Shiga Toxin Type 1a (Stx1a) Reduces the Toxicity of the More Potent Stx2a
            <i>In Vivo</i>
            and
            <i>In Vitro</i>

Petro, Courtney D.; Trojnár, Eszter; Sinclair, James F.; Liu, Zhimei; Smith, M. J.; O'Brien, A D; Melton‐Celsa, Angela R.

doi:10.1128/iai.00787-18

Cited by 25 publications

(23 citation statements)

References 36 publications

(41 reference statements)

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“…Furthermore, Stx2a cannot compete with Stx1a for binding to Gb3 in detergent-resistant membranes (53). This observation is consistent with our intoxication assay, which demonstrated that a 100-fold molar excess of Stx2a cannot outcompete Stx1a, and with published work demonstrating that the B subunit from Stx1a reduces the toxicity of Stx2a (48). The bimodal response to Stx2 subtypes thus appears to result from two linked events that limit the cytosolic pool of Stx2 in comparison to Stx1a, namely, (i) relatively weak overall binding to the target cell, and (ii) a weaker interaction than Stx1a with the detergent-resistant membranes that are required for toxin transport to the ER and cytosol.…”

Section: Discussionsupporting

confidence: 92%

“…Thus, Stx2a does not appear to effectively compete with Stx1a for binding to functional receptors on the target cell. A recent study documented the reduced potency of Stx2a in cell culture and animal models when mixed with the Stx1a B subunit (48), but our current work-which was only possible because of the different population responses to Stx1a versus Stx2a-provides the first experimental evidence that the Stx1a holotoxin can outcompete Stx2a in a cell culture model of intoxication.…”

Section: Resultsmentioning

confidence: 83%

“…Toxin inactivation could involve the administration of inactive Stx1a variants that compete with Stx2a for binding to target cells. This approach has been shown to reduce the toxicity of Stx2a in mice (48,59). Neutralizing antibodies could likewise reduce the amount of Stx2a that reaches the cytosol of host cells, either by blocking adherence to the target cell or by disrupting intracellular toxin trafficking (60,61).…”

Section: Discussionmentioning

confidence: 99%

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Bimodal Response to Shiga Toxin 2 Subtypes Results from Relatively Weak Binding to the Target Cell

et al. 2019

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There are two major antigenic forms of Shiga toxin (Stx), Stx1 and Stx2, which bind the same receptor and act on the same target but nonetheless differ in potency. Stx1a is more toxic to cultured cells, but Stx2 subtypes are more potent in animal models. To understand this phenomenon in cultured cells, we used a system that combines flow cytometry with a fluorescent reporter to monitor the Stx-induced inhibition of protein synthesis in single cells. We observed that Vero cells intoxicated with Stx1a behave differently than those intoxicated with Stx2 subtypes: cells challenged with Stx1a exhibited a population-wide loss of protein synthesis, while cells exposed to Stx2a or Stx2c exhibited a dose-dependent bimodal response in which one subpopulation of cells was unaffected (i.e., no loss of protein synthesis). Cells challenged with a hybrid toxin containing the catalytic subunit of Stx1a and the cell-binding subunit of Stx2a also exhibited a bimodal response to intoxication, while cells challenged with a hybrid toxin containing the catalytic subunit of Stx2a and the cell-binding subunit of Stx1a exhibited a population-wide loss of protein synthesis. Other experiments further supported a primary role for the subtype of the B subunit in the outcome of host-Stx interactions. Our collective observations indicate that the bimodal response to Stx2 subtypes is due to relatively weak binding between Stx2 and the host cell that reduces the total functional pool of Stx2 in comparison to that of Stx1a. This explains, in part, the molecular basis for the differential cellular toxicity between Stx1a and Stx2 subtypes.

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Section: Discussionsupporting

confidence: 92%

Section: Resultsmentioning

confidence: 83%

Section: Discussionmentioning

confidence: 99%

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Bimodal Response to Shiga Toxin 2 Subtypes Results from Relatively Weak Binding to the Target Cell

et al. 2019

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“…Our laboratory previously demonstrated in co-intoxication studies that Stx1a reduces Stx2a mediated toxicity in vivo particularly when more Stx1a than Stx2a is administered (Russo et al, 2016). We also recently found that the presence of Stx1a reduces the morbidity in Str-treated mice after infection with an STEC strain that makes both Stx1a and Stx2a (Petro et al, 2019).…”

Section: Discussionmentioning

confidence: 95%

The Virulence of Escherichia coli O157:H7 Isolates in Mice Depends on Shiga Toxin Type 2a (Stx2a)-Induction and High Levels of Stx2a in Stool

Hauser

Atitkar

Petro

et al. 2020

Front. Cell. Infect. Microbiol.

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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.

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“…Another distinct feature is the presence of stx1a in most of the Australian isolates. Stx1a has been shown to have antagonistic effects against Stx2a toxicity, shown in both in vitro and in vivo models, where Stx2a alone appears to be more potent (Petro et al, 2019). This reduction in Stx2a toxicity is potentially due to the stronger receptor binding affinity to the globotriaosylceramide (Gb3) receptor of the B subunit of Stx1a, blocking out the binding of Stx2a to the Gb3 receptor (Head et al, 1991;Tesh et al, 1993;Zumbrun et al, 2010;Karve and Weiss, 2014;Russo et al, 2014;Cherubin et al, 2019).…”

Section: Core Genome Analysismentioning

confidence: 99%

Core and Accessory Genome Comparison of Australian and International Strains of O157 Shiga Toxin-Producing Escherichia coli

et al. 2020

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Shiga toxin-producing Escherichia coli (STEC) is a foodborne pathogen, and serotype O157:H7 is typically associated with severe disease. Australian STEC epidemiology differs from many other countries, as severe outbreaks and HUS cases appear to be more often associated with non-O157 serogroups. It is not known why Australian strains of O157 STEC might differ in virulence to international strains. Here we investigate the reduced virulence of Australian strains. Multiple genetic analyses were performed, including SNP-typing, to compare the core genomes of the Australian to the international isolates, and accessory genome analysis to determine any significant differences in gene presence/absence that could be associated with their phenotypic differences in virulence. The most distinct difference between the isolates was the absence of the stx2a gene in all Australian isolates, with few other notable differences observed in the core and accessory genomes of the O157 STEC isolates analyzed in this study. The presence of stx1a in most Australian isolates was another notable observation. Acquisition of stx2a seems to coincide with the emergence of highly pathogenic STEC. Due to the lack of other notable genotypic differences observed between Australian and international isolates characterized as highly pathogenic, this may be further evidence that the absence of stx2a in Australian O157 STEC could be a significant characteristic defining its mild virulence. Further work investigating the driving force(s) behind Stx prophage loss and acquisition is needed to determine if this potential exists in Australian O157 isolates.

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Shiga Toxin Type 1a (Stx1a) Reduces the Toxicity of the More Potent Stx2a In Vivo and In Vitro

Cited by 25 publications

References 36 publications

Bimodal Response to Shiga Toxin 2 Subtypes Results from Relatively Weak Binding to the Target Cell

Bimodal Response to Shiga Toxin 2 Subtypes Results from Relatively Weak Binding to the Target Cell

The Virulence of Escherichia coli O157:H7 Isolates in Mice Depends on Shiga Toxin Type 2a (Stx2a)-Induction and High Levels of Stx2a in Stool

Core and Accessory Genome Comparison of Australian and International Strains of O157 Shiga Toxin-Producing Escherichia coli

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