The efficiency of cross-linking methods in eradication of bacteria is influenced by the riboflavin concentration and the irradiation time of ultraviolet light

PurposeTo determine bacterial eradication using numerous riboflavin concentrations and different ultraviolet light A (UVA) radiant and exposure time in an experimental model. MethodsDilutions of Staphylococcus epidermidis were mixed with riboflavin at varying concentrations (0.007-0.09%). Effects on bacterial growth were evaluated after 0, 3, 6, 30 and 60min of UVA exposure (irradiance 30 and 3mW/cm(2)). Standard settings of UVA were compared with high-power UVA approach. Different fluid thicknesses of the exposed dilutions were also examined to improve the model. ResultsBacterial eradication (%) was increased after 60 compared with 30min of UVA exposure for concentrations of 0.03-0.07% but not for 0.09% riboflavin. There was a significant difference between the efficacy between 0.03 and 0.09% and eradication dropped from 80% to 50% (p=0.01). A correlation could be calculated for the amount of riboflavin at 60min of UVA and the ability to kill bacteria (p=0.01). The antibacterial effect was more pronounced when the tested bacterial suspension thickness was reduced. High-power UVA method was less potent in microbial elimination, eradicating only 60% of bacteria after 6min versus 97-99% after 60min in the low-power setting, compared with respective controls (p=0.02). ConclusionsIn these in vitro experiments, a longer UVA exposure time in combination with lower riboflavin levels were found to be favourable in killing bacteria as compared to the standard cross-linking settings. Further studies are needed to evaluate the clinical relevance of these findings.