Characterization of Salmonella Thompson-specific bacteriophages and their preventive application against Salmonella Thompson biofilm on eggshell as a promising antimicrobial agent in the food industry

Abstract

Salmonella Thompson is a foodborne pathogen that has attracted attention in Korea since it was identified as the cause of a large-scale domestic food poisoning outbreak in 2018. The present study aims to isolate and characterize bacteriophages specific to Salmonella Thompson and evaluate their efficacy in reducing Salmonella Thompson biofilm on eggshell. In addition, advanced microscopic analysis using field-emission scanning electron microscopy and confocal laser scanning microscopy was conducted to confirm the anti-biofilm activity. The two isolated bacteriophages CAU-STP-1 and CAU-STP-2 showed very high specificity by targeting only Salmonella Thompson. They were determined to be stable at 60–65 °C and pH 4–11. Bacteriophage particles quickly adsorbed to the host cells, with a latent period and burst size of 30–40 min and 19–100 plaque-forming units per cell, respectively. When comparing the two bacteriophages individually, CAU-STP-1 exhibited the highest in vitro inhibition ability, but treatment with both bacteriophages together in a cocktail was significantly more effective than with CAU-STP-1 alone. This bacteriophage cocktail was consequently employed to treat Salmonella Thompson biofilm on eggshell at different storage temperatures. There was a significant reduction in the biofilm on the eggshell with bacteriophage treatment at 10 and 20 °C after 7 days. For example, After 7 days at 10 °C, the biofilm on eggshell was reduced by 0.26, 0.96, and 2.50 log CFU/cm2 for MOI 103, MOI 104, and MOI 105, respectively. On the other hand, at 20 °C, the biofilm on eggshells was reduced by 0.10, 0.24, and 0.33 log CFU/cm2 for MOI 103, MOI 104, and MOI 105, respectively This study thus provides promising information for the potential development of an effective biocontrol agent against Salmonella Thomson within the food industry. © 2023