparison method is a confident way to find specific targets for use in diagnostic tests. Accordingly, the 5KST-PCR designed in this study has high sensitivity and specificity and can be replaced for conventional TB PCR tests.

Performance of an in-house real-time polymerase chain reaction for identification of Mycobacterium tuberculosis isolates in laboratory routine diagnosis from a high burden setting

Brazil is one of the high burden countries for tuberculosis, and a rapid diagnosis is essential for effective control of the disease. In the present study, an in-house real-time polymerase chain reaction (PCR) assay targeting the mpt64 gene for identification of Mycobacterium tuberculosis complex isolates was evaluated under routine diagnosis conditions in a reference laboratory. From May 2011 to July 2012, 1,520 isolates of mycobacteria were prospectively submitted for phenotypic and/or PRA-hsp65 identification and to real-time PCR. The mpt64 real-time PCR showed 99.7% sensitivity and 96% specificity and detected 79.4% of the cases missed by phenotypic and PRA-hsp65 identification. The in-house real-time PCR assay showed high sensitivity and specificity and was successfully implemented in the routine diagnosis of tuberculosis in a reference laboratory from a high burden setting.

Development and clinical evaluation of sdaA loop-mediated isothermal amplification assay for detection of Mycobacterium tuberculosis with an approach to prevent carryover contamination

A rapid and sensitive loop-mediated isothermal amplification assay for the sdaA gene of Mycobacterium tuberculosis was developed using a dUTP-uracil-N-glycosylase (dUTP-UNG) strategy to prevent carryover contamination. Evaluation of the assay using clinical specimens (n = 648) showed high specificity (97.2%) and sensitivity (100%), demonstrating its potential as a diagnostic test for tuberculosis, especially in resource-limited settings.