The Impact of Cholesterol on Mycobacterium bovis-BCG Resistance to Glutathione

Currently, one-third of the world’s population is infected with Mycobacterium tuberculosis. Of those infections, 10% are characterized by their dormant latent phase and 50% of them are multidrug resistant. As tuberculosis is one of the top ten causes of death throughout the world (World Health Organization), it is pertinent to understand the intracellular response that the human immune response has on M. tuberculosis. When the immune response is activated glutathione (GSH), a thiol based detoxification molecule, is produced to protect the host tissue (Patel et al., 2016). When GSH is secreted it induces uncontrollable reductive stress in the mycobacterial cell, leading to its death.
M. tuberculosis has the ability to enter a latent stage which is characterized by a metabolic shift that allows it to remain dormant inside the host. This is also known as “non replicative persistence,” (NRP). Additionally, being able to hide and remain safe inside the host makes it very difficult to treat. Our research has shown that when BCG is in non replicative persistence, it is resistant to GSH induced reductive stress killing (Patel et al., 2016). Other labs have demonstrated that cholesterol, the sole carbon source for latent Tuberculosis, can be built up inside the mycobacterial cell creating excess NAD+ and NADP that can draw in excess electrons from GSH induced reductive stress (Vandervan et al., 2015). This leads us to hypothesize that the cholesterol induced metabolism will protect M. bovis-BCG from GSH killing similar to how NRP mycobacteria resists GSH. This connection led us to the idea for my project, The Impact of Cholesterol on Mycobacterium bovis-BCG Resistance to Glutathione.
In order to further understand the impact of a cholesterol rich environment, we will be using a NAD/NADH-GloTM Assay. Mycobacterium bovis-BCG will be used as a model organism as it is 99% genetically similar to M. tuberculosis. We expect to see BCG accumulating more NAD+/NADP when it is exposed to the cholesterol. This accumulation would suggest that there was a metabolic shift towards an oxidative environment in the bacterial cytoplasms that is preventing reductive stress killing. This project will further our understanding of the metabolic processes taking place during the infection, and would be beneficial to the development of new vaccinations.

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