Evaluation of the Photo-inactivation Efficacy and Killing Kinetics of 405 nm Visible Light against Multidrug-Resistant Acinetobacter baumannii

The Multidrug-resistant (MDR) Acinetobacter baumannii poses a critical threat in clinical settings due to its high environmental stability and resistance to conventional antibiotics. Antimicrobial blue light, particularly at 405 nm, has emerged as a promising non-invasive decontamination strategy. Objective: This study aimed to evaluate the photo-inactivation efficacy and determine the killing kinetics of 405 nm light against A. baumannii. Methods: Bacterial samples were exposed to a 405 nm light source for up to 120 minutes. Survival rates were compared with a dark control group, and the data were modeled using first-order Chick-Watson kinetics. Results: A significant time-dependent reduction in bacterial viability was observed. After 120 minutes of exposure, 405 nm light achieved a 98.6% inactivation success compared to the control group (p < 0.01). Kinetic analysis revealed an inactivation rate constant (k) of 0.0291 min-1 with a high coefficient of determination (R2 = 0.8888). The calculated half-life (t1/2) and decimal reduction time (D-value) were 23.84 and 79.19 minutes, respectively.These results demonstrate that 405 nm irradiation provides a potent and mathematically predictable bactericidal effect against MDR A. baumannii. The findings suggest that 405 nm light therapy serves as a viable alternative for the environmental decontamination of highly resistant pathogens.