Final Examination for the Degree of MSc - Safaa Fallatah

Date and Time


Food Science room 128


Final Examination for the Degree of MSc

Examining Committee
Dr. Lisa Duizer, Chair
Dr. Mansel Griffiths, Co-Advisor
Dr. Andrew Kropinski, Advisory Committee Member
Dr. Gisele LaPointe, Department Member

TITLE: Isolation and characterization of bacteriophages against Listeria Monocytogenes and their applications as biosensors for foodborne
pathogen detection

ABSTRACT: The aim of this study was to determine the potential application of bacteriophages for the detection of Listeria spp. on food contact surfaces (FCS). Twenty-four powerfully lytic Listeria phages were obtained from a Culture Collection at the Canadian Research Institute for Food Safety (CRIFS). Nineteen of these phages were selected for further characterization to determine the most appropriate phage for use in a detection assay. The nominated phages were characterized for host range using spot test and Bioscreen C against Listeria spp. and Gram-positive non-Listeria spp. Eight phages were chosen and characterized by TEM, stability to air dying for 24 h at 25 °C, and restriction endonuclease pattern. One strain of L. monocytogenes C716 was very resistant to all phages, however; a mutated phage, AG13M, was able to infect L. monocytogenes strain C716. Two phages (AG20 & AG23) were selected from a set of 8 similar phages as they showed high specificity against their host (Listeria spp). The genome sequence of AG20 was determined. Although, phages AG20 and AG23 were used for printing, it was only the AG20 phage that immobilized on ColorLok paper when used in the experiments to detect L. monocytogenes C519 in both broth and food contact surface. A phage capture-amplification assay based on the immobilized phage was able to detect as few as 50 CFU/mL of L. monocytogenes in TSB and 40 CFU/cm² on stainless steel using a plaque assay to detect progeny phage. In addition, the assessment of e stability of the immobilized phage on the paper indicated lost of infectivity after one week of the phage lost infectivity. When using the immobilized phage with detection of progeny phage by plaque assay, results were obtained within only 24 h. Immobilized phage-based assays need more improvement in their sensitivity, and stability to better detect L. monocytogenes in media, FCS or food.

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