Escherichia coli bacteria attached to a magnetic bead (detail). Magnetic beads are coated with specific antibodies against target bacteria. From a mixture of bacteria in a suspension, only the target bacteria will adhere to the magnetic beads. Using a magnet, it is then possible to pull the beads out from the suspension and thus isolate the target bacteria. Enhanced SEM. Image width: 8.53 micrometers. Magnification: 11,725x if the image is printed 10 cm wide.