Application of bacteriophages during depuration reduces the load of Salmonella Typhimurium in cockles

• Phages were applied during cockle depuration to reduce S. Typhimurium.
• Phages inactivated S. Typhimurium in naturally/artificially contaminated cockles.
• Single phage suspensions were more effective than phage cocktail.
• Depuration with phages increased the decontamination efficiency.

As bivalve molluscs are filter feeder, often consumed raw or lightly cooked and are frequently cultivated in contaminated waters, they are implicated in food-borne disease transmission to human. The present study investigated the potential application of bacteriophage (or phage) phSE-2, phage phSE-5 and phage cocktail phSE-2/phSE-5 to decrease the concentration of Salmonella enterica serovar Typhimurium (Salmonella Typhimurium) during the depuration of natural and artificially contaminated cockles (Cerastoderma edule). Cockles were artificially infected with 105 and 106 colony-forming units (CFU)/mL of S. Typhimurium in static seawater and infected group were treated with phages at four different MOI values: 0.1, 1, 10 and 100. Depuration in static seawater at multiplicity of infection (MOI) of 0.1 with single phage suspensions of phSE-2 and phSE-5 provided the best results, as it decreased by ~ 1.3 and 1.7 log CFU/g, respectively, the concentration of Salmonella spp. after a 4 h treatment. At a MOI of 0.1, the rate of inactivation with single phage suspensions was higher when compared with the results obtained using the phage cocktail. However, in naturally contaminated cockles treated in static seawater with single phage suspensions and phage cocktail phSE-2/phSE-5, similar decreases in cultivable bacteria concentration (~ 0.7–0.9 log CFU/g) were achieved after 6 h of treatment. When artificially contaminated cockles were depurated with phage phSE-5 in a recirculated seawater system (mimicking industrial depuration conditions), a 0.9 and 2.0 log CFU/g reduction of Salmonella spp. was reached after 4 and 6 h treatment. Once the depuration process was performed without phage, a 6 h treatment was needed to obtain a 1.1 log CFU/g reduction of Salmonella spp. Results indicated that combining phage biocontrol with depuration procedures enhance bivalve microbial safety for human consumption by improving decontamination efficiency, proving that this technology can be transposed to the bivalves industry. Moreover, this approach also displays the advantage of reducing the time required for depuration and consequently its associated costs.

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