The Role of the AggR Regulon in the Virulence of the Shiga Toxin-Producing Enteroaggregative Escherichia coli Epidemic O104:H4 Strain in Mice (original) (raw)
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A novel murine infection model for Shiga toxin–producing Escherichia coli
Journal of Clinical Investigation, 2012
Enterohemorrhagic E. coli (EHEC) is an important subset of Shiga toxin-producing (Stx-producing) E. coli (STEC), pathogens that have been implicated in outbreaks of food-borne illness and can cause intestinal and systemic disease, including severe renal damage. Upon attachment to intestinal epithelium, EHEC generates "attaching and effacing" (AE) lesions characterized by intimate attachment and actin rearrangement upon host cell binding. Stx produced in the gut transverses the intestinal epithelium, causing vascular damage that leads to systemic disease. Models of EHEC infection in conventional mice do not manifest key features of disease, such as AE lesions, intestinal damage, and systemic illness. In order to develop an infection model that better reflects the pathogenesis of this subset of STEC, we constructed an Stx-producing strain of Citrobacter rodentium, a murine AE pathogen that otherwise lacks Stx. Mice infected with Stx-producing C. rodentium developed AE lesions on the intestinal epithelium and Stx-dependent intestinal inflammatory damage. Further, the mice experienced lethal infection characterized by histopathological and functional kidney damage. The development of a murine model that encompasses AE lesion formation and Stx-mediated tissue damage will provide a new platform upon which to identify EHEC alterations of host epithelium that contribute to systemic disease.
Shiga toxin 2a and Enteroaggregative Escherichia coli - a deadly combination
Gut microbes, 2015
In 2011, a Shiga toxin (Stx) type 2a-producing enteroaggregative E. coli (EAEC) strain of serotype O104:H4 caused a large lethal outbreak in Northern Europe. Until recently, the pathogenic mechanisms explaining the high virulence of the strain have remained unclear. Our laboratories have shown that EAEC genes encoded on the pAA virulence plasmid, particularly the AggR-regulated AAF/I fimbriae, enhance inflammation and enable the outbreak strain to both adhere to epithelial cells and translocate Stx2a across the intestinal epithelium, possibly explaining the high incidence of the life threatening post-diarrheal sequelae of hemolytic uremic syndrome. Epidemiologic evidence supports a model of EAEC pathogenesis comprising the concerted action of multiple virulence factors along with induction of inflammation. Here, we suggest a model for the pathogenesis of the O104:H4 outbreak strain that includes contributions from EAEC alone, but incorporating additional injury induced by Stx2a.
Virulence
Whereas the O104:H4 enterohemorrhagic Escherichia coli (EHEC) outbreak strain from 2011 expresses aggregative adherence fimbriae of subtype I (AAF/I), its close relative, the O104:H4 enteroaggregative Escherichia coli (EAEC) strain 55989, encodes AAF of subtype III. Tight adherence mediated by AAF/I in combination with Shiga toxin 2 production has been suggested to result in the outbreak strain's exceptional pathogenicity. Furthermore, the O104:H4 outbreak strain adheres significantly better to cultured epithelial cells than archetypal EAEC strains expressing different AAF subtypes. To test whether AAF/I expression is associated with the different virulence phenotypes of the outbreak strain, we heterologously expressed AAF subtypes I, III, IV, and V in an AAF-negative EAEC 55989 mutant and compared AAF-mediated phenotypes, incl. autoaggregation, biofilm formation, as well as bacterial adherence to HEp-2 cells. We observed that the expression of all four AAF subtypes promoted bacterial autoaggregation, though with different kinetics. Disturbance of AAF interaction on the bacterial surface via addition of α-AAF antibodies impeded autoaggregation. Biofilm formation was enhanced upon heterologous expression of AAF variants and inversely correlated with the autoaggregation phenotype. Cocultivation of bacteria expressing different AAF subtypes resulted in mixed bacterial aggregates. Interestingly, bacteria expressing AAF/I formed the largest bacterial clusters on HEp-2 cells, indicating a stronger host cell adherence similar to the EHEC O104:H4 outbreak strain. Our findings show that, compared to the closely related O104:H4 EAEC strain 55989, not only the acquisition of the Shiga toxin phage, but also the acquisition of the AAF/I subtype might have contributed to the increased EHEC O104:H4 pathogenicity.
Infection and Immunity, 2013
ABSTRACTIn May 2011, a large food-borne outbreak was traced to an unusual O104:H4 enteroaggregativeEscherichia coli(EAEC) strain that produced Shiga toxin (Stx) type 2 (Stx2). We developed a mouse model to study the pathogenesis and treatment for this strain and examined the virulence of the isolate for Dutch belted rabbits. O104:H4 strain C227-11 was gavaged into C57BL/6 mice at 109to 1011CFU/animal. The infected animals were then given water with ampicillin (& 5 g/liter)ad libitum. The C227-11-infected, Amp-treated C57BL/6 mice exhibited both morbidity and mortality. Kidneys from mice infected with C227-11 showed acute tubular necrosis, a finding seen in mice infected with typical Stx-producingE. coli. We provided anti-Stx2 antibody after infection and found that all of the antibody-treated mice gained more weight than untreated mice and, in another study, that all of the antibody-treated animals lived, whereas 3/8 phosphate-buffered saline-treated mice died. We further compared t...
Frontiers in Cellular and Infection Microbiology, 2020
In this study we compared nine Shiga toxin (Stx)-producing Escherichia coli O157:H7 patient isolates for Stx levels, stx-phage insertion site(s), and pathogenicity in a streptomycin (Str)-treated mouse model. The strains encoded stx 2a , stx 1a and stx 2a , or stx 2a and stx 2c. All of the strains elaborated 10 5-10 6 cytotoxic doses 50% (CD 50) into the supernatant after growth in vitro as measured on Vero cells, and showed variable levels of increased toxin production after growth with sub-inhibitory levels of ciprofloxacin (Cip). The stx 2a +stx 2c + isolates were 90-100% lethal for Str-treated BALB/c mice, though one isolate, JH2013, had a delayed time-to-death. The stx 2a + isolate was avirulent. Both an stx 2a and a recA deletion mutant of one of the stx 2a +stx 2c + strains, JH2010, exhibited at least a three-log decrease in cytotoxicity in vitro and both were avirulent in the mice. Stool from Str-treated mice infected with the highly virulent isolates were 10-to 100-fold more cytotoxic than feces from mice infected with the clinical isolate, JH2012, that made only Stx2a. Taken together these findings demonstrate that the stx 2a-phage from JH2010 induces to higher levels in vivo than does the phage from JH2012. The stx 1a +stx 2a + clinical isolates were avirulent and neutralization of Stx1 in stool from mice infected with those strains indicated that the toxin produced in vivo was primarily Stx1a. Treatment of mice infected with Stx1a+Stx2a+ isolates with Cip resulted in an increase in Stx2a production in vivo and lethality in the mice. Our data suggest that high levels of Stx2a in stool are predictive of virulence in mice.
Reduced Virulence of an fliC Mutant of Shiga-Toxigenic Escherichia coli O113:H21
Infection and Immunity, 2006
The contribution of flagellin to the virulence of the O113:H21 Shiga-toxigenic Escherichia coli (STEC) strain 98NK2 was investigated in the streptomycin-treated mouse model. Groups of mice were challenged with either the wild-type STEC or a fliC deletion derivative thereof. There was no difference in the level of gut colonization by the two strains, but the fliC mutant was significantly less virulent than its parent; the overall survival rates were 43.7% and 81.2%, respectively (P < 0.025). This is the first report of a nontoxic accessory virulence factor contributing to a fatal outcome of STEC infection in this model. Although H21 FliC is known to be a potent inducer of CXC chemokines, including interleukin 8, there was no obvious difference in the recruitment of polymorphonuclear leukocytes to the intestinal epithelium of mice challenged with either strain. However, immunofluorescence microscopy suggested that the fliC mutant was less capable of forming a close association with the colonic epithelium. This may have reduced the uptake of Stx2 by mice infected with the mutant. by guest http://iai.asm.org/ Downloaded from on July 8, 2015 by guest http://iai.asm.org/ Downloaded from FIG. 5. Sections of colon from mice infected with the indicated STEC strain for 1 day were stained for O113 antigen and examined by fluorescence microscopy as described in the text. Bars, 0.2 mm.
RegR Virulence Regulon of Rabbit-Specific Enteropathogenic Escherichia coli Strain E22
Infection and Immunity, 2013
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Nature Communications, 2014
The outbreak of diarrhoea and haemolytic uraemic syndrome that occurred in Germany in 2011 was caused by a Shiga toxin-producing enteroaggregative Escherichia coli (EAEC) strain. The strain was classified as EAEC owing to the presence of a plasmid (pAA) that mediates a characteristic pattern of aggregative adherence on cultured cells, the defining feature of EAEC that has classically been associated with virulence. Here we describe an infant rabbit-based model of intestinal colonization and diarrhoea caused by the outbreak strain, which we use to decipher the factors that mediate the pathogen's virulence. Shiga toxin is the key factor required for diarrhoea. Unexpectedly, we observe that pAA is dispensable for intestinal colonization and development of intestinal pathology. Instead, chromosome-encoded autotransporters are critical for robust colonization and diarrhoeal disease in this model. Our findings suggest that conventional wisdom linking aggregative adherence to EAEC intestinal colonization is false for at least a subset of strains.