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In this study, the Enterobacteriaceae microbiota, including their diversity as well as the distribution of haemolytic and virulence gene-harbouring Escherichia coli of 56-day-old healthy piglets, was characterized. Both the composition and the diversity of Enterobacteriaceae populations varied considerably between individual pigs and intestinal sections. E. coli, Enterobacter cloacae, Citrobacter freundii and Klebsiella pneumoniae dominated the Enterobacteriaceae microbiota. However, mucosa-associated Enterobacteriaceae were scarce or in some cases undetectable. The majority of E. coli clones from the jejunum were also found in the colon, with up to 10 different E. coli clones in one intestinal section. Other Enterobacteriaceae species were represented by only one clone localized to one intestinal section. While several piglets did not harbour virulence gene-positive or haemolytic E. coli, such strains dominated intestinal sections of other animals. This study reveals that the diversity of intestinal Enterobacteriaceae is clearly individual. In general, Enterobacteriaceae do not appear to be a consistent fraction of the microbiota of the jejunum. High numbers of adherent bacteria do not appear to be essential for successful intestinal colonization, and E. coli clones do not necessarily colonize distinct intestinal sections based on the particular phylogenetic affiliation. Furthermore, dominance of haemolytic or virulence gene-positive E. coli does not correlate with disease. Finally, probiotic Enterococcus faecium feed supplementation does not affect the Enterobacteriaceae microbiota.

Eighty piglets aged 14, 28, 35 and 56 days -weaned at day 28 -were subjected to this investigation. Each age-group consisted of five animals which were fed an Enterococcus faecium NCIMB 10415 (Cylactin ) and Bacillus cereus var. toyoi (Toyocerin ) based diet. Five animals served as controls. Tissue samples were collected immediately after sacrifice at 8.30 h a.m. from duodenum, jejunum, ileum, cecum and colon to examine intestinal morphology and histochemistry. The results showed that with respect to villus height and crypt depth supplementation of probiotics in piglets feed seemed to influence the morphology and enlargement factor not at all or only to a certain extent. With respect to the number of goblet cells, the difference between probiotic fed animals and control animals was generally extremely low. The shape of the villi of the small intestinal segments greatly varied in all age groups of control and probiotic fed animals. However, this morphological variety does not depend on the mode of feeding.

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