Trace metals and their relation to bacterial infections studied by X-ray microscopy

Bacterial pathogens survive in different environments in the human host by responding with expression of virulence factors that enable them to adapt to changing conditions. Trace elements regulate the expression of many virulence genes in bacteria and are thus important for their survival in the host. Mycobacteria are intracellular pathogens that can cause diseases such as tuberculosis or secondary infections in immunocompromised patients. We have used a hard x-ray microprobe to study the trace element distribution in the mycobacterial phagosome after infection of macrophages. We have studied phagosomes with virulent (M. avium) and nonvirulent (M. smegmatis) mycobacteria. In this article, we will show that the iron concentration in phagosomes with macrophages infected with nonvirulent M. smegmatis is reduced 24 hours after infection but increased in phagosomes in cells infected with virulent M. avium. In addition, we will show the effect activation of macrophages with tumor necrosis factor (TNF-$\alpha$) or interferon (IFN-$\gamma$) has on the iron concentration in M. avium.