title: Recycling of Shiga toxin 2 genes in sorbitol-fermenting enterohemorrhagic Escherichia coli O157:NM.
abstract: Using colony blot hybridization with stx(2) and eae probes and agglutination in anti-O157 lipopolysaccharide serum, we isolated stx(2)-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 stx(2)-positive isolates fliC(H7), non-stx virulence traits, and multilocus sequence types, which indicates that they arose from the stx(2)-positive strains by loss of stx(2) during infection. Analysis of the integrity of the yecE gene, a possible stx phage integration site in EHEC O157, in the consecutive stx(2)-positive and stx-negative isolates demonstrated that yecE was occupied in stx(2)-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 stx(2)-harboring bacteriophage from one of the SF EHEC O157:NM isolates. The acquisition of the stx(2)-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 stx(2)-harboring phages. The ability to recycle stx(2), 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.
authors.affiliation: Institute of Hygiene, University of Münster, Robert-Koch-Str. 41, 48149 Münster, Germany. mellmann@uni-muenster.de
authors.forename: Alexander
authors.initials: A
authors.lastname: Mellmann
authors.forename: Shan
authors.initials: S
authors.lastname: Lu
authors.forename: Helge
authors.initials: H
authors.lastname: Karch
authors.forename: Jian-guo
authors.initials: JG
authors.lastname: Xu
authors.forename: Dag
authors.initials: D
authors.lastname: Harmsen
authors.forename: M Alexander
authors.initials: MA
authors.lastname: Schmidt
authors.forename: Martina
authors.initials: M
authors.lastname: Bielaszewska
mesh_terms: D018829:Adhesins, Bacterial / Q000235:genetics; D001287:Attachment Sites, Microbiological; D001435:Bacteriophages / Q000235:genetics; D001483:Base Sequence; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D004927:Escherichia coli Infections / Q000382:microbiology; D019453:Escherichia coli O157 / Q000235:genetics* / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics*; D005243:Feces / Q000382:microbiology; D005260:Female; D005408:Flagellin; D005838:Genotype; D006801:Humans; D007223:Infant; D008242:Lysogeny; D008297:Male; D022641:Shiga Toxin 2 / Q000235:genetics*; D013012:Sorbitol / Q000378:metabolism*; D037521:Virulence Factors / Q000235:genetics
chemical_list: D018829:Adhesins, Bacterial; D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; C516095:FliC protein, E coli; D022641:Shiga Toxin 2; D037521:Virulence Factors; D005408:Flagellin; C073819:eaeA protein, E coli; D013012:Sorbitol