Evaluation of immuno-dot-blot assay for detection of cholera-related enterotoxin antigen in Salmonella typhimurium

Abstract

Twenty-five strains of Salmonella typhimurium isolated in India were examined for the presence of cholera/coli-related enterotoxin antigen by a previously described latex particle agglutination test and by a newly developed immuno-dot-blot test using immunopurified goat antibody against the cholera-related enterotoxin isolated from an Escherichia coli strain of human origin. The immuno-dot-blot assay could detect 0.02 ng of purified enterotoxin. The amount of toxin antigen detected varied widely from strain to strain. Fourteen of the 25 polymyxin B-treated extracts of bacteria harvested from 6-h Casamino Acids-yeast extract broth cultures gave positive results in both serologic assays as well as in rabbit skin tests for delayed permeability factor. An additional strain was positive only in the immuno-dot-blot. Five of six stool isolates and six of seven blood isolates tested gave positive reactions. Two isolates of Salmonella enteritidis tested were also positive. The immuno-dot-blot test appears to be a simple, rapid, and reliable method for detection of cholera-related enterotoxin antigen in S. typhimurium. The demonstration of a cholera-related enterotoxin, even in small amounts, in a facultative intracellular pathogen raises interesting questions regarding its potential role in pathogenesis both of diarrheal disease and systemic infections caused by salmonellae.