Control of Listeria monocytogenes in processing/packing plants using antimicrobial blue light (aBL)

Contamination of produce remains a complex issue and could occur at different stages from farm to fork. L. monocytogenes is widespread in the environment and can be transmitted to fresh produce by contact to contaminated surfaces. The presence of native plant microbiota and organic matter can protect L. monocytogenes by reducing the efficacy of sanitizers as well as promoting biofilm formation. Post operation washing and sanitizing of produce contact surfaces might not be adequate in eliminating the presence of pathogens and commensal bacteria. The use of a dynamic light technology during down time and close of operation could serve as a useful tool in preventing Listeria establishment and persistence. In this project, our goal is to assess the efficacy of antimicrobial blue light (aBL) against L. monocytogenes in a variety of produce processing related surfaces including but not limited to stainless steel (SS), plastic, wall coating, floor covering, nylon, polyester, cotton canvas and conveyor belts. The aBL’s antibacterial effect against a wide range of microbes including Listeria has been demonstrated at wavelengths between 400 and 470 nm. However, to the best of our knowledge it has not been evaluated for the surface decontamination of packing and processing surfaces. This study is intended to assess the possibility of aBL as a viable complimentary intervention to enhance microbial safety.
A series of experiments will be conducted, using five L. monocytogenes strains from fresh produce origin. A cocktail of these strains will be used to form surface dried cells and biofilms on SS coupons. Light emitting diode (LED) lamps emitting at 405 420 and 460 nm wavelengths will be used for the surface exposure at different doses ranging from 30 to 600 J/cm2. Low (3 Log CFU/cm2) and high (6 Log CFU/cm2) inoculum levels will be used. The durations of exposure will consist of 4, 8 and 12 h, to mimic breaks and when operations cease. Following exposure, microbiological and statistical analyses will be performed, and optimal doses will be defined. The incorporation to surfaces of a photosensitizer, gallic acid, will also be evaluated as an aBL enhancing adjuvant. The minimum dose at which the largest reduction is obtained will be applied to all other target surfaces as well as on SS coupons to validate their inactivation results consistency with those of pathogenic L. monocytogenes. Finally, aBL decontamination effectiveness will be evaluated in pilot plant scale. This project will deliver novel experimental data supporting the idea of aBL as an effective intervention for surface decontamination for produce environment. aBL causes microbial damage affecting multiple molecules in bacteria by production of reactive oxygen species (ROS). This phenomenon also prevents tolerance development in bacterial cells. More importantly, aBL is safe for humans, unlike ultraviolet (UV) irradiation. Hence, data obtained in this project will provide a foundational blueprint for the design of blue light LED arrays for potential scaling up and an ultimate outcome as identification of suitable intervention points for the application of aBL for anti-Listeria treatment in produce processing/packaging plants.