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Journal of Clinical Microbiology, June 2000, p. 2134-2140, Vol. 38, No. 6
0095-1137/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

Molecular Characteristics and Epidemiological Significance of Shiga Toxin-Producing Escherichia coli O26 Strains

Wen-Lan Zhang,1 Martina Bielaszewska,2 Almut Liesegang,3 Helmut Tschäpe,3 Herbert Schmidt,1 Martin Bitzan,4 and Helge Karch1,*

Institut für Hygiene und Mikrobiologie der Universität Würzburg, 97080 Würzburg,1 and Robert Koch Institut, Bereich Wernigerode, 38855 Wernigerode,3 Germany; Institute for Medical Microbiology, Charles University, Prague, 150 06 Prague, Czech Republic2; and Department of Pediatrics, Wake Forest University School of Medicine, Winston-Salem, North Carolina 27157-10814

Received 5 November 1999/Returned for modification 21 February 2000/Accepted 20 March 2000

Fifty-five Shiga toxin (Stx)-producing Escherichia coli (STEC) O26:H11 and O26:H- strains isolated from humans between 1965 and 1999 in Germany and the Czech Republic were investigated for their chromosomal and plasmid characteristics. All motile (n = 23) and nonmotile (n = 32) STEC O26 strains were shown to possess the identical flagellin subunit-encoding gene (fliC). We observed a striking recent shift of the stx genotype from stx1 to stx2 among the STEC O26 isolates. While stx1 was the exclusive genotype identified in our collection until 1994, 94% of the isolates obtained after 1997 possessed stx2 either alone (71%) or together with stx1 (23%). Plasmid profiling demonstrated a remarkable heterogeneity with respect to plasmid sizes and combinations. Southern blot analysis of plasmid DNA with probes specific to potential accessory virulence genes revealed considerable additional variability in gene composition and arrangement. Pulsed-field gel electrophoresis (PFGE) differentiated 16 subgroups among the 55 STEC O26 strains. Using these techniques we demonstrate the emergence of a new clonal subgroup characterized by PFGE pattern A and a unique combination of virulence markers including stx2 and a single, approximately 90-kb plasmid harboring the enterhemorrhagic E. coli hlyA and etp genes. The proportion of PFGE subgroup A strains among STEC O26 isolates rose from 30% in 1996 to more than 50% in 1999. Four clusters of infections with the clonal subgroup A were identified. We conclude that the STEC serogroup O26 is diverse and that pathogenic clonal subgroups can rapidly emerge during short intervals. The extensive genetic diversity of STEC O26 provides a basis for molecular subtyping of this important non-O157 STEC serogroup.


* Corresponding author. Mailing address: Institut für Hygiene und Mikrobiologie der Universität Würzburg, Josef-Schneider-Str. 2, 97080 Würzburg, Germany. Phone: 49-931-201-5162. Fax: 49-931-201-5166. E-mail: hkarch{at}hygiene.uni-wuerzburg.de.


Journal of Clinical Microbiology, June 2000, p. 2134-2140, Vol. 38, No. 6
0095-1137/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.



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