Effect of competitive exclusion treatment on colonization of early-weaned pigs by Salmonella serovar Choleraesuis

Abstract

Methods: Litters from three and two sows, respectively, were treated at birth and again at weaning with either of two porcinederived competitive exclusion cultures, one less diverse than the other. Another litter was treated as above with the least diverse competitive exclusion culture that had been supplemented with Bacteroides thetaiotaomicron, a bacterium implicated in effecting gut cell development. Three other litters served as placebotreated or untreated controls. All piglets were challenged at 15 days of age (1 day postweaning) with 10 6 –10 7 colony-forming units (CFU) of Salmonella Choleraesuis. Rectal swabs (collected daily post challenge) and specimens (collected at necropsy 7–9 days postchallenge) were cultured for Salmonella Choleraesuis to assess the incidence of fecal shedding and colonization status of each piglet. Statistical analysis was not performed in this preliminary study due to the confounding of treatment effects with litter effects. Results: There were fewer pigs shedding in litters that received the competition exclusion culture. There were fewer piglets with salmonellae culture-positive tonsils within the litters treated with either competitive exclusion culture. Salmonella Choleraesuis was recovered from the ileocolic lymph nodes of all 32 of the placebo-treated or nontreated piglets and from most but not all of the piglets treated with either of the competitive exclusion cultures. While the incidence of shedding of Salmonella Choleraesuis was less for the litter treated with the least diverse competitive exclusion culture that had been spiked with Bacteroides thetaiotaomicron than for the controls, no other benefits were observed with this treatment. Implications: Competitive exclusion treatment of baby piglets may enhance colonization resistance to Salmonella Choleraesuis, which may reduce the potential for horizontal transmission of the host-adapted pathogen. However, in the absence of statistical analysis, our interpretation should be considered preliminary.