Magnetic nanoparticles (MNPs) have found increased applicability in drug delivery, cancer treatment, and immunoassays. There is a need for an improved understanding of how MNPs interact with living cell membranes in applied magnetic fields to use them effectively. The interactions between Escherichia coli (E. coli) and SiO2/γ-Fe2O3 composite particles in magnetic fields were studied using x-ray scattering. Magnetic field strengths up to 423 mT were applied to the samples to see the effects of the magnetic fields on the E. coli membranes in the presence of the magnetic particles in the cell cultures. X-ray scattering results from continuous cultures of E. coli showed two peaks, a sharp peak at q=0.528 Å-1 (1.189 nm) up to 362 mT of magnetic field strength and a diffuse one at q=0.612 Å-1 (1.027 nm). The sharp peak was shifted to the smaller side of q when magnetic particles were added and the magnitude of the applied magnetic field strength was increased from 227 to 298 mT, to 362 mT, whereas the diffuse peak did not changed. A critical magnetic field strength where the sharp peak disappears was found at 362 mT.