Taxonomy and description of Vibrio fluvialis sp. nov. (synonym group F vibrios, group EF6)

Isolation and characterization of an antimicrobial Bacillus subtilis strain O-741 against Vibrio parahaemolyticus

Vibrio parahaemolyticus is a marine bacterium that can infect and cause the death of aquatic organisms. V. parahaemolyticus can also cause human foodborne infection via contaminated seafood, with clinical syndromes which include diarrhea, abdominal cramps, nausea and so on. Since controlling V. parahaemolyticus is important for aquaculture and human health, various strategies have been explored. This study investigates the application of antagonistic microorganisms to inhibit the growth of V. parahaemolyticus. We screened aquaculture environment samples and identified a Bacillus subtilis strain O-741 with potent antimicrobial activities. This strain showed a broad spectrum of antagonistic activities against V. parahaemolyticus and other Vibrio species. Application of the O-741 bacterium significantly increased the survival of Artemia nauplii which were infected with V. parahaemolyticus. Furthermore, the cell-free supernatant (CFS) of O-741 bacterium exhibited inhibitory ability against V. parahaemolyticus, and its activity was stable to heat, acidity, UV, enzymes, and organic solvents. Next, the O-741 CFS was extracted by ethyl acetate, and analyzed by ultra-performance liquid chromatography-mass-mass spectrometry (UPLC-MS/MS), and the functional faction was identified as an amicoumacin A compound. The organic extracts of CFS containing amicoumacin A had bactericidal effects on V. parahaemolyticus, and the treated V. parahaemolyticus cells showed disruption of the cell membrane and formation of cell cavities. These findings indicate that B. subtilis strain O-741 can inhibit the V. parahaemolyticus in vitro and in vivo, and has potential for use as a biocontrol agent for preventing V. parahaemolyticus infection.

Comparative Physiology and Genomics of Hydrogen-Producing Vibrios

The Hyf-type formate hydrogen lyase (FHL) complex was first proposed based on sequence comparisons in Escherichia coli in 1997 (Andrews et al. in Microbiology 143:3633-3647, 1997). The hydrogenase in the Hyf-type FHL was estimated to be a proton-translocating energy-conserving [NiFe]-hydrogenase. Although the structure of FHL is similar to that of complex I, silent gene expression in E. coli has caused delays in unveiling the genetic and biochemical features of the FHL. The entire set of genes required for Hyf-type FHL synthesis has also been found in the genome sequences of Vibrio tritonius in 2015 (Matsumura et al. in Int J Hydrog Energy 40:9137-9146, 2015), which produces more hydrogen (H₂) than E. coli. Here we investigate the physiological characteristics, genome comparisons, and gene expressions to elucidate the genetic backgrounds of Hyf-type FHL, and how Hyf-type FHL correlates with the higher H₂ production of V. tritonius. Physiological comparisons among the seven H₂-producing vibrios reveal that V. porteresiae and V. tritonius, grouped in the Porteresiae clade, show greater capacity for H₂ production than the other species. The structures of FHL-Hyp gene clusters were closely related in both Porteresiae species, but differed from those of the other species with the presence of hupE, a possible nickel permease gene. Interestingly, deeper genome comparisons revealed the co-presence of nickel ABC transporter genes (nik) with the Hyf-type FHL gene only on the genome of the Porteresiae clade species. Therefore, active primary Ni transport might be one of the key factors characterizing higher H₂ production in V. tritonius. Furthermore, the expression of FHL gene cluster was significantly up-regulated in V. tritonius cells stimulated with formate, indicating that formate is likely to be a control factor for the gene expression of V. tritonius FHL in a similar way to the formate regulon encoding the E. coli FHL.

Genome sequence of Vibrio fluvialis 362.3 isolated from coral Mussismilia braziliensis reveals genes related to marine environment adaptation

Vibrio fluvialis is a halophilic bacterium frequently found in estuarine and coastal waters environments. The strain 362.3 was isolated from Mussismilia braziliensis coral of Abrolhos Bank. In this study, to gain insights into the marine adaptation in V. fluvialis, we sequenced the genome of 362.3 strain, which comprised 4,607,294 bp with a G + C content of 50.2%. In silico analysis showed that V. fluvialis 362.2 encodes genes related to chitin catabolic pathway, iron metabolism, osmotic stress and membrane transport.

CqsA/LuxS-HapR Quorum sensing circuit modulates type VI secretion system VflT6SS2 in Vibrio fluvialis

Vibrio fluvialis is an emerging enteric pathogen of increasing public health threat. Two quorum sensing (QS) systems, VfqI-VfqR and CqsA/LuxS-HapR, and two type VI secretion systems (T6SSs), VflT6SS1 and VflT6SS2, have been identified in V. fluvialis. Whether there exists any correlation between the two systems is unclear. In this study, we found that CqsA/LuxS-HapR circuit regulator LuxO represses while HapR activates VflT6SS2. The effect of LuxO is more pronounced at low cell density and is HapR-dependent. Deletion of hapR abolished Hcp expression and alleviated antibacterial virulence. However, these effects were rescued by HapR-expressing plasmid. Reporter fusion analyses showed that HapR is required for the promoter activities of VflT6SS2. Sequence inspection of the major cluster promoter revealed two potential Motif 1 HapR binding sites, and their bindings to HapR were confirmed by both electrophoretic mobility shift assay (EMSA) and DNase I footprinting assay. Meanwhile, two single Motif 2 sites were identified in tssD2_a (hcpA) and tssD2_b (hcpB) promoter regions of the orphan cluster which are less conserved and displayed lower affinities to HapR. Together, our study demonstrated that CqsA/LuxS-HapR QS manipulate VflT6SS2 in V. fluvialis, and this finding will enhance our understanding of possible crosstalk between T6SS and QS in microbes.

The organosulfur compound dimethylsulfoniopropionate (DMSP) is utilized as an osmoprotectant by Vibrio species

Dimethylsulfoniopropionate (DMSP), a key component of the global geochemical sulfur cycle, is a secondary metabolite produced in large quantities by marine phytoplankton and utilized as an osmoprotectant, thermoprotectant and antioxidant. Marine bacteria can use two pathways to degrade and catabolize DMSP, a demethylation pathway and a cleavage pathway that produces the climate active gas dimethylsulfide (DMS). Whether marine bacteria can also accumulate DMSP as an osmoprotectant to maintain the turgor pressure of the cell in response to changes in external osmolarity has received little attention. The marine halophile Vibrio parahaemolyticus, contains at least six osmolyte transporters, four betaine carnitine choline transport (BCCT) carriers BccT1-BccT4 and two ABC-family ProU transporters. In this study, we showed that DMSP is used as an osmoprotectant by V. parahaemolyticus and several other Vibrio species including V. cholerae and V. vulnificus Using a V. parahaemolyticus proU double mutant, we demonstrated that these ABC transporters are not required for DMSP uptake. However, a bccT null mutant lacking all four BCCTs had a growth defect compared to wild type in high salinity media supplemented with DMSP. Using mutants possessing only one functional BCCT in growth pattern assays, we identified two BCCT-family transporters, BccT1 and BccT2, which are carriers of DMSP. The only V. parahaemolyticus BccT homolog that V. cholerae and V. vulnificus possess is BccT3 and functional complementation in Escherichia coli MKH13 showed V. cholerae VcBccT3 could transport DMSP. In V. vulnificus strains, we identified and characterized an additional BCCT family transporter, which we named BccT5 that was also a carrier for DMSP.Importance DMSP is present in the marine environment, produced in large quantities by marine phytoplankton as an osmoprotectant, and is an important component of the global geochemical sulfur cycle. This algal osmolyte has not been previously investigated for its role in marine heterotrophic bacterial osmotic stress response. Vibrionaceae are marine species, many of which are halophiles exemplified by V. parahaemolyticus, a species that possesses at least six transporters for the uptake of osmolytes. Here, we demonstrated that V. parahaemolyticus and other Vibrio species can accumulate DMSP as an osmoprotectant and show that several BCCT family transporters uptake DMSP. These studies suggest that DMSP is a significant bacterial osmoprotectant, which may be important for understanding the fate of DMSP in the environment. DMSP is produced and present in coral mucus and Vibrio species form part of the microbial communities associated with them. The function of DMSP in these interactions is unclear, but could be an important driver for these associations allowing Vibrio proliferation. This work suggests that DMSP likely has an important role in heterotrophic bacteria ecology than previously appreciated.

Investigations of Dimethylglycine, Glycine Betaine, and Ectoine Uptake by a Betaine-Carnitine-Choline Transporter Family Transporter with Diverse Substrate Specificity in Vibrio Species

Fluctuations in osmolarity are one of the most prevalent stresses to which bacteria must adapt, both hypo- and hyperosmotic conditions. Most bacteria cope with high osmolarity by accumulating compatible solutes (osmolytes) in the cytoplasm to maintain the turgor pressure of the cell. Vibrio parahaemolyticus, a halophile, utilizes at least six compatible solute transporters for the uptake of osmolytes: two ABC family ProU transporters and four betaine-carnitine-choline transporter (BCCT) family transporters. The full range of compatible solutes transported by this species has yet to be determined. Using an osmolyte phenotypic microarray plate for growth analyses, we expanded the known osmolytes used by V. parahaemolyticus to include N,N-dimethylglycine (DMG), among others. Growth pattern analysis of four triple-bccT mutants, possessing only one functional BCCT, indicated that BccT1 (VP1456), BccT2 (VP1723), and BccT3 (VP1905) transported DMG. BccT1 was unusual in that it could take up both compounds with methylated head groups (glycine betaine [GB], choline, and DMG) and cyclic compounds (ectoine and proline). Bioinformatics analysis identified the four coordinating amino acid residues for GB in the BccT1 protein. In silico modeling analysis demonstrated that GB, DMG, and ectoine docked in the same binding pocket in BccT1. Using site-directed mutagenesis, we showed that a strain with all four residues mutated resulted in the loss of uptake of GB, DMG, and ectoine. We showed that three of the four residues were essential for ectoine uptake, whereas only one of the residues was important for GB uptake. Overall, we have demonstrated that DMG is a highly effective compatible solute for Vibrio species and have elucidated the amino acid residues in BccT1 that are important for the coordination of GB, DMG, and ectoine transport.IMPORTANCE Vibrio parahaemolyticus possesses at least six osmolyte transporters, which allow the bacterium to adapt to high-salinity conditions. In this study, we identified several additional osmolytes that were utilized by V. parahaemolyticus We demonstrated that the compound DMG, which is present in the marine environment, was a highly effective osmolyte for Vibrio species. We determined that DMG is transported via BCCT family carriers, which have not been shown previously to take up this compound. BccT1 was a carrier for GB, DMG, and ectoine, and we identified the amino acid residues essential for the coordination of these compounds. The data suggest that for BccT1, GB is more easily accommodated than ectoine in the transporter binding pocket.

Comparative Genomics Analysis of Vibrio anguillarum Isolated from Lumpfish (Cyclopterus lumpus) in Newfoundland Reveal Novel Chromosomal Organizations

Vibrio anguillarum is a Gram-negative marine pathogen causative agent of vibriosis in a wide range of hosts, including invertebrates and teleosts. Lumpfish (Cyclopterus lumpus), a native fish of the North Atlantic Ocean, is utilized as cleaner fish to control sea lice (Lepeophtheirus salmonis) infestations in the Atlantic salmon (Salmo salar) aquaculture industry. V. anguillarum is one of the most frequent bacterial pathogens affecting lumpfish. Here, we described the phenotype and genomic characteristics of V. anguillarum strain J360 isolated from infected cultured lumpfish in Newfoundland, Canada. Koch's postulates determined in naïve lumpfish showed lethal acute vibriosis in lumpfish. The V. anguillarum J360 genome was shown to be composed of two chromosomes and two plasmids with a total genome size of 4.56 Mb with 44.85% G + C content. Phylogenetic and comparative analyses showed that V. anguillarum J360 is closely related to V. anguillarum strain VIB43, isolated in Scotland, with a 99.8% genome identity. Differences in the genomic organization were identified and associated with insertion sequence elements (ISs). Additionally, V. anguillarum J360 does not possess a pJM1-like plasmid, typically present in virulent isolates from the Pacific Ocean, suggesting that acquisition of this extrachromosomal element and the virulence of V. anguillarum J360 or other Atlantic isolates could increase.

High Hydrostatic Pressure Inducible Trimethylamine N-Oxide Reductase Improves the Pressure Tolerance of Piezosensitive Bacteria Vibrio fluvialis

High hydrostatic pressure (HHP) exerts severe effects on cellular processes including impaired cell division, abolished motility and affected enzymatic activities. Transcriptomic and proteomic analyses showed that bacteria switch the expression of genes involved in multiple energy metabolism pathways to cope with HHP. We sought evidence of a changing bacterial metabolism by supplying appropriate substrates that might have beneficial effects on the bacterial lifestyle at elevated pressure. We isolated a piezosensitive marine bacterium Vibrio fluvialis strain QY27 from the South China Sea. When trimethylamine N-oxide (TMAO) was used as an electron acceptor for energy metabolism, QY27 exhibited a piezophilic-like phenotype with an optimal growth at 30 MPa. Raman spectrometry and biochemistry analyses revealed that both the efficiency of the TMAO metabolism and the activity of the TMAO reductase increased under high pressure conditions. Among the two genes coding for TMAO reductase catalytic subunits, the expression level and enzymatic activity of TorA was up-regulated by elevated pressure. Furthermore, a genetic interference assay with the CRISPR-dCas9 system demonstrated that TorA is essential for underpinning the improved pressure tolerance of QY27. We extended the study to Vibrio fluvialis type strain ATCC33809 and observed the same phenotype of TMAO-metabolism improved the pressure tolerance. These results provide compelling evidence for the determinant role of metabolism in the adaption of bacteria to the deep-sea ecosystems with HHP.

Functional Characterization and Conditional Regulation of the Type VI Secretion System in Vibrio fluvialis

Vibrio fluvialis is an emerging foodborne pathogen of increasing public health concern. The mechanism(s) that contribute to the bacterial survival and disease are still poorly understood. In other bacterial species, type VI secretion systems (T6SSs) are known to contribute to bacterial pathogenicity by exerting toxic effects on host cells or competing bacterial species. In this study, we characterized the genetic organization and prevalence of two T6SS gene clusters (VflT6SS1 and VflT6SS2) in V. fluvialis. VflT6SS2 harbors three “orphan” hcp-vgrG modules and was more prevalent than VflT6SS1 in our isolates. We showed that VflT6SS2 is functionally active under low (25°C) and warm (30°C) temperatures by detecting the secretion of a T6SS substrate, Hcp. This finding suggests that VflT6SS2 may play an important role in the survival of the bacterium in the aquatic environment. The secretion of Hcp is growth phase-dependent and occurs in a narrow range of the growth phase (OD₆₀₀ from 1.0 to 2.0). Osmolarity also regulates the function of VflT6SS2, as evidenced by our finding that increasing salinity (from 170 to 855 mM of NaCl) and exposure to high osmolarity KCl, sucrose, trehalose, or mannitol (equivalent to 340 mM of NaCl) induced significant secretion of Hcp under growth at 30°C. Furthermore, we found that although VflT6SS2 was inactive at a higher temperature (37°C), it became activated at this temperature if higher salinity conditions were present (from 513 to 855 mM of NaCl), indicating that it may be able to function under certain conditions in the infected host. Finally, we showed that the functional expression of VflT6SS2 is associated with anti-bacterial activity. This activity is Hcp-dependent and requires vasH, a transcriptional regulator of T6SS. In sum, our study demonstrates that VflT6SS2 provides V. fluvialis with an enhanced competitive fitness in the marine environment, and its activity is regulated by environmental signals, such as temperature and osmolarity.

Vibrio fluvialis: an emerging human pathogen

Vibrio fluvialis is a pathogen commonly found in coastal environs. Considering recent increase in numbers of diarrheal outbreaks and sporadic extraintestinal cases, V. fluvialis has been considered as an emerging pathogen. Though this pathogen can be easily isolated by existing culture methods, its identification is still a challenging problem due to close phenotypic resemblance either with Vibrio cholerae or Aeromonas spp. However, using molecular tools, it is easy to identify V. fluvialis from clinical and different environmental samples. Many putative virulence factors have been reported, but its mechanisms of pathogenesis and survival fitness in the environment are yet to be explored. This chapter covers some of the major discoveries that have been made to understand the importance of V. fluvialis.

Identification of genetic bases of vibrio fluvialis species-specific biochemical pathways and potential virulence factors by comparative genomic analysis

Vibrio fluvialis is an important food-borne pathogen that causes diarrheal illness and sometimes extraintestinal infections in humans. In this study, we sequenced the genome of a clinical V. fluvialis strain and determined its phylogenetic relationships with other Vibrio species by comparative genomic analysis. We found that the closest relationship was between V. fluvialis and V. furnissii, followed by those with V. cholerae and V. mimicus. Moreover, based on genome comparisons and gene complementation experiments, we revealed genetic mechanisms of the biochemical tests that differentiate V. fluvialis from closely related species. Importantly, we identified a variety of genes encoding potential virulence factors, including multiple hemolysins, transcriptional regulators, and environmental survival and adaptation apparatuses, and the type VI secretion system, which is indicative of complex regulatory pathways modulating pathogenesis in this organism. The availability of V. fluvialis genome sequences may promote our understanding of pathogenic mechanisms for this emerging pathogen.

Evidence of a new metabolic capacity in an emerging diarrheal pathogen: lessons from the draft genomes of Vibrio fluvialis strains PG41 and I21563

BACKGROUND

Vibrio fluvialis is an emerging diarrheal pathogen for which no genome is currently available. In this work, draft genomes of two closely related clinical strains PG41 and I21563 have been explored.

RESULTS

V. fluvialis strains PG41 and I21563 were sequenced on the Illumina HiSeq 1000 platform to obtain draft genomes of 5.3 Mbp and 4.4 Mbp respectively. Our genome data reveal the presence of genes involved in ethanolamine utilization, which is further experimentally confirmed by growth analysis.

CONCLUSIONS

Combined in silico and growth analysis establish a new metabolic capacity of V. fluvialis to harvest energy from ethanolamine.

Vibrio alfacsensis sp. nov., isolated from marine organisms

Five strains (CAIM 1831(T), CAIM 1832, CAIM 1833, CAIM 1834 and CAIM 1836) were isolated from cultured sole (Solea senegalensis) in two regions of Spain, two strains (CAIM 404 and CAIM 1294) from wild-caught spotted rose snapper (Lutjanus guttatus) in Mexico, and one strain (CAIM 1835) from corals in Brazil. The 16S rRNA gene sequences of the novel isolates showed similarity to Vibrio ponticus (98.2-98.3%, GenBank accession no. AJ630103) and to a lesser degree to Vibrio furnissii (97.2-97.3%, X76336) and to Vibrio fluvialis (96.9-97.1%, X74703). Multilocus sequence analysis clustered these strains closely together and clearly separated them from phylogenetically related species of the genus Vibrio. Genomic fingerprinting by rep-PCR clustered the novel strains according to their geographical origin. Phenotypic analyses showed a large variation among the new strains, but many tests enabled them to be differentiated from other species of the genus Vibrio. The mean ΔT(m) values between the strains analysed here and closely related type strains were above 6.79 °C. The values between the novel isolates were below 2.35 °C, well outside the limit suggested for the delineation of a bacterial species. The phenotypic and genotypic data presented here clearly place these new strains as a coherent group within the genus Vibrio, for which we propose the name Vibrio alfacsensis sp. nov. with CAIM 1831(T) ( = DSM 24595(T) = S277(T)) as the type strain.

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.

Enumeration, isolation, and characterization of n(2)-fixing bacteria from seawater

Marine pelagic N(2)-fixing bacteria have not, in general, been identified or quantified, since low or negligible rates of N(2) fixation have been recorded for seawater when blue-green algae (cyanobacteria) are absent. In the study reported here, marine N(2)-fixing bacteria were found in all samples of seawater collected and were analyzed by using a most-probable-number (MPN) method. Two different media were used which allowed growth of microaerophiles, as well as that of aerobes and facultative anaerobes. MPN values obtained for N(2)-fixing bacteria ranged from 0.4 to 1 x 10 per liter for water collected off the coast of Puerto Rico and from 2 to 5.5 x 10 per liter for Chesapeake Bay water. Over 100 strains of N(2)-fixing bacteria were isolated from the MPN tubes and classified, yielding four major groups of NaCl-requiring bacteria based on biochemical characteristics. Results of differential filtration studies indicate that N(2)-fixing bacteria may be associated with phytoplankton. In addition, when N(2)-fixing bacteria were inoculated into unfiltered seawater and incubated in situ, nitrogenase activity could be detected within 1 h. However, no nitrogenase activity was detected in uninoculated seawater or when bacteria were incubated in 0.2-mum-filtered (phytoplankton-free) seawater. The ability of these isolates to fix N(2) at ambient conditions in seawater and the large variety of N(2)-fixing bacteria isolated and identified lead to the conclusion that N(2) fixation in the ocean may occur to a greater degree than previously believed.

Occurrence of potentially pathogenic vibrios in final effluents of a wastewater treatment facility in a rural community of the Eastern Cape Province of South Africa

We assessed the occurrence of Vibrio pathogens in the final effluents of a rural wastewater treatment facility in the Eastern Cape Province of South Africa as free or plankton-associated (180 microm, 60 microm and 20 microm plankton sizes) entities using standard culture-based and molecular techniques. The free-living Vibrio densities varied from 0 to 3.45 x 10(1) cfu ml(-1), while the plankton-associated Vibrio densities vary with plankton sizes as follows: 180 microm (0-4.50 x 10(3) cfu ml(-1)); 60 microm (0-4.86 x 10(3) cfu ml(-1)); 20 microm (0-1.9 x 10(5) cfu ml(-1)). The seasonal variations in the Vibrio densities in the 180 and 60 microm plankton size samples were significant (p < 0.05), while the 20 microm plankton size and free-living Vibrio densities were not. Molecular confirmation of the presumptive vibrios isolates revealed fluvialis (36.5%), as the predominant species, followed by Vibrio vulnificus (34.6%), and Vibrio parahaemolyticus (23.1%); only API 20NE was employed to detect Vibrio metschnikovii (5.8%), suggesting a high incidence of pathogenic Vibrio species in the final effluent of the rural wastewater facility. Analysis suggested that the concentration of Vibrio species correlated negatively with salinity and temperature (p < 0.001 and p < 0.002 respectively) as well as with pH and turbidity (p < 0.001) in the final effluent. We conclude that rural wastewater treatment facilities in the Eastern Cape Province of South Africa are potential sources of Vibrio pathogens in the aquatic environment of the communities.

Mechanism of drug resistance in a clinical isolate of Vibrio fluvialis: involvement of multiple plasmids and integrons

The role of mobile genetic elements in imparting multiple drug resistance to a clinical isolate of Vibrio fluvialis (BD146) was investigated. This isolate showed complete or intermediate resistance to all of the 14 antibiotics tested. Polymerase chain reaction (PCR) revealed the presence of a class 1 integron and the absence of the SXT element in this isolate. The strain harboured a 7.5 kb plasmid and a very low copy number plasmid of unknown molecular size. Transformation of Escherichia coli with plasmid(s) from BD146 generated two kinds of transformants, one that harboured both of these plasmids and the other that harboured only the low copy number plasmid. PCR and antibiogram analysis indicated the association of the class 1 integron with the low copy number plasmid, which also conferred all the transferable resistance traits except trimethoprim to the parent strain. A BLAST search with the sequence of the 7.5kb plasmid showed that it was 99% identical to plasmid pVN84 from Vibrio cholerae O1 in Vietnam, indicating that these two plasmids are probably one and the same. To the best of our knowledge, this is the first report of horizontal transfer of a plasmid between V. fluvialis and V. cholerae.

Acute infectious peritonitis caused by Vibrio fluvialis

Vibrio fluvialis is a Gram-negative, oxidase-producing, halophilic bacterium that, as a pathogen, has been implicated mainly as a cause of gastroenteritis. We describe a case of V. fluvialis peritonitis after a traffic accident that is, to our knowledge, the 1st report of non-continuous ambulatory peritoneal dialysis-related acute peritonitis caused by this organism.

Sequence characterization and comparative analysis of three plasmids isolated from environmental Vibrio spp

The horizontal transfer of genes by mobile genetic elements such as plasmids and phages can accelerate genome diversification of Vibrio spp., affecting their physiology, pathogenicity, and ecological character. In this study, sequence analysis of three plasmids from Vibrio spp. previously isolated from salt marsh sediment revealed the remarkable diversity of these elements. Plasmids p0908 (81.4 kb), p23023 (52.5 kb), and p09022 (31.0 kb) had a predicted 99, 64, and 32 protein-coding sequences and G+C contents of 49.2%, 44.7%, and 42.4%, respectively. A phylogenetic tree based on concatenation of the host 16S rRNA and rpoA nucleotide sequences indicated p23023 and p09022 were isolated from strains most closely related to V. mediterranei and V. campbellii, respectively, while the host of p0908 forms a clade with V. fluvialis and V. furnissii. Many predicted proteins had amino acid identities to proteins of previously characterized phages and plasmids (24 to 94%). Predicted proteins with similarity to chromosomally encoded proteins included RecA, a nucleoid-associated protein (NdpA), a type IV helicase (UvrD), and multiple hypothetical proteins. Plasmid p0908 had striking similarity to enterobacteria phage P1, sharing genetic organization and amino acid identity for 23 predicted proteins. This study provides evidence of genetic exchange between Vibrio plasmids, phages, and chromosomes among diverse Vibrio spp.

Identification of a Vibrio furnissii oligopeptide permease and characterization of its in vitro hemolytic activity

We describe purification and characterization of an oligopeptide permease protein (Hly-OppA) from Vibrio furnissii that has multifaceted functions in solute binding, in in vitro hemolysis, in antibiotic resistance, and as a virulence factor in bacterial pathogenesis. The solute-binding function was revealed by N-terminal and internal peptide sequences of the purified protein and was confirmed by discernible effects on oligopeptide binding, by accumulation of fluorescent substrates, and by fluorescent substrate-antibiotic competition assay experiments. The purified protein exhibited host-specific in vitro hemolytic activity against various mammalian erythrocytes and apparent cytotoxicity in CHO-K1 cells. Recombinant Hly-OppA protein and an anti-Hly-OppA monoclonal antibody exhibited and neutralized the in vitro hemolytic activity, respectively, which further confirmed the hemolytic activity of the gene product. In addition, a V. furnissii hly-oppA knockout mutant caused less mortality than the wild-type strain when it was inoculated into BALB/c mice, indicating the virulence function of this protein. Finally, the in vitro hemolytic activity was also confirmed with homologous ATP-binding cassette-type transporter proteins from other Vibrio species.

Cholera-like presentation in Vibrio fluvialis enteritis

We describe a patient who presented with cholera-like diarrhea seven days after eating shellfish at a seafood buffet on the Gulf Coast. The patient's stool culture grew only Vibrio fluvialis on TCBS agar, and his diarrhea and profound acidosis completely resolved within 24 hours of initiating antibiotics. To our knowledge, a detailed case of V fluvialis diarrhea with cholera-like symptoms has not been reported.

Cytotoxic and cell vacuolating activity of Vibrio fluvialis isolated from paediatric patients with diarrhoea

Vibrio fluvialis is a halophilic Vibrio species associated with acute diarrhoeal illness in humans. It has the potential to cause outbreaks and has an association with paediatric diarrhoea. In this study, 11 V. fluvialis strains isolated from hospitalized patients with acute diarrhoea at the Infectious Diseases Hospital, Kolkata were extensively characterized. All the strains showed growth in peptone broth containing 7% NaCl. The strains showed variable results in Voges-Proskauer test and to a vibriostatic agent. There was also variation in their antibiograms, and some of the strains were multidrug resistant. Among the 11 strains, two showed only a single band difference in their PFGE profile and the remaining strains showed nine different PFGE patterns. However, unlike PFGE, the strains exhibited close matches and clustering in their ribotype patterns. The haemolytic effect on sheep red blood cells varied with strains. Partial sequence analysis revealed that the V. fluvialis haemolysin gene has 81% homology with that of the El Tor haemolysin of Vibrio cholerae. A striking finding was the capability of all the strains to evoke distinct cytotoxic and vacuolation effects on HeLa cells.

A variant type of Vibrio cholerae SXT element in a multidrug-resistant strain of Vibrio fluvialis

Vibrio fluvialis strain H-08942 was isolated from an infant aged 6 months who was suffering from cholera-like diarrhea in India. This strain showed the typical multidrug-resistance phenotype of an SXT element. It was resistant to sulfamethoxazole (Su), trimethoprim (Tm), chloramphenicol (Cm) and streptomycin (Sm), in addition to other antibiotics such as ampicillin (Am), furazolidone (Fz), nalidixic acid (Na), and gentamicin (Gm). The SXT element is a Vibrio cholerae-derived integrative and conjugative element (ICE) that has also been referred to as a conjugative transposon. Our goal was to find a relationship between these resistant phenotypes and the presence of the SXT element in this unique strain. By using PCR, we detected the antibiotic resistance genes, the integrase gene and the attP attachment site of SXT element. Cloning and DNA sequencing results showed that both the SXT integrase gene and its attP site of V. fluvialis were similar but not identical to those of V. cholerae. The SXT integrase gene of V. fluvialis has a 99% identity to that of V. cholerae, and the attP site of SXT of V. fluvialis is variant and shorter (641 bp) than that of V. cholerae (785 bp). It was possible for the SXT of V. fluvialis to be transferred by conjugation to a laboratory strain of Escherichia coli. Here, we report the detection of a variant SXT element in species other than V. cholerae, with molecular characterization and analysis of its integrase gene and its attP site.

Biodiversity of vibrios

Vibrios are ubiquitous and abundant in the aquatic environment. A high abundance of vibrios is also detected in tissues and/or organs of various marine algae and animals, e.g., abalones, bivalves, corals, fish, shrimp, sponges, squid, and zooplankton. Vibrios harbour a wealth of diverse genomes as revealed by different genomic techniques including amplified fragment length polymorphism, multilocus sequence typing, repetetive extragenic palindrome PCR, ribotyping, and whole-genome sequencing. The 74 species of this group are distributed among four different families, i.e., Enterovibrionaceae, Photobacteriaceae, Salinivibrionaceae, and Vibrionaceae. Two new genera, i.e., Enterovibrio norvegicus and Grimontia hollisae, and 20 novel species, i.e., Enterovibrio coralii, Photobacterium eurosenbergii, V. brasiliensis, V. chagasii, V. coralliillyticus, V. crassostreae, V. fortis, V. gallicus, V. hepatarius, V. hispanicus, V. kanaloaei, V. neonatus, V. neptunius, V. pomeroyi, V. pacinii, V. rotiferianus, V. superstes, V. tasmaniensis, V. ezurae, and V. xuii, have been described in the last few years. Comparative genome analyses have already revealed a variety of genomic events, including mutations, chromosomal rearrangements, loss of genes by decay or deletion, and gene acquisitions through duplication or horizontal transfer (e.g., in the acquisition of bacteriophages, pathogenicity islands, and super-integrons), that are probably important driving forces in the evolution and speciation of vibrios. Whole-genome sequencing and comparative genomics through the application of, e.g., microarrays will facilitate the investigation of the gene repertoire at the species level. Based on such new genomic information, the taxonomy and the species concept for vibrios will be reviewed in the next years.

Aeromonas simiae sp. nov., isolated from monkey faeces

Two Aeromonas strains, IBS S6874(T) and IBS S6652, were isolated from the faeces of two healthy monkeys (Macaca fascicularis) from Mauritius that were kept in quarantine in the Centre for Primatology, Strasbourg, France. Phylogenetic analysis based on 16S rRNA gene sequences showed that the two isolates formed an unknown genetic lineage within the genus Aeromonas. The two isolates had nearly identical sequences (0.1 % nucleotide substitution) that were related closely to those of recognized Aeromonas species (1.7-3.5 % nucleotide substitution). DNA-DNA hybridization showed that strains IBS S6874(T) and IBS S6652 had high DNA-DNA similarity (89 %) to each other and a low level of DNA-DNA similarity to closely related taxa (18 % relatedness to Aeromonas trota and 16 % relatedness to Aeromonas schubertii). Phenotypically, the two monkey isolates differed from most previously described mesophilic Aeromonas species by their lack of haemolysis on sheep-blood agar and inability to produce indole, gas from glucose or acid from mannitol. They differed from the most closely related species, A. schubertii, by their ability to produce acid from D-cellobiose and D-sucrose and by their pyrazinamidase activity. The name Aeromonas simiae sp. nov. is proposed for these isolates; strain IBS S6874(T) (=CIP 107798(T)=CCUG 47378(T)) is the type strain.

Characterization of Vibrio fluvialis-like strains implicated in limp lobster disease

Studies were undertaken to characterize and determine the pathogenic mechanisms involved in a newly described systemic disease in Homarus americanus (American lobster) caused by a Vibrio fluvialis-like microorganism. Nineteen isolates were obtained from eight of nine lobsters sampled. Biochemically, the isolates resembled V. fluvialis, and the isolates grew optimally at 20 degrees C; none could grow at temperatures above 23 degrees C. The type strain (1AMA) displayed a thermal reduction time (D value) of 5.77 min at 37 degrees C. All of the isolates required at least 1% NaCl for growth. Collectively, the data suggest that these isolates may embody a new biotype. Pulsed-field gel electrophoresis (PFGE) analysis of the isolates revealed five closely related subgroups. Some isolates produced a sheep hemagglutinin that was neither an outer membrane protein nor a metalloprotease. Several isolates possessed capsules. The isolates were highly susceptible to a variety of antibiotics tested. However, six isolates were resistant to erythromycin. Seventeen isolates harbored plasmids. Lobster challenge studies revealed that the 50% lethal dose of a plasmid-positive strain was 100-fold lower than that of a plasmid-negative strain, suggesting that the plasmid may enhance the pathogenicity of these microorganisms in lobsters. Microorganisms that were recovered from experimentally infected lobsters exhibited biochemical and PFGE profiles that were indistinguishable from those of the challenge strain. Tissue affinity studies demonstrated that the challenge microorganisms accumulated in heart and midgut tissues as well as in the hemolymph. Culture supernatants and polymyxin B lysates of the strains caused elongation of CHO cells in tissue culture, suggesting the presence of a hitherto unknown enterotoxin. Both plasmid-positive and plasmid-negative strains caused significant dose-related intestinal fluid accumulations in suckling mice. Absence of viable organisms in the intestinal contents of mice suggests that these microorganisms cause diarrhea in mice by intoxication rather than by an infectious process. Further, these results support the thermal reduction data at 37 degrees C and suggest that the mechanism(s) that led to fluid accumulation in mice differs from the disease process observed in lobsters by requiring neither the persistence of viable microorganisms nor the presence of plasmids. In summary, results of lobster studies satisfy Koch's postulates at the organismal and molecular levels; the findings support the hypothesis that these V. fluvialis-like organisms were responsible for the originally described systemic disease, which is now called limp lobster disease.

Phenotypic study by numerical taxonomy of strains belonging to the genus Aeromonas

AIMS

This study was undertaken to cluster and identify a large collection of Aeromonas strains.

METHODS AND RESULTS

Numerical taxonomy was used to analyse phenotypic data obtained on 54 new isolates taken from water, fish, snails, sputum and 99 type and reference strains. Each strain was tested for 121 characters but only the data for 71 were analysed using the 'SSM' and 'SJ' coefficients, and the UPGMA clustering algorithm. At SJ values of > or = 81.6% the strains clustered into 22 phenons which were identified as Aer. jandaei, Aer. hydrophila, Aer. encheleia, Aer. veronii biogroup veronii, Aer. trota, Aer. caviae, Aer. eucrenophila, Aer. ichthiosmia, Aer. sobria, Aer. allosaccharophila, Aer. media, Aer. schubertii and Aer. salmonicida. The species Aer. veronii biogroup sobria was represented by several clusters which formed two phenotypic cores, the first related to reference strain CECT 4246 and the second related to CECT 4835. A good correlation was generally observed among this phenotypic clustering and previous genomic and phylogenetic data. In addition, three new phenotypic groups were found, which may represent new Aeromonas species.

CONCLUSIONS

The phenetic approach was found to be a necessary tool to delimitate and identify the Aeromonas species.

SIGNIFICANCE AND IMPACT OF THE STUDY

Valuable traits for identifying Aeromonas as well as the possible existence of new Aeromonas species or biotypes are indicated.

Víbrios não coléricos na rotina enterobacteriológica

De 3.250 fezes diarréicas, recebidas para diagnóstico microbiológico em laboratório clínico particular, no Recife, Brasil, isolaram-se 55 (1,7%) linhagens de Vibrio. O estudo foi realizado entre maio de 1989 e maio de 1991. Para o isolamento de Vibrio, os espécimes fecais foram enriquecidos em água peptonada alcalina suplementada com 2% de NaCl e subcultivados em ágar tiosulfato-citrato-sais biliares-sacarose (TCBS). Das espécies isoladas, V. parahaemolyticus foi a mais freqüente (24 cepas), seguida de V. furnissii (15 cepas), V. cholerae não 01 (6 cepas), V. alginolyticus (4 cepas), V. fluvialis (2 cepas) e Vibrio sp. (1 cepa). Do ponto de vista custo-benefício, a baixa taxa de isolamento de Vibrio levanta dúvidas acerca da utilidade do TCBS na rotina enterobacteriológica dos laboratórios clínicos

Occurrence and distribution of Vibrio spp., Listonella spp., and Clostridium botulinum in the Seto Inland Sea of Japan

The distribution of Vibrio species in samples of surface water, bottom water (water 2 m above the sediment), and sediment from the Seto Inland Sea was studied. A simple technique using a membrane filter and short preenrichment in alkaline peptone water was developed to resuscitate the injured cells, followed by plating them onto TCBS agar. In addition, a survey was conducted to determine the incidence of Clostridium botulinum in sediment samples. Large populations of heterotrophs were found in surface water, whereas large numbers of total vibrios were found in bottom water. In samples from various water sampling regions, high counts of all bacterial populations were found in the inner regions having little exchange of seawater when compared with those of the open region of the inland sea. In the identification of 463 isolates, 23 Vibrio spp. and 2 Listonella spp. were observed. V. harveyi was prevalent among the members of the Vibrio genus. Vibrio species were categorized into six groups; an estimated 20% of these species were in the so-called "pathogenic to humans" group. In addition, a significant proportion of this group was hemolytic and found in the Bisan Seto region. V. vulnificus, V. fluvialis, and V. cholerae non-O1 predominated in the constricted area of the inland sea, which is eutrophic as a result of riverine influence. It was concluded that salinity indirectly governs the distribution of total vibrios and analysis of variance revealed that all bacterial populations were distributed homogeneously and the variance values were found to be significant in some water sampling regions.(ABSTRACT TRUNCATED AT 250 WORDS)

Current perspectives on the epidemiology and pathogenesis of clinically significant Vibrio spp

Recent taxonomic advances have now implicated several different Vibrio species as human pathogens. While the most common clinical presentation of Vibrio infection continues to be gastroenteritis, an increasing number of extraintestinal infections are being reported, particularly in immunocompromised individuals. Detection of Vibrio infections requires a good clinical history and the use of appropriate isolation and identification procedures by the laboratory to confirm illnesses attributed to Vibrio species. Except for Vibrio cholerae O1 and Vibrio parahaemolyticus, there is little direct evidence linking the production of a myriad of cell-associated or extracellular factors produced by each species with human disease and pathogenesis. Many questions regarding pathogenic Vibrio species remain unanswered, including their frequency and distribution in environmental specimens (water, shellfish), infective doses, virulence potential of individual isolates, and markers associated with such strains.

Gas-liquid chromatographic analysis of fatty acid methyl esters of Aeromonas hydrophila, Aeromonas sobria, and Aeromonas caviae

Clinical isolates of Aeromonas hydrophila, A. sobria, and A. caviae whose fatty acid content had been analyzed by gas-liquid chromatography (GLC) displayed the following qualitatively similar GLC profiles: 12:0, 14:0, 15:0, 16:0, 17:0, 18:0, 16:1, 18:1, a-15:0, a-17:0, and 3-OH 14:0. The 16:0/17:0 area-percentage ratio separated the clinical aeromonads in accordance with their species designations. Aeromonads treated with subminimal inhibitory concentrations of the antibiotic cerulenin displayed the following altered qualitative fatty acid GLC profiles: 12:0, 14:0, 16:0, 18:0, 16:1, 18:1, and 3-OH 14:0. Cerulenin-treated cells failed to reproducibly display detectable levels of all odd-numbered-carbon-chain-length fatty acids observed in untreated cells. Cerulenin-treated cells also exhibited overall increases in 14:0 and 3-OH 14:0 and a decrease in total unsaturated fatty acid content.

Immunobiological relationships between Vibrio fluvialis and Vibrio cholerae enterotoxins

A total of 26 strains of Vibrio fluvialis was included in this study, which were isolated from patients with diarrhoea and other sources. The GM1 enzyme linked immunosorbent assays performed with the culture filtrates of V. fluvialis yielded negative results, indicating that their receptor site is different from that of the known labile toxin. The cholera antitoxin failed to neutralize the skin permeability factor activities of all the V. fluvialis culture filtrates and none of the concentrated culture filtrates gave any precipitin band, when tested against the cholera antitoxin in Ouchterlony's gel diffusion test. These observations suggest that the toxin of V. fluvialis differs from the known cholera toxin in receptor site, mode of action and antigenicity.

A probability matrix for the identification of species of Vibrio and related genera

A matrix for the probabilistic identification of species of Vibrio and related genera has been constructed using the data from 1091 strains collected throughout the world and classified. Thirty-eight phenons are included in the matrix, 31 of these represent previously identified species or biovars and seven represent phenons which could not be identified and may represent new species. The identification matrix incorporates 81 characters although a subset of 30 tests can be used to distinguish the 38 phenons from each other. The additional 51 tests were included to assist the identification of some strains for which the initial 30 tests were inadequate. No significant cluster overlap was found at the 5% level and the identification score for the Hypothetical Median Organism of each cluster exceeded 0.9999 in all cases.