Klea Lila

Introduction: Biofilms are communities of microorganisms on wet or moist surfaces that are difficult to remove and can repeatedly release microorganisms. This causes significant problems in many areas, such as food technology and medicine, as biofilms can cause fatal infections in patients. One approach that has not yet been extensively researched is to prevent biofilm formation on surfaces by irradiating them with visible blue or violet light, which is known for its antimicrobial effect on planktonic bacteria. Methods: Various bacterial suspensions (Bacillus subtilis, Pseudomonas stutzeri, Streptococcus cristatus and Pseudomonas syringae) were placed in 24-well MTPs (microtiter plates) and irradiated with violet or blue light for up to 6 days. During this time, they were shaken at room temperature at a frequency of 100 rpm. The irradiation intensities were 0, 10 or 20 mW/cm². After each day, the bacterial suspension was aspirated and the biofilm at the bottom of the well was assessed by absorption measurement and microscopy images. Results: Besides B. subtilis, thin biofilms were found on all well bottoms after 24 h, even on the irradiated microtiter plates. In general, however, the biofilm absorption/scattering was lower on the irradiated MTPs than on the non-irradiated ones. For B. subtilis, irradiation prevented biofilm formation during the observation period. Surprisingly, in most experiments, blue light had a stronger effect than violet light, which does not correspond to the experiences with planktonic bacteria. Conclusion: Violet and blue light exhibits a positive effect on suppressing the formation of new biofilm, but the applied maximum irradiance of 20 mW/cm² was unable to prevent the formation of new biofilm for most of the examined bacteria. Further investigations with higher irradiance levels are necessary to determine whether it is possible to inhibit the formation of new biofilm altogether.