Development of an anti-Salmonella phage cocktail with increased host range

Salmonella shedding in many livestock species can increase significantly after transport and lairage. Preprocessing increases in shedding can amplify the amount of Salmonella that enters the processing facility and the likelihood of end-product contamination. We previously produced an anti-Salmonella phage cocktail that reduced colonization in swine when the pigs were exposed to an environment heavily contaminated with Salmonella, similar to what might be seen in a transport trailer or processing facility holding pen. The aim of this study was to increase the efficacy of the phage treatment by (1) expanding the host-range of the cocktail and (2) developing a more cost-effective microencapsulation technique. We collected samples from wastewater treatment facilities and isolated 20 distinct phages belonging to either the Siphoviridae or Myoviridae families. From this library we identified 10 phages that together lysed a mixed culture of Salmonella enterica Typhimurium, Enteriditis, and Kentucky--three serovars commonly associated with meat and poultry products. The phages were microencapsulated using two sodium-alginate-based methods that only reduced the cocktail titer by 1.0-1.5 logs (premicroencapsulation: 10.4 log(10) PFU/mL; postmicroencapsulation method one: 9.2 log(10) PFU/mL; postmicroencapsulation method two: 8.9 log(10) PFU/mL). Microencapsulated phages remained stable at both 4°C and 22°C for up to 14 days with no appreciable drop in titer (mean titer: 8.9 log(10) PFU/mL). These data indicate that phage cocktails with wider host ranges are possible and a cost-effective microencapsulation process can protect the phages over an extended period, making simultaneous treatment of large numbers of animals with feed- or water-based delivery possible.