Spectroscopic Imaging for the Detection and Identification of Bacterial Contaminations

There exist many types of harmful bacteria that can contaminate foods and cause serious illness, which often have their own best courses of treatment. This requires the classification of different types of bacteria. Traditional methods of bacterial identification, while able to provide accurate classification, are often very time-consuming processes. In the case of a potentially fatal bacterial infection, time is often of the essence. FTIR spectroscopy is a faster, more practical alternative that can discriminate different strains of bacteria, based on their spectral signatures, with high confidence.

Bacterial contaminations on food exist as small, localized colonies that must be found and identified. As FTIR spectroscopy is a fast technique for one sample location, it is advantageous to move towards spectroscopic imaging to do FTIR spectroscopy at many locations in parallel. The amount of information obtained at one time from this technique is large, thus it can be helpful to visualize this information by means of color images. A multivariate image analysis will produce such color images depicting the different chemical properties of a material as different colors. This enables the visual discrimination of a bacterial colony from its substrate, as they will have different chemical properties. Colonies can be found in a larger sample area by merging data cubes as presented here. Once a bacterial colony is found in an extended area, it must be identified. A method of bacterial identification has been developed here that can identify bacterial colonies based on chemical information obtained from spectroscopic imaging.

While spectroscopic imaging is useful for acquiring chemical information in two spatial dimensions, it inherently loses height information, which is important for investigating chemical reactions proceeding in three dimensions. This information is of key importance in the growth monitoring of bacterial colonies. Thus, novel illumination optics have been coupled with a spectroscopic imaging setup to probe the surface topography of a 3D sample while being able to acquire spectroscopic information simultaneously.