Factors influencing F18+ Escherichia coli receptor expression in weanling pigs

Enterotoxigenic Escherichia coli (ETEC) colonizes the small intestine of weanling pigs and causes post-weaning diarrhea, a disease responsible for severe economic loss in many production units. Several types of ETEC can cause post-weaning diarrhea, but F18+ ETEC is increasing in prevalence. F18 refers to the fimbrial adhesin present on E. coli responsible for attaching to intestinal epithelial cells. Receptors for the F18 fimbrial adhesin on the intestinal epithelial cells of pigs do not appear until after the pigs are several weeks of age, suggesting that conditions at weaning may be responsible for inducing receptor expression. To determine if environmental factors influence F18+ receptor expression, 3-week old gnotobiotic piglets were randomly divided into 4 treatment groups. Four groups of eight piglets were given either: (1) a sterile weanling diet, (2) a mixture of bacterial strains representing the normal microbial flora, (3) a weanling diet and the representative microbial flora, and (4) sterile milk replacer. At four weeks of age pigs were challenged with an F18+ E. coli strain. Twenty-four hours after challenge pigs were necropsied and examined for evidence of enteric disease. Small intestine sections (duodenum, jejunum, and ileum) were harvested for histological analysis, bacterial quantification, F18+ fimbrial expression, and bacterial adhesion assays. There were significant differences in colonization and adherence of F18+ E. coli in the groups given the bacteria representing normal microbial flora and the sterile weanling diet when compared with the control group that received only milk replacer. These findings suggest that diet and the microbial flora may be at least partially responsible for inducing F18+ receptor expression in weanling pigs.