Effect of alum on free-living and copepod-associated Vibrio cholerae O1 and O139

Induction of a viable but non-culturable state in Salmonella Typhimurium is correlated with free radicals generated by thermosonication

The viable but non-culturable (VBNC) state in bacteria is gaining more and more attention around the world, mainly due to it is not only an important strategy for adaption to a stressful environment but also may possibly pose a threat to food safety and public health. It was found that a small subpopulation of Salmonella Typhimurium in pure culture was induced into a VBNC state during thermosonication (TS) processing in our previous study, though few known about the situation in real food and how bacteria were induced into that special state. Base on the speculation that free radicals generated during TS affected induction of VBNC, the relationship between them was investigated preliminarily. It was observed that higher intensity of TS treatment, such as higher power, elevated temperature and prolonged duration resulted in more viable S. Typhimurium cells in carrot juice been inducted into VBNC state. The observed results showed that VBNC incidence indexes were 1000 as TS treatments at 57-62 °C and 380 W for 6 min, and 53 °C and 380 W for 8-10 min were applied, indicating a 100% VBNC state of viable cells in those cases. The ESR spectra revealed three kinds of free radicals, including carbon centered (ethanol) radicals, hydroxyl radical and hydrogen protons were generated in carrot juice during TS processing. The intensity of free radicals was tied to the TS processing parameters and also influenced the occurrence of VBNC. A nonlinear sigmoidal curve of the intensity of free radicals VS the VBNC incidence index in three stages, including a slow phase (with free radicals intensity of 0-0.10), a rapid growth phase (with free radicals intensity ranged 0.10-0.14) and a final equilibrium phase (with free radicals intensity greater than 0.14), was observed and well fitted with the Boltzmann model. Moreover, the significance of free radicals generated during TS processing for induction of VBNC state was verified and confirmed with 0-200 mM sodium pyruvate. The obtained results may contribute to understand the complicated phenomenon and guide the application of TS as a decontamination technique.

Vibrio cholerae Colonization of Soft-Shelled Turtles

Vibrio cholerae is an important human pathogen and environmental microflora species that can both propagate in the human intestine and proliferate in zooplankton and aquatic organisms. Cholera is transmitted through food and water. In recent years, outbreaks caused by V. cholerae-contaminated soft-shelled turtles, contaminated mainly with toxigenic serogroup O139, have been frequently reported, posing a new foodborne disease public health problem. In this study, the colonization by toxigenic V. cholerae on the body surfaces and intestines of soft-shelled turtles was explored. Preferred colonization sites on the turtle body surfaces, mainly the carapace and calipash of the dorsal side, were observed for the O139 and O1 strains. Intestinal colonization was also found. The colonization factors of V. cholerae played different roles in the colonization of the soft-shelled turtle's body surface and intestine. Mannose-sensitive hemagglutinin (MSHA) of V. cholerae was necessary for body surface colonization, but no roles were found for toxin-coregulated pili (TCP) or N-acetylglucosamine-binding protein A (GBPA). Both TCP and GBPA play important roles for colonization in the intestine, whereas the deletion of MSHA revealed only a minor colonization-promoting role for this factor. Our study demonstrated that V. cholerae can colonize the surfaces and the intestines of soft-shelled turtles and indicated that the soft-shelled turtles played a role in the transmission of cholera. In addition, this study showed that the soft-shelled turtle has potential value as an animal model in studies of the colonization and environmental adaption mechanisms of V. cholerae in aquatic organisms.IMPORTANCE Cholera is transmitted through water and food. Soft-shelled turtles contaminated with Vibrio cholerae (commonly the serogroup O139 strains) have caused many foodborne infections and outbreaks in recent years, and they have become a foodborne disease problem. Except for epidemiological investigations, no experimental studies have demonstrated the colonization by V. cholerae on soft-shelled turtles. The present studies will benefit our understanding of the interaction between V. cholerae and the soft-shelled turtle. We demonstrated the colonization by V. cholerae on the soft-shelled turtle's body surface and in the intestine and revealed the different roles of major V. cholerae factors for colonization on the body surface and in the intestine. Our work provides experimental evidence for the role of soft-shelled turtles in cholera transmission. In addition, this study also shows the possibility for the soft-shelled turtle to serve as a new animal model for studying the interaction between V. cholerae and aquatic hosts.

Interactions of Vibrio spp. with Zooplankton

Members of the genus Vibrio are known to interact with phyto- and zooplankton in aquatic environments. These interactions have been proven to protect the bacterium from various environmental stresses, serve as a nutrient source, facilitate exchange of DNA, and to serve as vectors of disease transmission. This review highlights the impact of Vibrio-zooplankton interactions at the ecosystem scale and the importance of studies focusing on a wide range of Vibrio-zooplankton interactions. The current knowledge on chitin utilization (i.e., chemotaxis, attachment, and degradation) and the role of these factors in attachment to nonchitinous zooplankton is also presented.

Biofilm Matrix Proteins

Proteinaceous components of the biofilm matrix include secreted extracellular proteins, cell surface adhesins, and protein subunits of cell appendages such as flagella and pili. Biofilm matrix proteins play diverse roles in biofilm formation and dissolution. They are involved in attaching cells to surfaces, stabilizing the biofilm matrix via interactions with exopolysaccharide and nucleic acid components, developing three-dimensional biofilm architectures, and dissolving biofilm matrix via enzymatic degradation of polysaccharides, proteins, and nucleic acids. In this article, we will review functions of matrix proteins in a selected set of microorganisms, studies of the matrix proteomes of Vibrio cholerae and Pseudomonas aeruginosa, and roles of outer membrane vesicles and of nucleoid-binding proteins in biofilm formation.

Quorum sensing-regulated chitin metabolism provides grazing resistance to Vibrio cholerae biofilms

Association of Vibrio cholerae with chitinous surfaces of zooplankton is important for its persistence in marine environments, as it provides accessibility to nutrients and resistance to stresses. Predation by heterotrophic protists has a major impact on the survival of V. cholerae. V. cholerae forms biofilms as its main defensive strategy, and quorum sensing (QS) additionally regulates the production of antiprotozoal factors. The role of chitin and QS regulation in V. cholerae grazing resistance was investigated by exposing V. cholerae wild-type (WT) and QS mutant biofilms grown on chitin flakes to the bacteriotrophic, surface-feeding flagellate Rhynchomonas nasuta. V. cholerae formed more biofilm biomass on chitin flakes compared with nonchitinous surfaces. The growth of R. nasuta was inhibited by WT biofilms grown on chitin flakes, whereas the inhibition was attenuated in QS mutant biofilms. The chitin-dependent toxicity was also observed when the V. cholerae biofilms were developed under continuous flow or grown on a natural chitin source, the exoskeleton of Artemia. In addition, the antiprotozoal activity and ammonium concentration of V. cholerae biofilm supernatants were quantified. The ammonium levels (3.5 mM) detected in the supernatants of V. cholerae WT biofilms grown on chitin flakes were estimated to reduce the number of R. nasuta by >80% in add-back experiments, and the supernatant of QS mutant biofilms was less toxic owing to a decrease in ammonium production. Transcriptomic analysis revealed that the majority of genes involved in chitin metabolism and chemotaxis were significantly downregulated in QS mutant biofilms when grown on chitin compared with the WT biofilms.

In silico analyses of primers used to detect the pathogenicity genes of Vibrio cholerae

In Vibrio cholerae, the etiological agent of cholera, most of the virulence genes are located in two pathogenicity islands, named TCP (Toxin-Co-regulated Pilus) and CTX (Cholera ToXins). For each V. cholerae pathogenicity gene, we retrieved every primer published since 1990 and every known allele in order to perform a complete in silico survey and assess the quality of the PCR primers used for amplification of these genes. Primers with a melting temperature in the range 55–60°C against any target sequence were considered valid. Our survey clearly revealed that two thirds of the published primers are not able to properly detect every genetic variant of the target genes. Moreover, the quality of primers did not improve with time. Their lifetime, i.e. the number of times they were cited in the literature, is also not a factor allowing the selection of valid primers. We were able to improve some primers or design new primers for the few cases where no valid primer was found. In conclusion, many published primers should be avoided or improved for use in molecular detection tests, in order to improve and perfect specificity and coverage. This study suggests that bioinformatic analyses are important to validate the choice of primers.

Role of zooplankton diversity in Vibrio cholerae population dynamics and in the incidence of cholera in the Bangladesh Sundarbans

Vibrio cholerae, a bacterium autochthonous to the aquatic environment, is the causative agent of cholera, a severe watery, life-threatening diarrheal disease occurring predominantly in developing countries. V. cholerae, including both serogroups O1 and O139, is found in association with crustacean zooplankton, mainly copepods, and notably in ponds, rivers, and estuarine systems globally. The incidence of cholera and occurrence of pathogenic V. cholerae strains with zooplankton were studied in two areas of Bangladesh: Bakerganj and Mathbaria. Chitinous zooplankton communities of several bodies of water were analyzed in order to understand the interaction of the zooplankton population composition with the population dynamics of pathogenic V. cholerae and incidence of cholera. Two dominant zooplankton groups were found to be consistently associated with detection of V. cholerae and/or occurrence of cholera cases, namely, rotifers and cladocerans, in addition to copepods. Local differences indicate there are subtle ecological factors that can influence interactions between V. cholerae, its plankton hosts, and the incidence of cholera.

www.aquaticmicrobial.net

Despite recent advances and new applications of molecular and biogeochemical methodology in aquatic microbial ecology, our perception of the aquatic microbial world remains one dominated by "free-living" bacteria that account for most of the microbial activities in the pelagic zone. Recent research has, however, shown that there exist vast and hidden "microbial networks" within the water column, connected via various microhabitats such as aggregates, fecal pellets and higher organisms. Bacterial abundance within these networks may rival or exceed that of the "free-living" bacteria. Hence, what we have learned in traditional aquatic microbial ecology represents merely a fraction of the microbial world. Within these networks a bacterium can travel long distances, communicate and closely interact with other bacteria and efficiently exchange genetic information with one another. The presence of microbial networks within the water column demands better sampling strategies and a new way to understand bacterial ecology, evolution and functions within the broader context of systems biology.

Levels of the secreted Vibrio cholerae attachment factor GbpA are modulated by quorum-sensing-induced proteolysis

Vibrio cholerae is the etiologic agent of cholera in humans. Intestinal colonization occurs in a stepwise fashion, initiating with attachment to the small intestinal epithelium. This attachment is followed by expression of the toxin-coregulated pilus, microcolony formation, and cholera toxin (CT) production. We have recently characterized a secreted attachment factor, GlcNAc binding protein A (GbpA), which functions in attachment to environmental chitin sources as well as to intestinal substrates. Studies have been initiated to define the regulatory network involved in GbpA induction. At low cell density, GbpA was detected in the culture supernatant of all wild-type (WT) strains examined. In contrast, at high cell density, GbpA was undetectable in strains that produce HapR, the central regulator of the cell density-dependent quorum-sensing system of V. cholerae. HapR represses the expression of genes encoding regulators involved in V. cholerae virulence and activates the expression of genes encoding the secreted proteases HapA and PrtV. We show here that GbpA is degraded by HapA and PrtV in a time-dependent fashion. Consistent with this, Delta hapA Delta prtV strains attach to chitin beads more efficiently than either the WT or a Delta hapA Delta prtV Delta gbpA strain. These results suggest a model in which GbpA levels fluctuate in concert with the bacterial production of proteases in response to quorum-sensing signals. This could provide a mechanism for GbpA-mediated attachment to, and detachment from, surfaces in response to environmental cues.

Effect of point-of-use disinfection, flocculation and combined flocculation-disinfection on drinking water quality in western Kenya

AIMS

Point-of-use drinking water disinfection with sodium hypochlorite has been shown to improve water quality and reduce diarrhoeal disease. However, the chlorine demand of highly turbid water may render sodium hypochlorite less effective.

METHODS AND RESULTS

We evaluated a novel combined flocculant-disinfectant point-of-use water treatment product and compared its effect on drinking water quality with existing technologies in western Kenya. In water from 30 sources, combined flocculant-disinfectant reduced Escherichia coli concentrations to <1 CFU100 ml(-1) for 29 (97%) and reduced turbidity to <5 nephelometric turbidity units (NTU) for 26 (87%). By contrast, water from 30 sources treated with sodium hypochlorite reduced E. coli concentrations to <1 CFU 100 ml(-1) for 25 (83%) and turbidity to <5 NTU for 5 (17%).

CONCLUSIONS

For source waters over a range of turbidities in western Kenya, combined flocculant-disinfectant product effectively reduces turbidity to <5 NTU and reduces E. coli concentrations to <1 CFU 100 ml(-1).

SIGNIFICANCE AND IMPACT OF THE STUDY

The novel flocculant-disinfectant product may be acceptable to consumers and may be effective in reducing diarrhoeal disease in settings where source water is highly turbid.

The mannose-sensitive hemagglutinin of Vibrio cholerae promotes adherence to zooplankton

The bacterium Vibrio cholerae, the etiological agent of cholera, is often found attached to plankton, a property that is thought to contribute to its environmental persistence in aquatic habitats. The V. cholerae O1 El Tor biotype and V. cholerae O139 strains produce a surface pilus termed the mannose-sensitive hemagglutinin (MSHA), whereas V. cholerae O1 classical biotype strains do not. Although V. cholerae O1 classical does not elaborate MSHA, the gene is present and expressed at a level comparable to that of the other strains. Since V. cholerae O1 El Tor and V. cholerae O139 have displaced V. cholerae O1 classical as the major epidemic strains over the last fifteen years, we investigated the potential role of MSHA in mediating adherence to plankton. We found that mutation of mshA in V. cholerae O1 El Tor significantly diminished, but did not eliminate, adherence to exoskeletons of the planktonic crustacean Daphnia pulex. The effect of the mutation was more pronounced for V. cholerae O139, essentially eliminating adherence. Adherence of the V. cholerae O1 classical mshA mutant was unaffected. The results suggest that MSHA is a factor contributing to the ability of V. cholerae to adhere to plankton. The results also showed that both biotypes of V. cholerae O1 utilize factors in addition to MSHA for zooplankton adherence. The expression of MSHA and these additional, yet to be defined, adherence factors differ in a serogroup- and biotype-specific manner.

Genetic diversity of Vibrio cholerae in Chesapeake Bay determined by amplified fragment length polymorphism fingerprinting

Vibrio cholerae is indigenous to the aquatic environment, and serotype non-O1 strains are readily isolated from coastal waters. However, in comparison with intensive studies of the O1 group, relatively little effort has been made to analyze the population structure and molecular evolution of non-O1 V. cholerae. In this study, high-resolution genomic DNA fingerprinting, amplified fragment length polymorphism (AFLP), was used to characterize the temporal and spatial genetic diversity of 67 V. cholerae strains isolated from Chesapeake Bay during April through July 1998, at four different sampling sites. Isolation of V. cholerae during the winter months (January through March) was unsuccessful, as observed in earlier studies (J. H. L. Kaper, R. R. Colwell, and S. W. Joseph, Appl. Environ. Microbiol. 37:91-103, 1979). AFLP fingerprints subjected to similarity analysis yielded a grouping of isolates into three large clusters, reflecting time of the year when the strains were isolated. April and May isolates were closely related, while July isolates were genetically diverse and did not cluster with the isolates obtained earlier in the year. The results suggest that the population structure of V. cholerae undergoes a shift in genotype that is linked to changes in environmental conditions. From January to July, the water temperature increased from 3 degrees C to 27.5 degrees C, bacterial direct counts increased nearly an order of magnitude, and the chlorophyll a concentration tripled (or even quadrupled at some sites). No correlation was observed between genetic similarity among isolates and geographical source of isolation, since isolates found at a single sampling site were genetically diverse and genetically identical isolates were found at several of the sampling sites. Thus, V. cholerae populations may be transported by surface currents throughout the entire Bay, or, more likely, similar environmental conditions may be selected for a specific genotype. The dynamic nature of the population structure of this bacterial species in Chesapeake Bay provides new insight into the ecology and molecular evolution of V. cholerae in the natural environment.

How Vibrio cholerae survive during starvation

Vibrio cholerae, a Gram-negative, motile, aquatic bacterium, is the causal agent of the diarrheal disease cholera. Cholera is a serious epidemic disease that has killed millions of people and continues to be a major health problem world-wide. The hypothesis that V. cholerae occupies an ecological niche in the estuarine environment requires that this organism is able to survive the dynamics of physiochemical stresses, including nutrient starvation. As a result of these stresses, bacteria in nature often exist in non-growth or very slow growth states with a low metabolic activity. Because microorganisms have little ability to control their environment, environmental changes have led to changes in cell function and structure. Such cellular responses can originate in one of two ways: by changes in genetic constitution or by phenotypic adaptation. In this review, we will focus on the phenotypic responses of V. cholerae of a given genotype to starvation stress.