Interactions between bacterial toxins and intestinal cells

Klebsiella pneumoniae producing bacterial toxin colibactin as a risk of colorectal cancer development - A systematic review

Microbiota can significantly contribute to colorectal cancer initiation and development. It was described that E. coli harbouring polyketide synthase (pks) genes can synthetize bacterial toxin colibactin, which was first described by Nougayrede's group in 2006. E. coli positive for pks genes were overrepresented in colorectal cancer biopsies and, therefore, prevalence and the effect of pks positive bacteria as a risk factor in colorectal cancer development is in our interest. Interestingly, pks gene cluster in E. coli shares a striking 100% sequence identity with K. pneumoniae, suggesting that their function and regulation are conserved. Moreover, K. pneumoniae can express a variety of virulence factors, including capsules, siderophores, iron-scavenging systems, adhesins and endotoxins. It was reported that pks cluster and thereby colibactin is also related to the hypervirulence of K. pneumoniae. Acquisition of the pks locus is associated with K. pneumoniae gut colonisation and mucosal invasion. Colibactin also increases the likelihood of serious complications of bacterial infections, such as development of meningitis and potentially tumorigenesis. Even though K. pneumoniae is undoubtedly a gut colonizer, the role of pks positive K. pneumoniae in GIT has not yet been investigated. It seems that CRC-distinctive microbiota is already present in the early stages of cancer development and, therefore, microbiome analysis could help to discover the early stages of cancer, which are crucial for effectiveness of anticancer therapy. We hypothesize, that pks positive K. pneumoniae can be a potential biomarker of tumour prevalence and anticancer therapy response.

Effector glycosyltransferases in legionella

Legionella causes severe pneumonia in humans. The pathogen produces an array of effectors, which interfere with host cell functions. Among them are the glucosyltransferases Lgt1, Lgt2 and Lgt3 from L. pneumophila. Lgt1 and Lgt2 are produced predominately in the post-exponential phase of bacterial growth, while synthesis of Lgt3 is induced mainly in the lag-phase before intracellular replication of bacteria starts. Lgt glucosyltransferases are structurally similar to clostridial glucosylating toxins. The enzymes use UDP–glucose as a donor substrate and modify eukaryotic elongation factor eEF1A at serine-53. This modification results in inhibition of protein synthesis and death of target cells.In addition to Lgts, Legionella genomes disclose several genes, coding for effector proteins likely to possess glycosyltransferase activities, including SetA (subversion of eukaryotic vesicle trafficking A), which influences vesicular trafficking in the yeast model system and displays tropism for late endosomal/lysosomal compartments of mammalian cells. This review mainly discusses recent results on the structure–function relationship of Lgt glucosyltransferases.

[Hygiene provisions for the processing of food in nurseries and child care facilities. Approaching problems in practical experience]

In Germany more than 2 million children under the age of six attend child care institutions. Among the duties, these institutions have to provide meals to the children. Several food-borne viruses pose a particular threat to infants. In accordance with the new European Law on Food Hygiene nurseries and child care facilities are business premises as they process and dispense food. Law requires guarding all stages of food acquisition, storage, preparation and dispersal against health hazards. Furthermore, facilities are legally required to provide risk control and to ensure that food issued by their kitchen does not pose a health hazard upon consumption. Overall, child care facilities are given by far a more comprehensive responsibility under the new European Law. This article introduces a hygiene manual for child care facilities in accordance with the EU Law on Hygiene, which was field tested in more than 70 child care facilities during the course of the extensive organisational process. The manual supplies easy-tohandle instructions and form sheets for documentation and hence assists in realising legal provisions.

Modulation of purinergic signaling by NPP-type ectophosphodiesterases

Extracellular nucleotides can elicit a wide array of cellular responses by binding to specific purinergic receptors. The level of ectonucleotides is dynamically controlled by their release from cells, synthesis by ectonucleoside diphosphokinases and ectoadenylate kinases, and hydrolysis by ectonucleotidases. One of the four structurally unrelated families of ectonucleotidases is represented by the NPP-type ectophosphodiesterases. Three of the seven members of the NPP family, namely NPP1–3, are known to hydrolyze nucleotides. The enzymatic action of NPP1–3 (in)directly results in the termination of nucleotide signaling, the salvage of nucleotides and/or the generation of new messengers like ADP, adenosine or pyrophosphate. NPP2 is unique in that it hydrolyzes both nucleotides and lysophospholipids and, thereby, generates products that could synergistically promote cell motility. We review here the enzymatic properties of NPPs and analyze current evidence that links their nucleotide-hydrolyzing capability to epithelial and neural functions, the immune response and cell motility.

Pore formation, polymerization, hemolytic and leukotoxic effects of a new Enterobacter cloacae toxin neutralized by antiserum

A new toxin of Enterobacter cloacae was purified and studied by SDS-PAGE electrophoresis with the purpose of investigating its ability to generate polymers and their molecular mass. Monomer of 13.3 kDa and structures of multimeric mass were detected. The toxin of 66 kDa was the most abundant form of toxin. This polymer and the monomer were selected to examine blood cells damage. Membrane pores caused by both toxin forms seemed to be of similar dimension (estimated in 3.6 nm by experiments with osmotic protectors) and were able to lyse erythrocytes and leukocytes. The results obtained indicate that polymerization and pore formation are involved in the molecular events that participate in the cytotoxic effects of E. cloacae toxin. Immunization of rabbits with 13.3kDa toxin generated antibody response capable of inhibiting oxidative stress as well as hemolytic and leukotoxic effects. Immunoblotting indicated that monomer and polymer reacted with antihemolysin serum. The importance of E. cloacae toxin "in vivo" was studied in animals by means of assays performed in peritoneum of rats, inoculated with the hemolytic strain (C1) and a non-hemolytic variant (C4). Both strains stimulated infiltration of leukocytes in peritoneum, but C1 caused cell death and lysis wheras assays with C4 maintained the viability of leukocytes even within 5 h after extraction of samples.

The Structure of the Neurotoxin-associated Protein HA33/A from Clostridium botulinum Suggests a Reoccurring β-Trefoil Fold in the Progenitor Toxin Complex

The hemagglutinating protein HA33 from Clostridium botulinum is associated with the large botulinum neurotoxin secreted complexes and is critical in toxin protection, internalization, and possibly activation. We report the crystal structure of serotype A HA33 (HA33/A) at 1.5 A resolution that contains a unique domain organization and a carbohydrate recognition site. In addition, sequence alignments of the other toxin complex components, including the neurotoxin BoNT/A, hemagglutinating protein HA17/A, and non-toxic non-hemagglutinating protein NTNHA/A, suggests that most of the toxin complex consists of a reoccurring beta-trefoil fold.

Clostridium perfringens epsilon toxin rapidly decreases membrane barrier permeability of polarized MDCK cells

Epsilon toxin is produced by Clostridium perfringens types B and D which are responsible for fatal intestinal diseases in animals. The main biological activity of epsilon toxin is the production of oedema in various organs. We have previously found that epsilon toxin forms a large membrane complex in MDCK cells which is not internalized into cell, and induces cell volume enlargement and loss of cell viability (Petit, L., Gibert, M., Gillet, D., Laurent-Winter, C., Boquet, P., Popoff, M. R. (1997) J Bacteriol 179, 6480-6487). Here, we show that epsilon toxin is very potent to decrease the trans-epithelial electrical resistance of polarized MDCK cells grown on filters without altering the organization of the junctional complexes. The dose-dependent decrease in trans-epithelial electrical resistance, more marked when the toxin was applied to the apical side than to the basal side of MDCK cells, was associated with a moderate increase of the paracellular permeability to low-molecular-weight compounds but not to macromolecules. Epsilon toxin probably acts by forming large membrane pores which permit the flux of ions and other molecules such as the entry of propidium iodide and finally to the loss of cell viability.

Phosphorylation of tyrosine 972 of the Helicobacter pylori CagA protein is essential for induction of a scattering phenotype in gastric epithelial cells

Helicobacter pylori colonizes the human stomach and is the causative agent of a variety of gastric diseases. After bacterial attachment, the H. pylori CagA protein is translocated into gastric epithelial cells and tyrosine phosphorylated. This process is associated with characteristic cytoskeletal rearrangements, resulting in a scatter factor-like ('hummingbird') phenotype. In this study, using a cagA mutant complemented with wild-type cagA and transiently expressing CagA in AGS cells, we have demonstrated that translocated CagA is necessary for rearrangements of the actin cytoskeleton to occur. Anti-phosphotyrosine immunoblotting studies and treatment of infected cells with phosphotyrosine kinase inhibitors suggested that not only translocation but also phosphorylation of CagA is important in this process. Transient expression of CagA-green fluorescent protein (GFP) fusion proteins and two-dimensional gel electrophoresis of CagA protein species demonstrated tyrosine phosphorylation in the C-terminus. Site-directed mutagenesis of CagA revealed that tyrosine residue 972 is essential for induction of the cellular phenotype. We have also demonstrated that translocation and phosphorylation of CagA is necessary but not sufficient for induction of the hummingbird phenotype in AGS cells, indicating the involvement of as yet unidentified bacterial factor(s).

In vivo covalent cross-linking of cellular actin by the Vibrio cholerae RTX toxin

Enteric pathogens often export toxins that elicit diarrhea as a part of the etiology of disease, including toxins that affect cytoskeletal structure. Recently, we discovered that the intestinal pathogen Vibrio cholerae elicits rounding of epithelial cells that is dependent upon a gene we designated rtxA. Here we investigate the association of rtxA with the cell-rounding effect. We find that V. cholerae exports a large toxin, RTX (repeats-in-toxin) toxin, to culture supernatant fluids and that this toxin is responsible for cell rounding. Furthermore, we find that cell rounding is not due to necrosis, suggesting that RTX toxin is not a typical member of the RTX family of pore-forming toxins. Rather, RTX toxin causes depolymerization of actin stress fibers and covalent cross-linking of cellular actin into dimers, trimers and higher multimers. This RTX toxin-specific cross-linking occurs in cells previously rounded with cytochalasin D, indicating that G-actin is the toxin target. Although several models explain our observations, our simultaneous detection of actin cross-linking and depolymerization points toward a novel mechanism of action for RTX toxin, distinguishing it from all other known toxins.

Influenza virus inhibits amiloride-sensitive Na+ channels in respiratory epithelia

Many pathogens causing diarrhea do so by modulating ion transport in the gut. Respiratory pathogens are similarly associated with disturbances of fluid balance in the respiratory tract, although it is not known whether they too act by altering epithelial ion transport. Here we show that influenza virus A/PR/8/34 inhibits the amiloride-sensitive Na(+) current across mouse tracheal epithelium with a half-time of about 60 min. We further show that the inhibitory effect of the influenza virus is caused by the binding of viral hemagglutinin to a cell-surface receptor, which then activates phospholipase C and protein kinase C. Given the importance of epithelial Na(+) channels in controlling the amount of fluid in the respiratory tract, we suggest that down-regulation of Na(+) channels induced by influenza virus may play a role in the fluid transport abnormalities that are associated with influenza infections.

How botulinum and tetanus neurotoxins block neurotransmitter release

Botulinum neurotoxins (BoNT, serotypes A-G) and tetanus neurotoxin (TeNT) are bacterial proteins that comprise a light chain (M(r) approximately 50) disulfide linked to a heavy chain (M(r) approximately 100). By inhibiting neurotransmitter release at distinct synapses, these toxins cause two severe neuroparalytic diseases, tetanus and botulism. The cellular and molecular modes of action of these toxins have almost been deciphered. After binding to specific membrane acceptors, BoNTs and TeNT are internalized via endocytosis into nerve terminals. Subsequently, their light chain (a zinc-dependent endopeptidase) is translocated into the cytosolic compartment where it cleaves one of three essential proteins involved in the exocytotic machinery: vesicle associated membrane protein (also termed synaptobrevin), syntaxin, and synaptosomal associated protein of 25 kDa. The aim of this review is to explain how the proteolytic attack at specific sites of the targets for BoNTs and TeNT induces perturbations of the fusogenic SNARE complex dynamics and how these alterations can account for the inhibition of spontaneous and evoked quantal neurotransmitter release by the neurotoxins.

Altered states: involvement of phosphorylated CagA in the induction of host cellular growth changes by Helicobacter pylori

Helicobacter pylori, present in half of the world's population, is a very successful pathogen. It can survive for decades in the human stomach with few obvious consequences to the host. However, it is also the cause of gastric diseases ranging from gastritis to ulcers to gastric cancer and has been classified a type 1 carcinogen by the World Health Organization. We have previously shown that phosphorylation of a 145-kDa protein and activation of signal transduction pathways are associated with the attachment of H. pylori to gastric cells. Here we identify the 145-kDa protein as the H. pylori CagA protein. We also show that CagA is necessary to induce a growth-factor-like phenotype (hummingbird) in host gastric cells similar to that induced by hepatocyte growth factor (HGF). Additionally, we identify a second cellular phenotype induced after attachment by H. pylori, which we call SFA (stress fiber associated). SFA is CagA independent and is produced by type I and type II H. pylori.

Intestinal toxins

The application of molecular techniques to the study of bacterial pathogenesis has made possible discoveries that are changing the way scientists view the bacterium-host interaction. Today, research on the molecular basis of the pathogenesis of infective diarrheal diseases of necessity transcends established boundaries between cell biology, bacteriology, intestinal pathophysiology, and immunology. A comprehensive approach has been taken here to outline the most recent findings on the interaction between enteric pathogens and their target eukaryotic cells through the elaboration of toxins.

Secretory diarrhea

Diarrhea, defined as loose stools, occurs when the intestine does not complete absorption of electrolytes and water from luminal contents. This can happen when a nonabsorbable, osmotically active substance is ingested ("osmotic diarrhea") or when electrolyte absorption is impaired ("secretory diarrhea"). Most cases of acute and chronic diarrhea are due to the latter mechanism. Secretory diarrhea can result from bacterial toxins, reduced absorptive surface area caused by disease or resection, luminal secretagogues (such as bile acids or laxatives), circulating secretagogues (such as various hormones, drugs, and poisons), and medical problems that compromise regulation of intestinal function. Evaluation of patients with secretory diarrhea must be tailored to find the likely causes of this problem. Specific and nonspecific treatment can be valuable.