Surface and virulence properties of environmental Vibrio cholerae non-O1 from Albufera Lake (Valencia, Spain)

Putative virulence traits and pathogenicity of Vibrio cholerae Non-O1, Non-O139 isolates from surface waters in Kolkata, India

Vibrio cholerae non-O1, non-O139 was isolated from natural surface waters from different sites sampled in diarrhea endemic zones in Kolkata, India. Twenty-one of these isolates were randomly selected and included in the characterization. The multiserogroup isolates were compared by their virulence traits with a group of clinical non-O1, non-O139 isolates from the same geographic area. Of the 21 environmental isolates, 6 and 14 strains belonged to Heiberg groups I and II, respectively. Three of the environmental isolates showed resistance to 2,2-diamine-6,7-diisopropylpteridine phosphate. All of the non-O1, non-O139 strains were positive for toxR, and except for one environmental isolate, none of them were positive for tcpA in the PCR assay. None of the isolates were positive for genes encoding cholera toxin (ctxA), heat-stable toxin (est), heat-labile toxin (elt), and Shiga toxin variants (stx) of Escherichia coli. Additionally, except for one environmental isolate (PC32), all were positive for the gene encoding El Tor hemolysin (hly). The culture supernatants of 86% (18 of 21) of the environmental isolates showed a distinct cytotoxic effect on HeLa cells, and some of these strains also produced cell-rounding factor. The lipase, protease, and cell-associated hemagglutination activities and serum resistance properties of the environmental and clinical isolates did not differ much. However, seven environmental isolates exhibited very high hemolytic activities (80 to 100%), while none of the clinical strains belonged to this group. The environmental isolates manifested three adherence patterns, namely, carpet-like, diffuse, and aggregative adherence, and the clinical isolates showed diffuse adherence on HeLa cells. Of the 11 environmental isolates tested for enteropathogenic potential, 8 (73%) induced positive fluid accumulation (>/=100) in a mouse model, and the reactivities of these isolates were comparable to those of clinical strains of non-O1, non-O139 and toxigenic O139 V. cholerae. Comparison of the counts of the colonized environmental and clinical strains in the mouse intestine showed that the organisms of both groups had similar colonizing efficiencies. These findings indicate the presence of potentially pathogenic V. cholerae non-O1, non-O139 strains in surface waters of the studied sites in Kolkata.

Antibiotic-resistant Vibrio cholerae in Parangipettai coastal environs, south east India

This study was undertaken to determine the comparative incidence of drug-resistant Vibrio cholerae non-01 in the environmental samples (water, sediment, and plankton) and in the seafood samples (finfish, shellfish, and crustacean) of estuarine, coastal, and mangrove communities. A total of 770 V. cholerae isolates were examined--all of the strains were sensitive to 100% against cephalothin (30 mcg), chloramphenical (30 mcg), and polymyxin-B (300 mcg). However, all of the strains isolated form environmental and seafood samples showed higher resistance (> 25%) to oxytetracycline, streptomycin, sulphadiazine, tetracycline, and to streptomycin, sulphadiazine, and tetracycline, respectively. The percentage of strains resistant to other antimicrobial substances depended on the antibiotic and on the isolation source. Among the isolates tested, a significantly higher number of drug-resistant bacteria was found to occur in water and finfish samples.

Differences among marine and hospital strains of Vibrio cholerae during Peruvian epidemic

During a period of 18 months of an epidemic of Vibrio cholerae, cultures from 450 samples of fish, shellfish and seawater were isolated. The highest frequencies of occurrence observed were 5.2% in fish from inshore waters, 3.9% in marine snails, and 1.8% in mussels and crabs. No incidents were isolated from cultures of fish in the open seas or cultures from frozen shrimp. Cultures of marine origin were compared with cultures from hospitalized patients, and these revealed marked serological and toxigenic differences. Marine strains were mainly non-O1 V. cholerae, non toxigenic. We presume fishing off-shore not to be the cause of this outbreak. However, marine species from contaminated waters could contain toxigenic V. cholerae remaining viable and potentially pathogenic. Methods used were more sensitive and specific for detecting marine strains. In this paper the need to use more specific methods is discussed.

High Prevalence of Vibrio cholerae Non-O1 Carrying Heat-Stable-Enterotoxin-Encoding Genes among Vibrio Isolates from a Temperate-Climate River Basin of Central Italy

Vibrio spp. of clinical interest from the Arno River basin (Tuscany, Italy) were investigated in this study. Vibrios were isolated from 70% of water samples. Vibrio cholerae non-O1 was the most prevalent species (82% of isolates), followed by Vibrio mimicus (10%) and Vibrio metschnikovii (8%). Recovery of vibrios was correlated with temperature, pH, and various indicators of municipal pollution. None of the 150 Vibrio isolates carried ctx-related genomic sequences, whereas 18 (14.6%) of the 123 V. cholerae non-O1 isolates and 1 (6.7%) of the 15 V. mimicus isolates carried sto alleles. These findings indicate that considerable circulation of sto-positive vibrios may occur in temperate-climate freshwater environments.

Purification and characterization of an extracellular secretogenic non-membrane-damaging cytotoxin produced by clinical strains of Vibrio cholerae non-O1

Some clinical strains of Vibrio cholerae non-O1 produce an extracellular factor that evokes a rapid and dramatic cytotoxic response which manifests as cell rounding of Chinese hamster ovary (CHO) and HeLa cells without accompanying membrane damage. This study was performed to establish the identity of the non-membrane-damaging cytotoxin (NMDCY), which was not inhibited by antitoxins against cholera toxin, heat-labile toxin of enterotoxigenic Escherichia coli, El Tor hemolysin, Shiga-like toxin I, and Shiga-like toxin II, indicating that NMDCY did not bear an apparent immunological relationship with the above toxins and hemolysin. Brain heart infusion broth and AKI medium supported the maximal production of NMDCY; culture supernatant of AKI medium was found to be free of hemolysin activity, whereas in brain heart infusion broth hemolysin was coproduced with NMDCY. Maximal production of NMDCY in AKI medium was observed at 37 degrees C under shaking conditions with the pH of the medium adjusted to 8.5. NMDCY was purified to homogeneity by a three-step purification procedure which increased the specific activity of the cytotoxin by 1.7 X 10(5)-fold. The denatured molecular weight of the purified toxin was 35,000, and the cytotoxin was heat labile and sensitive to trypsin. Purification of the cytotoxin revealed an enterotoxic activity as reflected by its ability to accumulate fluid in the rabbit ileal loop. Both the cytotoxic and enterotoxic activities of NMDCY could be inhibited or neutralized by antiserum raised against purified cytotoxin but not by preimmune serum. Immunodiffusion test between purified NMDCY and antiserum gave a single well-defined precipitin band which showed reactions of complete identity, while, in an immunoblot assay, a well-defined single band was observed in the 35-kDa region. Our results indicate that the cytotoxic and enterotoxic activities expressed by NMDCY appear to contribute to the pathogenesis of the disease associated with V. cholerae non-O1 strains which produce this cytotoxin.

Analysis of some factors involved in the virulence mechanism of Vibrio cholerae non-01

A study was carried out to evaluate the potential intestinal toxicity of 188 samples of Vibrio cholerae non-01 isolated from seawater found along the beaches of Rio de Janeiro city. Three different assays were carried out involving: (a) detection of vascular permeability factor (PF) in guinea pigs (together with assessment of two culture media for production of the toxin); (b) intestinal fluid accumulation (FA) in suckling mice; and (c) detection of haemolysin. The results demonstrated that both culture media gave a similar level of performance. In the animal assays, 43% of the samples induced PF in guinea pigs, 28.7% caused intestinal fluid accumulation in suckling mice, and 63.28% contained haemolysin. Only 4.25% of the samples gave positive results in all three tests.

Presence of a capsule in Vibrio vulnificus biotype 2 and its relationship to virulence for eels

Strains of Vibrio vulnificus biotype 2, isolated from internal organs of diseased European eels as pure cultures of opaque cells, together with some reference strains from Japanese eels, were used in this study. Spontaneous translucent-phase variants were obtained from the corresponding parent strains and compared for a variety of phenotypic traits related to virulence for eels. The rate of colony dissociation from opaque to translucent cells was higher (around 10(-2)) than that observed for translucent to opaque cells (10(-3) to 10(-4)). Electron microscopy with ruthenium red revealed the presence of a capsule of variable thickness on opaque cells, whereas translucent-type colonies had no observable capsular materials. No differences in plasmid profiles were detected between the two cell types so that plasmids do not seem to be implicated in the mechanism of phase shift of biotype 2 strains. No apparent difference in outer membrane protein and lipopolysaccharide patterns could be observed between the cell types. Both isogenic morphotypes were able to grow in eel serum and minimal medium supplemented with ethylenediamine di(O-hydroxyphenyl-acetic acid) or transferrin. Therefore, the presence of capsule was not required for the acquisition of iron from iron chelators or for resistance to serum bactericidal action. Both morphotypes were highly virulent for elvers, although the 50% lethal dose for translucent cells was higher than that for the corresponding opaque cells. The latter observation, together with the overall data, suggests that the production of capsular materials by biotype 2 of V. vulnificus is not essential for the development of vibriosis in eels, at least when cells are injected intraperitoneally.

Incidence of toxigenic vibrios in foods available in Taiwan

A total of 1088 vibrios and related species were isolated from seafood and aquacultured foods available in Taiwan. They were identified as Vibrio alginolyticus, V. cholerae, V. fluvialis I, V. fluvialis II, V. parahaemolyticus, V. mimicus, Aeromonas caviae, A. hydrophila, A. sobria and other species. Incidence of these Vibrio and Aeromonas species in these foods was high. Vibrio parahaemolyticus was frequently found in seawater and in foods of freshwater origin. The Vibrio isolates were examined for enzymatic and toxigenic activities. Most of them showed strong lipase or protease activities. Haemolytic activities of V. cholerae, V. fluvialis I and V. fluvialis II isolates were mostly strong. About 49% showed cytotoxic activity and 5% cytotonic activity in Chinese hamster ovary cell culture assay. Nevertheless, only three non-O1 V. cholerae (2.07%) and two V. parahaemolyticus isolates (1.65%) produced cholera toxin and thermostable direct haemolysin activity, respectively. Various toxigenic vibrios may be important food-borne pathogens in this region because of their high incidence in foods.