Comparison of the inactivation of seven foodborne pathogens and spoilage bacteria under 405 nm blue light treatment in liquid media and on solid surfaces

Antimicrobial blue light (aBL; 405 nm) can reduce the viability of multiple bacteria, but there are few reports comparing the susceptibility of foodborne bacteria when exposed to similar conditions. This study was undertaken to evaluate the efficacy of aBL against foodborne pathogens and spoilage bacteria when treated in liquid media and on different surfaces. Cocktails of <i>Listeria</i>, <i>Salmonella</i>, <i>Escherichia</i>, <i>Pseudomonas</i>, <i>Cronobacter</i>, <i>Lactobacillus</i>, and <i>Staphylococcus</i> were incubated in tryptic soy broth (TSB) and phosphate-buffered saline (PBS), as well as on stainless steel (SS) coupons, avocados, and cherry tomatoes as dried cells. Reductions in cell viability were determined after exposure to 405 nm aBL at two temperatures. aBL doses for liquid, SS coupons, and fruits were 1,512, 1,739, and 1,944 J/cm², respectively. Microbiological counts were determined using standard complex media, and Analysis of variance (ANOVA) was used to determine significant differences (<i>P</i> < 0.05). The viability of <i>Pseudomonas</i> in PBS was reduced by more than 8 Log CFU/mL of aBL exposure, but the reduction of other bacteria was less than 4 Log CFU/mL. In TSB, more than 5 Log CFU/mL were inactivated in all genera. Reductions in viable <i>Cronobacter</i> and <i>Salmonella</i> dried cells on SS coupons were less than 2 Log CFU/coupon. Treatment of cells on avocados resulted in small reductions of <i>Cronobacter</i> and <i>Salmonella</i> (<1.5 Log CFU/skin spot) at 20°C compared to other species. These findings suggest that the susceptibility of different bacterial genera may be quite variable in response to aBL treatment, and these differences should be considered for potential applications.IMPORTANCEReady-to-eat (RTE) foods have been associated with multiple outbreaks caused by foodborne pathogens. While the safety of many RTE foods such as fresh produce relies on traditional cleaning and sanitation systems, they are often insufficient to keep bacteria off food-contact surfaces within the processing and packing environment. Antimicrobial blue light (aBL) in the range of 400-470 nm of wavelength may be a promising disinfectant alternative. However, more comprehensive studies are needed to better assess the effectiveness of aBL against a wide range of foodborne pathogens and spoilage. Such research could provide valuable insights into aBL's potential as a crucial tool for ensuring food safety.