  Rapid identification of bacterial species is crucial in medicine and food
hygiene. In order to achieve rapid and label-free identification of bacterial
species at the single bacterium level, we propose and experimentally
demonstrate an optical method based on Fourier transform light scattering
(FTLS) measurements and statistical classification. For individual rod-shaped
bacteria belonging to four bacterial species (Listeria monocytogenes,
Escherichia coli, Lactobacillus casei, and Bacillus subtilis), two-dimensional
angle-resolved light scattering maps are precisely measured using FTLS
technique. The scattering maps are then systematically analyzed, employing
statistical classification in order to extract the unique fingerprint patterns
for each species, so that a new unidentified bacterium can be identified by a
single light scattering measurement. The single-bacterial and label-free nature
of our method suggests wide applicability for rapid point-of-care bacterial
diagnosis.
