Assay method for Vibrio cholerae and Escherichia coli enterotoxins by automated counting of floating chinese hamster ovary cells in culture medium.

As Chinese hamster ovary (CHO) cells on plastic proliferate, many cells float off into the medium instead of piling up after they form a monolayer. Fewer cells were floating in the medium when CHO cells were incubated with cholera toxin at a concentration as low as 10 pg/ml. The toxin increased the adhesiveness of the cells forming confluent monolayers so that the floating cells accumulated on the adherent monolayers. On the basis of this finding, a simple, quantitative assay method for cholera and Escherichia coli enterotoxins was devised by cultivating CHO cells in a Linbro multidish and counting the cells in the medium with a Coulter Counter. The method was sensitive enough to detect toxins in 100- to 200-fold-diluted culture media of toxigenic E. coli strains. Little or no activity was detected by this method in the culture medium of nontoxigenic E. coli.