Long-term-survival phase cells of Salmonella Enteritidis ATCC 13076 exhibit significantly greater tolerance to atmospheric cold plasma treatment of shell eggs

Authors: BARRY, KIA - Iowa State University; MENDONCA, AUBREY - Iowa State University; PHILLIPS, GREGORY - Iowa State University; BOYLSTON, TERRI - Iowa State University; DASILVA, PAULO - Iowa State University; BREHM-STECHER, BYRON - Iowa State University; Juneja, Vijay; WAN, ZIFAN - University Of Wisconsin

Submitted to: Food Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/30/2024
Publication Date: 10/17/2024
Citation: Barry, K., Mendonca, A., Phillips, G., Boylston, T., Dasilva, P.F., Brehm-Stecher, B., Juneja, V.K., Wan, Z. 2024. Long-term-survival phase cells of Salmonella Enteritidis ATCC 13076 exhibit significantly greater tolerance to atmospheric cold plasma treatment of shell eggs. Food Control. 4. Volume 4 - 2024 | https://doi.org/10.3389/frfst.2024.1442761.
DOI: https://doi.org/10.3389/frfst.2024.1442761

Interpretive Summary: Salmonella, a deadly foodborne pathogen, is commonly associated with food poisoning outbreaks associated with consumption of contaminated eggs. The bacterium most often contaminates the outer surface of shell eggs. Chlorine, the most widely used sanitizer, has limitations including its inactivation by organic matter as well as reaction with organic matter to form harmful chloro-organic by-products. Therefore, a novel non-thermal method, atmospheric cold plasma (ACP) to kill pathogens on the outer surface of shell eggs was assessed. Our results suggested that ACP can be used as an effective antimicrobial and has negligible impact on eggshell strength and yolk color. Egg processors can use the information to ensure the microbial safety of shell eggs.

Technical Abstract: The main objective of this study was to evaluate the tolerance of stationary phase (STAT) and long-term survival phase (LTS) Salmonella Enteritidis ATCC 13076 to atmospheric cold plasma (ACP) in phosphate buffered saline (PBS, pH 7.0) and on shell eggs. Salmonella Enteritidis was cultured in tryptic soy broth supplemented with 0.6% (w/v) yeast extract (35C) for 20 h (STAT) and 21 days (LTS). Cell morphology was determined by light microscopy. The PBS and shell eggs were inoculated with STAT or LTS cells to obtain approx. 7.0 log10 CFU/ml or egg. The ACP was applied at 45 kV (PBS) and 60 kV (shell eggs) for 1 to 4 min and 1 to 5 min, respectively. Pathogen survivors were enumerated on thin agar layer (TAL) medium and on xylose lysine tergitol-4 (XLT-4) agar after 48 h of incubation (35C). For survivors on shell eggs, R2 and mean square error values were obtained using Log-linear with Tail and Weibull models. The STAT cells were predominantly rod-shaped whereas LTS cells were coccoid. In PBS, reductions (log10 CFU/mL) of STAT cells were 1.0, 0.95, 1.45, and 1.44 after exposure to ACP for 1, 2, 3, and 4 min, respectively. In contrast, reductions in LTS cells were significantly lower (p less than 0.05) at 0.04 (1 min), 0.06 (2 min) 0.01 (3 min), and 0.11 (4 min). A similar pattern was observed for shell eggs whereby LTS cells exhibited much higher tolerance to ACP than STAT cells (p less than 0.05). The Log-linear with Tail model produced a better fit of the survival data for STAT cells; times to achieve a 4- and 5- log reduction were 5.29 and 5.78 min, respectively. Sub-lethal injury occurred in both STAT and LTS survivors; however, differences were not significant (P more than 0.05). Additionally, there were no observed differences in eggshell strength and yolk color between ACP-treated and control eggs. Based on these results, LTS cells of S. Enteritidis are more tolerant to ACP than STAT cells and should be considered when developing process validation protocols involving application of ACP to inactivate Salmonella on shell eggs.