A UNIQUE DNA-SEQUENCE OF HUMAN ENTEROTOXIGENIC ESCHERICHIA-COLI ENTEROTOXIN ENCODED BY CHROMOSOMAL DNA

We detected Ent plasmids in 300 strains of human enterotoxigenic Esche richia coli, but one strain, E coli 240-3, had neither a small nor a l arge plasmid and encoded the heat-labile enterotoxin (LTh(240-3)) gene on its chromosome. DNA sequences showed that LTh(240-3) differed by 1 2 and 14 base pairs from LT (LTh) and LT (LTp) from human H10407 and p orcine EWD299 strains, respectively. In deduced precursor toxins, LTh( 240-3), LTh and LTp differed from LTh, LTp and LTh(240-3) at nine, eig ht and eleven positions, respectively. These data suggest that althoug h LTh(240-3) encoded in the chromosome is antigenically similar to LTh , it cannot be grouped with LTh due to differences in its DNA and amin o acids sequences.