Study of colonization resistance for Enterobacteriaceae in man by experimental contamination and biotyping as well as the possible role of antibodies in the clearance of these bacteria from the intestines.

The colonization resistance (CR) of the digestive tract was determined in 10 healthy volunteers by oral contamination with a neomycin resistant Escherichia coli (NR-E. coli) strain and measurement of the faecal concentration of this strain during 14 days after the contamination. This 'gold standard' was compared with another parameter of CR; the determination of the mean number of different biotypes of Enterobacteriaceae isolated from four faecal samples per volunteer. Both measures are significantly correlated (P less than 0.01). The NR-E. coli strain could be cultured from faecal samples of 4/10 volunteers as long as 300 days after contamination. Serum antibody titres against endogenous E. coli strains and the NR-E. coli strain used for experimental oral contamination were measured by an indirect immunofluorescence (IIF) assay. The assay was read by a video camera connected to an image processing system. The 95% confidence limits of antibody titres (log2) against endogenous E. coli strains ranged between less than 3 and 7.1 for IgA, between less than 3 and 8.7 for IgG and between less than 3 and 7.4 for IgM. Antibody titres against the NR-E. coli4 strain were within this (normal) range. The serum antibody titres against the NR-E. coli strain increased slowly after oral contamination, especially IgG and IgM. Little increase in IgA titres could be observed. An increase of serum antibody titres did not correlate with the elimination of the oral contaminant from the intestines. Therefore, we conclude that the CR is not IgG nor IgM antibody mediated.