scholarly journals Nitric Oxide Induced stx2 Expression Is Inhibited by the Nitric Oxide Reductase, NorV, in a Clade 8 Escherichia coli O157:H7 Outbreak Strain

2022 ◽  
Vol 10 (1) ◽  
pp. 106
Author(s):  
Rim Al Safadi ◽  
Michelle L. Korir ◽  
Shannon D. Manning

Escherichia coli O157:H7 pathogenesis is due to Shiga toxin (Stx) production, though variation in virulence has been observed. Clade 8 strains, for instance, were shown to overproduce Stx and were more common among hemolytic uremic syndrome cases. One candidate gene, norV, which encodes a nitric oxide (NO) reductase found in a clade 8 O157:H7 outbreak strain (TW14359), was thought to impact virulence. Hence, we screened for norV in 303 O157 isolates representing multiple clades, examined stx2 expression following NO exposure in TW14359 for comparison to an isogenic mutant (ΔnorV), and evaluated survival in THP-1 derived macrophages. norV was intact in strains representing clades 6–9, whereas a 204 bp deletion was found in clades 2 and 3. During anaerobic growth, NO induced stx2 expression in TW14359. A similar increase in stx2 expression was observed for the ΔnorV mutant in anaerobiosis, though it was not impaired in its ability to survive within macrophages relative to TW14359. Altogether, these data suggest that NO enhances virulence by inducing Stx2 production in TW14359, and that toxin production is inhibited by NorV encoded by a gene found in most clade 8 strains. The mechanism linked to these responses, however, remains unclear and likely varies across genotypes.

2014 ◽  
Vol 82 (12) ◽  
pp. 4968-4977 ◽  
Author(s):  
T. Zangari ◽  
A. R. Melton-Celsa ◽  
A. Panda ◽  
M. A. Smith ◽  
I. Tatarov ◽  
...  

ABSTRACTShiga toxin (Stx)-producingEscherichia coli(STEC) causes hemorrhagic colitis and the hemolytic-uremic syndrome (HUS). STEC strains may produce Stx1a and/or Stx2a or variants of either toxin. A 2006 spinach-associated outbreak of STEC O157:H7 resulted in higher hospitalization and HUS rates than previous STEC outbreaks. The spinach isolate, strain K3995, contains bothstx2aandstx2c. We hypothesized that the enhanced virulence of K3995 reflects the combination ofstx2alleles (carried on lysogenic phages) and/or the amount of Stx2 made by that strain. We compared the virulence of K3995 to those of other O157:H7 isolates and an isogenic Stx2 mutant in rabbits and mice. We also measured the relative levels of Stx2 produced from those strains with or without induction of thestx-carrying phage. Some rabbits infected with K3995 exhibited intestinal pathology and succumbed to infection, while none of those infected with O157:H7 strain 2812 (Stx1a+Stx2a+) died or showed pathological signs. Rabbits infected with the isogenic Stx2a mutant K3995stx2a::catwere not colonized as well as those infected with K3995 and exhibited no signs of disease. In the streptomycin-treated mouse model, more animals infected with K3995 died than did those infected with O157:H7 strain 86-24 (Stx2a+). Additionally, K3995 produced higher levels of total Stx2 and toxin phage DNA in cultures after phage induction than did 86-24. Our results demonstrate the greater virulence of K3995 compared to other O157:H7 strains in rabbits and mice. We conclude that this enhanced virulence is linked to higher levels of Stx2 expression as a consequence of increased phage induction.


2012 ◽  
Vol 75 (2) ◽  
pp. 408-418 ◽  
Author(s):  
LOTHAR BEUTIN ◽  
ANNETT MARTIN

An outbreak that comprised 3,842 cases of human infections with enteroaggregative hemorrhagic Escherichia coli (EAHEC) O104:H4 occurred in Germany in May 2011. The high proportion of adults affected in this outbreak and the unusually high number of patients that developed hemolytic uremic syndrome makes this outbreak the most dramatic since enterohemorrhagic E. coli (EHEC) strains were first identified as agents of human disease. The characteristics of the outbreak strain, the way it spread among humans, and the clinical signs resulting from EAHEC infections have changed the way Shiga toxin–producing E. coli strains are regarded as human pathogens in general. EAHEC O104:H4 is an emerging E. coli pathotype that is endemic in Central Africa and has spread to Europe and Asia. EAHEC strains have evolved from enteroaggregative E. coli by uptake of a Shiga toxin 2a (Stx2a)–encoding bacteriophage. Except for Stx2a, no other EHEC-specific virulence markers including the locus of enterocyte effacement are present in EAHEC strains. EAHEC O104:H4 colonizes humans through aggregative adherence fimbrial pili encoded by the enteroaggregative E. coli plasmid. The aggregative adherence fimbrial colonization mechanism substitutes for the locus of enterocyte effacement functions for bacterial adherence and delivery of Stx2a into the human intestine, resulting clinically in hemolytic uremic syndrome. Humans are the only known natural reservoir known for EAHEC. In contrast, Shiga toxin–producing E. coli and EHEC are associated with animals as natural hosts. Contaminated sprouted fenugreek seeds were suspected as the primary vehicle of transmission of the EAHEC O104:H4 outbreak strain in Germany. During the outbreak, secondary transmission (human to human and human to food) was important. Epidemiological investigations revealed fenugreek seeds as the source of entry of EAHEC O104:H4 into the food chain; however, microbiological analysis of seeds for this pathogen produced negative results. The survival of EAHEC in seeds and the frequency of human carriers of EAHEC should be investigated for a better understanding of EAHEC transmission routes.


2010 ◽  
Vol 73 (4) ◽  
pp. 649-656 ◽  
Author(s):  
M. O. MASANA ◽  
G. A. LEOTTA ◽  
L. L. DEL CASTILLO ◽  
B. A. D'ASTEK ◽  
P. M. PALLADINO ◽  
...  

In Argentina, Escherichia coli O157:H7/NM (STEC O157) is the prevalent serotype associated with hemolytic uremic syndrome (HUS), which is endemic in the country with more than 400 cases per year. In order to estimate the prevalence and characteristics of STEC O157 in beef cattle at slaughter, a survey of 1,622 fecal and carcass samples was conducted in nine beef exporting abattoirs from November 2006 to April 2008. A total of 54 samples were found positive for STEC O157, with an average prevalence of 4.1% in fecal content and 2.6% in carcasses. Calves and heifers presented higher percentages of prevalence in feces, 10.5 and 8.5%, respectively. All STEC O157 isolates harbored stx2 (Shiga toxin 2), eae (intimin), ehxA (enterohemolysin), and fliCH7 (H7 flagellin) genes, while stx1 (Shiga toxin 1) was present in 16.7% of the strains. The prevalent (56%) stx genotype identified was stx2 combined with variant stx2c (vh-a), the combination of which is also prevalent (>90%) in STEC O157 post–enteric HUS cases in Argentina. The clonal relatedness of STEC O157 strains was established by phage typing and pulsed-field gel electrophoresis (PFGE). The 54 STEC isolates were categorized into 12 different phage types and in 29 XbaI-PFGE patterns distributed in 27 different lots. STEC O157 strains isolated from 5 of 21 carcasses were identical by PFGE (100% similarity) to strains of the fecal content of the same or a contiguous bovine in the lot. Five phage type–PFGE–stx profiles of 10 strains isolated in this study matched with the profiles of the strains recovered from 18 of 122 HUS cases that occurred in the same period.


2000 ◽  
Vol 63 (6) ◽  
pp. 819-821 ◽  
Author(s):  
DAVID W. K. ACHESON

Escherichia coli O157:H7 is but one of a group of Shiga toxin-producing E. coli (STEC) that cause both intestinal disease such as bloody and nonbloody diarrhea and serious complications like hemolytic uremic syndrome (HUS). While E. coli O157: H7 is the most renowned STEC, over 200 different types of STEC have been documented in meat and animals, at least 60 of which have been linked with human disease. A number of studies have suggested that non-O157 STEC are associated with clinical disease, and non-O157 STEC are present in the food supply. Non-O157 STEC, such as O111 have caused large outbreaks and HUS in the United States and other countries. The current policy in the United States is to examine ground beef for O157:H7 only, but restricting the focus to O157 will miss other important human STEC pathogens.


2014 ◽  
Vol 1 (2) ◽  
Author(s):  
Sunao Iyoda ◽  
Shannon D. Manning ◽  
Kazuko Seto ◽  
Keiko Kimata ◽  
Junko Isobe ◽  
...  

Abstract Background.  Enterohemorrhagic Escherichia coli (EHEC) O157:H7 infection causes severe diseases such as bloody diarrhea and hemolytic uremic syndrome (HUS). Although EHEC O157:H7 strains have exhibited high genetic variability, their abilities to cause human diseases have not been fully examined. Methods.  Clade typing and stx subtyping of EHEC O157:H7 strains, which were isolated in Japan during 1999–2011 from 269 HUS patients and 387 asymptomatic carriers (ACs) and showed distinct pulsed-field gel electrophoresis patterns, were performed to determine relationships between specific lineages and clinical presentation. Results.  Clades 6 and 8 strains were more frequently found among the isolates from HUS cases than those from ACs (P = .00062 for clade 6, P < .0001 for clade 8). All clade 6 strains isolated from HUS patients harbored stx2a and/or stx2c, whereas all clade 8 strains harbored either stx2a or stx2a/stx2c. However, clade 7 strains were predominantly found among the AC isolates but less frequently found among the HUS isolates, suggesting a significant association between clade 7 and AC (P < .0001). Logistic regression analysis revealed that 0–9 year old age is a significant predictor of the association between clade 8 and HUS. We also found an intact norV gene, which encodes for a nitric oxide reductase that inhibits Shiga toxin activity under anaerobic condition, in all clades 1–3 isolates but not in clades 4–8 isolates. Conclusions.  Early detection of EHEC O157:H7 strains that belonged to clades 6/8 and harbored specific stx subtypes may be important for defining the risk of disease progression in EHEC-infected 0- to 9-year-old children.


2012 ◽  
Vol 56 (6) ◽  
pp. 3277-3282 ◽  
Author(s):  
Martina Bielaszewska ◽  
Evgeny A. Idelevich ◽  
Wenlan Zhang ◽  
Andreas Bauwens ◽  
Frieder Schaumburg ◽  
...  

ABSTRACTThe role of antibiotics in treatment of enterohemorrhagicEscherichia coli(EHEC) infections is controversial because of concerns about triggering hemolytic-uremic syndrome (HUS) by increasing Shiga toxin (Stx) production. During the recent large EHEC O104:H4 outbreak, antibiotic therapy was indicated for some patients. We tested a diverse panel of antibiotics to which the outbreak strain is susceptible to interrogate the effects of subinhibitory antibiotic concentrations on induction ofstx2-harboring bacteriophages,stx2transcription, and Stx2 production in this emerging pathogen. Ciprofloxacin significantly increasedstx2-harboring phage induction and Stx2 production in outbreak isolates (Pvalues of <0.001 to <0.05), while fosfomycin, gentamicin, and kanamycin insignificantly influenced them (P> 0.1) and chloramphenicol, meropenem, azithromycin, rifaximin, and tigecycline significantly decreased them (P≤ 0.05). Ciprofloxacin and chloramphenicol significantly upregulated and downregulatedstx2transcription, respectively (P< 0.01); the other antibiotics had insignificant effects (P> 0.1). Meropenem, azithromycin, and rifaximin, which were used for necessary therapeutic or prophylactic interventions during the EHEC O104:H4 outbreak, as well as tigecycline, neither inducedstx2-harboring phages nor increasedstx2transcription or Stx2 production in the outbreak strain. These antibiotics might represent therapeutic options for patients with EHEC O104:H4 infection if antibiotic treatment is inevitable. We await further analysis of the epidemic to determine if usage of these agents was associated with an altered risk of developing HUS.


1998 ◽  
Vol 36 (7) ◽  
pp. 2135-2137 ◽  
Author(s):  
Martina Bielaszewska ◽  
Herbert Schmidt ◽  
Mohamed A. Karmali ◽  
Rasik Khakhria ◽  
Jan Janda ◽  
...  

Two sorbitol-fermenting (SF) Shiga toxin-producingEscherichia coli (STEC) O157:H− strains were isolated from patients with hemolytic-uremic syndrome in the Czech Republic in 1995. Their phenotypic and genotypic characteristics and genomic DNA fingerprints were identical or closely related to those of SF STEC O157:H− strains isolated in Germany in 1988 to 1997. This indicates that the Czech isolates belong to the SF STEC O157 clone which is widespread in Germany. It is the first finding of the clone outside Germany.


2000 ◽  
Vol 38 (9) ◽  
pp. 3470-3473 ◽  
Author(s):  
Martina Bielaszewska ◽  
Herbert Schmidt ◽  
Almut Liesegang ◽  
Rita Prager ◽  
Wolfgang Rabsch ◽  
...  

Using the immunomagnetic separation procedure, we isolated sorbitol-fermenting (SF) Shiga toxin-producing Escherichia coli (STEC) O157:H− strains from two patients, one with hemolytic-uremic syndrome and the other with diarrhea, and from a dairy cow epidemiologically associated with the patients. The phenotypic and genotypic characteristics of all isolates were identical or closely related. Moreover, the bovine isolate showed a clonal relatedness to SF STEC O157:H− strains isolated from patients in Germany and the Czech Republic from 1988 to 1998. This is the first evidence that cattle can be a reservoir of SF STEC O157:H− and a source of human diseases.


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