Genotype analysis of enterohemorrhagic Escherichia coli O157:H7 strains isolated in Iwate Prefecture from 1996 to February 1997

Genotypes of 38 isolates of enterohemorrhagic Escherichia coli (EHEC) O157:H7 isolated from 11 sporadic cases and one outbreak in Iwate Prefecture from 1996 to February 1997 were studied by pulsed-field gel electrophoresis (PFGE), in comparison with a strain of EHEC O157:H7 isolated in 1992 in Ohazama-Cho, Iwate Prefecture, and two isolates of EHEC O157:NM. In order to substantiate the genotypes classified by PFGE, Southern blotting was performed to investigate integration sites of the Shiga toxin genes (stx) in the XbaI-digested genome DNA fragments. The stx1 gene existed on an approximately 130 kb fragment in all isolates except two ones. On the other hand, the stx2 gene was observed on 11 DNA fragments in different length from 600 kb to 155 kb, indicating that the stx2 gene integrates into more heterogeneous sites of genome DNA than stx1 does. From these analyses, EHEC O157:H7 isolates examined were classified into 7 genotypes. Since half of the isolates were the same genotype as that of the isolate in 1992, it is suggested that this type of EHEC O157:H7 strain is expanding from Ohazama-Cho and Morioka City in Iwate Prefecture.     

Cloning of a cDNA encoding SjIrV1, a Schistosoma japonicum calcium-binding protein similar to calnexin, and expression of the recombinant protein in Escherichia coli

Membrane-associated proteins were isolated from adult Philippine strain Schistosoma japonicum by partitioning into the detergent phase of Triton X-114. A rabbit polyclonal antiserum raised against these proteins was used to screen an S. japonicum expression cDNA library. Positive clones were identified which encoded the species orthologue of SmIrV1, a Schistosoma mansoni protein which was initially identified by screening with sera from mice protectively vaccinated with irradiated cercariae [Hawn et al., J. Biol. Chem. 268 (1993) 7692-7698]. The S. japonicum molecule, which we term SjIrV1, is 83% identical to SmIrV1 at the predicted amino acid level and is a member of the calreticulin family of non-EF-hand, calcium-binding proteins. The Chinese strain S. japonicum orthologue of SjIrV1 was obtained by screening with the radiolabelled insert of the Philippine strain clone. Northern blot analysis revealed a single message of around 2.4 kb and gave no indication of alternative splicing. Southern blot analysis gave a simple pattern, indicating a single-copy gene, and showed a single restriction fragment length polymorphism between the genomes of Chinese and Philippine strains of S. japonicum. Recombinant, full-length SjIrV1 was expressed with a hexahistidine tag in Escherichia coli and the recombinant protein isolated by nickel-chelate chromatography. Recombinant SjIrV1 was shown to exhibit calcium-dependent, differential electrophoretic migration and to bind ruthenium red in the absence but not in the presence of calcium ions. The presence of conserved Ca(2+)-binding motifs predicted from the primary sequence, together with the Ca(2+)-dependent electrophoretic mobility of recombinant SjIrV1, confirmed that SjIrV1 was a functional calcium-binding protein.