Quantitative analysis by reversed Mancini test of cross-reacting antibodies in rabbit antisera against porcine and humanEscherichia coliheat-labile enterotoxins and cholera toxin

Detection of a heat-labile enterotoxin gene in enterotoxigenic Escherichia coli by densitometric evaluation using highly specific enzyme-linked oligonucleotide probes

Two alkaline phosphatase-conjugated 24-mer oligonucleotide probes were developed to detect the heat-labile enterotoxin gene in enterotoxigenic Escherichia coli. Probes were antisense codon sequences, which are transcribed into mRNA, of the heat-labile enterotoxin gene of enterotoxigenic Escherichia coli of human origin. Using dot-blot hybridization, probes were tested with 100 clinical isolates and evaluated by a reflectance-type densitometer. Results agreed very well with those of an immunological test, the Biken test, and a 32P-labelled recombinant DNA probe. The oligonucleotide probes did not react with nucleic acids prepared from other diarrhoeagenic bacterial pathogens. Thus, the alkaline phosphatase-conjugated oligonucleotide probes seem to be highly sensitive and specific for detection of heat-labile enterotoxin-producing enterotoxigenic Escherichia coli. Moreover, the results indicate a potential usefulness for densitometric evaluation of DNA hybridization.

A unique amino acid sequence of the B subunit of a heat-labile enterotoxin isolated from a human enterotoxigenic Escherichia coli

The purified B subunit of heat-labile enterotoxin produced from a human strain, 240-3, of enterotoxigenic Escherichia coli (LTh(240-3] was carboxymethylated, succinylated, digested with chymotrypsin and subjected to high performance liquid chromatography (HPLC), and the amino acid compositions of the peptide peaks from the column were analyzed and compared with the data reported by Yamamoto and Yokota (J. Bacteriol. 155, 728.1983), who deduced the amino acid sequence of LTh(H10407) from the DNA sequence of a human strain H10407. Only one fraction differed in amino acid composition from that reported by them. This fraction was found to consist of peptides with the sequences Arg-Asn-Thr-Gln-Ile-Tyr and Arg-Ile-Ala-Tyr. Yamamoto and Yokota reported the sequence of the latter peptide as Arg-Ile-Thr*-Tyr, which corresponds to the peptide from 73rd to 76th from amino (N-) terminus. Thus amino acid residue 75 from the N-terminus of LTh-B(240-3) is alanine, not threonine. The B subunit of cholera toxin also has alanine at position 75. LTh(240-3) appeared similar to LTh(H10407) in an Ouchterlony test, vascular permeability test and GMI ganglioside ELISA. These data show that substitution of threonine for alanine at position 75 from the N-terminus does not affect the immunological and biological characteristics of LTh.