PHENOTYPIC CHARACTERIZATION OF INTESTINAL ESCHERICHIA-COLI OF PIGS DURING SUCKLING, POSTWEANING, AND FATTENING PERIODS

A highly discriminatory and standardized biochemical fingerprinting method was used to monitor the persistence and colonization of intestinal Escherichia coli isolated from the feces of four sows and their litters (four piglets from each) during the suckling, postweaning, and fattening periods. Altogether, 195 fecal samples were collected and 1,827 E. coli strains were tested (mean number of isolates tested per fecal sample per pig, 9.5). Strains were divided into similarity groups on the basis of their biochemical phenotypes (BPTs). The diversity of E. coli strains in each sample was measured with Simpson's index of diversity, and similarity between E. coli floras of piglets was calculated with a population similarity index. Each fecal sample contained several BPTs of E. coli, some of which dominated that population. The intestinal colonization of piglets consisted of successive waves of different E. coli BPTs, the tenure of which varied from a few days to 2 weeks. Most of these BPTs disappeared in the succeeding samples and were not recovered again from the same piglets. On the other hand, some E. coli strains which colonized piglets early during the suckling period persisted for a long period and were referred to as resident BPTs. Each piglet carried more than one resident BPT (mean of 2.4 BPTs per pig), some of which were also found in other piglets. This finding indicates that both strain and host specificity are important for colonization and persistence of E. coli in pigs. During the first week of life, E. coli floras of piglets were quite different from those of their dams, suggesting that the dominant E. coli strains in piglets might be quite different from those of their sow. Despite the similarity in E. coli floras between littermates during suckling, each piglet developed a unique flora during postweaning and fattening periods. Pigs which were kept together in one litter until the end of the study had E. coli floras more similar to each other than those mixed with other pigs.