Anti-biofilm effect of 405-nm LEDs against Listeria monocytogenes in simulated ready-to-eat fresh salmon storage conditions

- 405 nm LED illumination inhibited the growth of L. monocytogenes cells in biofilm.
- LED illumination inactivated planktonic cells but not cells detached from biofilms.
- LED illumination failed to inhibit pre-formed biofilm cells.
- Illuminated pre-formed biofilm cells were more susceptible to sanitizer treatment.

The objective of this study was to evaluate the anti-biofilm effect of 405-nm light-emitting diodes (LEDs) against Listeria monocytogenes in salmon exudate at 4, 15, and 25 °C, and to compare the susceptibility of LED-illuminated and non-illuminated pre-formed biofilm cells to sanitizer treatment. For the biofilm-forming scenario, stainless-steel (SS) or acrylic (AC) coupons in sterilized salmon exudate were inoculated with L. monocytogenes and then illuminated with 405-nm LEDs (26 ± 2 mW/cm2) at each temperature for 8 h. For the pre-formed biofilm scenario, L. monocytogenes biofilms were pre-formed onto each coupon at 25 °C for 24 h and subsequently illuminated at each temperature, followed by treatment with 200 ppm quaternary ammonium compound (QAC) for 10 s to compare the sensitivity of LED-illuminated biofilm cells to the sanitizer treatment. Regardless of illumination temperature, the results showed that 405-nm LED illumination significantly (P < 0.05) reduced both planktonic and biofilm cell populations on SS and AC coupons during biofilm formation. There were no significant (P ≥ 0.05) changes in the planktonic and biofilm cell populations, for the pre-formed biofilm scenario, in response to LED illumination at 4 and 15 °C. However, significant biofilm cell reductions were observed on SS and AC coupons in response to LED illumination at 25 °C for 8 h. Regardless of coupon type, LED-illuminated biofilm cells were found to be more sensitive to QAC treatment under the pre-formed biofilm scenario than non-illuminated cells. These results indicate that 405-nm LED illumination may be effective in controlling L. monocytogenes during the biofilm formation process, and at inducing sensitivity to sanitizer treatment in pre-formed biofilm cells. Thus, this study suggests the potential of LED technology in controlling L. monocytogenes biofilms during the processing and storage of ready-to-eat salmon, minimizing the chance of cross-contamination from contaminated surfaces.