RETENTION OF ENTEROPATHOGENICITY BY VIABLE BUT NONCULTURABLE ESCHERICHIA-COLI EXPOSED TO SEAWATER AND SUNLIGHT

The effect of natural sunlight on culturability and persistence of pat hogenicity of Escherichia coli was examined in the field, i.e., in the Morlaix Estuary, France, using an enterotoxigenic strain of Escherich ia coli H10407, Results showed that E. coli responds to the estuarine diurnal solar cycle by entering the viable but nonculturable state upo n exposure to sunlight, That is, direct counts of viable cells remaine d stable without significant change, but E. coli cells remained fully culturable only when exposed to seawater in control chambers in the da rk, i.e., without solar irradiation, The effect of sunlight on the pat hogenicity off. coli H10407 was studied, using both the rabbit intesti nal loop assay and ganglioside-enzyme-linked immunosorbent assay (GM1- ELISA), a sensitive procedure for testing for production of enterotoxi n. Results of the GM1-ELISA demonstrated that strains off. coli, after exposure to sunlight and entering the viable but nonculturable state, as well as culturable E. coli, retained pathogenicity, i.e., produced enterotoxin. The GM1-ELISA is concluded to be more sensitive than the rabbit intestinal loop assay for analysis of enterotoxin in natural w ater samples.