UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Characterization and application of bacteriophages for the biocontrol of Shiga-toxin producing Escherichia coli Lu, Yu Tong


Shiga-toxin-producing Escherichia coli (STEC) have been implicated with numerous outbreaks associated with the contamination of food products. Fresh produce, a minimally processed commodity, may become contaminated during production, processing, and distribution. Bacteriophages are viruses that specifically target and utilize bacterial hosts for replication. The availability of phage-based antibacterial strategies has provided the food industry with a sustainable, natural, and cost-effective method to control contamination. Although phage products for biocontrol are currently available, the risk of potential bacterial resistance mandates continuing the characterization of new strains for future formulations. Previously isolated phages (n = 13) were sequenced and assembled de-novo. Sequences were then probed for their phylogenetic origin and annotated for the identification of potential integrase genes, and virulence or pathogenic genes. Phages (n = 3) were selected based on their ease of propagation and ability to target STEC O157. Select phages were tested for their efficacy against four strains of STEC O157 both in broth culture and on fresh Romaine lettuce at a temperature of 10°C. Whole-genome nucleotide alignment based on the large subunit of the terminase gene identified that phages were closely related, clustering into three distinct clusters and two singletons. The lack of integrase, virulence, and pathogenic genes demonstrated their suitability for the food industry. Of the three phages tested for efficacy against STEC serogroup O157 strains, all were equally effective in reducing STEC populations significantly compared to the control in liquid culture (P<0.05). Likewise, phages VE04, VE05 and VE07 were effective against the tested STEC O157 strains on Romaine lettuce. Compared to control groups, log-reduction ranged from 2.6 log colony forming units (CFU) /cm2 to approximately 6 log CFU/cm2 after 3 days of storage at a temperature of 10°C (P<0.05). Phages remained stable and persisted despite the absence of a STEC host in broth culture and on Romaine lettuce, confirming their stability as biocontrol agents in the food industry during storage, transport, and retail. The added understanding of phage treatments will support optimized novel strategies for the control of STEC O157 contamination in fresh produce and therefore reduce the economic and health burden associated with outbreaks.

Item Media

Item Citations and Data


Attribution-NonCommercial-NoDerivatives 4.0 International