Magnetic Resonance Imaging of Fe3O4 Nanoparticles Embedded in Living Magnetotactic Bacteria for Potential Use as Carriers for In Vivo Applications

MC-1 Magnetotactic Bacteria (MTB) are studied for their potential use as bio-carriers for drug delivery. The exploitation of the flagella combined with nanoparticles magnetite or magnetosomes chain embedded in each bacterium and used to change the swimming direction of each MTB through magnetotaxis provide both propulsion and steering in small diameters blood vessels. But for guiding these MTB towards a target, being capable to image these living bacteria in vivo using an existing medical imaging modality is essential. Here, it is shown that the magnetosomes embedded in each MTB can be used to track the displacement of these bacteria using an MRI system. In fact, these magnetosomes disturb the local magnetic field affecting T₁ and T₂-relaxation times during MRI. MR T₁- weighted and T₂-weighted images as well as T₂-relaxivity of MTB are studied in order to validate the possibility of monitoring MTB drug delivery operations using a clinical MR scanner. This study proves that MTB affect much more the T₂-relaxation than T₁-relaxation rate and can be though as a negative contrast agent. The signal decay in the T₂-weighted images is found to change proportionally to the bacterial concentration. These results show that a bacterial concentration of 2.2times10⁷ cells/mL can be detected using a T₂-weighted image, which is very encouraging to further investigate the application of MTB for in vivo applications.