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Applied and Environmental Microbiology, January 2008, p. 67-72, Vol. 74, No. 1
0099-2240/08/$08.00+0     doi:10.1128/AEM.01906-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Recycling of Shiga Toxin 2 Genes in Sorbitol-Fermenting Enterohemorrhagic Escherichia coli O157:NM{triangledown}

Alexander Mellmann,1,2* Shan Lu,1,3 Helge Karch,1,2 Jian-guo Xu,3 Dag Harmsen,4 M. Alexander Schmidt,5 and Martina Bielaszewska1,2

Institute of Hygiene, University of Münster, Robert-Koch-Str. 41, 48149 Münster, Germany,1 Interdisciplinary Center for Clinical Research, Münster, Domagkstr. 3, 48149 Münster, Germany,2 State Key Laboratory of Infectious Diseases Prevention and Control, National Institute for Communicable Disease Prevention and Control, China CDC, Beijing, People's Republic of China,3 Department of Periodontology, University of Münster, Waldeyer Str. 30, 48149 Münster, Germany,4 Institute of Infectiology, Center for Molecular Biology of Inflammation, University of Münster, Von-Esmarch-Str. 56, 48149 Münster, Germany5

Received 19 August 2007/ Accepted 25 October 2007

Using colony blot hybridization with stx2 and eae probes and agglutination in anti-O157 lipopolysaccharide serum, we isolated stx2-positive and eae-positive sorbitol-fermenting (SF) enterohemorrhagic Escherichia coli (EHEC) O157:NM (nonmotile) strains from initial stool specimens and stx-negative and eae-positive SF E. coli O157:NM strains from follow-up specimens (collected 3 to 8 days later) from three children. The stx-negative isolates from each patient shared with the corresponding stx2-positive isolates fliCH7, non-stx virulence traits, and multilocus sequence types, which indicates that they arose from the stx2-positive strains by loss of stx2 during infection. Analysis of the integrity of the yecE gene, a possible stx phage integration site in EHEC O157, in the consecutive stx2-positive and stx-negative isolates demonstrated that yecE was occupied in stx2-positive but intact in stx-negative strains. It was possible to infect and lysogenize the stx-negative E. coli O157 strains in vitro using an stx2-harboring bacteriophage from one of the SF EHEC O157:NM isolates. The acquisition of the stx2-containing phage resulted in the occupation of yecE and production of biologically active Shiga toxin 2. We conclude that the yecE gene in SF E. coli O157:NM is a hot spot for excision and integration of Shiga toxin 2-encoding bacteriophages. SF EHEC O157:NM strains and their stx-negative derivatives thus represent a highly dynamic system that can convert in both directions by the loss and gain of stx2-harboring phages. The ability to recycle stx2, a critical virulence trait, makes SF E. coli O157:NM strains ephemeral EHEC that can exist as stx-negative variants during certain phases of their life cycle.

* Corresponding author. Mailing address: Institut für Hygiene, Universität Münster, Robert-Koch-Str. 41, 48149 Münster, Germany. Phone: 49-251/8352316. Fax: 49-251/8355688. E-mail: mellmann{at}uni-muenster.de

{triangledown} Published ahead of print on 2 November 2007.

Applied and Environmental Microbiology, January 2008, p. 67-72, Vol. 74, No. 1
0099-2240/08/$08.00+0     doi:10.1128/AEM.01906-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.



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