Prevalence, sequence diversity, and amplification of an IS-associated enterotoxin gene, astA, in Escherichia coli

The results showed that 185 (6.8%) of the Kagoshima strains and 690 (7.6%) of the database strains had similar possession rates. We identified 31 sequence variations (four known and 27 new variants [V8-34]) which were widely distributed in the <i>E. coli</i> lineages. Detailed sequence analyses revealed that 31 of the 35 <i>astA</i> gene types are intact and encode 23 types of EAST1 peptides. Although all 35 types were associated with IS<i>1414</i>, only three (prototype, V30, and V31) of the 31 intact <i>astA</i> gene types were encoded in the intact IS<i>1414</i>. A notable number of prototype-bearing strains (43/146 strains) possessed multiple copies (two to 11 copies) of this type of <i>astA</i> gene, indicating that the amplification has predominantly occurred in the prototype, which was driven by IS1414 amplification. However, given that the IS1414 associated with V30 and V31 also remain structurally intact, it is plausible that similar amplification events may occur in these variants in the future. These results provide an important basis to investigate the virulence of the <i>astA</i>-positive strains and the role of EAST1 as a virulence factor.