A comparison of the ecology of Escherichia coli in the intestine of healthy unweaned pigs and pigs after weaning.

A total of 51 clinically healthy pigs (14 unweaned and 37 weaned) from five litters, and aged 21 to 35 d, were studied. Escherichia coli isolates from the duodenum, jejunum, ileum, caecum and colon were differentiated on the basis of O-serogroup, biotype and resistance pattern. The complexity of the flora was influenced considerably by the presence or absence of the enterotoxigenic serotype 0149: K91, K88a,c (Abbotstown strain). When it was absent the E. coli flora of both weaned and unweaned pigs was complex with up to 25 strains being identified. The majority of these E. coli strains identified in each pig were isolated from only one of the five intestinal sites sampled. On the other hand, when the enterotoxigenic strain was present (14 pigs) it tended to dominate the E. coli flora at all levels of the intestine and this dominance was reflected in a corresponding fall in the total number of E. coli strains isolated per pig.