A unique DNA sequence of human enterotoxigenic Escherichia coli enterotoxin encoded by chromosomal DNA

Abstract

We detected Ent plasmids in 300 strains of human enterotoxigenic Escherichia coli, but one strain, E. coli 240‐3, had neither a small nor a large plasmid and encoded the heat‐labile enterotoxin (LTh(240‐3)) gene on its chromosome. DNA sequences showed that LTh(240‐3) differed by 12 and 14 base pairs from LT (LTh) and LT (LTp) from human H10407 and porcine EWD299 strains, respectively. In deduced precursor toxins, LTh(240‐3), LTh and LTp differed from LTh, LTp and LTh(240‐3) at nine, eight and eleven positions, respectively. These data suggest that although 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 amino acids sequences.

Genetic Diversity of Heat-Labile Toxin Expressed by Enterotoxigenic Escherichia coli Strains Isolated from Humans

“…The same LT has also been detected in an ETEC strain isolated from a Japanese tourist, further demonstrating the distribution of the type on a worldwide scale (20). Interestingly, the same group reported that, in contrast to other ETEC strains, the gene encoding this variant LT was integrated into the chromosomal DNA of the strain (20). In our strains, preliminary data indicated that, at least in some strains, the elt operon encoding the LT2 type is located on episomal plasmids, but further analyses should evaluate in more detail the locations of the replicons encoding different LT types.…”

“…This LT type was detected in six different serotypes and was recovered from subjects in different regions in Brazil and Bangladesh (represented by the 258909-3 strain). The same LT has also been detected in an ETEC strain isolated from a Japanese tourist, further demonstrating the distribution of the type on a worldwide scale (20). Interestingly, the same group reported that, in contrast to other ETEC strains, the gene encoding this variant LT was integrated into the chromosomal DNA of the strain (20).…”

“…This LT type seems to have a widespread distribution; it was detected among both LT ϩ and LT ϩ /ST ϩ strains and in an ETEC strain (258909-3) derived from a subject in Bangladesh. This LT allele was also independently reported 10 years ago in a Japanese tourist returning from Israel (20). LT3, displayed by two O88:H25 strains, showed two polymorphic sites in the A subunit (K213E and R235G), while LT4 showed the same amino acid sequence as the previously described LTp (20, 50) with two polymorphic sites (K4R and K213E) in the A and three polymorphic sites (S4T, A46E, and E102K) in the B subunit.…”

“…Based on the nucleotide sequences of the elt operons present in these two strains, five polymorphic sites have been detected, leading to four amino acid replacements: three in the A subunit (K212R, E213K, and D238N) and one in the B subunit (H13R). More recently, one LT variant with five polymorphic sites in the A subunit and one in the B subunit was reported to be encoded by a chromosomally integrated elt operon of a strain recovered from a Japanese tourist (20). Thus, a better knowledge of LT diversity among ETEC strains isolated from humans awaits a more detailed scrutiny of elt operons carried by strains belonging to different clonal groups or with different geographic origins.…”

Allele Variants of Enterotoxigenic Escherichia coli Heat-Labile Toxin Are Globally Transmitted and Associated with Colonization Factors

“…The MEGA program (version 5.2) was used to extract the variables in the translated amino acid sequence of each strain. Sequences were compared to LT variants reported in previous studies: LT1 (15), LT2 (20) (15). Phylogenetic trees were generated in MEGA (version 5.2) using the neighbor-joining algorithm.…”