Submitted to: American Society for Microbiology Branch Meeting
Publication Type: Abstract Only
Publication Acceptance Date: October 15, 1999
Publication Date: N/A
Technical Abstract: In ruminants, such as cattle and sheep, feed withdrawal prior to slaughter may reduce fecal contamination of carcasses. The effect of interrupted feeding in the monogastric animals, such as the pig, is unknown. We have developed a pig caecal cannulation model which allows us to evaluate the effects in vivo of feed withdrawal on (i) the caecal environment, including gpH and volatile fatty acid (VFA) concentration, and (ii) the growth of foodborne pathogens in the caecum. In vitro studies evaluated growth of Yersinia enterocolitica and Salmonella typhimurium at 5 concentrations of VFA at 4 pH levels. Minimal growth occurred in VFA and pH levels which simulated the caecum of a well-fed pig. Maximal occurs in the absence of VFA (0 mM/ml) at pH 7.0. When cultured in the caecal contents of a fasted pig, Yersinia and Salmonella replicate and survive. In contrast, caecal contents of a well-fed pig inhibit their growth in vitro. When instilled directly into the pig caecum, Y. enterocolitica and S. typhimurium are detected in fecal and cecal samples for up to 1 month. Infected pigs were subjected to four cycles of interrupted feeding. No predictable change occurs in the number of Yersinia or Salmonella in the caecum or in feces of pigs subjected to interrupted feedings when compared with controls maintained on a normal feeding regimen. In contrast, a fasting cycle predictably reduced volatile fatty acid concentrations and increased the pH of the caecum. Thus, the pig caecal cannulation model is a practical way of monitoring the long-term dynamics of growth and survival of foodborne pathogens in the live animal.