A major emphasis of immunology research conducted at the CBTBR is directed at the search for host biomarkers of different TB treatment outcomes. Such markers could have clinical use by identifying patients with a high risk for treatment failure and could shorten clinical trials of new TB drugs. We are developing prognostic models by using flow cytometry and measurement of cytokine levels. A high prevalence of gastrointestinal worm/TB co-infection exists in our population and might play a role in our TB epidemic. A mouse model of helminth/M. bovis BCG co-infection has been established that shows that concurrent infection with worms and mycobacteria has an adverse effect on the clearance of the bacteria. We are interested in examining the mechanisms for this effect.
This project is driven by the basic question of whether the investigation of disease dynamics of TB and the study of the various strains of M. tuberculosis assist with the identification, development and implementation of new control tools and strategies that will reduce the incidence of this disease. The molecular epidemiology research program is structured to address both molecular epidemiological and some mycobacterial genomic questions with a view to gaining an insight into the mechanisms that perpetuate the epidemic and to provide suitable samples and information to aid our understanding of the genome of M. tuberculosis.
Research is aimed at applying an integrated molecular genetic, genomic, biochemical and physiological approach to studying those areas of mycobacterial metabolism that are associated with genome evolution, drug resistance, drug tolerance, stress adaptation, persistence and resuscitation. Focal areas of research include: (1) DNA metabolism, with emphasis on the role of specialized DNA polymerases in long-term survival and genetic adaptation to stress; (2) the regulation and function of dNTP biosynthesis enzymes; (2) respiration and energy metabolism; (3) the role of resuscitation-promoting factors in growth, culturability and resuscitation of mycobacteria; and (4) the function of cobalamin-dependent enzymes in growth and persistence of mycobacteria.
A challenging area of tuberculosis research is understanding how M. tuberculosis responds to the unfavourable conditions encountered in the host. Using a variety of different models that mimic the host environment we aim to analyse the expression of genes involved in energy metabolism and the respiration pathway. Using a range of techniques to measure protein expression, we have showed that protein expression by M.tuberculosis varies according to strain genotype and growth stage. We are currently conducting proteomic studies to investigate whether resistance to isoniazid is associated with expression of different M. tuberculosis antigens.
Susceptibility to tuberculosis probably involves a moderate number of genes in the host, and these are identified by means of whole genome scans or association studies. We have investigated many genes, and found IFNg, DC-SIGN, MBL and NRAMP1, amongst others, to affect the chance of becoming ill after infection with TB, and in some cases, to affect the clinical manifestation of TB.
Multi-drug Resistant TB
This project focuses on the understanding of drug resistance in local communities. Our recent results can be summarized as follows: (1) Drug resistance is due to mutations in certain genes. (2) About 60% of drug resistance in local communities is due to transmission from person to person and this indicates limitations in the control program. (3) Molecular techniques can be implemented to quickly screen for drug resistance. (4) Micro-epidemics of drug resistant strains have been identified in the local communities. We have established a study site to investigate the clinical usefulness of molecular prediction of drug resistance to identify patients infected with drug resistant M. tuberculosis as an adjunct to the local TB control program. We hope this research will lead to the implementation of some community intervention activities in the future.
The ever increasing burden of drug resistance in M.tuberculosis and the lengthy treatment periods of TB patients with existing drugs necessitate the search for new drugs and new drug targets. When glutamine synthetase (GS), an essential gene in M.tuberculosis, is inhibited, M.tuberculosis is killed. Our research indicates novel mechanisms of protein transport and function of GS. These mechanisms are possible new drug targets as they are unique to M.tuberculosis and specificity can be achieved. Collaborators on this project have also designed new inhibitors specific for M.tuberculosis GS.
The CBTBR has begun and intends to continue with the testing of new potential anti-tuberculosis medication developed by industry. The CBTBR laboratory is conducting some early bactericidal activity (EBA) testing (phase II) of various drugs. In addition to conducting clinical trials, researchers at the CBTBR are trying to develop alternative methods for determination of EBA.