title: Structural analysis of phage-borne stx genes and their flanking sequences in shiga toxin-producing Escherichia coli and Shigella dysenteriae type 1 strains.
abstract: The stx-flanking regions of 49 Shiga toxin-producing Escherichia coli strains and nine Shigella dysenteriae serotype 1 strains containing either stx, stx(1), stx(2), or stx(2) variant genes, were examined. We analyzed these regions by PCR using a set of primers with one primer specific for the respective stx gene and a second primer complementary to sequences of Stx phages H-19B and 933W. We further characterized the amplification products by restriction endonuclease digestion and nucleotide sequencing. PCR products of stx(1)-containing E. coli strains of serogroups O157, O26, and 0103 showed the same lengths and similar restriction patterns. However, we failed to amplify the 3' stx-flanking region in stx(1)-harboring E. coli O111:H(-) strains. Stx2-producing E. coli strains revealed amplification products of different lengths and restriction patterns, suggesting greater heterogeneity than in stx(1)-positive strains. We also obtained specific PCR products for two Stx2c-producing and seven Stx2f-producing E. coli strains when they were subjected to PCR analysis. In nine S. dysenteriae type 1 strains, H-19B- and 933W-specific primers amplified only the 3' stx-flanking region. The results of our study demonstrate that the stx genes of all strains investigated are continuous with phage sequences. Whereas almost all strains except E. coli O111:H(-) strains were associated with a S-like gene, association with Q could not be demonstrated in nine S. dysenteriae type 1 strains and three E. coli strains. Furthermore, we showed that the organization of the stx-flanking regions is similar in all strains investigated, whereas fine-structure analysis showed subtle differences among the sequences examined. Our results support the hypothesis that stx genes in E. coli and S. dysenteriae are generally phage-borne.
authors.affiliation: Institut für Hygiene und Mikrobiologie der Universität Würzburg, D-97080 Würzburg, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Unkmeir
authors.forename: H
authors.initials: H
authors.lastname: Schmidt
mesh_terms: D001427:Bacterial Toxins / Q000235:genetics*; D001435:Bacteriophages / Q000235:genetics*; D001483:Base Sequence; D004926:Escherichia coli / Q000472:pathogenicity*; D006801:Humans; D016133:Polymerase Chain Reaction; D022603:Shiga Toxins; D012762:Shigella dysenteriae / Q000472:pathogenicity*
chemical_list: D001427:Bacterial Toxins; D022603:Shiga Toxins