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

Abstract

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 Listeria, Salmonella, Escherichia, Pseudomonas, Cronobacter, Lactobacillus, and Staphylococcus 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 (P < 0.05). The viability of Pseudomonas 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 Cronobacter and Salmonella dried cells on SS coupons were less than 2 Log CFU/coupon. Treatment of cells on avocados resulted in small reductions of Cronobacter and Salmonella (<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.

Keywords: Lactobacillus; Pseudomonas; blue light; food safety; foodborne pathogens.

Fig 1

The effect of blue light exposure (405 nm) on the viability of cell suspension of different bacterial genera in PBS. Cocktails of 4–5 strains per genera were treated with total doses of 504 and 1,512 J/cm² after 2 and 6 h, respectively.

Fig 2

The effect of blue light exposure (405 nm) on the viability of TSB cultures of different bacterial genera. Cocktails of 4–5 strains per genera were treated with total doses of 504 and 1,512 J/cm² after 2 and 6 h, respectively.

Fig 3

The effect of blue light exposure (405 nm) on the viability of cells dried on SS coupons of different bacteria genera. Cocktails of 4–5 strains per genera were treated with total doses of 869.4 and 1,738.8 J/cm² after 1.5 and 3 h, respectively.

Fig 4

The effect of blue light exposure (405 nm) on the viability of cells of different bacteria genera dried on avocado surfaces. Cocktails of 4–5 strains per genera were dried overnight on avocado skins treated with total doses of 648 and 1,944 J/cm² after 6 and 18 h, respectively.

Fig 5

The effect of blue light exposure (405 nm) on the viability of cells of different bacteria genera dried on surfaces of cherry tomatoes. Cocktails of 4–5 strains per genera were dried overnight and treated with total doses of 648 and 1,944 J/cm² after 6 and 18 h, respectively.