Effect of novel phage cocktail on Salmonella recovered from broiler sources and its anti-biofilm effect on food contact surface model

The contamination of Salmonella in poultry products remains an important food safety and economic issue as the products have been recalled or rejected. Traditional antibiotic-based therapy in the animal production chain can cause antibiotic resistance (ABR) in bacteria, leading to severe illness and failure to treat diseases. Some strains of Salmonella produce genotoxin and extracellular polymeric substances called “biofilm” that support the survival of this bacterium. From this study, phages were applied to control cytolethal distending toxin B (CdtB)-producing, antibiotic-resistant, and biofilm-producing Salmonella isolated from the broiler sources. Out of 116 isolates, only 11 isolates (9.5%) representing six serovars were characterized. Of these, seven isolates were characterized as multidrug-resistant (MDR), three were resistant to one antibiotic, and only one isolate was susceptible to all antibiotics tested. For biofilm formation ability, 18.2% of the isolates were identified as strong biofilm producers, while 63.6% and 18.2% were moderate and weak, respectively. Up to 12 Salmonella phages from our collection were chosen to test their ability on given Salmonella. All the phages showed a strong lytic ability up to 90.9%. Three phages with the highest lysis potential (100% lytic ability) were further selected for a phage cocktail preparation, including WPX5, WPX8, and WPX9. Overall, the phage cocktail completely reduced representative Salmonella counts by three log units in vitro at a multiplicity of infection (MOI) of 10⁴ and 10⁵ at 6 h of treatment. The phage cocktail was tested to reduce Salmonella on different food contact surfaces. At MOI at 10³, the highest reduction of Salmonella attachment was observed in stainless steel surfaces, indicated by a 67% reduction, followed by polyvinyl chloride (PVC) and ceramic by 64% and 58%, respectively. These results suggest that a developed phage cocktail could be a potential biocontrol to control toxin-producing, biofilm-producing, and MDR Salmonella in the poultry industry.