Affinity of adherence in vitro and colonization of mice intestine by enterotoxigenic Escherichia coli (ETEC)

The correlation between affinity of adherence in vitro to mice intestinal segments and infectivity in vivo was examined in an enterotoxigenic Escherichia coli (ETEC) strain. Two unstable phenotypes of the same strain were obtained by growing bacteria in agar or broth. Affinity of adherence in vitro calculated by Scatchard plot analysis of agar-grown bacteria was significantly higher than that of broth-grown bacteria. The effective dose of infection of agar-grown bacteria at 3, 24 and 72 h after infection, was one-tenth, one-half and the same, respectively, of that of broth-grown bacteria. The results suggest that the differences in the adhering ability of the inoculum influenced the number of bacteria retained in the intestine during the early phases of infection.