Effect of subinhibitory concentrations of antibiotics on extracellular Shiga-like toxin I

Antimicrobial growth promoters approved in food-producing animals in South Africa induce shiga toxin-converting bacteriophages from Escherichia coli O157:H7

In this study, four antimicrobial growth promoters, including virginiamycin, josamycin, flavophospholipol, poly 2-propenal 2-propenoic acid and ultraviolet light, were tested for their capacity to induce stx-bacteriophages in 47 Shiga toxin-producing E. coli O157:H7 isolates. Induced bacteriophages were characterized for shiga toxin subtypes and structural genes by PCR, DNA restriction fragment length polymorphisms (RFLP) and morphological features by electron microscopy. Bacteriophages were induced from 72.3% (34/47) of the STEC O157:H7 isolates tested. Bacteriophage induction rates per induction method were as follows: ultraviolet light, 53.2% (25/47); poly 2-propenal 2-propenoic acid, 42.6% (20/47); virginiamycin, 34.0% (16/47); josamycin, 34.0% (16/47); and flavophospholipol, 29.8% (14/47). A total of 98 bacteriophages were isolated, but only 59 were digestible by NdeI, revealing 40 RFLP profiles which could be subdivided in 12 phylogenetic subgroups. Among the 98 bacteriophages, stx2a, stx2c and stx2d were present in 85.7%, 94.9% and 36.7% of bacteriophages, respectively. The Q, P, CIII, N1, N2 and IS1203 genes were found in 96.9%, 82.7%, 69.4%, 40.8%, 60.2% and 73.5% of the samples, respectively. Electron microscopy revealed four main representative morphologies which included three bacteriophages which all had long tails but different head morphologies: long hexagonal head, oval/oblong head and oval/circular head, and one bacteriophage with an icosahedral/hexagonal head with a short thick contractile tail. This study demonstrated that virginiamycin, josamycin, flavophospholipol and poly 2-propenal 2-propenoic acid induce genetically and morphologically diverse free stx-converting bacteriophages from STEC O157:H7. The possibility that these antimicrobial growth promoters may induce bacteriophages in vivo in animals and human hosts is a public health concern. Policies aimed at minimizing or banning the use of antimicrobial growth promoters should be promoted and implemented in countries where these compounds are still in use in animal agriculture.

Characterizing a Silver Nanoparticle-Based Electrochemical Biosensor for Shiga Toxin Detection

Shiga toxins (1, 2) regularly cause outbreaks and food recalls and pose a significant health risk to the infected population. Therefore, new reliable tools are needed to rapidly detect Shiga toxin cost-effectively in food, water, and wastewater before human consumption. Enzyme immunoassay and polymerase chain reaction approaches are the gold standard detection methods for the Shiga toxin. However, these methods require expensive instruments along with expensive reagents, which makes them hard to convert into point-of-use and low-cost systems. This study introduces an electrochemical biosensing method that utilizes silver nanoparticles (AgNPs) as electrochemical tags and commercially available low-cost screen-printed carbon electrodes for detection. This study introduces the modification of reference electrodes on commercially available screen-printed carbon electrodes to detect AgNPs dissolved in nitric acid. This biosensor achieved a 2 ng/mL lowest measured concentration for Shiga toxin-1 in less than 3 h. These biosensor results also showed that the AgNP-based sensor has better linearity (for graph between peak current vs concentration) and lower standard deviation compared to gold nanoparticles (AuNP)-based electrochemical biosensors.

Mechanism for inhibition of cytotoxicity of Shiga toxin by luteolin

Enterohemorrhagic or Shiga toxin-producing Escherichia coli is a food-poisoning bacterium that grows in the intestine to produce Shiga toxin (Stx). In this study, the effects of 20 polyphenols on the cytotoxicity of Stx1 and Stx2 in Vero cells were investigated. Among these, epigallocatechin gallate, butein, isorhapontigenin, hesperetin, morin, luteolin, resveratrol, and rhapontigenin showed inhibitory effects on the cytotoxicity of Stxs at 0.4 mmol/L. Furthermore, Vero cells pre-treated with these polyphenols were resistant to Stx at 0.4 mmol/L. However, luteolin showed the most potent inhibitory and cytoprotective effect against Stxs at 0.08 mmol/L or more. This inhibitory mechanism of luteolin was determined using a cell-free protein synthesis system and quantitative reverse transcription PCR assay to detect depurination of 28S rRNA in Vero cells. Luteolin did not inhibit the cell-free protein synthesis by Stxs, suggesting that the enzymatic activity of the Stx A subunit was not inhibited by luteolin. The depurination of 28S rRNA by Stxs was also investigated in Vero cells. The 28S rRNA depurination by Stxs was suppressed in Vero cells treated with Stxs which had been pretreated with luteolin. These results suggest that luteolin inhibits the incorporation of Stxs into Vero cells. This is the first report to show that luteolin inhibits the cytotoxicity of both Stx1 and Stx2 by inhibiting the incorporation of Stxs into Vero cells.

Diagnosis and Treatment for Shiga Toxin-Producing Escherichia coli Associated Hemolytic Uremic Syndrome

Shiga toxin-producing Escherichia coli (STEC)-associated hemolytic uremic syndrome (STEC-HUS) is a clinical syndrome involving hemolytic anemia (with fragmented red blood cells), low levels of platelets in the blood (thrombocytopenia), and acute kidney injury (AKI). It is the major infectious cause of AKI in children. In severe cases, neurological complications and even death may occur. Treating STEC-HUS is challenging, as patients often already have organ injuries when they seek medical treatment. Early diagnosis is of great significance for improving prognosis and reducing mortality and sequelae. In this review, we first briefly summarize the diagnostics for STEC-HUS, including history taking, clinical manifestations, fecal and serological detection methods for STEC, and complement activation monitoring. We also summarize preventive and therapeutic strategies for STEC-HUS, such as vaccines, volume expansion, renal replacement therapy (RRT), antibiotics, plasma exchange, antibodies and inhibitors that interfere with receptor binding, and the intracellular trafficking of the Shiga toxin.

Why antibiotics should not be used to treat Shiga toxin-producing Escherichia coli infections

PURPOSE OF REVIEW

There has been much debate about treating Shiga toxin-producing Escherichia coli (STEC) infections with antibiotics. No data convincingly demonstrate that antibiotics are better than no antibiotic treatment at all, and many studies suggest antibiotics increase the risk of developing the hemolytic uremic syndrome (HUS). This topic is timely, because emerging technology enables rapid identification of STEC-infected patients, and we anticipate questions about management will increase. This review is designed to familiarize readers with the series of observations that underlie our recommendations.

RECENT FINDINGS

The long debate over antibiotics in STEC infections appears resolved by gradually accruing information that show that antibiotics do not benefit infected patients. In fact, they are associated with an increased likelihood of developing HUS. A meta-analysis published in 2016 demonstrated that low risk of bias studies find a clear association between antibiotic use and development of HUS. Subsequent publications do not refute these findings.

SUMMARY

In high-income countries, antibiotics should not routinely be given to patients with acute diarrhea unless testing demonstrates a pathogen for which antibiotics are indicated, and STEC infection has been excluded. Future work to prevent HUS should focus on preventing primary infections, and mitigating extraintestinal consequences of STEC gut infections.

Tamoxifen Derivatives Alter Retromer-Dependent Endosomal Tubulation and Sorting to Block Retrograde Trafficking of Shiga Toxins

Shiga toxin 1 and 2 (STx1 and STx2) undergo retrograde trafficking to reach the cytosol of cells where they target ribosomes. As retrograde trafficking is essential for disease, inhibiting STx1/STx2 trafficking is therapeutically promising. Recently, we discovered that the chemotherapeutic drug tamoxifen potently inhibits the trafficking of STx1/STx2 at the critical early endosome-to-Golgi step. We further reported that the activity of tamoxifen against STx1/STx2 is independent of its selective estrogen receptor modulator (SERM) property and instead depends on its weakly basic chemical nature, which allows tamoxifen to increase endolysosomal pH and alter the recruitment of retromer to endosomes. The goal of the current work was to obtain a better understanding of the mechanism of action of tamoxifen against the more disease-relevant toxin STx2, and to differentiate between the roles of changes in endolysosomal pH and retromer function. Structure activity relationship (SAR) analyses revealed that a weakly basic amine group was essential for anti-STx2 activity. However, ability to deacidify endolysosomes was not obligatorily necessary because a tamoxifen derivative that did not increase endolysosomal pH exerted reduced, but measurable, activity. Additional assays demonstrated that protective derivatives inhibited the formation of retromer-dependent, Golgi-directed, endosomal tubules, which mediate endosome-to-Golgi transport, and the sorting of STx2 into these tubules. These results identify retromer-mediated endosomal tubulation and sorting to be fundamental processes impacted by tamoxifen; provide an explanation for the inhibitory effect of tamoxifen on STx2; and have important implications for the therapeutic use of tamoxifen, including its development for treating Shiga toxicosis.

Potentiation of Antibiotics by a Novel Antimicrobial Peptide against Shiga Toxin Producing E. coli O157:H7

Infection with Shiga toxin-producing Escherichia coli (STEC) results in hemorrhagic colitis and can lead to life-threatening sequelae including hemolytic uremic syndrome (HUS). Conventional treatment is intravenous fluid volume expansion. Antibiotic treatment is contraindicated, due in part to the elevated risk of HUS related to increased Shiga toxin (Stx) release associated with some antibiotics. Given the lack of effective strategies and the increasing number of STEC outbreaks, new treatment approaches are critically needed. In this study, we used an antimicrobial peptide wrwycr, previously shown to enhance STEC killing without increasing Stx production, in combination with antibiotic treatments. Checkerboard and time-kill assays were used to assess peptide wrwycr-antibiotic combinations for synergistic STEC killing. Cytotoxicity and real-time PCR were used to evaluate Stx production and stx expression, respectively, associated with these combinations. The synergistic combinations that showed rapid killing, no growth recovery and minimal Stx production were peptide wrwycr-kanamycin/gentamicin. Transmission electron microscopy revealed striking differences in bacterial cell morphology associated with various treatments. This study provides proof of principle for the design of an antibiotic-peptide wrwycr combination effective in killing STEC without enhancing release of Shiga toxins. It also offers a strategy for the repurposing of antibiotics for treatment of STEC infection.

Treatment Strategies for Infections With Shiga Toxin-Producing Escherichia coli

Infections with Shiga toxin-producing Escherichia coli (STEC) cause outbreaks of severe diarrheal disease in children and the elderly around the world. The severe complications associated with toxin production and release range from bloody diarrhea and hemorrhagic colitis to hemolytic-uremic syndrome, kidney failure, and neurological issues. As the use of antibiotics for treatment of the infection has long been controversial due to reports that antibiotics may increase the production of Shiga toxin, the recommended therapy today is mainly supportive. In recent years, a variety of alternative treatment approaches such as monoclonal antibodies or antisera directed against Shiga toxin, toxin receptor analogs, and several vaccination strategies have been developed and evaluated in vitro and in animal models. A few strategies have progressed to the clinical trial phase. Here, we review the current understanding of and the progress made in the development of treatment options against STEC infections and discuss their potential.

Identification of Antibiotics That Diminish Disease in a Murine Model of Enterohemorrhagic Escherichia coli Infection

Infections with enterohemorrhagic Escherichia coli (EHEC) cause disease ranging from mild diarrhea to hemolytic-uremic syndrome (HUS) and are the most common cause of renal failure in children in high-income countries. The severity of the disease derives from the release of Shiga toxins (Stx). The use of antibiotics to treat EHEC infections is generally avoided, as it can result in increased stx expression. Here, we systematically tested different classes of antibiotics and found that their influence on stx expression and release varies significantly. We assessed a selection of these antibiotics in vivo using the Citrobacter rodentium ϕstx _2dact mouse model and show that stx _2d-inducing antibiotics resulted in weight loss and kidney damage despite clearance of the infection. However, several non-Stx-inducing antibiotics cleared bacterial infection without causing Stx-mediated pathology. Our results suggest that these antibiotics might be useful in the treatment of EHEC-infected human patients and decrease the risk of HUS development.

Gastrointestinal infection-related disseminated intravascular coagulation mimicking Shiga toxin-mediated hemolytic uremic syndrome - implications of classical clinical indexes in making the diagnosis: A case report and literature review

BACKGROUND

Thrombocytopenia associated with acute kidney injury is a challenging disorder. Thrombotic microangiopathy (TMA) is a potentially life- or organ-threatening syndrome that can be induced by several disorders or medical interventions. There is overlap between the clinical presentation and pathophysiology of thrombotic thrombocytopenia purpura and hemolytic uremic syndrome (HUS), and to a lesser extent, disseminated intravascular coagulation (DIC). We describe a case to illustrate the potential diagnostic difficulty, especially at initial presentation.

CASE SUMMARY

We reported a case of a 44-year-old woman that presented with diarrhea, thrombocytopenia, schistocytes, elevated serum lactate dehydrogenase (LDH) level and acute kidney injury. While the clinical presentation resembled that of Shiga toxin–induced HUS, the disease course was more consistent with gastrointestinal infection-related DIC. To aid in the accurate diagnosis of TMA and other associated disorders, we have undertaken a review and provided a clear interpretation of some typical biomarkers including schistocytes, LDH and platelet count, coagulation profile and more specific indexes of ADAMTS13, complement profile, and the isolation of Shiga toxin-producing Escherichia coli (commonly referred to as STEC).

CONCLUSION

The use and correct interpretation of classical indexes of schistocyte, LDH, and platelet count is vital in diagnosing TMA and associated disorders. Understanding the characteristics of these biomarkers in the context of thrombocytopenia purpura, HUS and DIC will facilitate the accurate diagnosis and early initiation of appropriate treatment.

Type 1 Diabetes: an Association Between Autoimmunity, the Dynamics of Gut Amyloid-producing E. coli and Their Phages

The etiopathogenesis of type 1 diabetes (T1D), a common autoimmune disorder, is not completely understood. Recent studies suggested the gut microbiome plays a role in T1D. We have used public longitudinal microbiome data from T1D patients to analyze amyloid-producing bacterial composition and found a significant association between initially high amyloid-producing Escherichia coli abundance, subsequent E. coli depletion prior to seroconversion, and T1D development. In children who presented seroconversion or developed T1D, we observed an increase in the E. coli phage/E. coli ratio prior to E. coli depletion, suggesting that the decrease in E. coli was due to prophage activation. Evaluation of the role of phages in amyloid release from E. coli biofilms in vitro suggested an indirect role of the bacterial phages in the modulation of host immunity. This study for the first time suggests that amyloid-producing E. coli, their phages, and bacteria-derived amyloid might be involved in pro-diabetic pathway activation in children at risk for T1D.

Prophage induction, but not production of phage particles, is required for lethal disease in a microbiome-replete murine model of enterohemorrhagic E. coli infection

Enterohemorrhagic Escherichia coli (EHEC) colonize intestinal epithelium by generating characteristic attaching and effacing (AE) lesions. They are lysogenized by prophage that encode Shiga toxin 2 (Stx2), which is responsible for severe clinical manifestations. As a lysogen, prophage genes leading to lytic growth and stx2 expression are repressed, whereas induction of the bacterial SOS response in response to DNA damage leads to lytic phage growth and Stx2 production both in vitro and in germ-free or streptomycin-treated mice. Some commensal bacteria diminish prophage induction and concomitant Stx2 production in vitro, whereas it has been proposed that phage-susceptible commensals may amplify Stx2 production by facilitating successive cycles of infection in vivo. We tested the role of phage induction in both Stx production and lethal disease in microbiome-replete mice, using our mouse model encompassing the murine pathogen Citrobacter rodentium lysogenized with the Stx2-encoding phage Φstx2dact. This strain generates EHEC-like AE lesions on the murine intestine and causes lethal Stx-mediated disease. We found that lethal mouse infection did not require that Φstx2dact infect or lysogenize commensal bacteria. In addition, we detected circularized phage genomes, potentially in the early stage of replication, in feces of infected mice, confirming that prophage induction occurs during infection of microbiota-replete mice. Further, C. rodentium (Φstx2dact) mutants that do not respond to DNA damage or express stx produced neither high levels of Stx2 in vitro or lethal infection in vivo, confirming that SOS induction and concomitant expression of phage-encoded stx genes are required for disease. In contrast, C. rodentium (Φstx2dact) mutants incapable of prophage genome excision or of packaging phage genomes retained the ability to produce Stx in vitro, as well as to cause lethal disease in mice. Thus, in a microbiome-replete EHEC infection model, lytic induction of Stx-encoding prophage is essential for lethal disease, but actual phage production is not.

After the Fact(or): Posttranscriptional Gene Regulation in Enterohemorrhagic Escherichia coli O157:H7

To adapt to ever-changing environments, pathogens quickly alter gene expression. This can occur through transcriptional, posttranscriptional, or posttranslational regulation. Historically, transcriptional regulation has been thoroughly studied to understand pathogen niche adaptation, whereas posttranscriptional and posttranslational gene regulation has only relatively recently been appreciated to play a central role in bacterial pathogenesis. Posttranscriptional regulation may involve chaperones, nucleases, and/or noncoding small RNAs (sRNAs) and typically controls gene expression by altering the stability and/or translation of the target mRNA. In this review, we highlight the global importance of posttranscriptional regulation to enterohemorrhagic Escherichia coli (EHEC) gene expression and discuss specific mechanisms of how EHEC regulates expression of virulence factors critical to host colonization and disease progression. The low infectious dose of this intestinal pathogen suggests that EHEC is particularly well adapted to respond to the host environment.

Inhibition of the lethality of Shiga-like toxin-1 by functional gold nanoparticles

Escherichia coli O157:H7 is a pathogen, which can generate Shiga-like toxins (SLTs) and cause hemolytic-uremic syndrome. Foodborne illness outbreaks caused by E. coli O157:H7 have become a global issue. Since SLTs are quite toxic, effective medicines that can reduce the damage caused by SLTs should be explored. SLTs consist of a single A and five B subunits, which can inhibit ribosome activity for protein synthesis and bind with the cell membrane of host cells, respectively. Pigeon ovalbumin (POA), i.e. a glycoprotein, is abundant in pigeon egg white (PEW) proteins. The structure of POA contains Gal-α(1→4)-Gal-β(1→4)-GlcNAc ligands, which have binding affinity toward the B subunit in SLT type-1 (SLT-1B). POA immobilized gold nanoparticles (POA-Au NPs) can be generated by reacting PEW proteins with aqueous tetrachloroauric acid in one-pot. The generated POA-Au NPs have been demonstrated to have selective trapping-capacity toward SLT-1B previously. Herein, we explore that POA-Au NPs can be used as protective agents to neutralize the toxicity of SLT-1 in SLT-1-infected model cells. The results show that the cells can be completely rescued when a sufficient amount of POA-Au NPs is used to treat the SLT-1-infected cells within 1 h.

Antibacterial and immunomodulatory activities of bovine lactoferrin against Escherichia coli O157:H7 infections in cattle

Enterohemorrhagic Escherichia coli (EHEC) O157:H7 is a zoonotic pathogen that causes food-borne disease in humans ranging from watery diarrhea to bloody diarrhea and severe hemorrhagic colitis, renal failure and hemolytic uremic syndrome. Cattle, the most important source of E. coli O157:H7 transmission to humans, harbor the bacteria in their gastrointestinal tract without showing clinical symptoms. Prevention of E. coli O157:H7 infections in ruminants could diminish the public health risk. However, there is no specific treatment available nor a vaccine or a therapeutic agent which completely prevents E. coli O157:H7 infections in cattle. This paper provides an overview of latest research data on eradicating enterohemorrhagic E. coli O157:H7 in ruminants by use of bovine lactoferrin administration. The article provides insights into the anti-microbial and immunomodulatory activities of bovine lactoferrin against E. coli O157:H7 infections in cattle.

Genome-wide siRNA screen identifies UNC50 as a regulator of Shiga toxin 2 trafficking

Toxins produced by Shigella bacteria undergo endosome-to-Golgi retrograde trafficking to evade degradation in the lysosome and reach the cytosol. Selyunin et al. performed a genome-wide siRNA screen and identify host factors required for the transport and toxicity of Shiga toxins.

Shiga toxins 1 and 2 (STx1 and STx2) undergo retrograde trafficking to reach the cytosol. Early endosome-to-Golgi transport allows the toxins to evade degradation in lysosomes. Targeting this trafficking step has therapeutic promise, but the mechanism of trafficking for the more potent toxin STx2 is unclear. To identify host factors required for early endosome-to-Golgi trafficking of STx2, we performed a viability-based genome-wide siRNA screen in HeLa cells. 564, 535, and 196 genes were found to be required for toxicity induced by STx1 only, STx2 only, and both toxins, respectively. We focused on validating endosome/Golgi-localized hits specific for STx2 and found that depletion of UNC50 blocked early endosome-to-Golgi trafficking and induced lysosomal degradation of STx2. UNC50 acted by recruiting GBF1, an ADP ribosylation factor–guanine nucleotide exchange factor (ARF-GEF), to the Golgi. These results provide new information about STx2 trafficking mechanisms and may advance efforts to generate therapeutically viable toxin-trafficking inhibitors.

Different drugs for bad bugs: antivirulence strategies in the age of antibiotic resistance

The rapid evolution and dissemination of antibiotic resistance among bacterial pathogens are outpacing the development of new antibiotics, but antivirulence agents provide an alternative. These agents can circumvent antibiotic resistance by disarming pathogens of virulence factors that facilitate human disease while leaving bacterial growth pathways - the target of traditional antibiotics - intact. Either as stand-alone medications or together with antibiotics, these drugs are intended to treat bacterial infections in a largely pathogen-specific manner. Notably, development of antivirulence drugs requires an in-depth understanding of the roles that diverse virulence factors have in disease processes. In this Review, we outline the theory behind antivirulence strategies and provide examples of bacterial features that can be targeted by antivirulence approaches. Furthermore, we discuss the recent successes and failures of this paradigm, and new developments that are in the pipeline.

Adsorption of Shiga Toxin to Poly-γ-Glutamate Precipitated

We screened foods containing indigestible ingredients in the ability to adsorb Shiga toxin (Stx). When 5 mg of foods and dietary fibers such as dry vegetables and inulin were mixed and incubated with 0.5 mL of Stx solution (100 ng/mL) containing 0.5% bovine serum albumin, both Stx1 and Stx2 seemed to be adsorbed by only a fermented food, natto (a traditional Japanese food prepared from steamed soybeans by the biological action of Bacillus subtilis). We purified the Stx-adsorbing substance from natto by extraction with H₂ O, acid treatment, Proteinase K treatment, and an ion exchange chromatography. The purified substance showed an average molecular mass of about 600 kDa. We identified it as poly-γ-glutamate (PGA) by amino acid analysis of its hydrolysate and peptide analysis after its treatment with Proteinase K. Purified PGA (MW: molecular weight = about 600 kDa) was considered to adsorb both Stx1 and Stx2 when we separated adsorbed and unadsorbed Stxs (MW = about 72 kDa) by an ultrafiltration method with a centrifugal filter unit (MWCO: molecular weight cut-off = 100 K). However, PGA with the ability to adsorb Stx was an insoluble form precipitated in the filter unit during centrifugation. PGA precipitated beyond the saturated density was also confirmed to well adsorb both Stx1 and Stx2 by an equilibrated dialysis method. To the best of our knowledge, this is the 1st report on food-adsorbing Stx.

Postinfectious Hemolytic Uremic Syndrome

Post-infectious hemolytic uremic syndrome (HUS) is caused by specific pathogens in patients with no identifiable HUS-associated genetic mutation or autoantibody. The majority of episodes is due to infections by Shiga toxin (Stx) producing Escherichia coli (STEC). This chapter reviews the epidemiology and pathogenesis of STEC-HUS, including bacterial-derived factors and host responses. STEC disease is characterized by hematological (microangiopathic hemolytic anemia), renal (acute kidney injury) and extrarenal organ involvement. Clinicians should always strive for an etiological diagnosis through the microbiological or molecular identification of Stx-producing bacteria and Stx or, if negative, serological assays. Treatment of STEC-HUS is supportive; more investigations are needed to evaluate the efficacy of putative preventive and therapeutic measures, such as non-phage-inducing antibiotics, volume expansion and anti-complement agents. The outcome of STEC-HUS is generally favorable, but chronic kidney disease, permanent extrarenal, mainly cerebral complication and death (in less than 5 %) occur and long-term follow-up is recommended. The remainder of this chapter highlights rarer forms of (post-infectious) HUS due to S. dysenteriae, S. pneumoniae, influenza A and HIV and discusses potential interactions between these pathogens and the complement system.

Effect of lactoferrin on release and bioactivity of Shiga toxins from different Escherichia coli O157:H7 strains

Prevention of enterohemorrhagic Escherichia coli (EHEC) O157:H7 infections and of their severe clinical sequelae in humans remain to be a current challenge. Administration of bovine lactoferrin (bLF) proved to be effective in clearing EHEC from the bovine intestine, an important EHEC reservoir, suggesting that bLF may also be beneficial in human application against EHEC infections. To estimate the biological safety of this approach, we analyzed the effects of bLF on the main EHEC virulence factor, Shiga toxin (Stx). We quantified the release of Stx 1 and 2 from two O157:H7 EHEC strains (Stx1⁺Stx2⁺ and Stx2⁺ producing, respectively) cultured in the presence of bLF using ELISA assays and assessed cytotoxic effects of bLF and co-cultured EHEC on Vero cells. Effects of bLF on the stability of Stx2 were investigated using western blotting. ELISA results indicate a bLF concentration-dependent decrease of active, cell-free Stx2, but not Stx1 in EHEC cultures. High concentrations (100 and 50mg/ml) of bLF resulted in significantly reduced (p<0.05) metabolic activity rates of Vero cells, whereas a concentration of 10mg/ml bLF was considered non-toxic for Vero cells. At concentrations of 1 or 0.1mg/ml, bLF mitigated the verocytotoxicity of EHEC strains in a co-culture model up to 48h after inoculation. When only colonizing bacteria were taken into account, cytotoxicity could be significantly reduced by 10 and 1mg/ml bLF during 48h. This effect of bLF at least partly results from degradation of the Stx2 receptor-binding B-subunit.

Shiga Toxin-Producing Escherichia coli Infection, Antibiotics, and Risk of Developing Hemolytic Uremic Syndrome: A Meta-analysis

BACKGROUND

Antibiotic administration to individuals with Shiga toxin-producing Escherichia coli (STEC) infection remains controversial. We assessed if antibiotic administration to individuals with STEC infection is associated with development of hemolytic uremic syndrome (HUS).

METHODS

The analysis included studies published up to 29 April 2015, that provided data from patients (1) with STEC infection, (2) who received antibiotics, (3) who developed HUS, and (4) for whom data reported timing of antibiotic administration in relation to HUS. Risk of bias was assessed; strength of evidence was adjudicated. HUS was the primary outcome. Secondary outcomes restricted the analysis to low-risk-of-bias studies employing commonly used HUS criteria. Pooled estimates of the odds ratio (OR) were obtained using random-effects models.

RESULTS

Seventeen reports and 1896 patients met eligibility; 8 (47%) studies were retrospective, 5 (29%) were prospective cohort, 3 (18%) were case-control, and 1 was a trial. The pooled OR, including all studies, associating antibiotic administration and development of HUS was 1.33 (95% confidence interval [CI], .89-1.99; I(2) = 42%). The repeat analysis including only studies with a low risk of bias and those employing an appropriate definition of HUS yielded an OR of 2.24 (95% CI, 1.45-3.46; I(2) = 0%).

CONCLUSIONS

Overall, use of antibiotics was not associated with an increased risk of developing HUS; however, after excluding studies at high risk of bias and those that did not employ an acceptable definition of HUS, there was a significant association. Consequently, the use of antibiotics in individuals with STEC infections is not recommended.

Identification of potential drug targets by subtractive genome analysis of Escherichia coli O157:H7: an in silico approach

Bacterial enteric infections resulting in diarrhea, dysentery, or enteric fever constitute a huge public health problem, with more than a billion episodes of disease annually in developing and developed countries. In this study, the deadly agent of hemorrhagic diarrhea and hemolytic uremic syndrome, Escherichia coli O157:H7 was investigated with extensive computational approaches aimed at identifying novel and broad-spectrum antibiotic targets. A systematic in silico workflow consisting of comparative genomics, metabolic pathways analysis, and additional drug prioritizing parameters was used to identify novel drug targets that were essential for the pathogen’s survival but absent in its human host. Comparative genomic analysis of Kyoto Encyclopedia of Genes and Genomes annotated metabolic pathways identified 350 putative target proteins in E. coli O157:H7 which showed no similarity to human proteins. Further bio-informatic approaches including prediction of subcellular localization, calculation of molecular weight, and web-based investigation of 3D structural characteristics greatly aided in filtering the potential drug targets from 350 to 120. Ultimately, 44 non-homologous essential proteins of E. coli O157:H7 were prioritized and proved to have the eligibility to become novel broad-spectrum antibiotic targets and DNA polymerase III alpha (dnaE) was the top-ranked among these targets. Moreover, druggability of each of the identified drug targets was evaluated by the DrugBank database. In addition, 3D structure of the dnaE was modeled and explored further for in silico docking with ligands having potential druggability. Finally, we confirmed that the compounds N-coeleneterazine and N-(1,4-dihydro-5H-tetrazol-5-ylidene)-9-oxo-9H-xanthene-2-sulfon-amide were the most suitable ligands of dnaE and hence proposed as the potential inhibitors of this target protein. The results of this study could facilitate the discovery and release of new and effective drugs against E. coli O157:H7 and other deadly human bacterial pathogens.

Comparison of the BD MAX® Enteric Bacterial Panel assay with conventional diagnostic procedures in diarrheal stool samples

Although infectious diarrhea is one of the most predominant diseases around the world, the identification of the causative microorganism is still challenging. The aim of this study was the evaluation of the BD MAX® Enteric Bacterial Panel assay in comparison to conventional diagnostic procedures concerning the detection of the enteric pathogens Salmonella spp., Campylobacter spp., Shigella spp., and Shiga toxin-producing Escherichia coli. For this purpose, 971 prospectively collected stool samples were evaluated. Utilization of the BD MAX Enteric Bacterial Panel elevated the overall detection rate from 5.26 % to 8.06 %. The positive percent agreement of the BD MAX Enteric Bacterial Panel assay and stool culture or enzyme immunoassay was 0.97 for Campylobacter spp., 0.75 for Salmonella spp., 1.00 for Shigella spp., and 0.88 for Shiga toxins. Furthermore, a negative percent agreement of 0.98 for Campylobacter spp., 0.99 for Salmonella spp., 0.99 for Shigella spp., and 0.99 for Shiga toxins has been demonstrated. This study highlighted the superior detection rate of molecular assays compared to conventional diagnostic procedures.

A Conserved Structural Motif Mediates Retrograde Trafficking of Shiga Toxin Types 1 and 2

Shiga toxin-producing Escherichia coli (STEC) produce two types of Shiga toxin (STx): STx1 and STx2. The toxin A-subunits block protein synthesis, while the B-subunits mediate retrograde trafficking. STEC infections do not have definitive treatments, and there is growing interest in generating toxin transport inhibitors for therapy. However, a comprehensive understanding of the mechanisms of toxin trafficking is essential for drug development. While STx2 is more toxic in vivo, prior studies focused on STx1 B-subunit (STx1B) trafficking. Here, we show that, compared with STx1B, trafficking of the B-subunit of STx2 (STx2B) to the Golgi occurs with slower kinetics. Despite this difference, similar to STx1B, endosome-to-Golgi transport of STx2B does not involve transit through degradative late endosomes and is dependent on dynamin II, epsinR, retromer and syntaxin5. Importantly, additional experiments show that a surface-exposed loop in STx2B (β4-β5 loop) is required for its endosome-to-Golgi trafficking. We previously demonstrated that residues in the corresponding β4-β5 loop of STx1B are required for interaction with GPP130, the STx1B-specific endosomal receptor, and for endosome-to-Golgi transport. Overall, STx1B and STx2B share a common pathway and use a similar structural motif to traffic to the Golgi, suggesting that the underlying mechanisms of endosomal sorting may be evolutionarily conserved.

Virulence Gene Regulation in Escherichia coli

Escherichia colicauses three types of illnesses in humans: diarrhea, urinary tract infections, and meningitis in newborns. The acquisition of virulence-associated genes and the ability to properly regulate these, often horizontally transferred, loci distinguishes pathogens from the normally harmless commensal E. coli found within the human intestine. This review addresses our current understanding of virulence gene regulation in several important diarrhea-causing pathotypes, including enteropathogenic, enterohemorrhagic,enterotoxigenic, and enteroaggregativeE. coli-EPEC, EHEC, ETEC and EAEC, respectively. The intensely studied regulatory circuitry controlling virulence of uropathogenicE. coli, or UPEC, is also reviewed, as is that of MNEC, a common cause of meningitis in neonates. Specific topics covered include the regulation of initial attachment events necessary for infection, environmental cues affecting virulence gene expression, control of attaching and effacing lesionformation, and control of effector molecule expression and secretion via the type III secretion systems by EPEC and EHEC. How phage control virulence and the expression of the Stx toxins of EHEC, phase variation, quorum sensing, and posttranscriptional regulation of virulence determinants are also addressed. A number of important virulence regulators are described, including the AraC-like molecules PerA of EPEC, CfaR and Rns of ETEC, and AggR of EAEC;the Ler protein of EPEC and EHEC;RfaH of UPEC;and the H-NS molecule that acts to silence gene expression. The regulatory circuitry controlling virulence of these greatly varied E. colipathotypes is complex, but common themes offerinsight into the signals and regulators necessary forE. coli disease progression.

Enhanced detection sensitivity of Escherichia coli O157:H7 using surface-modified gold nanorods

Escherichia coli O157:H7 (O157) is a Gram negative and highly virulent bacteria found in food and water sources, and is a leading cause of chronic diseases worldwide. Diagnosis and prevention from the infection require simple and rapid analysis methods for the detection of pathogens, including O157. Endogenous membrane peroxidase, an enzyme present on the surface of O157, was used for the colorimetric detection of bacteria by catalytic oxidation of the peroxidase substrate. In this study, we have analyzed the impact of the synthesized bare gold nanorods (AuNRs) and silica-coated AuNRs on the growth of E. coli O157. Along with the membrane peroxidase activity of O157, other bacteria strains were analyzed. Different concentrations of nanorods were used to analyze the growth responses, enzymatic changes, and morphological alterations of bacteria by measuring optical density, 3,3',5,5'-tetramethylbenzidine assay, flow cytometry analysis, and microscopy studies. The results revealed that O157 showed higher and continuous membrane peroxidase activity than other bacteria. Furthermore, O157 treated with bare AuNRs showed a decreased growth rate in comparison with the bacteria with surface modified AuNRs. Interestingly, silica-coated AuNRs favored the growth of bacteria and also increased membrane peroxidase activity. This result can be particularly important for the enzymatic analysis of surface treated AuNRs in various microbiological applicants.

Combating pathogenic microorganisms using plant-derived antimicrobials: a minireview of the mechanistic basis

The emergence of antibiotic resistance in pathogenic bacteria has led to renewed interest in exploring the potential of plant-derived antimicrobials (PDAs) as an alternative therapeutic strategy to combat microbial infections. Historically, plant extracts have been used as a safe, effective, and natural remedy for ailments and diseases in traditional medicine. Extensive research in the last two decades has identified a plethora of PDAs with a wide spectrum of activity against a variety of fungal and bacterial pathogens causing infections in humans and animals. Active components of many plant extracts have been characterized and are commercially available; however, research delineating the mechanistic basis of their antimicrobial action is scanty. This review highlights the potential of various plant-derived compounds to control pathogenic bacteria, especially the diverse effects exerted by plant compounds on various virulence factors that are critical for pathogenicity inside the host. In addition, the potential effect of PDAs on gut microbiota is discussed.

The molecular mechanism of Shiga toxin Stx2e neutralization by a single-domain antibody targeting the cell receptor-binding domain

Shiga toxin Stx2e is the major known agent that causes edema disease in newly weaned pigs. This severe disease is characterized by neurological disorders, hemorrhagic lesions, and frequent fatal outcomes. Stx2e consists of an enzymatically active A subunit and five B subunits that bind to a specific glycolipid receptor on host cells. It is evident that antibodies binding to the A subunit or the B subunits of Shiga toxin variants may have the capability to inhibit their cytotoxicity. Here, we report the discovery and characterization of a VHH single domain antibody (nanobody) isolated from a llama phage display library that confers potent neutralizing capacity against Stx2e toxin. We further present the crystal structure of the complex formed between the nanobody (NbStx2e1) and the Stx2e toxoid, determined at 2.8 Å resolution. Structural analysis revealed that for each B subunit of Stx2e, one NbStx2e1 is interacting in a head-to-head orientation and directly competing with the glycolipid receptor binding site on the surface of the B subunit. The neutralizing NbStx2e1 can in the future be used to prevent or treat edema disease.

Management of hemolytic-uremic syndrome in children

Acute renal failure associated with a fulminant, life-threatening systemic disease is rare in previously healthy young children; however, when it occurs, the most common cause is hemolytic-uremic syndrome (HUS). In most cases (90%), this abrupt and devastating illness is a result of ingestion of food or drink contaminated with pathogens that produce very potent toxins. Currently, there are no proven treatment options that can directly inactivate the toxin or effectively interfere with the cascade of destructive events triggered by the toxin once it gains access to the bloodstream and binds its receptor. However, HUS is self-limited, and effective supportive management during the acute phase is proven to be a life saver for children affected by HUS. A minority of childhood HUS cases, approximately 5%, are caused by various genetic mutations causing uncontrolled activation of the complement system. These children, who used to have a poor prognosis leading to end-stage renal disease, now have access to exciting new treatment options that can preserve kidney function and avoid disease recurrences. This review provides a summary of the current knowledge on the epidemiology, pathophysiology, and clinical presentation of childhood HUS, focusing on a practical approach to best management measures.

Phenethyl isothiocyanate inhibits shiga toxin production in enterohemorrhagic Escherichia coli by stringent response induction

The pathogenicity of enterohemorrhagic Escherichia coli (EHEC) depends on production of Shiga toxins, which are encoded by stx genes located in the genomes of lambdoid prophages. Efficient expression of these genes requires prophage induction and lytic development of phages. Treatment of EHEC infections is problematic due to not only the resistance of various strains to antibiotics but also the fact that many antibiotics cause prophage induction, thus resulting in high-level expression of stx genes. Here we report that E. coli growth, Shiga toxin-converting phage development, and production of the toxin by EHEC are strongly inhibited by phenethyl isothiocyanate (PEITC). We demonstrate that PEITC induces the stringent response in E. coli that is mediated by massive production of a global regulator, guanosine tetraphosphate (ppGpp). The stringent response induction arises most probably from interactions of PEITC with amino acids and from amino acid deprivation-mediated activation of ppGpp synthesis. In mutants unable to synthesize ppGpp, development of Shiga toxin-converting phages and production of Shiga toxin are significantly enhanced. Therefore, ppGpp, which appears at high levels in bacterial cells after stimulation of its production by PEITC, is a negative regulator of EHEC virulence and at the same time efficiently inhibits bacterial growth. This is in contrast to stimulation of virulence of different bacteria by this nucleotide reported previously by others.

[Management of patients with EHEC/HUS. Lessons and perspectives from clinical infectious disease specialists]

The 2011 EHEC/HUS outbreak created uncertainty regarding the previous recommendations of withholding antibiotic therapy and regarding rational measures for prevention of invasive meningococcal disease after treatment with the monoclonal antibody eculizumab. For both these areas, an expert panel of the German Society for Infectious Diseases in cooperation with representatives of other learned societies and health institutions has drafted and consented guidelines that were published online on 1 June 2011 (i.e., ~10 days after the peak of the epidemic) and 4 June 2011. A summary of the guidelines in English was made available online on 4 June 2011. The time until ad hoc guidelines are made publicly available should and can be shortened in similar scenarios in the future. To this end-among other things-scientific societies in Germany linked to infectious diseases and medical microbiology have established a permanent working group called AFIM. This working group will facilitate timely identification and appointment of experts and expert panels, and will make use of new ways of rapid and effective sharing and dissemination of knowledge and ad hoc guidelines in the medical community and public domain if needed. In the case of disease outbreaks, immediate telephone conferences among all professionals involved, close cooperation between institutions and expert groups, and avoidance of premature unconsented information and press releases will be critical. We expect that proceeding in this way will also have a major impact on proper planning, professional design, and adequate analysis of clinical studies and endpoints appropriate for the outbreak situation.

Shiga toxin-producing Escherichia coli O104:H4: an emerging pathogen with enhanced virulence

Pathogenic Escherichia coli are genetically diverse and encompass a broad variety of pathotypes, such as enteroaggregative E. coli (EAEC) or enterohemorrhagic E. coli (EHEC), which cause distinct clinical syndromes. The historically large 2011 German outbreak of hemolytic uremic syndrome (HUS), caused by a Shiga-toxin producing E. coli (STEC) of the serotype O104:H4, illustrated the emerging importance of non-O157 STEC. STEC O104:H4, with features characteristic of both enteroaggregative E. coli and enterohemorrhagic E. coli, represents a unique and highly virulent pathotype. The German outbreak both allowed for the evaluation of several potential therapeutic approaches to STEC-induced HUS and emphasizes the importance of early and specific detection of both O157 and non-O157 STEC.

Does levofloxacin induce hemolytic uremic syndrome in patients infected with verotoxin-producing Escherichia coli O157 infections?

Fifteen Japanese colitis patients, aged above 16 years old, infected with verotoxin-producing Escherichia coli O157 (VTEC O157) were divided into 2 treatment groups. Of the 15 patients, 6 (mean ± SD, 41.3 ± 19.0 years old) were treated with levofloxacin (LVFX), while the remaining 9 patients (32.0 ± 10.0 years old) were not treated with any antimicrobial agents. All patients complained of abdominal pain and bloody stool and were not administered antidiarrheals. Hemolytic uremic syndrome (HUS) did not develop in any of the 6 patients treated with LVFX, but developed in 1 of the 9 patients not treated with antimicrobial agents. No statistical difference was found in the occurrence rate of HUS between LVFX-treated patients and patients not treated with antimicrobial agents. Our results suggest that oral administration of LVFX is not associated with risk of HUS in hemorrhagic colitis patients aged above 16 years infected with VTEC O157.

Pharmacokinetics of antibacterial agents in the CSF of children and adolescents

The adequate management of central nervous system (CNS) infections requires that antimicrobial agents penetrate the blood-brain barrier (BBB) and achieve concentrations in the CNS adequate for eradication of the infecting pathogen. This review details the currently available literature on the pharmacokinetics (PK) of antibacterials in the CNS of children. Clinical trials affirm that the physicochemical properties of a drug remain one of the most important factors dictating penetration of antimicrobial agents into the CNS, irrespective of the population being treated (i.e. small, lipophilic drugs with low protein binding exhibit the best translocation across the BBB). These same physicochemical characteristics determine the primary disposition pathways of the drug, and by extension the magnitude and duration of circulating drug concentrations in the plasma, a second major driving force behind achievable CNS drug concentrations. Notably, these disposition pathways can be expected to change during the normal process of growth and development. Finally, CNS drug penetration is influenced by the nature and extent of the infection (i.e. the presence of meningeal inflammation). Aminoglycosides have poor CNS penetration when administered intravenously. Intrathecal gentamicin has been studied in children with more promising results, often exceeding the minimum inhibitory concentration. There are very limited data with intrathecal tobramycin in children. However, in the few patients that have been studied, the CSF concentrations were highly variable. Penicillins generally have good CNS penetration. Aqueous penicillin G reaches greater concentrations than procaine or benzathine penicillin. Concentrations remain detectable for ≥ 12 h. Of the aminopenicillins, both ampicillin and parenteral amoxicillin reach adequate CNS concentrations; however, orally administered amoxicillin resulted in much lower concentrations. Nafcillin and piperacillin are the final two penicillins with pediatric data: their penetration is erratic at best. Cephalosporins vary greatly in regard to their CSF penetration. Few first- and second-generation cephalosporins are able to reach higher CSF concentrations. Cefuroxime is the only exception and is usually avoided due to its adverse effects and slower sterilization of the CSF than third-generation agents. Ceftriaxone, cefotaxime, ceftazidime, cefixime and cefepime have been studied in children and are all able to adequately penetrate the CSF. As with penicillins, concentrations are greatest in the presence of meningeal inflammation. Meropenem and imipenem are the only carbapenems with pediatric data. Imipenem reaches higher CSF concentrations; however, meropenem is preferred due to its lower incidence of seizures. Aztreonam has also demonstrated favorable penetration but only one study has been completed in children. Both chloramphenicol and sulfamethoxazole/trimethoprim (cotrimoxazole) penetrate into the CNS well; however, significant toxicities limit their use. The small size and minimal protein binding of fosfomycin contribute to its favorable CNS PK. Although rarely used, it achieves higher concentrations in the presence of inflammation and accumulation is possible. Linezolid reaches high CSF concentrations; however, more frequent dosing might be required in infants due to their increased elimination. Metronidazole also has very limited information but it demonstrated favorable results similar to adult data; CSF concentrations even exceeded plasma concentrations at certain time points. Rifampin (rifampicin) demonstrated good CNS penetration after oral administration. Vancomycin demonstrates poor CNS penetration after intravenous administration. When combined with intraventricular therapy, CNS concentrations are much greater. Of the antituberculosis agents, isoniazid, pyrazinamide and streptomycin have been studied in children. Isoniazid and pyrazinamide have favorable CSF penetration. Streptomycin appears to produce unpredictable CSF levels. No pediatric-specific data are available for clindamycin, daptomycin, macrolides, tetracyclines, and fluoroquinolones. Daptomycin, fluoroquinolones, and tetracyclines have demonstrated favorable CNS penetration in adults; however, data are limited due to their potential pediatric-specific toxicities and newness within the marketplace. Macrolides and clindamycin have demonstrated poor CNS penetration in adults and thus have not been studied in pediatrics.

Therapeutic concentrations of antibiotics inhibit Shiga toxin release from enterohemorrhagic E. coli O104:H4 from the 2011 German outbreak

Background

The shiga toxin-producing E. coli (STEC) O104:H4 caused a major outbreak in Germany in spring 2011. STEC are usually susceptible to common antibiotics. However, antibiotic treatment of STEC-infected patients is not recommended because STEC may enhance production and release of shiga toxins (STX) in response to antibiotics, which eventually enhances the frequency and severity of clinical symptoms, including haemolytic uraemic syndrome (HUS) and fatalities.

Results

We characterized the response to antibiotics of STEC O104:H4 isolates from two HUS patients during the German STEC outbreak in spring 2011 in comparison to the common STEC O157:H7. Liquid cultures of STEC O157:H7 and O104:H4 were incubated with graded dilutions of the antibiotics ciprofloxacin, meropenem, fosfomycin, gentamicin, rifampicin, and chloramphenicol. At defined times of antibiotic treatment, transcriptional activation of the STX2 gene, contents of STX and STX-activity in the culture supernatants were quantified. Unlike the common serotype O157:H7, STEC O104:H4 does not release STX in response to therapeutic concentrations of ciprofloxacin, meropenem, fosfomycin, and chloramphenicol.

Conclusions

In future outbreaks, the response of the respective epidemiologic STEC strain to antibiotics should be rapidly characterized in order to identify antibiotics that do not enhance the release of STX. This will eventually allow clinical studies tackling the question whether antibiotic treatment impacts on the eradication of STEC, clinical course of disease, and frequency of carriers.

Effect of Preservatives on Shiga Toxigenic Phages and Shiga Toxin of Escherichia coli O157:H7

Toxin synthesis by Shiga toxin–producing Escherichia coli (STEC) appears to be coregulated through the induction of the integrated bacteriophages that encode the toxin genes. These phages might be the principal means for the dissemination and release of Shiga toxins. We evaluated the effect of three common food preservatives, potassium sorbate, sodium benzoate, and sodium propionate, on the propagation of the phages and Shiga toxins. We tested each preservative at four concentrations, 1, 1.25, 2.5, and 5 mg/ml, both on free phages and on lysogenic phages in bacteria. We also evaluated the expression of a lambdoid phage, which was exposed to increasing concentrations of preservatives, by measuring β-galactosidase activity from SPC105, a transductant strain. Furthermore, we tested the effect of the preservatives on cytotoxigenic activity of Shiga toxin on Vero cells. We detected an increase of the inhibitory effect of the phage lytic activity, both in lysogenic and free phages, as the preservative concentration increased. However, the inhibition was higher on the lysogenic phages release than on free phages. Sodium benzoate and potassium sorbate were about equal at inhibiting phages; they were more effective than sodium propionate. A significant decrease of lacZ expression, encoded in a lambda phage, was observed. We also found a reduction in Shiga toxin titer caused by exposure of E. coli O157:H7 to 5 mg/ml sodium benzoate or potassium sorbate. These results imply that these three preservatives, used to inhibit microbial spoilage of foods, also act to inhibit lytic activity and dispersion of a phage carrying the gene encoding powerful Shiga cytotoxins. Also notable was the inactivation of Shiga toxin activity, although this effect was detected using concentrations of preservatives greater than those allowed by the Argentine Food Code.

Acid resistance and verocytotoxin productivity of enterohemorrhagic Escherichia coli O157:H7 exposed to microwave

We examined the acid resistance and verocytotoxin (VT) productivity of enterohemorrhagic Escherichia coli O157:H7 irradiated by microwave with a domestic microwave oven and a commercial microwave radiator equipped with a thermo-regulator. When the cell suspension (5 mL) chilled at 0 °C was treated with a domestic microwave oven at weak power (2.45 GHz, 100 W) for 60 s, the living cell number was reduced by 2 orders (final temperature, about 65 °C). The surviving cells showed lower acid resistance and VT productivity than nonirradiated cells. To examine the nonthermal effect of microwave on acid resistance and VT productivity, the cells in Luria-Bertani medium were intermittently irradiated to keep the culture temperature at 37 °C with the microwave radiator (2.45 GHz, 0.6 W/mL). The intermittent radiation slightly reduced the acid resistance, but clearly suppressed the VT productivity. Microwave oven is probably useful for reducing not only the living cell number but also the acid resistance and VT productivity of EHEC O157:H7.