Violet 405 nm light: A novel therapeutic agent against β‐lactam‐resistant Escherichia coli

Background and Objective Approximately 1.7 million patients are affected by hospital-acquired infections every year in the United States. The increasing prevalence of multidrug-resistant bacteria associated with these infections prompts the investigation of alternative sterilization and antibacterial therapies. One method currently under investigation is the antibacterial properties of visible light. This study examines the effect of a visible light therapy (VLT) on β-lactam-resistant Escherichia coli, a common non-skin flora pathogen responsible for a large percentage of indwelling medical device-associated clinical infection. Materials and Methods 405 nm light-emitting diodes were used to treat varying concentrations of a common laboratory E. coli K-12 strain transformed with the pCIG mammalian expression vector. This conferred ampicillin resistance via expression of the β-lactamase gene. Bacteria were grown on sterile polystyrene Petri dishes plated with Luria-Bertani broth. Images of bacterial growth colonies on plates were processed and analyzed using ImageJ. Irradiance levels between 2.89 ± 0.19 and 9.45 ± 0.63 mW cm−2 and radiant exposure levels between 5.60 ± 0.39 and 136.91 ± 4.06 J cm−2 were tested. Results VLT with variable irradiance and constant treatment time (120 minutes) demonstrated significant reduction (P