Intestinal Microbial Flora of the Pig

Surface properties of lactobacilli isolated from the small intestine of pigs

One hundred wild-type strains of the genus Lactobacillus were isolated from the small intestine of newly-slaughtered pigs up to 6 months of age. Cell surface hydrophobicity and capsule formation were studied on a number of strains. Strains showing high surface hydrophobicity as measured by the salt-aggregation test and hydrophobic interaction chromatography on Octyl Sepharose were commonly found to adhere in high numbers to isolated pig intestinal epithelial cells. Heat and protease treatment of bacteria of high surface hydrophobicity, including autoaggregating strains in phosphate-buffered saline, showed a drastic decline in this surface property. Three hydrophilic strains (LBp 1044, 1068 and 1073) also showed binding to intestinal cells but at a lower level (approx. 5 bacteria/cell) as compared with the best binding hydrophobic strain (LBp 1063, approx. 11 bacteria/cell). These findings suggest that different or multiple adhesion mechanisms may be involved in the colonization of the small intestinal mucosa of pigs. Cultures of selected strains grown in liquid media rich in carbohydrates did not affect their hydrophobic cell surface character. Therefore it seems less likely that carbohydrate capsule polymers are the major determinants of intestinal colonization of lactobacilli in pigs.

Types and Distribution of Anaerobic Bacteria in the Large Intestine of Pigs

An examination was made of various sites along the length of the swine large intestine, using strictly anaerobic culture methods. Sites were separated by differential washing into fractions described as lumenal content, lumenal surface layer, and intestinal wall tissue. Direct microscopic clump counts averaged 13.3 × 10 10 organisms per g (dry weight) of material in the lumenal content, 14.0 × 10 10 in the surface layer, and 5.1 × 10 10 in the intestinal wall tissue. Both direct microscopic counts and viable culture counts were higher from the lumenal content and surface layer than from the intestinal tissue at all sites sampled in the intestine. Cultural counts averaged 56.2% of the direct microscopic counts in lumenal content and surface layer and 20.2% in intestinal tissue. Over 90% of the bacteria isolated were gram positive and consisted mainly of gram-positive cocci, lactobacilli, eubacteria, and clostridia. Of 192 isolates recovered, only 124 could be assigned to recognized species.