  We report on a new technique which was used to detect single Escherichia coli
that is based on the changes in the nonlinear rotation of a magnetic
microsphere driven by an external magnetic field. The presence of one
Escherichia Coli bacterium on the surface of a 2.0 micron magnetic microsphere
caused an easily measurable change in the drag of the system and, therefore, in
the nonlinear rotation rate. The straight-forward measurement uses standard
microscopy techniques and the observed average shift in the nonlinear rotation
rate changed by a factor of ~3.8.
