Identification And Characterization Of Nutrient Transporters In Mycobacterium Smegmatis

Finding cures against tuberculosis (TB) is an on-going battle for humans. TB is one of the world's deadliest diseases and one third of the world's population are infected with TB although only 10 % of the TB infected population developed to TB disease. Decline of TB disease was observed in the United States from over 16,000 to just below 8000 between 1993 and 2008 [13]. Worldwide, an incidence of TB disease increased from 125 cases per 100,000 population in 1990 to 142 cases per 100,000 population in 2004. This increase was primarily due to prevalence of the human immunodeficiency virus (HIV) infection among TB patients and a lack of access to proper treatments among them. In fact, mortality of the TB patients co-infected with HIV was drastically reduced when the patients were treated with antiretroviral therapy (ART) along with TB chemotherapy [13]. Without the concurrent treatment of HIV, up to 50 % of the patients with TB/HIV co-infection will die during the TB treatment. There are 10 drugs currently approved by the U.S. Food and Drug Administration (FDA) for use in TB chemotherapy. Of those, a cocktail of isoniazid (INH), rifampin (RIF), ethambutal (EMB), and pyrazinamide (PZA) is used as a frontline anti-TB agents, and patients are treated between 4 to 7 months. This long-term anti-TB regimen works efficient as long as the patients religiously take the medication throughout the treatment period. However, the length of this regimen is long and side effects are severe that many patients ended the regimen without completion after they started to feel better. This inappropriate termination of the regimen lead to the emergence of multi-drug resistant TB (MDR-TB). The outbreak of MDR-TB cases in HIV infected persons has contributed to increase of TB incidents in the U.S.A. from the mid-1980's through early 1990's [12, 81, 1, 91]: TB disease was otherwise believed to be eradicated like smallpox. All the TB drugs target the genes in metabolic pathways therefore they are more potent against actively growing bacilli. However, slowly growing or metabolizing bacilli (non-replicative bacilli) are not eliminated by the TB drugs thus remain persistent in patients. The non-replicative bacilli can become active by yet unknown environmental factors and re-emerge to develop TB disease long after initial eradication. Also, it is these non-replicative bacilli, which are prone to undergo mutation and emerge as mutlidrug resistant strains [17]. Therefore, it is critical to develop drugs against the non-replicative bacilli. Understanding the biology of the non-replicative bacilli will give us a better strategy to eradicate TB. The purpose of my Ph.D. dissertation is to contribute to the understanding of how the bacilli acquire nutrients. The non-replicative bacilli are believed to be stable and non-propagative, shown as the loss of acid-fastness. They are also viable but not culturable (VBNC) [15] at this stage, however they still require nutrients to survive. Most transporter studies are focused on drug efflux systems whereas many of the transporters involved in nutrient acquisition remain unknown. Understanding of nutrient uptake systems not only provides us with information as to how the bacilli acquire nutrients but also allows us to design drugs, which can gain access into the cells through essential pathways