Multi-Probe-Fluorescence in situ Hybridization for the Rapid Enumeration of Viable Vibrio parahaemolyticus

Vibrio parahaemolyticus Epidemiology and Pathogenesis: Novel Insights on an Emerging Foodborne Pathogen

The epidemiological dynamics of V. parahaemolyticus´ infections have been characterized by the abrupt appearance of outbreaks in remote areas where these diseases had not been previously detected, without knowing the routes of entry of the pathogens in the new area. However, there are recent studies that show the link between the appearance of epidemic outbreaks of Vibrio and environmental factors such as oceanic transport of warm waters, which has provided a possible mechanism for the dispersion of Vibrio diseases globally. Despite this evidence, there is little information on the possible routes of entry and transport of infectious agents from endemic countries to the entire world. In this sense, the recent advances in genomic sequencing tools are making it possible to infer possible biogeographical patterns of diverse pathogens with relevance in public health like V. parahaemolyticus. In this chapter, we will address several general aspects about V. parahaemolyticus, including their microbiological and genetic detection, main virulence factors, and the epidemiology of genotypes involved in foodborne outbreaks globally.

Efficiency and specificity of CARD-FISH probes in detection of marine vibrios

Vibrio is a bacterial genus widely distributed in natural aquatic systems. Some Vibrio species can cause severe diseases in both marine organisms and humans. Previous studies revealed a link between the current climate change and increased incidence of the Vibrio-associated diseases recently causing sanitary, economic and/or ecological problems worldwide. The conventional culture-based methods (e.g. selection on TCBS agar) used to monitor the presence of Vibrio spp. in environmental samples are not always straightforward and can underestimate the number of cells, especially in microbial populations containing a fraction of 'dormant' cells (e.g. cells in the Viable but Non Culturable [VBNC] state). This problem can be overcome by using alternative culture-free approaches such as Catalysed Reporter Deposition-Fluorescence In situ Hybridization (CARD-FISH). To select an efficient CARD-FISH probe for detection of Vibrio spp. in environmental samples, we have assessed the most promising probes described in the literature by using both computer-assisted and experimental approaches. Our results demonstrate that the use of the optimized protocol along with a very specific probe, ViB572a, can offer the high sensitivity and selectivity of CARD-FISH detection of marine vibrios in natural seawater.

Combination of Direct Viable Count and Fluorescent In Situ Hybridization (DVC-FISH) as a Potential Method for Identifying Viable Vibrio parahaemolyticus in Oysters and Mussels

Vibrio parahaemolyticus is a human food-borne pathogen with the ability to enter the food chain. It is able to acquire a viable, non-cultivable state (VBNC), which is not detected by traditional methods. The combination of the direct viable count method and a fluorescent in situ hybridization technique (DVC-FISH) makes it possible to detect microorganisms that can present VBNC forms in complex samples The optimization of the in vitro DVC-FISH technique for V. parahaemolyticus was carried out. The selected antibiotic was ciprofloxacin at a concentration of 0.75 μg/mL with an incubation time in DVC broth of 5 h. The DVC-FISH technique and the traditional plate culture were applied to detect and quantify the viable cells of the affected pathogen in artificially contaminated food matrices at different temperatures. The results obtained showed that low temperatures produced an important logarithmic decrease of V. parahaemolyticus, while at 22 °C, it proliferated rapidly. The DVC-FISH technique proved to be a useful tool for the detection and quantification of V. parahaemolyticus in the two seafood matrices of oysters and mussels. This is the first study in which this technique has been developed to detect viable cells for this microorganism.

Recent methods and biosensors for foodborne pathogen detection in fish: progress and future prospects to sustainable aquaculture systems

The aquaculture industry has advanced toward sustainable recirculating systems, in where parameters of food quality are strictly monitored. Despite that, as in the case of conventional aquaculture practices, the recirculating systems also suffer threats from Aeromonas spp., Vibrio spp., Streptococcus spp., among other foodborne pathogens infecting farmed fish. The aquaculture pathogens are routinely detected by conventional PCR methods or antibody-based tests, with the detection protocols confined to laboratory use. Emerging assay technologies and biosensors recently reported in the literature open new opportunities to the development of sensitive, specific, and portable analytical devices to use in the field. Techniques of DNA/RNA analysis, immunoassays and other nanomolecular technologies have been facing important advances in response time, sensitivity, and enhanced power of discrimination among and within species. Moreover, the recent developments of electrochemical and optical signal transduction have facilitated the incorporation of the innovative assays to practical miniaturized devices. In this work, it is provided a critical review over foodborne pathogen detection by existing and promising methods and biosensors applied to fish samples and extended to other food matrices. While isothermal DNA/RNA amplification methods can be highlighted among the assay methods for their promising analytical performance and suitability for point-of-care testing, the electrochemical transduction provides a way to achieve cost-effective biosensors amenable to use in the aquaculture field. The adoption of new methods and biosensors would constitute a step forward in securing sustainable aquaculture systems.

Characterization of Mixed-Species Biofilm Formed by Vibrio parahaemolyticus and Listeria monocytogenes

Mixed-species biofilms are the predominant form of biofilms found in nature. Research on biofilms have typically concentrated on single species biofilms and this study expands the horizon of biofilm research, where the characterization and dynamic changes of mono and mixed-species biofilms formed by the pathogens, Vibrio parahaemolyticus and Listeria monocytogenes were investigated. Compared to mono-species biofilm, the biomass, bio-volume, and thickness of mixed-species biofilms were significantly lower, which were confirmed using crystal violet staining, confocal laser scanning microscopy and scanning electron microscopy. Further experimental analysis showed these variations might result from the reduction of bacterial numbers, the down-regulation of biofilm-regulated genes and loss of metabolic activity in mixed-species biofilm. In addition, V. parahaemolyticus was located primarily on the surface layers of the mixed-species biofilms thus accruing competitive advantage. This competitive advantage was evidenced in a higher V. parahaemolyticus population density in the mixed-species biofilms. The adhesion to surfaces of the mixed-species biofilms were also reduced due to lower concentrations of extracellular polysaccharide and protein when the structure of the mixed-species was examined using Raman spectral analysis, phenol-sulfuric acid method and Lowry method. Furthermore, the minimum biofilm inhibitory concentration to antibiotics obviously decreased when V. parahaemolyticus co-exited with L. monocytogenes. This study firstly elucidated the interactive behavior in biofilm development of two foodborne pathogens, and future studies for biofilm control and antibiotic therapy should take into account interactions in mixed-species biofilms.

Spatiotemporal Dynamics of Total Viable Vibrio spp. in a NW Mediterranean Coastal Area

A cellular approach combining Direct Viable Counting and Fluorescent In Situ Hybridization using a one-step multiple-probe technique and Solid Phase Cytometry (DVC-FISH-SPC) was developed to monitor total viable vibrios and cover the detection of a large diversity of vibrios. FISH combined three probes in the same assay and targeted sequences located at different positions on the 16S rRNA of Vibrio and Aliivibrio members. We performed a 10-month in situ study to investigate the weekly dynamics of viable vibrios relative to culturable counts at two northwestern Mediterranean coastal sites, and identified the key physicochemical factors for their occurrence in water using a multivariate analysis. Total viable and culturable cell counts showed the same temporal pattern during the warmer season, whereas the ratios between both methods were inverted during the colder seasons (<15°C), indicating that some of the vibrio community had entered into a viable but non-culturable (VBNC) state. We confirmed that Seawater Surface Temperature explained 51–62% of the total variance in culturable counts, and also showed that the occurrence of viable vibrios is controlled by two variables, pheopigment (15%) and phosphate (12%) concentrations, suggesting that other unidentified factors play a role in maintaining viability.

Development of a quadruplex loop-mediated isothermal amplification assay for field detection of four Vibrio species associated with fish disease

A quadruplex loop-mediated isothermal amplification (LAMP) method was developed to detect four Vibrio species, including Vibrio ichthyoenteri, Vibrioparahaemolyticus, Vibrioscophthalmi, and Vibrio vulnificus, simultaneously. Four sets of species-specific primers were designed with different restriction sites contained in the inner primers. The quadruplex LAMP method could distinguish four Vibrio species via the subsequent restriction enzyme analysis. The sensitivity of the quadruplex LAMP method were 10²–10³ times higher than the sensitivity of conventional PCR. V. scophthalmi, V. vulnificus, V. parahaemolyticus and V. ichthyoenteri could be detected in the different tissues of the infected fish by the quadruplex LAMP method simply and conveniently through using SYBR Green I to facilitate visual inspection of the LAMP products. The method we developed in this study could be a simple and convenient diagnostic tool for field detection of Vibrio infection in fish.

Vibrio parahaemolyticus: a review on the pathogenesis, prevalence, and advance molecular identification techniques

Vibrio parahaemolyticus is a Gram-negative halophilic bacterium that is found in estuarine, marine and coastal environments. V. parahaemolyticus is the leading causal agent of human acute gastroenteritis following the consumption of raw, undercooked, or mishandled marine products. In rare cases, V. parahaemolyticus causes wound infection, ear infection or septicaemia in individuals with pre-existing medical conditions. V. parahaemolyticus has two hemolysins virulence factors that are thermostable direct hemolysin (tdh)-a pore-forming protein that contributes to the invasiveness of the bacterium in humans, and TDH-related hemolysin (trh), which plays a similar role as tdh in the disease pathogenesis. In addition, the bacterium is also encodes for adhesions and type III secretion systems (T3SS1 and T3SS2) to ensure its survival in the environment. This review aims at discussing the V. parahaemolyticus growth and characteristics, pathogenesis, prevalence and advances in molecular identification techniques.

Detection of torque teno sus virus 1 and 2 in porcine tissues by in situ hybridization using multi-strained pooled probes

Porcine torque teno sus virus (TTSuV) has been suggested as a co-factor for the development of porcine circovirus-associated diseases. However, the pathogenic role of TTSuV is still inconclusive, and the target cell and tissue tropism of this virus are also ambiguous. In the present study, a multi-strained pooled probe-based in situ hybridization was established to detect the nucleic acids of TTSuV1 and TTSuV2 in the tissue. The strategy of using polymerase chain reaction-derived digoxigenin-labeled multi-strained pooled probe, instead of single-strained probe or oligonucleotide, was to overcome the fact of high sequence diversity among TTSuV strains and simultaneous infection with distinct strains of TTSuV in the same animal. The cell tropism and tissue distribution were evaluated by grading system with tissues from major organs. Lymphoid tissues, including superficial inguinal, mesenteric, and hilar lymph nodes, tonsil, intestinal lamina propria of mucosa and Peyer's patches, and sometimes spleen, generally contained higher levels of positive signals and are considered as the target sites for TTSuV. Morphologically, the distribution of TTSuV-positive signals had a strong correlation with the T lymphocyte zone. T lymphocytes are, thus, speculated as the major target cells for TTSuV.

Microbial communities associated with holothurians: presence of unique bacteria in the coelomic fluid

Marine invertebrates interact with various microorganisms ranging from pathogens to symbionts. One-to-one symbiosis between a single microbial species and a single host animal has served as a model for the study of host-microbe interactions. In addition, increasing attention has recently been focused on the complex symbiotic associations, e.g., associations between sponges and their symbionts, due to their biotechnological potential; however, relatively little is known about the microbial diversity associated with members of the phylum Echinodermata. Here, for the first time, we investigated microbial communities associated with a commercially important holothurian species, Apostichopus japonicus, using culture-dependent and -independent methods. Diverse and abundant heterotrophs, mostly Gammaproteobacteria members, were cultured semi-quantitatively. Using the cloning and sequencing technique, different microbial communities were found in different holothurian tissues. In the holothurian coelomic fluid, potentially metabolically active and phylogenetically unique members of Epsilonproteobacteria and Rickettsiales were discovered. This study suggests that coelomic fluids of marine invertebrates, at least those inhabiting intertidal areas where physical and chemical conditions fluctuate, provide microbes with unique and stable habitats.

A great leap forward in microbial ecology

Ribosomal RNA (rRNA) sequence-based molecular techniques emerged in the late 1980s, which completely changed our general view of microbial life. Coincidentally, the Japanese Society of Microbial Ecology (JSME) was founded, and its official journal "Microbes and Environments (M&E)" was launched, in 1985. Thus, the past 25 years have been an exciting and fruitful period for M&E readers and microbiologists as demonstrated by the numerous excellent papers published in M&E. In this minireview, recent progress made in microbial ecology and related fields is summarized, with a special emphasis on 8 landmark areas; the cultivation of uncultured microbes, in situ methods for the assessment of microorganisms and their activities, biofilms, plant microbiology, chemolithotrophic bacteria in early volcanic environments, symbionts of animals and their ecology, wastewater treatment microbiology, and the biodegradation of hazardous organic compounds.