In Vitro Assessment of the Susceptibility of Planktonic and Attached Cells of Foodborne Pathogens to Bacteriophage P22-Mediated Salmonella Lysates

This study was designed to evaluate the lytic activity of bacteriophage P22 against Salmonella Typhimurium ATCC 19585 (Salmonella Typhimurium P22⁻) at various multiplicities of infections (MOIs), the susceptibility of preattached Salmonella cells against bacteriophage P22, and the effect of P22-mediated bacterial lysates (extracellular DNA) on the attachment ability of Listeria monocytogenes ATCC 7644 and enterohemorrhagic Escherichia coli ATCC 700927 to surfaces. The numbers of attached Salmonella Typhimurium P22⁻ cells were effectively reduced to below the detection limit (1 log CFU/ml) at the fixed inoculum levels of 3 × 10² CFU/ml (MOI = 3.12) and 3 × 10³ CFU/ml (MOI = 4.12) by bacteriophage P22. The attached Salmonella Typhimurium P22⁻ cells remained more than 2 log CFU/ml, with increasing inoculum levels from 3 × 10⁴ to 3 × 10⁷ CFU/ml infected with 4 × 10⁸ PFU/ml of P22. The number of preattached Salmonella Typhimurium P22⁻ cells was noticeably reduced by 2.72 log in the presence of P22. The highest specific attachment ability values for Salmonella Typhimurium P22⁻, Salmonella Typhimurium ATCC 23555 carrying P22 prophage (Salmonella Typhimurium P22⁺), L. monocytogenes, and enterohemorrhagic E. coli were 2.09, 1.06, 1.86, and 1.08, respectively, in the bacteriophage-mediated cell-free supernatants (CFS) containing high amounts of extracellular DNA. These results suggest that bacteriophages could potentially be used to effectively eliminate planktonic and preattached Salmonella Typhimurium P22⁻ cells with increasing MOI. However, further research is needed to understand the role of bacteriophage-induced lysates in bacterial attachment, which can provide useful information for the therapeutic use of bacteriophage in the food system.