Distribution and expression of the astA gene (EAST1 toxin) in Escherichia coli and Salmonella

The distribution and expression of the astA gene (EAST1 toxin) among 358 strains of Enterobacteriaceae were studied. The gene was found in 32.6% and 11.9% of Escherichia coli and Salmonella strains, respectively. The majority of E. coli EAST1-positive strains were found among EHEC (88.0%), EAggEC (86.6%), and A-EPEC (58.3%). The gene was present in 16.6% of E. coli strains without known virulence genes. There was no significant variation among the different serotypes of E. coli tested regarding the presence of the gene. For EPEC, 13.7% of the tested strains were astA-positive. Among atypical EPEC (eae+, bfp-, EAF-) and (eae+, bfp+, EAF-) 46.2 and 72.7%, respectively, were positive. The majority of the A-EPEC (87%) and EaggEC (83%) strains expressed the EAST-1 toxin as judged from Ussing chamber experiments. Of 32 EIEC strains studied, 2 possessed and expressed the gene as determined in Ussing chamber experiments. Among the Salmonella strains studied, five strains isolated from food were positive for astA and one strain of S. agona showed biological activity in Ussing chamber experiments.