Biocontrol of foodborne bacterial pathogens using immobilized bacteriophages
The goal of the present research was to develop a simple technique to immobilize isolated lytic phages and explore the potential use of these immobilized phages to control certain foodborne pathogens in a real food system. More than one hundred phages were isolated from different environmental samples against different strains of four major foodborne pathogens; 'E. coli ' O157:H7, 'Salmonella, Listeria monocytogenes' and ' Shigella'. A turbidimetric method in high throughput format using the Bioscreen C was used to monitor phage lytic activity and determine the host range of the isolated phages. This enabled identification of isolated phages with similar characteristics and the selection of twelve good phage candidates for biocontrol purposes. These phages were characterized by TEM, restriction endonuclease pattern, one-step growth curve, BIM (bacteriphage insensitve mutant) development, cross infectivity and determination of their stability and infectivity under different conditions. A novel 'Shigella ' phage, [Phi]SboM-AG3, was isolated and its genome sequenced. Its genome did not show any homology to any reported virulent or lysogenic genes and it was considered as a member of the "T4 superfamily". Phage cocktails made from the isolated phages were very effective for specific control of the four target pathogens in both broth media and contaminated food stored under different environmental conditions. The phages were immobilized using positively charged carrier substrates, which allowed specific 'binding of phages through their heads and leaving tail fibers free to interact with bacteria. These immobilized phages retained infectivity and immobilized 'Listeria ' and 'E. coli' phage cocktails were able to control the growth of 'L. monocytogenes' and 'E. coli' O157:H7, respectively, in food under different temperatures and packaging conditions.