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Description
Staphylococcus aureus-induced infective endocarditis (IE) is a life threatening disease. To investigate and characterize IE in vivo, we have recently established a mouse model [1], [2]. IE is induced by placing a permanent catheter into the right carotid artery to irritate the aortic valves and provide a seed for formation of bacterial vegetations. Pathology of IE accumulates different amounts of chemical elements. The competition for metals between host and pathogen is one of the most important factors dictating the outcome of infection. Here, we assess whether mass spectrometry can identify IE.
A 32G-catheter was placed on the aortic valves for 48 h. Next, 24 h after catheter placement, C57Bl/6 mice were infected with S. aureus or PBS (MOCK-infected). Mice were sacrificed and the hearts were embedded in paraffin. Aortic valves were sliced 10 µm thick to perform laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to determine the amount of Ca, Cu, Fe, Mg, , Zn, and Mn. A qualitative measurement was done for P. Consecutive tissue slices were stained for Gram or H&E to relate element concentrations to infection or inflammation.
IE was successfully induced as confirmed by Gram staining that revealed S. aureus vegetations on the aortic valves. Focusing on this infected tissue, LA-ICP-MS showed a high concentration of Ca (maximum value: 800 µg/g) and a high qualitative intensity of P. High amount of Zn (maximum value: 250 µg/g) was detected where histology suggested an increased presence of immune cells. Increased Mn (maximum value: 4 µg/g) was observed where histology showed the presence of osteoblasts.
Calcium, phosphor and zinc in combination may be used to identify bacterial vegetations in IE. LA-ICP-MS may become a valuable tool to differentiate between calcification and infection.
References:
[1] Ring J et al. (2014). PLoS ONE 9(9): e107179. [2] Hoerr V et al. (2013). J Cardiovasc Magn Reson.15:59.
