Expression and diagnostic value of proteins in Mycobacterium tuberculosis

Ultrasensitive detection of Mycobacterium tuberculosis by a rapid and specific probe-triggered one-step, simultaneous DNA hybridization and isothermal amplification combined with a lateral flow dipstick

Mycobacterium tuberculosis (Mtb) is an insidious scourge that has afflicted millions of people worldwide. Although there are many rapid methods to detect it based on loop-mediated isothermal amplification (LAMP) and a lateral flow dipstick (LFD), this study made further improvements using a new set of primers to enhance LAMP performance and a novel DNA probe system to simplify detection and increase specificity. The new probe system eliminates the post-LAMP hybridization step typically required for LFD assays by allowing co-hybridization and amplification of target DNA in one reaction while preventing self-polymerization that could lead to false-positive results. The improved assay was named Probe-Triggered, One-Step, Simultaneous DNA Hybridization and LAMP Integrated with LFD (SH-LAMP-LFD). SH-LAMP-LFD was simpler to perform and more sensitive than previously reported LAMP-LFD and PCR methods by 100 and 1000 times, respectively. It could detect a single cell of Mtb. The absence of cross-reactivity with 23 non-TB bacteria, and accurate test results with all 104 blind clinical samples have highlighted its accuracy. Its robustness and portability make SH-LAMP-LFD suitable for users in both low and high resource settings.

Mycobacterium tuberculosis hypoxic response protein 1 (Hrp1) augments the pro-inflammatory response and enhances the survival of Mycobacterium smegmatis in murine macrophages

PURPOSE

The DosR/DosS two-component regulatory system of Mycobacterium tuberculosis regulates the expression of numerous genes under stress conditions and is important for the long-term survival of M. tuberculosis in the host. The rv2626c gene of M. tuberculosis is one of the most strongly induced transcripts of the dormancy regulon. This study focused on the immunological effects and possible function of Rv2626c in maintaining mycobacterial survival under various stress conditions.

METHODOLOGY

We heterologously expressed the Rv2626c protein in Mycobacterium smegmatis by constructing a recombinant strain Ms_rv2626c. The viability of Ms_rv2626c was evaluated both in vivo and ex vivo. Different stress conditions, including acidified sodium nitrite, malachite green, low pH, SDS and lysozyme, were used to evaluate the effect of Rv2626c on bacterial resistance. An in vitro assay using a macrophage infection model was utilized to investigate the potential effect of Rv2626c to alter the immune response of host cell and its associated pathways. The effect of Rv2626c on cell necrosis was also explored.

RESULTS

The expression of Rv2626c-enhanced M. smegmatis survival under hypoxia and nitric oxide stress in vitro, and this enhancement was maintained within macrophages and in mouse tissues. In addition, macrophages infected with M. smegmatis expressing Rv2626c showed significantly higher interleukin-1β (IL-1β), IL-6, tumour necrosis factor-α (TNF-α) and inducible nitric oxide synthase (iNOS) expression, as well as a higher level of cell necrosis, compared with the control.

CONCLUSION

M. tuberculosis protein Rv2626c plays a significant role in stimulating macrophages to provoke a pro-inflammatory response and in mycobacterial survival during infection.

Fast and efficient detection of tuberculosis antigens using liposome encapsulated secretory proteins of Mycobacterium tuberculosis

PURPOSE

A rapid and efficient diagnostic test was developed for the detection of Mycobacterium tuberculosis antigens in serum samples of active tuberculosis (TB) and extrapulmonary TB patients via a liposomal agglutination-based method.

METHODS

A rapid card test has been developed to facilitate the recognition of high-affinity binding rabbit raised purified culture filtrate protein antibodies coupled on the surface of activated liposomal preparation. In the presence of TB antigens, the polyclonal antibodies bound to the liposomal particles demonstrate a visible agglutination reaction.

RESULTS

The developed assay was simple, rapid, reliable, sensitive, and specific as a diagnostic test for the detection of antigens in serum samples of clinically confirmed cases of TB within 4-5 minutes' duration. The test was evaluated at different hospitals, medical colleges, and pathology centers, and involved 1483 participants. This investigation was conducted to detect the presence of these antigens during the period of active growth of the microorganism in serum samples for pulmonary TB and processed tissue biopsy for other extrapulmonary TB. Results obtained using this test were compared with acid-fast bacilli smear and culture results.

CONCLUSION

Our study demonstrated that the newly developed liposome tuberculosis antigen card test detected antigens in our study population with approximately 97.48% sensitivity and 95.79% specificity. This is the first study to report the liposomal encapsulation of culture filtrate proteins from M. tuberculosis for diagnostic application.