Submitted to: Letters in Applied Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/18/2012
Publication Date: 9/25/2012
Citation: De Lucca II, A.J., Carter Wientjes, C.H., Williams, K.A., Bhatnagar, D. 2012. Blue light (470 nm) effectively inhibits bacterial and fungal growth. Letters in Applied Microbiology. 55:460-466. Interpretive Summary: Visible light is comprised on a number of colors such as red, blue, and green. Blue light was found to have potent antibacterial properties against three bacteria. Among the tested bacteria were (1) a bacterium (Leuconostoc mesenteroides) that decreases sucrose yield from sugar cane and produces a gummy substance that clogs the sugar factory equipment, (3) a bacterium (Pseudomonas aeruginosa) that infects burns, and (3) a bacterium (Bacillus atrophaeus) that replaces the anthrax bacillus in lab tests. A few food grade dyes are known to produce bacteria-killing substances in the presence of red or white light. A combination of one such dye, FD&C red #3, and blue light significantly reduced the viability of two fungi, Penicillium digitatum and Fusarium verticillioides, that cause problems in stored citrus and corn, respectively. Results suggest that blue light may be a safe and effective alternative for chemical, physical (e.g., heat, steam) or irradiation (UV) sterilization.
Technical Abstract: The activity of blue light (470nm) alone on (1) bacterial viability, and (2) with a food grade photosensitizer on filamentous fungal viability, was studied. Suspensions of the bacteria Leuconostoc mesenteroides (LM), Bacillus atrophaeus (BA), and Pseudomonas aeruginosa (PA) were prepared and aliquots exposed on agar plates (0-300 J/cm**2) to LEDs (peak: 470nm) on Array 1 (AR1, 2.2mW/cm**2) which emitted impure blue light or Array 2 (AR2) which produced pure blue light (80mW/cm**2). Room light and control (no light) plates were incubated (48hr) at 25, 30 or 37°C (BA, PA) and 25°C (LM) in separate runs and colonies enumerated. The effect of blue light in combination with the photosensitizer erythrosine (ERY, 11.4 and 22.8µM) on nongerminated (NG) and germinating (G) conidia of Penicillium digitatum (PD) and Fusarium graminearum (FG) was determined. Separate suspensions of NG and G conidia of PD and FG were prepared. Conidial controls of (1) no light, (2) room light-treated conidia, and (3) ERY plus room light were prepared. Treated conidial (ERY + blue light) samples were exposed only to AR2 (0-100 J/cm**2). At the appropriate time, sample aliquots were spread on potato dextrose agar plates, incubated (48 hr, 30°C), and colonies counted. Blue light significantly reduced all test bacterial viability while incubation temperature significantly affected PA viability after light exposure. Blue light combined with ERY significantly reduced the NG and G conidial viability of FG and PD. Blue light may be a safe and effective alternative for chemical, physical (e.g., heat, steam) or irradiation (UV) sterilization.