Exposure to 222 nm far UV-C effectively inactivates planktonic foodborne pathogens and inhibits biofilm formation

This study investigated the performance of a 222 nm far-UV-C krypton-chloride excilamp for inactivation of major foodborne pathogenic and spoilage bacteria in thin liquid films (TLF, 1.2 mm thickness), on solid stainless steel surfaces (SS), and against biofilm formation on SS. Both gram-positives (Listeria monocytogenes, Staphylococcus aureus) and gram-negatives (Escherichia coli O157:H7, Pseudomonas aeruginosa) (109 CFU/mL starting concentration) were exposed to 222 nm light at cumulative doses of up to 354 mJ/cm2. Significant (P < 0.05) reductions (1.4–5.1 log CFU) were found for all bacteria, and inactivation kinetics was described well by the Weibull model (0.77 ≤ R2 ≤ 0.95). Substrate type (i.e., TLF vs. SS) substantially impacted treatment efficacy. No detectable resistance of L. monocytogenes was developed after repeated exposure to 222 nm in TLF. The 222 nm treatment also effectively minimized biofilm formation and growth by S. aureus and P. aeruginosa and increased the surviving cells' susceptibility to sodium hypochlorite by at least 2 fold. This work demonstrates that 222 nm krypton-chloride excilamps can be used to effectively inactivate planktonic bacteria and inhibit biofilm formation and growth. This recommends them for use as novel nonthermal light-based systems for mitigation of pathogens and biofilms in a range of applications, including food processing, food service, and clinical environments.