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T4-06 Antibacterial Effect and Mechanism of High-intensity 405 nm Light Emitting Diode on Bacillus cereus, Listeria monocytogenes, and Staphylococcus aureus under Refrigerated Condition

Sunday, July 26, 2015: 2:45 PM
C124 (Oregon Convention Center)
Min-Jeong Kim , National University of Singapore , Singapore , Singapore
Marta Mikš-Krajnik , National University of Singapore , Singapore , Singapore
Amit Kumar , National University of Singapore , Singapore , Singapore
Hyun-Jung Chung , Inha University , Incheon , Korea, Republic of (South)
Hyun-Gyun Yuk , National University of Singapore , Singapore , Singapore
Audio File Recorded Presentation
Introduction: Antibacterial effect of 405 nm light emitting diode (LED) on several pathogenic bacteria has been investigated, demonstrating that the LED could be useful to control bacterial growth. For food application, it is also necessary to evaluate its antibacterial effect on various foodborne pathogens at low temperature that simulates refrigerated storage condition. Moreover, its antibacterial mechanism on these pathogens should be elucidated well.

Purpose: The objective of this study was to investigate the inactivation of Bacillus cereus, Listeria monocytogenes, and Staphylococcus aureus by 405 nm LED illumination under refrigerated condition and to elucidate its antibacterial mechanism by examining bacterial membrane and DNA damage. 

Methods: A 405 nm LED with irradiance of 18.2 mW/cm2 illuminated bacteria in phosphate-buffered saline for 7.5 h (a total dose of 486 J/cm2) at 4°C. The effect of LED illumination on bacterial membrane was determined using 4 - 7% NaCl and Live/Dead®Cell Viability assay. Comet assay and DNA ladder analysis were used to examine DNA degradation. 

Results: The LED illumination inactivated 1.9, 2.1, and 1.0 log CFU/ml for B. cereus, L. monocytogenes, and S. aureus, respectively, exhibiting that L. monocytogenes was the most sensitive strain to the LED illumination. Regardless of bacterial strain, more than 90% of LED-illuminated cell populations became sensitive to NaCl within 4.5 h, while non-illuminated cells were still resistant to NaCl. A Live/Dead®assay clearly revealed that the LED illumination resulted in a loss of bacterial membrane integrity, whereas no DNA degradation was observed by both comet assay and DNA ladder analysis.

Significance: This study proposes the potential of 405 nm LED in controlling these Gram-positive pathogens in food matrix and suggests that the antibacterial mechanism of the LED illumination might be due to cell membrane damage rather than DNA degradation.

Back to: Technical Session 4 – General Microbiology
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