Evolutionary origin of pathogenic determinants in enterotoxigenic Escherichia coli and Vibrio cholerae O1

Three families of the evolutionarily related pathogenic determinants in enterotoxigenic Escherichia coli and Vibrio cholerae O1, a family of cholera enterotoxin (CT) and heat-labile enterotoxin (LT) including CT, LTh, and LTp, a family of heat-stable enterotoxin I (STI) including STIa and STIb, and a family of K88 enteroadhesion fimbriae including K88ab, K88ac, and K88ad were analyzed for synonymous (silent) nucleotide substitutions by using the gene nucleotide sequences of earlier reports and the LTp gene nucleotide sequence presented in this paper. The data suggested that the divergences between LT and CT and between STIa and STIb occurred in the remote past, whereas those between LTh and LTp and between members of the K88 family occurred very recently. We concluded that the LT gene is a foreign gene that has been acquired by E. coli to form an enteropathogen. This provides evolutionary evidence of species-to-species transfer of pathogenic determinants in procaryotes.