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

Background and ObjectiveApproximately 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 -lactam-resistant Escherichia coli, a common non-skin flora pathogen responsible for a large percentage of indwelling medical device-associated clinical infection. Materials and Methods405nm 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 -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 2.890.19 and 9.450.63mW cm(-2) and radiant exposure levels between 5.600.39 and 136.914.06 J cm(-2) were tested. ResultsVLT with variable irradiance and constant treatment time (120 minutes) demonstrated significant reduction (P<0.001) in E. coli between an irradiance of 2.89mW cm(-2) (81.70%) and 9.37mW cm(-2) (100.00%). Similar results were found with variable treatment time with constant irradiance. Log(10) reduction analysis produced between 1.980.53 (60 minute treatment) and 6.27 +/- 0.54 (250 minute treatment) log(10) reduction in bacterial concentration (P<0.001). ConclusionsWe have successfully demonstrated a significant bacterial reduction using high intensity 405nm light. Illustrating the efficacy of this technology against a -lactam-resistant E. coli is especially relevant to the need for novel methods of sterilization in healthcare settings. These results suggest that VLT using 405nm light could be a suitable clinical option for eradication of -lactam-resistant E. coli. Lasers Surg. Med. 48:311-317, 2016. (c) 2015 Wiley Periodicals, Inc.