In 18 out of 67 sows with mastitis, e.coli of the same o types present in samples of mammary secretion were isolated from the feces. This underlines the endogenous character of most extraintestinal infections in the pig as well.
The primary habitat of procine e.coli is the gastrointestinal tract. The e.coli flora of individual pigs is extremely complex. When strains were distinguished by the combined application of O serogrouping, biotyping, and resistogram typing, up to 25 strains were identified in the gastrointestinal tract of one individual.
Numerically dominant strains change at interval from 1 day to several weeks, leading to successive waves of dominant strains. Proliferation of e.coli takes place mainly in the course of the passage through the small intestine.
Increase from the ileum to the rectum is minimal or absent. Number in the large intestine fluctuate around 10 colony-forming units/g. However, e.coli contribute less than 1% to the total bacterial count. When found elsewhere, e.coli are derived from this habitat, usually by fecal contamination. Long survival times in the environment are promoted by low temperature and sufficient available water, among other factors. In an experiment with five slurry samples, a porcine e.coli O139:K82(B) retained viability for between 5 and over 11 weeks.