[Characteristics of enterotoxigenic Escherichia coli and E. coli harboring enteroaggregative E. coli heat-stable enterotoxin-1 (EAST-1) gene isolated from a water-borne outbreak].

A water-borne outbreak occurred in A Town in Akita prefecture on March 1995. Enterotoxigenic Escherichia coli (ETEC) strains were isolated from 6 of 13 feces of patients with food poisoning disease and from 1 of 4 drinking water samples. In addition, E. coli strains harboring Enteroaggregative E. coli (EAggEC) heat-stable enterotoxin-1 (EAST-1) gene were isolated from 5 of 13 patient's feces and 1 feces sample obtained from the septic tank. Both of the E. coli strains were isolated from the 3 patient's feces, suggesting that this outbreak was a mixed infectious case. All of the ETEC strains possessed both heat-stable enterotoxin (ST) and EAST-1 genes and their serotype was O148:H28. The EAST-1 gene was detected on a ca. 80 kb plasmid by a southern blot analysis using EAST-1 DNA probe in the 5 of 7 ETEC strains. The southern blot analysis suggested that the location of the EAST-1 gene was genome in the rest of the 2 ETEC strains. A southern blot analysis using ST DNA probe also suggested that the location of the ST gene was genome in all of the ETEC strains. On the other hand, all of the 6 E. coli strains harboring EAST-1 gene could not be serotyped with commercially available OH sera. The location of the EAST-1 gene in all of the isolates was suggested to be genome by the southern blot analysis. All of the isolates lacked aggA gene which has been demonstrated to be involved in expression of aggregative adherence phenotype in EAggEC, suggesting that the EAST-1 gene-harboring strains isolated in this case were distinct from EAggEC. These results indicated that the EAST-1 gene was also harbored by E. coli strains distinct from EAggEC. In addition, a possibility was also suggested that the EAST-1 gene might be a transposon, as well as ST gene. Further study should be conducted in order to elucidate the significance of EAST-1 as a vilurence factor of diarrheagenic E. coli.