This paper describes an immuno-electrophoretic method to detect soluble antigens of enteropathogenic Escherichia coli strains. The researchers prepared antisera from living (L) and dead (D) vaccine preparations of E. coli strains and tested them against antigens from rabbit gut loop exudates and culture extracts using immuno-electrophoresis. A distinctive precipitin line designated "line 1" appeared only when L sera from enterotoxic strains were tested against exudates or extracts from strains causing rabbit intestinal loop dilatation. This line was absent in D sera and was never produced by non-pathogenic strains. A survey of 375 human E. coli isolates showed that 99 of 316 strains from babies with diarrhea produced line 1, while all 39 strains from healthy babies were negative. Importantly, line 1 was not produced by strains from urinary infections, vaginal swabs, or cerebrospinal fluid. The findings suggest that line 1 represents a soluble antigen associated with enterotoxic potential, independent of classical O, K, and H antigens, providing a potential serological marker for identifying pathogenic E. coli strains.

Key findings

• A precipitin line (line 1) detected by immuno-electrophoresis appears only with antisera from living cultures of enterotoxic E. coli strains, distinguishing pathogenic from non-pathogenic isolates
• Line 1 production correlates with E. coli strains causing rabbit intestinal loop dilatation, a marker of enterotoxin production
• Among 316 E. coli strains from babies with diarrhea, 99 produced line 1, while all 39 strains from healthy babies were negative, suggesting line 1 indicates enteropathogenic potential
• Line 1 antigen is independent of known O, K, and H somatic antigens and represents a novel soluble antigen associated with enterotoxicity
• The immuno-electrophoretic method may provide a more practical alternative to the cumbersome rabbit gut loop test for identifying enteropathogenic E. coli strains