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He, Jiangning

University of British Columbia

Nontyphoidal Salmonella, specifically Salmonella enterica subspecies enterica serovar Enteritidis (SE), is a significant global cause of foodborne illness, often linked to egg contamination. Current antimicrobial interventions primarily target the egg surface, leaving the egg content susceptible to contamination. Bacteriophages, natural viral predators of bacteria, offer a promising biocontrol treatment due to their abundance, self-replication, specificity, and safety. This study evaluated the inhibitory effects of eight phages against three SE strains isolated from the chicken environment. The most effective phages were selected to formulate different phage cocktails, enhancing their efficacy and prolonging inhibition. Five phage cocktails were tested at an Multiplication of Infection (MOI) of 100 in tryptic soy broth, and at MOIs of 100 and 1000 in liquid egg white and yolk, incubated at 8°C for 30 days. The effectiveness of the phage cocktails varied significantly among bacterial strains, yet all demonstrated significant reductions compared to the positive control in liquid culture (P < 0.05). Similarly, the tested SE strains in both egg white and egg yolk showed significant reductions with phage treatments (P < 0.005), although the effectiveness was influenced by the MOI and medium composition. Treating egg yolk proved to be more challenging, with lower magnitudes of reduction and longer treatment durations required, compared to egg white. Log reduction ranged from 1 to over 4 log CFU/mL in egg white and yolk after 30 days, with consistently higher reductions achieved at MOI 1000. Additionally, phage titers decreased initially but remained stable at later stage when SE was inoculated in broth and liquid eggs at 8°C, indicating the involvement of lysis-from-without mechanisms contributing to the inhibitory effect. Notably, phages exhibited stronger attachment to Salmonella in egg white, which can be attributed to be less viscous nature of egg white compared to egg yolk. This study demonstrated that phage applications to both egg yolk and egg white effectively reduced Salmonella contamination at 8°C, with no regrowth during long-term storage. These findings contribute to the development of biocontrol methods that enhance food safety and reduce foodborne outbreaks associated with contaminated egg products.

Text

2024-09-30

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/85692

Food Science

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/