Enhanced oral bacterial discrimination by using Mueller matrix polarimetry

We introduce a pioneering study where an optical method, Mueller matrix polarimetry, was used for the detection and distinction of bacteria biofilms, which are the main cause of implant-associated infections. However, bacteria identification so far can only be done using time-consuming molecular biological methods. The physiological form and growth of the bacterial microstructures form the basis of their polarimetric response signal. We investigated several bacterial species (Streptococcus oralis, Staphylococcus aureus, Streptococcus mutans, Staphylococcus epidermidis, and Porphyromonas gingivalis) grown on titanium discs, a common implant material, in a reflection mode polarimetry setup. Therefore, unlike previous studies where bacterial colonies were grown on agar plates, we grew bacteria in their clinical morphology and analysed them directly on the surface of interest. The usage of titanium medium for bacterial growth gives insights on implant longevity and performance, surface texture modifications and infection prevention strategies. From Mueller matrix element analysis, we could qualitatively distinguish the different biofilms. For a more comprehensive characterization, we also analysed bacterial monolayers to understand the polarization signal dependence on the bacterial species, and reduce confounding factors. The statistical method applied is presented, as well as typical example results through box plots and frequency distribution histograms. From Lu-Chipman decomposition parameters such as retardation, polarizance, diattenuation, and depolarization, additional distinctions were calculated for each of the species. We present decomposition imaging for each species investigated. With the results obtained, our approach has a very high potential for fast and non-destructive investigation for implant infection detection.