Label-free distinction of implant infection-associated bacterial biofilms by Mueller matrix polarimetry

Bacterial biofilm agglomerates are the cause of hard-to-treat implant-associated infections but currently can only be distinguished using sophisticated microbiological or molecular biological methods. Optical methods can potentially provide a label-free, noncontact approach to detect the presence of bacterial species associated with implant infections that could aid in the early diagnosis of implant-associated diseases.

Our aim is to measure the polarization signal from implant-associated bacteria biofilms using Mueller matrix polarimetry. Furthermore, we present an analysis of the Mueller matrix element to detect and distinguish the different bacterial biofilm species.

Several biofilms formed by bacterial species associated with orthopedic (Staphylococcus aureus and Staphylococcus epidermidis) and dental implants (Streptococcus oralis, Streptococcus mutans, and Porphyromonas gingivalis) were grown on titanium, a typical implant material. Polarization signals were acquired in a reflection mode using a calibrated polarimetry setup.

The results show that different biofilms could be qualitatively distinguished using the Mueller matrix element analysis. The values derived from bacterial species measurements were distinctly different from those of the bare titanium discs. From the Lu-Chipman decomposition, parameters such as polarizance and diattenuation were calculated for each of the species.

The results provide deeper insight into the interaction of polarized light with bacterial microcolonies. The physiologically growing biofilms form the basis of their polarimetric response signal. Our approach has potential for fast and nondestructive investigation for implant infection detection, potentially in situ and in vivo.