Carbohydrate-binding specificity of the Escherichia coli cytolethal distending toxin CdtA-II and CdtC-II subunits

Intoxication by cytolethal distending toxin depends on assembly of CdtB, the active A component of this AB toxin, with the cell surface-binding (B) component, composed of the CdtA-CdtC heterodimer, to form the active holotoxin. Here we examine the cell surface binding properties of Escherichia coli-derived CdtA-II (CdtA-II(Ec)) and CdtC-II(Ec) and their capacity to provide a binding platform for CdtB-II(Ec). Using a flow cytometry-based binding assay, we demonstrate that CdtB-II(Ec) binds to the HeLa cell surface in a CdtA-II(Ec)- and CdtC-II(Ec)-dependent manner and that CdtA-II(Ec) and CdtC-II(Ec) compete for the same structure on the HeLa cell surface. Preincubation of cells with glycoproteins (thyroglobulin and fetuin), but not simple sugars, blocks surface binding of CdtA-II(Ec) and CdtC-II(Ec). Moreover, CdtA-II(Ec) and CdtC-II(Ec) bind immobilized fetuin and thyroglobulin as well as fucose and to a lesser degree N-acetylgalactoseamine and N-acetylglucoseamine. Removal of N- but not O-linked carbohydrates from fetuin and thyroglobulin prevents binding of CdtA-II(Ec) and CdtC-II(Ec) to these glycoproteins. In addition, removal of N- but not O-linked surface sugar attachments prevents CDT-II(Ec) intoxication. To characterize the cell surface ligand recognized by CdtA-II(Ec) and CdtC-II(Ec), lectins having various carbohydrate specificities were used to block CDT activity and the cell surface binding of CdtA-II(Ec) and CdtC-II(Ec). Pretreatment of cells with AAA, SNA-I, STA, UEA-I, GNA, and NPA partially or completely blocked CDT activity. AAA, EEA, and UEA-I lectins, all having specificity for fucose, blocked surface binding of CdtA-II(Ec) and CdtC-II(Ec). Together, our data indicate that CdtA-II(Ec) and CdtC-II(Ec) bind an N-linked fucose-containing structure on HeLa cells.

Cyanobacterial toxins: risk management for health protection

This paper reviews the occurrence and properties of cyanobacterial toxins, with reference to the recognition and management of the human health risks which they may present. Mass populations of toxin-producing cyanobacteria in natural and controlled waterbodies include blooms and scums of planktonic species, and mats and biofilms of benthic species. Toxic cyanobacterial populations have been reported in freshwaters in over 45 countries, and in numerous brackish, coastal, and marine environments. The principal toxigenic genera are listed. Known sources of the families of cyanobacterial toxins (hepato-, neuro-, and cytotoxins, irritants, and gastrointestinal toxins) are briefly discussed. Key procedures in the risk management of cyanobacterial toxins and cells are reviewed, including derivations (where sufficient data are available) of tolerable daily intakes (TDIs) and guideline values (GVs) with reference to the toxins in drinking water, and guideline levels for toxigenic cyanobacteria in bathing waters. Uncertainties and some gaps in knowledge are also discussed, including the importance of exposure media (animal and plant foods), in addition to potable and recreational waters. Finally, we present an outline of steps to develop and implement risk management strategies for cyanobacterial cells and toxins in waterbodies, with recent applications and the integration of Hazard Assessment Critical Control Point (HACCP) principles.

Anatoxins and degradation products, determined using hybrid quadrupole time-of-flight and quadrupole ion-trap mass spectrometry: forensic investigations of cyanobacterial neurotoxin poisoning

The potent neurotoxins from cyanobacteria, anatoxin-a (AN), its methyl analogue, homoanatoxin-a (HMAN), and their degradation products, have been studied using nano-electrospray hybrid quadrupole time-of-flight mass spectrometry (QqTOF-MS). The anatoxin degradation products, which are readily produced in vivo by either reduction or epoxidation, were also examined in this study. The high mass accuracy QqTOF-MS data was used to confirm formula assignments for major product ions and quadrupole ion-trap (QIT)-MS was used to construct fragmentation pathways for anatoxins. Significant differences between these fragmentation pathways were observed. Comparisons between the spectra of compounds that differ in side-chain length (the AN and HMAN series) were used to identify ions that are characteristic of the homologues. The application to forensic samples in which the principal neurotoxin had undergone rapid biodegradation has been demonstrated and used to confirm anatoxin poisoning of dogs.

Protective efficacy and the recovery profile of certain chemoprotectants against lethal poisoning by microcystin-LR in mice

The cyclic peptide toxins microcystins and nodularins are the most common and abundant cyanotoxins present in diverse water systems. They have been the cause of human and animal health hazards and even death. Development of suitable chemoprotectants against microcystin is essential considering the human health importance. In the present study, three agents cyclosporin-A (10mg/kg), rifampin (25mg/kg) and silymarin (400mg/kg) pre-treatment gave 100% protection against lethal dose of microcystin-LR (100 microg/kg). Various biochemical parameters were evaluated to study the recovery profile of protected animals at 1, 3, 7 and 14 days post-toxin treatment. There was significant depletion of hepatic glutathione in protected animals compared to control group till 7 days post-treatment but normalised by 14 days. Similarly enhanced hepatic lipid peroxidation, inhibition of protein phosphatase activity was observed till 3-7 days post-treatment in protected animals. Elevated levels of enzymes alanine amino transferase, lactate dehydrogenase and sorbitol dehydrogenase were observed in serum at 1 day post-treatment. All the biochemical variables reached control levels by 14 day post-treatment. Immunoblotting analyses of liver homogenates showed microcystin-protein phosphatase adduct in liver samples of toxin treated as well as antidote-protected animals. The adduct could be seen even after 14 days post-toxin treatment. The study shows that though cyclosporin-A, rifampin and silymarin could offer 100% protection against microcystin-LR induced lethality many of the toxic manifestations are persistent and could not be reversed till 7 days.

Need to differentiate lethal toxin-producing strains of Burkholderia gladioli, which cause severe food poisoning: description of B. gladioli pathovar cocovenenans and an emended description of B. gladioli

Burkholderia cocovenenans produces a lethal toxin (Bongkrekic acid) that leads to high fatality in food poisoning cases. However, B. cocovenenans was combined in Burkholderia gladioli in 1999. B. gladioli was originally described as a phytopathogenic bacteria that sometimes causes pneumonia in humans and that acts as an opportunistic pathogen. We thought that it was clinically dangerous to describe these two species without considering their pathogenicities. From our data of 16S rRNA sequence analysis, DNA-DNA hybridization, and fatty acid analysis, we could confirm that B. cocovenenans and B. gladioli should be categorized as a single species. However the species really weaved lethal toxin-producing strains with non-lethal strains. To emphasize that B. gladioli contains two different pathogens, we describe a new pathovar, B. gladioli pathovar cocovenenans, for the lethal toxin-producing strains. We provide characteristics that differentiate this lethal toxin-producing pathovar from other phytopathogenic pathovars within B. gladioli, together with an emended description of B. gladioli.

Health hazards for terrestrial vertebrates from toxic cyanobacteria in surface water ecosystems

Toxigenic cyanobacteria are photosynthetic prokaryotes that are most often recognized in marine and freshwater systems, such as lakes, ponds, rivers, and estuaries. When environmental conditions (such as light, nutrients, water column stability, etc.) are suitable for their growth, cyanobacteria may proliferate and form toxic blooms in the upper, sunlit layers. The biology and ecology of cyanobacteria have been extensively studied throughout the world during the last two decades, but we still know little about the factors and processes involved in regulating toxin production for many cyanobacterial species. In this minireview, we discuss these microorganisms, and more especially the toxins they produce, as a potential and important health risk for wild and domestic animals.

The Palm Island mystery disease 20 years on: a review of research on the cyanotoxin cylindrospermopsin

Poisoning of humans resulting from consumption of water affected by the toxic cyanobacterium Cylindrospermopsis raciborskii was first reported almost 20 years ago from Palm Island, northern Queensland, Australia. Since that time a great deal has been learned about this organism and cylindrospermopsin (CYN), the toxin it produces. This article reviews the information now available to us. It summarizes aspects of the chemistry of the toxin-now known to be produced by some cyanobacterial species other than C. raciborskii-and its biosynthesis and chemical synthesis in vitro, as well as its detection and measurement by chemical and biological assay. Some of the factors affecting toxin production by cultured isolates of C. raciborskii are reviewed and the conditions that cause its release from the cells described. The occurrence of CYN in water bodies and the management strategies used to minimize the harmful effects of the toxin are outlined. These include a range of water-treatment practices now in place to remove CYN-producing organisms and/or to neutralize the toxin together with some management procedures that have been tried, with varying degrees of success, to prevent buildup of blooms of the offending organisms. Some of the public-health considerations arising from exposure to water supplies affected by CYN are summarized along with the risk factors and guidance values as they are currently applied. Among the more recent developments described are those that come from the application of molecular techniques for characterizing toxic and nontoxic strains and for exploring the genetic aspects of CYN production.

Toxicology and evaluation of microcystins

This paper reviews the toxicity and tumor-promoting properties of microcystins. Methods for screening and/or identification of microcystins in environmental samples are discussed and compared. Specific emphasis is placed on newly developed extraction/detection methods, e.g., solid phase microextraction (SPME) technique, and capillary electrophoresis coupled with laser-induced fluorescence detection. The results of a kinetic analysis of the effects of microcystins on phosphorylase-a binding to phosphatase-2A using a surface plasmon resonance biosensor are also presented.

Preformed bacterial toxins

Food poisoning syndromes caused by four different bacteria are described. For all types, food kept at a permissive temperature allows growth of the vegetative forms of the bacteria and production of a toxin or toxins. The key features of these syndromes, as well as possible new trends of concern, are summarized in Table 1.

Active and passive immunization with the Pseudomonas V antigen protects against type III intoxication and lung injury

Pseudomonas aeruginosa is an opportunistic bacterial pathogen that can cause fatal acute lung infections in critically ill individuals. Damage to the lung epithelium is associated with the expression of toxins that are directly injected into eukaryotic cells through a type Ill-mediated secretion and translocation mechanism. Here we show that the P. aeruginosa homolog of the Yersinia V antigen, PcrV, is involved in the translocation of type III toxins. Vaccination against PcrV ensured the survival of challenged mice and decreased lung inflammation and injury. Antibodies to PcrV inhibited the translocation of type III toxins.

Fatal microcystin intoxication in haemodialysis unit in Caruaru, Brazil

BACKGROUND

After a drought in February, 1996, all 126 patients in a haemodialysis unit in Caruaru, north-east Brazil, developed signs and symptoms of acute neurotoxicity and subacute hepatotoxicity following the use of water from a lake with massive growth of cyanobacteria (blue-green algae). 60 patients died.

METHODS

Besides recording clinical details and outcome at follow-up, we arranged laboratory, radiological, and histological investigations on the patients and toxicological studies of serum and haemodialysis water filters.

FINDINGS

The acute presentation was with malaise, myalgia and weakness, nausea and vomiting, and tender hepatomegaly, with a range of neurological symptoms from tinnitus, vertigo, headaches, and deafness to blindness and convulsions. Liver injury ranged from abnormal liver-function test results to rapidly progressive and fatal hepatic failure. Biochemical investigations revealed gross hyperbilirubinaemia, abnormal liver enzyme activities, and hypertriglyceridaemia, but there was no evidence of haemolysis or microangiopathy. Histology revealed a novel acute toxic hepatitis with diffuse panlobular hepatocyte necrosis, neutrophil infiltration, canalicular cholestasis, and regenerative multinucleate hepatocytes. Samples of serum, dialysis filters, and water-treatment columns contained microcystins, the highly toxic low-molecular-weight hepatotoxins produced by cyanobacteria.

INTERPRETATION

Cyanobacteria present water-borne hazards to health via drinking water and recreational water. Haemodialysis presents an additional high-risk exposure route: when they enter directly into the circulation, microcystins can lead to fatal clinical syndromes ranging from acute neurotoxic illness to subacute liver failure.

[Sudden death of Alpine cattle in the canton Graubünden]

The aetiology of sudden deaths of cattle in the Kanton Graubünden has been elucidated by a multi-disciplinary approach. Certain small rivers and ponds located in the affected Alpine pastures in the areas of Misox, Rheinwald and Engadin provide favourable habitats for the growth of hepatotoxic cyanobacteria, particularly during long periods of hot and dry weather. As cattle frequently take up water from these sources, the toxins produced by cyanobacteria may lead to lethal poisonings that are typically associated with hemorrhagic liver necrosis. The latest reported case of cyanobacteria poisoning of Alpine cattle occurred during the summer of 1996. Further animal losses may be avoided by the implementation of appropriate pasture management schemes. To identify sites of potential hazards to human or animal health, we have developed a sensitive screening assay for the detection of cyanobacteria hepatotoxins in algae and water samples.

Detection of an anatoxin-a(s)-like anticholinesterase in natural blooms and cultures of cyanobacteria/blue-green algae from Danish lakes and in the stomach contents of poisoned birds

Ten natural bloom samples of cyanobacteria from the Danish lakes Knud sø (5), Ravn sø (4), and Salten Langsø (1) collected during 1993-1995 were assayed for toxicity by mouse bioassay, for acetylcholinesterase inhibiting activity by a colorimetric method, and for microcystins by enzyme-linked immunosorbent assay. In the mouse bioassay, seven samples were neurotoxic, two were non-toxic and one gave a protracted toxic response. One of the non-toxic and the single protracted toxic sample both contained anticholinesterase activity equivalent to 4 micrograms anatoxin-a(s) g-1. The neurotoxic samples contained equivalents to 20-3300 micrograms anatoxin-a(s) g-1. The highest anticholinesterase activities (equivalent to 2300 and 3300 micrograms anatoxin-a(s) g-1, respectively) were found in samples collected from Lake Knud sø in connection with bird-kills in 1993 and 1994. Small amounts of microcystins (0.1-0.9 microgram g-1) were detected in all samples but one. All Lake Knud sø and Lake Ravn sø samples were dominated by Anabaena lemmermannii, and the Lake Salten Langsø sample by several species of Anabaena. Gel filtration profiles indicated similarity between the toxic component from the Lake Knud sø 1994 bloom with registered bird-kills and anatoxin-a(s) isolated from Anabaena flos-aquae NRC-525-17. Anticholinesterase-producing cultures of A. lemmermannii were isolated from the Lake Knud sø 1993 bloom. These laboratory cultures produced anatoxin-a(s) equivalents of 29-743 micrograms g-1. Other cultures of A. lemmermannii isolated from Lake Knud sø and Lake Ravn sø were hepatotoxic or non-toxic. Dead birds collected from Lake Knud sø during the neurotoxic 1993 Anabaena bloom possibly died from cyanobacterial toxicosis. The stomach contents contained colonies and single trichomes of Anabaena, and anticholinesterase activities equivalent to 2.1-89.7 micrograms anatoxin-a(s) kg-1 body weight and microcystins (53-95 ng kg-1) were also detected.

Fulminant liver failure in association with the emetic toxin of Bacillus cereus

BACKGROUND

A 17-year-old boy and his father had acute gastroenteritis after eating spaghetti and pesto that had been prepared four days earlier. Within two days, fulminant liver failure and rhabdomyolysis developed in the boy and he died. The father had hyperbilirubinemia and rhabdomyolysis but recovered. We investigated the cause of these illnesses.

METHODS

Bacteria were isolated and characterized by conventional methods, and bacterial toxins were quantified by immunoassays and cell-culture techniques. The effect of the isolated toxin on the rates of oxidation of various substrates was analyzed in rat-liver mitochondria.

RESULTS

Autopsy of the boy's liver revealed diffuse microvesicular steatosis and midzonal necrosis that suggested impaired beta-oxidation of liver mitochondria due to a mitochondrial toxin. There was no evidence of ingestion of heavy metals, halogenated compounds, hepatotoxic drugs, or staphylococcal enterotoxin. However, high concentrations of Bacillus cereus emetic toxin were found in both the residue from the pan used to reheat the food and the boy's liver and bile. B. cereus was cultured from the intestinal contents and the pan residue. The emetic toxin isolated from the B. cereus cultures was found to be a mitochondrial toxin.

CONCLUSIONS

Fulminant liver failure developed after the ingestion of food contaminated with the B. cereus emetic toxin. The toxin inhibits hepatic mitochondrial fatty-acid oxidation, indicating that it caused liver failure in this patient.

Staphylococcal toxins and protein A differentially induce cytotoxicity and release of tumor necrosis factor-alpha from human keratinocytes

It has been proposed that toxins and other bacterial protein products of Staphylococcus aureus can act as triggers or persistence factors in several inflammatory skin diseases. In this study, we examined the S. aureus isolates from the skin of patients with atopic dermatitis and psoriasis. We found that the bacterial isolates from these patients exhibited either characteristic superantigenic toxins or thermolabile toxins believed to be staphylococcal alpha-toxin. All of these staphylococcal strains also secreted extracellular staphylococcal protein A. We found significant differences in the action of these toxins on human keratinocytes and keratinocyte cell lines. The superantigenic toxins toxic shock syndrome toxin-1, staphylococcal enterotoxins A and B, and exfoliative toxin-A, as well as staphylococcal protein A, did not induce significant cytotoxic damage in the keratinocyte cell line HaCaT, whereas the staphylococcal alpha-toxin produced profound cytotoxicity. Keratinocyte cytotoxicity induced by staphylococcal alpha-toxin was time and concentration dependent and demonstrated the morphologic and functional characteristics of necrosis, not apoptosis. Addition of alpha-toxin to keratinocytes simultaneously induced cell lysis and tumor necrosis factor-alpha release into the medium within 30 min; apparently, it was constitutive tumor necrosis factor-alpha. On the other hand, superantigenic toxins and, in particular, protein A showed stimulation of tumor necrosis factor-alpha secretion in keratinocytes and release of this cytokine after 6-12 h of incubation. Thus, staphylococcal protein A, alpha-toxin, and superantigenic toxins found in S. aureus isolates from patients with psoriasis and atopic dermatitis can produce direct pro-inflammatory effects on keratinocytes through the release of tumor necrosis factor-alpha. We propose that these effects may be relevant to the induction and persistence of lesions in these two diseases.

Biliary excretion of biochemically active cyanobacteria (blue-green algae) hepatotoxins in fish

Previous reports demonstrated that microcystin and related cyanobacteria polypeptides are rapidly cleared from plasma and accumulate in liver tissue. In the present study, we have used their ability to inhibit protein phosphatases to show that these cyanobacteria hepatotoxins are excreted into the bile of experimentally poisoned rainbow trout. At various times after oral administration of hepatotoxic Microcystis aeruginosa, bile samples were analysed for microcystin content by methanol extraction and protein phosphatase assays. An inhibitory principle that specifically suppressed protein phosphatase activity was detected in all bile samples removed between 1 and 72 h after oral exposure to toxic algae. These results indicate that biochemically active microcystin molecules are excreted into the biliary tract of poisoned fish.

Enzymatic analysis of liver samples from rainbow trout for diagnosis of blue-green algae-induced toxicosis

Microcystin and related toxic peptides produced by cyanobacteria (blue-green algae) are potent and selective inhibitors of protein phosphatases 1 and 2A. We adapted existing enzymatic techniques to analyze the liver of rainbow trout after oral administration of hepatotoxic cyanobacteria. Liver tissue was removed 3 and 12 hours after treatment, and phosphatase activity was determined in liver extracts, using a specific phosphoprotein substrate. In all samples from fish exposed to toxic cyanobacteria, phosphatase activity was suppressed, whereas the control enzyme, lactate dehydrogenase, present in the same liver extract, was not affected by cyanobacteria. Thus, experimental poisoning by hepatotoxic cyanobacteria resulted in an abnormally low ratio of phosphatase to lactate dehydrogenase activity in the liver extracts. These results indicate that specific inhibition of phosphatases 1 and 2A may provide a useful diagnostic tool to determine the early effects of cyanobacteria toxic peptides directly in liver samples from poisoned animals. Although this test was developed with rainbow trout, it should be possible to extend the analysis of liver phosphatase activity to other species, including sheep and cattle, which are frequently affected by hepatotoxic cyanobacteria.