Photodynamic Antibiofilm and Antibacterial Activity of a New Gel with 5-Aminolevulinic Acid on Infected Titanium Surfaces

The use of a new gel containing aminolevulinic acid and red light (ALAD-PDI) was tested in order to counteract bacterial biofilm growth on different titanium implant surfaces. The varying antibacterial efficacy of ALAD-PDI against biofilm growth on several titanium surfaces was also evaluated. A total of 60 titanium discs (30 machined and 30 double-acid etched, DAE) were pre-incubated with saliva and then incubated for 24 h with Streptococcus oralis to form bacterial biofilm. Four different groups were distinguished: two exposed groups (MACHINED and DAE discs), covered with S. oralis biofilm and subjected to ALAD + PDI, and two unexposed groups, with the same surfaces and bacteria, but without the ALAD + PDI (positive controls). Negative controls were non-inoculated discs alone and combined with the gel (ALAD) without the broth cultures. After a further 24 h of anaerobic incubation, all groups were evaluated for colony-forming units (CFUs) and biofilm biomass, imaged via scanning electron microscope, and tested for cell viability via LIVE/DEAD analysis. CFUs and biofilm biomass had significantly higher presence on unexposed samples. ALAD-PDI significantly decreased the number of bacterial CFUs on both exposed surfaces, but without any statistically significant differences among them. Live/dead staining showed the presence of 100% red dead cells on both exposed samples, unlike in unexposed groups. Treatment with ALAD + red light is an effective protocol to counteract the S. oralis biofilm deposited on titanium surfaces with different tomography.