Applicability of commercial phage-based products against Listeria monocytogenes for improvement of food safety in Spanish dry-cured ham and food contact surfaces

Abstract

The efficacy of bacteriophages as antimicrobials has fostered the approval and commercialization of several products intended to reduce the risk of food contamination by pathogenic bacteria. ListShield™ and Listex™ P100 are bacteriophage preparations that aim to combat Listeria monocytogenes in food industries. Here, we assessed the effectiveness of these phage-based products against L. monocytogenes strains from food origin. Both, removal of L. monocytogenes biofilms and inhibition of growth in Spanish dry-cured ham were evaluated for this bacterium. ListShield™ was effective in lysing 100% of L. monocytogenes strains examined, whereas Listex™ P100 lysed only 64% of the same strains. According to the manufacturers’ recommendations, ListShield™ was used in a lower concentration than Listex™ P100 for the efficacy studies. Despite these differences, both products were effective in removing 72 h-old biofilms formed on stainless steel surfaces by most of the assayed strains after a 4 h treatment at 12 °C. For some strains, moreover, complete removal of adhered bacteria from 48 h-old biofilms formed on polystyrene surfaces was obtained after 4 h of treatment at 32 °C with Listex™ P100. Evaluation of phage-based products as biopreservatives in dry-cured ham showed that the application of Listex™ P100 resulted in a reduction of L. monocytogenes contamination below the detection limit (<10 CFU/cm2) after 24 h at 4 °C and 12 °C. Treatment with ListShield™ showed similar results with the exception of samples with a high level of contamination (105 CFU/cm2), in which a reduction of 3.5 log units was achieved after 14 days of incubation at 4 °C. In contrast, the antibacterial activity of ListShield™ decreased in samples stored at 12 °C, although a complete elimination of bacteria was observed after 8 days of treatment in low contaminated samples (103 CFU/cm2). All these results suggest that phage-based products can be useful for biocontrol of L. monocytogenes in food contact surfaces and dry-cured ham.