Efficacy of the CHRONOlight biodynamic lighting system for control of nosocomial Gram-negative pathogens

Health care-associated infections are a growing public health concern, with hospitals acting as reservoirs for pathogens. The rise in antimicrobial resistance worsens the issue. This study tested the effectiveness of the biodynamic lighting system (CHRONOlight) at varying ultraviolet (UV) light times and energy levels to reduce nosocomial gram-negative pathogens.

Eight clinical isolates, representing different gram-negative pathogens, were selected from the Andalusian reference laboratory. Escherichia coli, Pseudomonas aeruginosa, and Acinetobacter baumannii ATCC were used as control strains. Different inoculums were exposed to type C UV light (UV-C) doses 2.0, 1.5, and 1.0 W/m² (corresponding to an irradiation flux of 100%, 75%, and 50%, respectively, with spectral peaks at 270 nm) during 15, 30, 45, 60, and 300 seconds and type A UV light (UV-A) (380 nm) during 30 minutes. The bactericidal effect was considered when cellular viability decreased by ≥3-log10 colony forming unit/ml. UV-C light-surviving isolates were sequenced (Illumina MiSeq) and analyzed to identify mutations associated with UV-C light survival. The development of antibiotic resistance after UV-C exposure were also studied for the same surviving isolates.

The efficacy of the CHRONOlight biodynamic lighting system varied by exposure time, UV dose, and bacterial species. E. coli isolates showed bactericidal effects within 15-30 seconds at 100% UV-C intensity, whereas Klebsiella pneumoniae required 30-45 seconds. P. aeruginosa and A. baumannii showed activity in 15-30 seconds, but clinical A. baumannii needed longer exposure, especially at lower UV-C intensities. No reduction in cell viability was seen with UV-A exposure. Gene mutations related to metabolism, stress response, motility, and virulence were found in survivors, and no cross-antibiotic resistance developed in surviving isolates.

CHRONOlight biodynamic lighting system is a novel broad-spectrum lighting prototype designed to effectively reduce the viability of gram-negative bacteria within short exposure times (30-300 seconds) through UV-C emission. This makes it a promising strategy for minimizing nosocomial infections in health care settings.