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Infection and Immunity, September 2000, p. 4856-4864, Vol. 68, No. 9
0019-9567/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

Structural Analysis of Phage-Borne stx Genes and Their Flanking Sequences in Shiga Toxin-Producing Escherichia coli and Shigella dysenteriae Type 1 Strains

Alexandra Unkmeir and Herbert Schmidt*

Institut für Hygiene und Mikrobiologie der Universität Würzburg, D-97080 Würzburg, Germany

Received 11 February 2000/Returned for modification 18 April 2000/Accepted 30 May 2000

The stx-flanking regions of 49 Shiga toxin-producing Escherichia coli strains and nine Shigella dysenteriae serotype 1 strains containing either stx, stx1, stx2, or stx2 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 stx1-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 stx1-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 stx1-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.

* Corresponding author. Mailing address: Institut für Mikrobiologie und Hygiene der Universität Würzburg, Josef-Schneider-Str.2, D-97080 Würzburg, Germany. Phone: 49-931-2013905. Fax: 49-931-2013445. E-mail: hschmidt{at}hygiene.uni-wuerzburg.de.

Infection and Immunity, September 2000, p. 4856-4864, Vol. 68, No. 9
0019-9567/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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