Direct feeding of microencapsulated bacteriophages to reduce Salmonella colonization in pigs.

Salmonella shedding often increases in pigs after transportation and/or lairage. We previously showed that administering anti-Salmonella bacteriophages to pigs by gavage significantly reduced Salmonella colonization when the pigs were exposed to a Salmonella-contaminated holding pen. Here we tested whether a microencapsulated phage cocktail would remain effective if the treatment was administered to pigs in the feed. Pigs (n=21) were randomly placed into three groups: feed, gavage, and control. The feed group was direct-fed a microencapsulated phage cocktail daily for 5 days. On the fifth day, the gavage group received the same phage cocktail by gavage, whereas control pigs received a mock treatment containing no phage. All pigs were then orally challenged with Salmonella enterica serovar Typhimurium. Fecal swab samples were collected every 2 h. At 6 h postchallenge, all pigs were euthanized, and ileal and cecal contents and mesenteric lymph nodes were collected and analyzed for the challenge organism. Pigs in the feed group were less likely to shed Salmonella Typhimurium at 2 h (38.1%) and 4 h (42.9%) postchallenge than pigs in both the gavage (2 h: 71.4%; 4 h: 81.1%) and control (2 h: 71.4%; 4 h: 85.7%) groups (p<0.05). Likewise, concentrations of Salmonella Typhimurium in ileal (2.0 log(10) colony forming units [CFU]/mL [contents]) and cecal (2.7 log(10) CFU/mL) contents from feed pigs were lower than ileal (3.0 log(10) CFU/mL) and cecal (3.7 log(10) CFU/mL) contents from control pigs. High concentrations of anti-Salmonella phages were detected in ileal and cecal contents from both feed and gavage pigs (feed ileal: 1.4×10(6); feed cecal 8.5×10(6); gavage ileal 2.0×10(4); gavage cecal: 2.2×10(3)). It is concluded that direct feeding of microencapsulated phages is a practical and effective means of reducing Salmonella colonization and shedding in pigs.

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.