Antibacterial effect and mechanism of high-intensity 405 ± 5 nm light emitting diode on Bacillus cereus, Listeria monocytogenes, and Staphylococcus aureus under refrigerated condition

This study investigated the antibacterial effect of 405 +/- 5 nm light emitting diode (LED) on Bacillus cereus, Listeria monocytogenes, and Staphylococcus aureus, and examined its antibacterial mechanism by determining the bacterial membrane and DNA damages. A 405 +/- 5 nm LED illuminated the Gram-positive pathogens until 486 J/cm(2) at 4 degrees C. Weibull model was used to calculate reliable life (t(R)) to compare bacterial sensitivities to LED illumination. The membrane damage was determined by NaCl and LIVE/DEAD (R) assay, while comet assay and DNA ladder analysis were conducted to determine DNA degradation. The illumination resulted in 1.9, 2.1, and 1.0 log reductions for B. cereus, L. monocytogenes, and S. aureus at 486 J/cm(2), respectively. The comparison of tit values revealed that L. monocytogenes was identified as the most susceptible strain to LED illumination. The percentage of the bacterial sensitivity to NaCl remarkably increased in LED-illuminated cells compared to non-illuminated cells. Moreover, loss of membrane integrity was confirmed for LED-illuminated cells by LIVE/DEAD (R) assay, whereas no DNA breakage was indicated by comet assay and DNA ladder analysis. Thus, these findings suggest that the antibacterial effect of 405 +/- 5 nm LED illumination on these pathogens might be due to physical damage to bacterial membrane rather than DNA degradation. (C) 2015 Elsevier B.V. All rights reserved.