Traditional biological and chemical methods for pathogen identification require complicated sample preparation for
reliable results. Optical scattering technology has been used for identification of bacterial cells in suspension, but with
only limited success. Our published reports have demonstrated that scattered light based identification of Listeria
colonies growing on solid surfaces is feasible with proper pattern recognition tools. Recently we have extended this
technique to classification of other bacterial genera including, Salmonella, Bacillus, and Vibrio. Our approach may be highly applicable to early detection and classification of pathogens in food-processing industry and in healthcare.
The unique scattering patterns formed by colonies of different species are created through differences in colony
microstructure (on the order of wavelength used), bulk optical properties, and the macroscopic morphology. While it is
difficult to model the effect on scatter-signal patterns owing to the microstructural changes, the influence of bulk optical
properties and overall shape of colonies can be modeled using geometrical optics. Our latest research shows that it is
possible to model the scatter pattern of bacterial colonies using solid-element optical modeling software (TracePro), and
theoretically assess changes in macro structure and bulk refractive indices. This study allows predicting the theoretical
limits of resolution and sensitivity of our detection and classification methods. Moreover, quantification of changes in
macro morphology and bulk refractive index provides an opportunity to study the response of colonies to various
reagents and antibiotics.