Effects of divalent cations and saccharides on Vibrio metschnikovii cytolysin-induced hemolysis of rabbit erythrocytes

Zinc Cations Uniquely Stabilize Cell Membrane for Cell Cryopreservation

We report, for the first time, merely using a small amount of (0.039% w/w) Zn(II) instead of very high concentration (25%-50% w/w) of conventional cryoprotective agents (CPAs), i.e., glycerol, during the cryopreservation of red blood cells (RBCs) can lead to a comparable post-thaw recovery rate of ∼95% while avoiding the tedious gradient washout process for the removal of CPA afterward. The result is remarkable, since Zn(II) does not have the ice-controlling ability reported to be critical for CPA. It benefits from its moderate interaction with lipid molecules, facilitating the formation of small and dynamic lipid clusters. Consequently, the membrane fluidity is maintained, and the cells are resilient to osmotic and mechanical stresses during cryopreservation. This study first reports the ion-specific effect on stabilizing the cell membrane; meanwhile, reversibly tuning the structure of biological samples against injuries during the cooling and rewarming provides a new strategy for cryopreservation.

Identification of Vibrio metschnikovii and Vibrio injensis Isolated from Leachate Ponds: Characterization of Their Antibiotic Resistance and Virulence-Associated Genes

This study aimed to evaluate the antibiotic resistance of 22 environmental Vibrio metschnikovii isolates and 1 Vibrio injensis isolate from landfill leachates in southwestern Colombia. Isolates were identified by Matrix-Assisted Laser Desorption/Ionization-Time-Of-Flight (MALDI-TOF), and 16S ribosomal RNA gene sequencing. Analysis of the susceptibility to six antibacterial agents by the Kirby-Bauer method showed susceptibility of all the isolates to ciprofloxacin and imipenem. We recorded resistance to beta-lactams and aminoglycosides, but no multidrug resistance was observed. The genome of one of the isolates was sequenced to determine the pathogenic potential of V. injensis. Genes associated with virulence were identified, including for flagellar synthesis, biofilm formation, and hemolysins, among others. These results demonstrate that landfill leachates are potential reservoirs of antibiotic-resistant and pathogenic bacteria and highlight the importance of monitoring Vibrio species in different aquatic environments.

Luminescent/magnetic hybrid nanoparticles with folate-conjugated peptide composites for tumor-targeted drug delivery

We developed a novel chitosan-based luminescent/magnetic hybrid nanoparticles with folate-conjugated tetrapeptide composites (CLMNPs-tetrapeptide-FA) by conjugation in situ. First, chitosan, CdTe quantum dots (QDs), and superparamagnetic iron oxide were directly gelled into ternary hybrid nanogels. Subsequently, tetrapeptides (GFFG and LGPV) and folate were conjugated orderly into the hybrid nanoparticles. The morphology, composition, and properties of the as-prepared copolymers have also been characterized and determined using TEM, EDX, XRD, FTIR spectra, DLS, fluorescence spectroscopy, VSM, and fluorescence microscopy imaging studies. The size range of the end product CLMNPs-tetrapeptide-FA copolymers was from 150 to 190 nm under simulated physiological environment. In vivo, the experimental results of magnetic accumulation showed that the copolymers could be trapped in the tumor tissue under magnetic guidance. Under the present experimental conditions, the loading efficiencies of CPT were approximately 8.6 wt % for CLMNPs-GFFG-FA and 1.1 wt % for CLMNPs-LGPV-FA, respectively. The CPT cumulative release under dialysis condition mainly occurred for the first 28 h, and could reach 55% at pH 5.3 and 46% at pH 7.4 from CPT-loaded CLMNPs-GFFG-FA, and 69% at pH 5.3 and 57% at pH 7.4 from CPT-loaded CLMNPs-LGPV-FA within 28 h, respectively. The hemolysis percentages (<2%) and coagulation properties of blank and CPT-loaded copolymers were within the scope of safe values. Compared to free CPT, the CPT-loaded CLMNPs-tetrapeptide-FA copolymers showed specific targeting to A549 cells in vitro. More than 75% viability in L02 cells were seen in CLMNPs-GFFG-FA and CLMNPs-LGPV-FA copolymer concentration of 500 μg/mL, respectively. It was found that the two kinds of copolymers were transported into the A549 cells by a folate-receptor-mediated endocytosis mechanism. These results indicate that the multifunctional CLMNPs-tetrapeptide-FA copolymers possess a moderate CPT loading efficiency, low cytotoxicity, and favorable biocompatibility, and are promising candidates for tumor-targeted drug delivery.

Vibrio fluvialis: an unusual enteric pathogen of increasing public health concern

In developing countries, the fraction of treated wastewater effluents being discharged into watersheds have increased over the period of time, which have led to the deteriorations of the qualities of major rivers in developing nations. Consequently, high densities of disease causing bacteria in the watersheds are regularly reported including incidences of emerging Vibrio fluvialis. Vibrio fluvialis infection remains among those infectious diseases posing a potentially serious threat to public health. This paper addresses the epidemiology of this pathogen; pathogenesis of its disease; and its clinical manifestations in humans.

Temperature-dependent hemolytic activity of membrane pore-forming peptide toxin, tolaasin

Tolaasin, a pore-forming peptide toxin produced by Pseudomonas tolaasii, causes brown blotch disease on cultivated mushrooms. Hemolysis using red blood cells was measured to evaluate the cytotoxicity of tolaasin. To investigate the mechanism of tolaasin-induced cell disruption, we studied the effect of temperature on the hemolytic process. At 4 degrees Celsius, poor binding of the tolaasin molecules to the erythrocyte membrane was observed and most of the tolaasin molecules stayed in the solution. However, once tolaasin bound to erythrocytes at 37 degrees Celsius and the temperature was decreased, complete hemolysis was observed even at 4 degrees Celsius. These results indicate that tolaasin binding to cell membrane is temperature-sensitive while tolaasin-induced membrane disruption is less sensitive to temperature change. The effect of erythrocyte concentration was measured to understand the membrane binding and pore-forming properties of tolaasin. The percentage of hemolysis measured by both hemoglobin release and cell lysis decreased as erythrocyte concentration increased in the presence of a fixed amount of tolaasin. The result shows that hemolysis is dependent on the amount of tolaasin and multiple binding of tolaasin is required for the hemolysis of a single cell. In analysis of dose-dependence, the hemolysis was proportional to the tenth power of the amount of tolaasin, implying that tolaasin-induced hemolysis can be explained by a multi-hit model.

Effect of various factors on Pelagia noctiluca (Cnidaria, Scyphozoa) crude venom-induced haemolysis

The haemolytic power of isolated nematocysts from the scyphozoan Pelagia noctiluca was studied with attention to the effect of osmotic protectants as carbohydrates at different MW, cations as Mg2+, Ca2+, Ba2+,Cu2+, K+; proteases as collagenase, trypsin, alpha-chymotrypsin, papain; and antioxidants. Crude venom was at first obtained by sonication of holotrichous-isorhiza nematocysts previously isolated from oral arms of P. noctiluca and then haemolytically tested upon human erythrocytes. Osmotic protectants were effective in inhibiting the haemolytic power depending on their molecular weight so that total inhibition of crude venom-induced haemolysis was observed after PEG treatment (polyethyleneglycol 6000Da). Amongst divalent cations only Ba2+ and Cu2+ significantly inhibited the haemolytic power of crude venom. Proteases seem not to alter the haemolytic activity while antioxidant compounds only slightly reduced the haemolytic power. Such findings may suggest a pore-forming mechanism for P. noctiluca crude venom rather than an oxidative damage to the cell membrane.

NetB, a new toxin that is associated with avian necrotic enteritis caused by Clostridium perfringens

For over 30 years a phospholipase C enzyme called alpha-toxin was thought to be the key virulence factor in necrotic enteritis caused by Clostridium perfringens. However, using a gene knockout mutant we have recently shown that alpha-toxin is not essential for pathogenesis. We have now discovered a key virulence determinant. A novel toxin (NetB) was identified in a C. perfringens strain isolated from a chicken suffering from necrotic enteritis (NE). The toxin displayed limited amino acid sequence similarity to several pore forming toxins including beta-toxin from C. perfringens (38% identity) and alpha-toxin from Staphylococcus aureus (31% identity). NetB was only identified in C. perfringens type A strains isolated from chickens suffering NE. Both purified native NetB and recombinant NetB displayed cytotoxic activity against the chicken leghorn male hepatoma cell line LMH; inducing cell rounding and lysis. To determine the role of NetB in NE a netB mutant of a virulent C. perfringens chicken isolate was constructed by homologous recombination, and its virulence assessed in a chicken disease model. The netB mutant was unable to cause disease whereas the wild-type parent strain and the netB mutant complemented with a wild-type netB gene caused significant levels of NE. These data show unequivocally that in this isolate a functional NetB toxin is critical for the ability of C. perfringens to cause NE in chickens. This novel toxin is the first definitive virulence factor to be identified in avian C. perfringens strains capable of causing NE. Furthermore, the netB mutant is the first rationally attenuated strain obtained in an NE-causing isolate of C. perfringens; as such it has considerable vaccine potential.

Clostridium perfringens can cause gas gangrene and food poisoning in humans and causes several enterotoxemic diseases in animals including avian necrotic enteritis. This disease affects all chicken producing countries worldwide and is a considerable burden on the commercial chicken production industry. Until recently alpha-toxin was thought to be the major virulence factor involved in necrotic enteritis. However, by using an alpha-toxin null mutant it has been demonstrated that this toxin is not essential for disease. This paper details the identification and characterisation of a novel toxin, NetB, and provides evidence that the protein is an essential factor in causing necrotic enteritis in chickens. NetB has limited protein sequence identity to the beta-toxin of C. perfringens, which causes mucosal necrosis of the small intestine in humans and animals. We demonstrate that NetB null mutants can no longer cause disease in chickens, whereas both the wild-type and mutant complemented with a wild-type netB gene caused significant levels of necrotic enteritis. The identification of this important toxin advances our understanding of the pathogenesis of the disease and opens significant opportunities for the development of novel vaccines against necrotic enteritis in poultry.

Pore formation of thermostable direct hemolysin secreted from Vibrio parahaemolyticus in lipid bilayers

Vibrio parahaemolyticus secretes thermostable direct hemolysin (TDH), a major virulence factor. Earlier studies report that TDH is a pore-forming toxin. However, the characteristics of pores formed by TDH in the lipid bilayer, which is permeable to small ions, remain to be elucidated. Ion channel-like activities were observed in lipid bilayers containing TDH. Three types of conductance were identified. All the channels displayed relatively low ion selectivity, and similar ion permeability. The Cl- channel inhibitors, DIDS, glybenclamide, and NPPB, did not affect the channel activity of pores formed by TDH. R7, a mutant toxin of TDH, also forms pores with channel-like activity in lipid bilayers. The ion permeability of these channels is similar to that of TDH. R7 binds cultured cells and liposomes to a lower extent, compared to TDH. R7 does not display significant hemolytic activity and cell cytotoxicity, possibly owing to the difficulty of insertion into lipid membranes. Once R7 is assembled within lipid membranes, it may assume the same structure as TDH. The authors propose that the single glycine at position 62, substituted with serine in the R7 mutant toxin, plays an important role in TDH insertion into the lipid bilayer.

Purification, characterization and molecular cloning of Vibrio fluvialis hemolysin

Hemolysin of Vibrio fluvialis (VFH) was purified from culture supernatants by ammonium sulfate precipitation and successive column chromatographies on DEAE-cellulose and Mono-Q. N-terminal amino acid sequences of the purified VFH were determined. The purified protein exhibited hemolytic activity on many mammalian erythrocytes with rabbit erythrocytes being the most sensitive to VFH. Activity of the native VFH was inhibited by the addition of Zn2+, Ni2+, Cd2+ and Cu2+ ions at low concentrations. Pores formed on rabbit erythrocytes were approximately 2.8-3.7 nm in diameter, as demonstrated by osmotic protection assay. Nucleotide sequence analysis of the vfh gene revealed an open reading frame (ORF) consisting of 2200 bp which encodes a protein of 740 amino acids with a molecular weight of 82 kDa. Molecular weight of the purified VFH was estimated to be 79 kDa by SDS-PAGE and N-terminal amino acid sequence revealed that the 82 kDa prehemolysin is synthesized in the cytoplasm and is then secreted into the extracellular environment as the 79 kDa mature hemolysin after cleavage of 25 N-terminal amino acids. Deletion of 70 amino acids from the C-terminus exhibited a smaller hemolytic activity, while deletion of 148 C-terminal amino acids prevented hemolytic activity.

Hyperproduction, purification, and mechanism of action of the cytotoxic enterotoxin produced by Aeromonas hydrophila

A gene encoding the cytotoxic enterotoxin (Act) from Aeromonas hydrophila was hyperexpressed with the pET, pTRX, and pGEX vector systems. Maximum toxin yield was obtained with the pTRX vector. Approximately 40 to 60% of Act was in a soluble form with the pTRX and pET vector systems. The toxin protein was purified to homogeneity by a combination of ammonium sulfate precipitation and fast protein liquid chromatography-based column chromatographies, including hydrophobic, anion-exchange, sizing, and hydroxylapatite chromatographies. Purified mature toxin migrated as a 52-kDa polypeptide on a sodium dodecyl sulfate (SDS)polyacrylamide gel that reacted with Act-specific antibodies in immunoblots. The minimal amount of toxin needed to cause fluid secretion in rat ileal loops was 200 ng, and the 50% lethal dose for mice was 27.5 ng when injected intravenously. Binding of the toxin to erythrocytes was temperature dependent, with no binding occurring at 4 degrees C. However, at 37 degrees C the toxin bound to erythrocytes within 1 to 2 min. It was determined that the mechanism of action of the toxin involved the formation of pores in erythrocyte membranes, and the diameter of the pores was estimated to be 1.14 to 2.8 nm, as determined by the use of saccharides of different sizes and by electron microscopy. Calcium chloride prevented lysis of erythrocytes by the toxin; however, it did not affect the binding and pore-forming capabilities of the toxin. A dose-dependent reduction in hemoglobin release from erythrocytes was observed when Act was preincubated with cholesterol, but not with myristylated cholesterol. With 14C-labeled cholesterol and gel filtration, the binding of cholesterol to Act was demonstrated. None of the other phospholipids and glycolipids tested reduced the hemolytic activity of Act. The toxin also appeared to undergo aggregation when preincubated with cholesterol, as determined by SDS-polyacrylamide gel electorphoresis. As a result of this aggregation, Act's capacity to form pores in the erythrocyte membrane was inhibited.

Purification and characterization of a hemolysin produced by Vibrio mimicus

Vibrio mimicus is a causative agent of human gastroenteritis. This pathogen secretes a pore-forming toxin, V. mimicus hemolysin (VMH), which causes hemolysis by three sequential steps: binding to an erythrocyte membrane, formation of a transmembrane pore, and disruption of the cell membrane. VMH with a molecular mass of 63 kDa was purified by ammonium sulfate precipitation and column chromatography with phenyl Sepharose HP and Superose 6 HR. The hemolytic reaction induced by VMH continued up to disruption of all erythrocytes in the assay system. Moreover, VMH that bound preliminarily to erythrocyte ghosts showed a sufficient ability to attack intact erythrocytes. These results suggest reversible binding of the toxin molecule to the membrane. The final cell-disrupting stage was effectively inhibited by various divalent cations. Additionally, some cations, such as Zn2+ and Cu2+, blocked the pore-forming stage at high concentrations. Although VMH could disrupt all kinds of mammalian erythrocytes tested, those from horses were most sensitive to the hemolysin. Horse erythrocytes were found to have the most toxin-binding sites and to be hemolyzed by the least amount of membrane-bound toxin molecules, suggesting that toxin binding to and pore formation on erythrocytes are more effective in horses than in other mammals. Purified VMH induced fluid accumulation in a ligated rabbit ileal loop in a dose-dependent manner. In addition, the antibody against the hemolysin obviously reduced enteropathogenicity of living V. mimicus cells. These findings clearly demonstrate that VMH is probably involved in the virulence of this human pathogen.

Mechanism of action of hemolysin III from Bacillus cereus

Bacillus cereus hemolysin III activity was tested in crude extracts, from Escherichia coli carrying the hly-III gene. It was concluded that hemolysin III is a pore-forming hemolysin with functional pore diameter of about 3-3.5 nm. Hemolysis occurs in at least three steps: (i) the temperature-dependent binding of the Hly-III monomers to the erythrocyte membrane; (ii) the temperature-dependent formation of the transmembrane oligomeric pore; (iii) the temperature-independent erythrocyte lysis.

Monoclonal antibody developed against a hemolysin of Bacillus thuringiensis

A total of five hybridoma cell lines that produced monoclonal antibodies (MAb) against a hemolysin (Bt-hemolysin) produced by Bacillus thuringiensis were established and characterized. All of these monoclonal antibodies reacted similarly not only to Bt-hemolysin but also to a hemolysin (Bc-hemolysin) produced by B. cereus, suggesting that the two hemolysins are immunologically indistinguishable. The MAb developed in this study was also successfully applied for rapid and simple purification of both Bt- and Bc-hemolysins by immunoaffinity column chromatography. The partial N-terminal amino acid sequence of the purified hemolysins was determined to be Ile-Glu-Gln-Thr.

Characterization of Vibrio cholerae El Tor cytolysin as an oligomerizing pore-forming toxin

V. cholerae El Tor cytolysin is a secreted, water-soluble protein of M(r) 60,000 that may be relevant to the pathogenesis of acute diarrhea. In this communication, we demonstrate that the toxin binds to and oligomerizes in target membranes to form SDS-stable aggregates of M(r) 200,000-250,000 that generate small transmembrane pores. Pores formed in erythrocytes were approximately 0.7 nm in size, as demonstrated by osmotic protection experiments. Binding was shown to occur in a temperature-independent manner preceding the temperature-dependent oligomerization step. Pores were also shown to be formed in L929 and HEp-2 cells, human fibroblasts and keratinocytes, albeit with highly varying efficacy. At neutral pH and in the presence of serum, human fibroblasts were able to repair a limited number of lesions. The collective data identify V. cholerae El Tor cytolysin as an oligomerizing toxin that damages cells by creating small transmembrane pores.

Activation and mechanism of Clostridium septicum alpha toxin

Clostridium septicum produces a single lethal factor, alpha toxin (AT), which is a cytolytic protein with a molecular mass of approximately 48 kDa. The 48 kDa toxin was found to be an inactive protoxin (ATpro) which could be activated via a carboxy-terminal cleavage with trypsin. The cleavage site was located approximately 4 kDa from the carboxy-terminus. Proteolytically activated ATpro had a specific activity of approximately 1.5 x 10(6) haemolytic units mg-1. The trypsin-activated toxin (ATact) was haemolytic, stimulated a prelytic release of potassium ions from erythrocytes which was followed by haemoglobin release, induced channel formation in planar membranes and aggregated into a complex of M(r) > 210,000 on erythrocyte membranes. ATpro did not exhibit these properties. ATact formed pores with a diameter of at least 1.3-1.6 nm. We suggest that pore formation on target cell membranes is responsible for the cytolytic activity of alpha toxin.

Studies on hemolytic action of a hemolysin produced by Vibrio mimicus

Some properties and mechanism of action of a hemolysin (VMH) produced by an enteropathogenic Vibrio mimicus strain was examined. VMH was heat-labile and inhibited by addition of divalent cations, including Ca2+, Mg2+ and Mn2+. The hemolysis by VMH was inhibited by incubating with gangliosides, suggesting that the ganglioside was the binding site on the erythrocyte membrane for VMH. Existence of a galactose moiety on reducing end of the ganglioside molecule and a sialic acid on the galactose moiety was suggested to be important for the binding of VMH molecule. Colloid osmotic manner of the hemolysis by VMH was demonstrated.

The mode of action of Vibrio cholerae cytolysin. The influences on both erythrocytes and planar lipid bilayers

The interaction with erythrocytes of cholera cytolysin (CC) obtained from a non-01 Vibrio cholerae strain results in the osmotic rupture of target cells upon formation by CC of the waterfilled pores in their membranes. The aggregation of several toxin monomers is required for the formation of one CC channel with a radius of 0.9-1.0 nm. The investigations using planar bilayer lipid membranes suggest that the CC-induced pore is an interprotein anion selective channel carrying a fixed positive charge. The role of the charge was supported by the influence of pH on the selectivity, single conductance and voltage gating of the CC channels. The ability of the CC to modify both model and natural membranes has a maximum at pH 6.0-7.0. It was found that CC channels insert into the membrane asymmetrically. The effect of proteolytic treatment of the channel by papain also indicates that the two entrances of the channel protrude from the plane of the membrane into the solution for different distances. It is proposed that the biological effects of the non-01 V. cholera cytolysin are based on its channel-forming activity.

Effects of cations and osmotic protectants on cytolytic activity of Actinobacillus actinomycetemcomitans leukotoxin

Actinobacillus actinomycetemcomitans leukotoxin permeabilized the plasma membrane of HL-60 promyelocytic leukemia cells, resulting in colloid osmotic lysis. These events were associated with efflux of 51chromium (from prelabeled cells), influx of propidium iodide, and ultrastructural evidence of cellular damage. Target cell lysis was inhibited by procedures which may interfere with the initial interaction of the toxin with the plasma membrane. For example, washing cultures (to dilute and remove toxin) or the addition of monoclonal antibodies (to neutralize toxin) or trypsin (to inactivate toxin) limited lysis when undertaken within the first 5 min of the reaction. The extent of injury was also diminished when radiolabeled HL-60 cells were exposed to toxin in the presence of unlabeled, toxin-sensitive cells (e.g., HL-60 cells or human neutrophils) or certain toxin-resistant target cells (e.g., human K562 erythroleukemia cells). This suggests that the association of the toxin with the cell membrane may not be sufficient to cause lysis without activation of additional effector mechanisms. The addition of specific trivalent (e.g., La3+) or divalent (e.g., Ca2+ and Zn2+) cations to toxin-treated cells appeared to enhance their capacity to repair or minimize the extent of toxin-mediated membrane damage. Depending on size, certain saccharides served as osmotic protectants: maltose almost completely inhibited radiolabel release, while smaller molecules provided correspondingly less protection. The results imply that the leukotoxin has membranolytic activity, producing pores in target cells with a functional diameter approximately the size of maltose (0.96 nm).

Production of monoclonal antibody against a hemolysin (Vp-TRH) produced by Vibrio parahaemolyticus

The antigenicity of a hemolysin (Vp-TRH: Vp-TDH related hemolysin) produced by Kanagawa phenomenon-negative clinical isolates of Vibrio parahaemolyticus was studied using monoclonal antibodies (MAbs). A total of 12 hybridoma clones which produced MAbs against Vp-TRH were established. All MAbs contained the Kappa light chain and were IgG type. These MAbs were divided into a minimum of 5 different specificity groups, including antibodies specific to Vp-TRH and common to both Vp-TRH and Vp-TDH, a possible pathogenic toxin of Kanagawa phenomenon-positive V. parahaemolyticus. These results clearly show the immunological similarity and dissimilarity (specificity) of Vp-TRH and Vp-TDH.

Production of monoclonal antibodies against thermostable direct hemolysin of Vibrio parahaemolyticus and application of the antibodies for enzyme-linked immunosorbent assay

A total nine hybridoma cell lines that produced monoclonal antibodies against thermostable direct hemolysin (Vp-TDH), a possible pathogenic toxin, of Kanagawa phenomenon-positive Vibrio parahaemolyticus was isolated and characterized. These monoclonal antibodies (mAbs) were divided into a minimum of five different specificity groups, including mAbs specific to Vp-TDH and common to Vp-TDH and Vp-TRH, a Vp-TDH-related hemolysin produced by Kanagawa phenomenon-negative V. parahaemolyticus. An enzyme-linked immunosorbent assay (ELISA) using mAb-1-D, a mAb specific for Vp-TDH, was developed for specific detection of Vp-TDH. On the other hand, the ELISA using mAb-9-D, and mAb common to both Vp-TDH and Vp-TRH, could be used for detection of both Vp-TDH and Vp-TRH. Thus, by combining these two ELISAs differential detection of Vp-TDH and Vp-TRH can be performed. Hence, the two ELISAs were applied for various strains of V. parahaemolyticus and it was found that most Kanagawa phenomenon-positive and -negative clinical isolates produced Vp-TDH and Vp-TRH, respectively, but all environmental strains, that were Kanagawa phenomenon-negative, produced neither toxin.

The human pathogenic vibrios--a public health update with environmental perspectives

Pathogenic Vibrio species are naturally-occurring bacteria in freshwater and saline aquatic environments. Counts of free-living bacteria in water are generally less than required to induce disease. Increases in number of organisms towards an infective dose can occur as water temperatures rise seasonally followed by growth and concentration of bacteria on higher animals, such as chitinous plankton, or accumulation by shellfish and seafood. Pathogenic Vibrio species must elaborate a series of virulence factors to elicit disease in humans. Activities which predispose diarrhoeal and extraintestinal infections include ingestion of seafood and shellfish and occupational or recreational exposure to natural aquatic environments, especially those above 20 degrees C. Travel to areas endemic for diseases due to pathogenic Vibrio species may be associated with infections. Host risk factors strongly associated with infections are lack of gastric acid and liver disorders. Involvement of pathogenic Vibrio species in cases of diarrhoea should be suspected especially if infection is associated with ingestion of seafood or shellfish, raw or undercooked, in the previous 72 h. Vibrio species should be suspected in any acute infection associated with wounds sustained or exposed in the marine or estuarine environment. Laboratories serving coastal areas where infection due to pathogenic Vibrio species are most likely to occur should consider routine use of TCBS agar and other detection regimens for culture of Vibrio species from faeces, blood and samples from wound and ear infections.