Exploring the Feasibility of 16S rRNA Short Amplicon Sequencing-Based Microbiota Analysis for Microbiological Safety Assessment of Raw Oyster

16S rRNA short amplicon sequencing-based microbiota profiling has been thought of and suggested as a feasible method to assess food safety. However, even if a comprehensive microbial information can be obtained by microbiota profiling, it would not be necessarily sufficient for all circumstances. To prove this, the feasibility of the most widely used V3-V4 amplicon sequencing method for food safety assessment was examined here. We designed a pathogen (Vibrio parahaemolyticus) contamination and/or V. parahaemolyticus-specific phage treatment model of raw oysters under improper storage temperature and monitored their microbial structure changes. The samples stored at refrigerator temperature (negative control, NC) and those that were stored at room temperature without any treatment (no treatment, NT) were included as control groups. The profiling results revealed that no statistical difference exists between the NT group and the pathogen spiked- and/or phage treated-groups even when the bacterial composition was compared at the possible lowest-rank taxa, family/genus level. In the beta-diversity analysis, all the samples except the NC group formed one distinct cluster. Notably, the samples with pathogen and/or phage addition did not form each cluster even though the enumerated number of V. parahaemolyticus in those samples were extremely different. These discrepant results indicate that the feasibility of 16S rRNA short amplicon sequencing should not be overgeneralized in microbiological safety assessment of food samples, such as raw oyster.

Host and Water Microbiota Are Differentially Linked to Potential Human Pathogen Accumulation in Oysters

Oysters play an important role in coastal ecology and are a globally popular seafood source. However, their filter-feeding lifestyle enables coastal pathogens, toxins, and pollutants to accumulate in their tissues, potentially endangering human health. While pathogen concentrations in coastal waters are often linked to environmental conditions and runoff events, these do not always correlate with pathogen concentrations in oysters. Additional factors related to the microbial ecology of pathogenic bacteria and their relationship with oyster hosts likely play a role in accumulation but are poorly understood. In this study, we investigated whether microbial communities in water and oysters were linked to accumulation of Vibrio parahaemolyticus, Vibrio vulnificus, or fecal indicator bacteria. Site-specific environmental conditions significantly influenced microbial communities and potential pathogen concentrations in water. Oyster microbial communities, however, exhibited less variability in microbial community diversity and accumulation of target bacteria overall and were less impacted by environmental differences between sites. Instead, changes in specific microbial taxa in oyster and water samples, particularly in oyster digestive glands, were linked to elevated levels of potential pathogens. For example, increased levels of V. parahaemolyticus were associated with higher relative abundances of cyanobacteria, which could represent an environmental vector for Vibrio spp. transport, and with decreased relative abundance of Mycoplasma and other key members of the oyster digestive gland microbiota. These findings suggest that host and microbial factors, in addition to environmental variables, may influence pathogen accumulation in oysters. IMPORTANCE Bacteria in the marine environment cause thousands of human illnesses annually. Bivalves are a popular seafood source and are important in coastal ecology, but their ability to concentrate pathogens from the water can cause human illness, threatening seafood safety and security. To predict and prevent disease, it is critical to understand what causes pathogenic bacteria to accumulate in bivalves. In this study, we examined how environmental factors and host and water microbial communities were linked to potential human pathogen accumulation in oysters. Oyster microbial communities were more stable than water communities, and both contained the highest concentrations of Vibrio parahaemolyticus at sites with warmer temperatures and lower salinities. High oyster V. parahaemolyticus concentrations corresponded with abundant cyanobacteria, a potential vector for transmission, and a decrease in potentially beneficial oyster microbes. Our study suggests that poorly understood factors, including host and water microbiota, likely play a role in pathogen distribution and pathogen transmission.

Deep learning-based ensemble modeling of Vibrio parahaemolyticus concentration in marine environment

Vibrio parahaemolyticus (V.p) is a marine pathogenic bacterium that poses a high risk to human health and shellfish industry, yet an effective regional-scale nowcasting model for managing the risk remains lacking. This study presents the first regional-scale model for nowcasting the level of V.p in oysters in the marine environment by developing an ensemble modeling approach. The ensemble modeling approach involves the integration of genetic programming (GP) and deep artificial neural networks (DNN)-based modeling. The new approach was demonstrated by developing three GP-DNN ensemble models for predicting the V.p level in North Carolina, New Hampshire, and the combined region. Specifically, GP was employed to establish nonlinear functions between the V.p level and antecedent conditions of environmental variables. The nonlinear GP functions and current conditions of individual environmental variables were then utilized as inputs into a DNN model, forming a GP-DNN ensemble model. Modeling results indicated that the GP-DNN ensemble models were capable of predicting the V.p level with the correlation coefficient of 0.91, 0.90, and 0.80 for North Carolina, New Hampshire, and the combined region, respectively, demonstrating the impact of distinct environmental conditions in the local areas on accuracy of the combined regional-scale model. Sensitivity analysis results showed that sea surface temperature and sea surface salinity are the two most important environmental predictors for the abundance of V.p in oysters, followed by water level, pH, chlorophyll-a, and turbidity. The findings suggested that the GP-DNN ensemble models could be utilized as effective predictive tools for mitigating the V.p risk.

Growth Rates of Vibrio parahaemolyticus Sequence Type 36 Strains in Live Oysters and in Culture Medium

The pathogenic marine bacterium Vibrio parahaemolyticus can cause seafood-related gastroenteritis via the consumption of raw or undercooked seafood. Infections originating from relatively cool waters in the northeast United States are typically rare, but recently, this region has shown an increase in infections attributed to the ecological introduction of pathogenic sequence type 36 (ST36) strains, which are endemic to the cool waters of the Pacific Northwest. A 2005 risk assessment performed by the Food and Drug Administration (FDA) modeled the postharvest growth of V. parahaemolyticus in oysters as a function of air temperature and the length of time the oysters remained unrefrigerated. This model, while useful, has raised questions about strain growth differences in oyster tissue and whether invasive pathogenic strains exhibit different growth rates than nonclinical strains, particularly at lower temperatures. To investigate this question, live eastern oysters were injected with ST36 clinical strains and non-ST36 nonclinical strains, and growth rates were measured using the most probable number (MPN) enumeration. The presence of V. parahaemolyticus was confirmed using PCR by targeting the thermolabile hemolysin gene (tlh), thermostable direct hemolysin (tdh), tdh-related hemolysin (trh), and a pathogenesis-related protein (prp). The growth rates of the ST36 strains were compared to the FDA model and several other data sets of V. parahaemolyticus growth in naturally inoculated oysters harvested from the Chesapeake Bay. Our data indicate that the growth rates from most studies fall within the mean of the FDA model, but with slightly higher growth at lower temperatures for ST36 strains injected into live oysters. These data suggest that further investigations of ST36 growth capability in oysters at temperatures previously thought unsuitably low for Vibrio growth are warranted. IMPORTANCE Vibrio parahaemolyticus is the leading cause of seafood-related gastroenteritis in the United States, with an estimated 45,000 cases per year. Most individuals who suffer from vibriosis consume raw or undercooked seafood, including oysters. While gastroenteritis vibriosis is usually self-limiting and treatable, V. parahaemolyticus infections are a stressor on the growing aquaculture industry. Much effort has been placed on modeling the growth of Vibrio cells in oysters in order to aid oyster growers in designing harvesting best practices and ultimately, to protect the consumer. However, ecological invasions of nonnative bacterial strains make modeling their growth complicated, as these strains are not accounted for in current models. The National Shellfish Sanitation Program (NSSP) considers 10°C (50°F) a temperature too low to enable Vibrio growth, where 15°C is considered a cutoff temperature for optimal Vibrio growth, with temperatures approaching 20°C supporting higher growth rates. However, invasive strains may be native to cooler waters. This research aimed to understand strain growth in live oysters by measuring growth rates when oysters containing ST36 strains, which may be endemic to the U.S. Pacific Northwest, were exposed to multiple temperatures postharvest. Our results will be used to aid future model development and harvesting best practices for the aquaculture industry.

Vibrio ostreae sp. nov., a novel gut bacterium isolated from a Yellow Sea oyster

A Gram-stain-negative, oxidase- and catalase-positive, facultative anaerobic motile bacterium, designated strain OG9-811^T, was isolated from the gut of an oyster collected in the Yellow Sea, Republic of Korea. The strain grew at 10-37 °C, pH 6.0-9.0 and with 0.5-10% (w/v) NaCl. Phylogenetic analysis based on the 16S rRNA gene sequences revealed that strain OG9-811^T affiliated with the genus Vibrio, with the highest sequence similarity of 98.2% to Vibrio coralliilyticus ATCC BAA-450^T followed by Vibrio variabilis R-40492^T (98.0 %), Vibrio hepatarius LMG 20362^T (97.7 %) and Vibrio neptunius LMG 20536^T (97.6 %); other relatives were Vibrio tritonius JCM 16456^T (97.4 %), Vibrio fluvialis NBRC 103150^T (97.0 %) and Vibrio furnissii CIP 102972^T (97.0 %). The complete genome of strain OG9-811^T comprised two chromosomes of a total 4 807 684 bp and the G+C content was 50.2 %. Results of analysis based on the whole genome sequence showed the distinctiveness of strain OG9-811^T. The average nucleotide identity (ANI) values between strain OG9-811^T and the closest strains V. coralliilyticus ATCC BAA-450^T, V. variabilis R-40492^T, V. hepatarius LMG 20362^T, V. neptunius KCTC 12702^T , V. tritonius JCM 16456^T, V. fluvialis ATCC 33809^T and V. furnissi CIP 102972^T were 73.0, 72.6, 73.3, 73.0, 72.7, 78.5 and 77.8 %, respectively, while the digital DNA-DNA hybridization values between strain OG9-811^T and the above closely related strains were 20.8, 21.2, 20.8, 21.7, 20.7, 23.2 and 22.4 %, respectively. The major fatty acids of strain OG9-811^T were summed feature 3 (C_16:1 ω7c and/or C_16:1 ω6c), summed feature 8 (C_18:1 ω6c and/or C_18:1 ω7c) and C_16:0. The polar lipids contained phosphatidylethanolamine, phosphatidylglycerol and diphosphatidylglycerol. Strain OG9-811^T contained Q-8 as a quinone. On the basis of polyphasic taxonomic characteristics, strain OG9-811^T is considered to represent a novel species, for which the name Vibrio ostreae sp. nov. is proposed. The type strain is OG9-811^T (=KCTC 72623^T=GDMCC 1.2610^T).

Effects of curcumin-mediated photodynamic treatment on lipid degradation of oysters during refrigerated storage

BACKGROUND

Oyster's lipid degradation leads to a decrease in edible and nutritional value. Curcumin-mediated photodynamic treatment (PDT) is an innovative non-thermal technology, although evaluation of the oyster's lipid degradation has been scarce. In the present study, we investigated peroxide value, thiobarbituric acid reactive substance, triacylglycerol and free fatty acids to evaluate the effect of curcumin-mediated PDT on lipid degradation of oysters during refrigerated storage.

RESULTS

The results showed that curcumin-mediated PDT could delay oyster's lipid degradation. Next, the activities of enzymes were detected to determine the mechanisms behind the effects of curcumin-mediated PDT. It was revealed that the activities of lipase, phospholipase A₂ (PLA₂ ), phospholipase C (PLC), phospholipase D (PLD) and lipoxygenase (LOX) were significantly inhibited after curcumin-mediated PDT (P < 0.05). Furthermore, 16 s rRNA analysis established that the relative abundances of Pseudoalteromonas and Psychrilyobacter were reduced by 51.58% and 43.82%, respectively, after curcumin-mediated PDT.

CONCLUSION

Curcumin-mediated PDT could delay oyster's lipid degradation by inhibiting the activities of lipase, PLA₂ , PLC, PLD and LOX, as well as by changing the oyster's microbial composition, reducing the relative abundance of Pseudoalteromonas and Psychrilyobacter. © 2021 Society of Chemical Industry.

Sewage Promotes Vibrio vulnificus Growth and Alters Gene Transcription in Vibrio vulnificus CMCP6

Vibrio vulnificus is a naturally occurring, potentially lethal pathogen found in coastal waters, fish, and shellfish. Sewage spills in coastal waters occur when infrastructure fails due to severe storms or age, and may affect bacterial populations by altering nutrient levels. This study investigated effects of sewage on clonal and natural V. vulnificus populations in microcosms. Addition of 1% sewage to estuarine water caused the density of a pure culture of V. vulnificus CMCP6 and a natural V. vulnificus population to increase significantly, by two to three orders of magnitude, whether measured by quantitative PCR (qPCR) or culture and in batch and continuous cultures. Changes in the transcription of six virulence- and survival-associated genes in response to sewage were assessed using continuous culture. Exposure to sewage affected transcription of genes that may be associated with virulence, i.e., it modulated the oxidative stress response by altering superoxide dismutase transcription, significantly increasing sodB transcription while repressing sodA. Sewage also repressed transcription of nptA, which encodes a sodium-phosphate cotransporter. Sewage had no effect on sodC transcription or the putative virulence-associated genes hupA or wza. The effects of environmentally relevant levels of sewage on V. vulnificus populations and gene transcription suggest that sewage spills that impact warm coastal waters could lead to an increased risk of V. vulnificus infections. IMPORTANCE Vibrio vulnificus infections have profound impacts such as limb amputation and death for individuals with predisposing conditions. The warming climate is contributing to rising V. vulnificus prevalence in waters that were previously too cold to support high levels of the pathogen. Climate change is also expected to increase precipitation in many regions, which puts more pressure on wastewater infrastructure and will result in more frequent sewage spills. The finding that 1% wastewater in estuarine water leads to 100 to over 1,000-fold greater V. vulnificus concentrations suggests that human exposure to oysters and estuarine water could have greater health impacts in the future. Further, wastewater had a significant effect on gene transcription and has the potential to affect virulence during the initial environment-to-host transition.

Microbiomes of an oyster are shaped by metabolism and environment

Microbiomes can both influence and be influenced by metabolism, but this relationship remains unexplored for invertebrates. We examined the relationship between microbiome and metabolism in response to climate change using oysters as a model marine invertebrate. Oysters form economies and ecosystems across the globe, yet are vulnerable to climate change. Nine genetic lineages of the oyster Saccostrea glomerata were exposed to ambient and elevated temperature and PCO2 treatments. The metabolic rate (MR) and metabolic by-products of extracellular pH and CO2 were measured. The oyster-associated bacterial community in haemolymph was characterised using 16 s rRNA gene sequencing. We found a significant negative relationship between MR and bacterial richness. Bacterial community composition was also significantly influenced by MR, extracellular CO2 and extracellular pH. The effects of extracellular CO2 depended on genotype, and the effects of extracellular pH depended on CO2 and temperature treatments. Changes in MR aligned with a shift in the relative abundance of 152 Amplicon Sequencing Variants (ASVs), with 113 negatively correlated with MR. Some spirochaete ASVs showed positive relationships with MR. We have identified a clear relationship between host metabolism and the microbiome in oysters. Altering this relationship will likely have consequences for the 12 billion USD oyster economy.

Ecological diversification reveals routes of pathogen emergence in endemic Vibrio vulnificus populations

Pathogen emergence is a complex phenomenon that, despite its public health relevance, remains poorly understood. Vibrio vulnificus, an emergent human pathogen, can cause a deadly septicaemia with over 50% mortality rate. To date, the ecological drivers that lead to the emergence of clinical strains and the unique genetic traits that allow these clones to colonize the human host remain mostly unknown. We recently surveyed a large estuary in eastern Florida, where outbreaks of the disease frequently occur, and found endemic populations of the bacterium. We established two sampling sites and observed strong correlations between location and pathogenic potential. One site is significantly enriched with strains that belong to one phylogenomic cluster (C1) in which the majority of clinical strains belong. Interestingly, strains isolated from this site exhibit phenotypic traits associated with clinical outcomes, whereas strains from the second site belong to a cluster that rarely causes disease in humans (C2). Analyses of C1 genomes indicate unique genetic markers in the form of clinical-associated alleles with a potential role in virulence. Finally, metagenomic and physicochemical analyses of the sampling sites indicate that this marked cluster distribution and genetic traits are strongly associated with distinct biotic and abiotic factors (e.g., salinity, nutrients, or biodiversity), revealing how ecosystems generate selective pressures that facilitate the emergence of specific strains with pathogenic potential in a population. This knowledge can be applied to assess the risk of pathogen emergence from environmental sources and integrated toward the development of novel strategies for the prevention of future outbreaks.

Planococcus maritimus ML1206 Isolated from Wild Oysters Enhances the Survival of Caenorhabditis elegans against Vibrio anguillarum

With the widespread occurrence of aquaculture diseases and the broad application of antibiotics, drug-resistant pathogens have increasingly affected aquatic animals’ health. Marine probiotics, which live under high pressure in a saltwater environment, show high potential as a substitute for antibiotics in the field of aquatic disease control. In this study, twenty strains of non-hemolytic bacteria were isolated from the intestine of wild oysters and perch, and a model of Caenorhabditis elegans infected by Vibrio anguillarum was established. Based on the model, ML1206, which showed a 99% similarity of 16S rRNA sequence to Planococcus maritimus, was selected as a potential marine probiotic, with strong antibacterial capabilities and great acid and bile salt tolerance, to protect Caenorhabditis elegans from being damaged by Vibrio anguillarum. Combined with plate counting and transmission electron microscopy, it was found that strain ML1206 could significantly inhibit Vibrio anguillarum colonization in the intestinal tract of Caenorhabditis elegans. Acute oral toxicity tests in mice showed that ML1206 was safe and non-toxic. The real-time qPCR results showed a higher expression level of genes related to the antibacterial peptide (ilys-3) and detoxification (ugt-22, cyp-35A3, and cyp-14A3) in the group of Caenorhabditis elegans protected by ML1206 compared to the control group. It is speculated that ML1206, as a potential probiotic, may inhibit the infection caused by Vibrio anguillarum through stimulating Caenorhabditis elegans to secrete antibacterial effectors and detoxification proteins. This paper provides a new direction for screening marine probiotics and an experimental basis to support the potential application of ML1206 as a marine probiotic in aquaculture.

Phylogenetic and Biogeographic Patterns of Vibrio parahaemolyticus Strains from North America Inferred from Whole-Genome Sequence Data

Vibrio parahaemolyticus is the most common cause of seafood-borne illness reported in the United States. The draft genomes of 132 North American clinical and oyster V. parahaemolyticus isolates were sequenced to investigate their phylogenetic and biogeographic relationships. The majority of oyster isolate sequence types (STs) were from a single harvest location; however, four were identified from multiple locations. There was population structure along the Gulf and Atlantic Coasts of North America, with what seemed to be a hub of genetic variability along the Gulf Coast, with some of the same STs occurring along the Atlantic Coast and one shared between the coastal waters of the Gulf and those of Washington State. Phylogenetic analyses found nine well-supported clades. Two clades were composed of isolates from both clinical and oyster sources. Four were composed of isolates entirely from clinical sources, and three were entirely from oyster sources. Each single-source clade consisted of one ST. Some human isolates lack tdh, trh, and some type III secretion system (T3SS) genes, which are established virulence genes of V. parahaemolyticus Thus, these genes are not essential for pathogenicity. However, isolates in the monophyletic groups from clinical sources were enriched in several categories of genes compared to those from monophyletic groups of oyster isolates. These functional categories include cell signaling, transport, and metabolism. The identification of genes in these functional categories provides a basis for future in-depth pathogenicity investigations of V. parahaemolyticusIMPORTANCEVibrio parahaemolyticus is the most common cause of seafood-borne illness reported in the United States and is frequently associated with shellfish consumption. This study contributes to our knowledge of the biogeography and functional genomics of this species around North America. STs shared between the Gulf Coast and the Atlantic seaboard as well as Pacific waters suggest possible transport via oceanic currents or large shipping vessels. STs frequently isolated from humans but rarely, if ever, isolated from the environment are likely more competitive in the human gut than other STs. This could be due to additional functional capabilities in areas such as cell signaling, transport, and metabolism, which may give these isolates an advantage in novel nutrient-replete environments such as the human gut.

Alterins Produced by Oyster-Associated Pseudoalteromonas Are Antibacterial Cyclolipopeptides with LPS-Binding Activity

Discovery after discovery, host-associated microbiota reveal a growing list of positive effects on host homeostasis by contributing to host nutrition, improving hosts' immune systems and protecting hosts against pathogens. In that context, a collection of oyster associated bacteria producing antibacterial compounds have been established to evaluate their role in non-host-derived immunity. Here, we described alterins; potent anti-Gram negative compounds produced by Pseudoalteromonas hCg-6 and hCg-42 isolated from different healthy oyster hemolymph. The strains hCg-6 and hCg-42 produce a set of at least seven antibacterial compounds, ranging from 926 to 982 Da structurally characterized as cyclolipopeptides (CLPs). Alterins share the same cationic heptapeptidic cycle connected via an amido bond to different hydrophobic hydrocarbon tails. Their MICs disclosed a potent antibacterial activity directed against Gram-negative bacteria including oyster and human pathogens that may confer a beneficial defense mechanism to the host but also represents an untapped source of new antibiotics. The alterins' mechanisms of action have been deciphered: after binding to lipopolysaccharides (LPS), alterins provoke a membrane depolarization and permeabilization leading to bacterial lysis. As hCg-6 and hCg-42 produced a set of natural derivatives, the structure/activity relationship linked to the carbon tail is clarified. We showed that the hydrocarbon tail determines the LPS-binding properties of alterins and consequently their antibacterial activities. Its length and saturation seem to play a major role in this interaction.

Altruistic and Private Values For Saving Lives With an Oyster Consumption Safety Program

We use data from an Internet-based survey and estimate the benefits of an oyster consumption safety policy with the contingent valuation method. In addition to providing a context-specific estimate of willingness-to-pay for oyster safety, we consider an important issue in the contingent valuation mortality risk reduction literature. A number of studies find that willingness-to-pay for mortality risk reduction is not sensitive to the scope of the risk change. We present the scope test as a difference in the number of lives saved by the program, instead of small changes in risk, and find that referendum votes are responsive to scope. A third feature of this article is that we identify those at-risk respondents who would most benefit from the policy and decompose willingness-to-pay into use values and altruistic nonuse values. We find that willingness-to-pay per life saved ranges from $3.95 million to $7.69 million for the private good of lives saved when the respondent is at risk (i.e., use values). Willingness-to-pay per life saved including both use and altruistic nonuse values ranges from $6.89 million to $12.87 million.

Recombinase polymerase amplification-lateral flow (RPA-LF) assay combined with immunomagnetic separation for rapid visual detection of Vibrio parahaemolyticus in raw oysters

This study was the first attempt to optimize a recombinase polymerase amplification (RPA) and lateral flow (LF) assay combined with immunomagnetic separation (IMS) for the detection of Vibrio parahaemolyticus in raw oysters. The newly developed IMS-RPA-LF assay effectively combines sample preparation, amplification, and detection into a single platform. Under optimal conditions, the average capture efficiency (CE) for 10⁴ colony forming units (CFU)/mL of four V. parahaemolyticus strains with 0.4 mg of immunomagnetic beads within 45 min was 80.3%. After optimization, the RPA-LF assay was able to detect V. parahaemolyticus within 15 min, comprising DNA amplification with RPA for 10 min at 37 °C and visualization of the amplicons through LF strips for 5 min. The RPA-LF assay exhibited good specificity by showing a test line for eight V. parahaemolyticus strains with different serotypes but no cross-reaction with 12 non-V. parahaemolyticus bacteria. RPA-LF assay was found to be sensitive and detected as low as 10 pg genomic DNA of V. parahaemolyticus. For spiked oyster samples, the detection sensitivity of V. parahaemolyticus was improved to 2 CFU/g by IMS-RPA-LF after enrichment for 4 h; in contrast, the IMS-PCR method required 8 h. Hence, even when V. parahaemolyticus was present in very low numbers in samples, the IMS-RPA-LF assay could be completed within half a workday. Because of the high sensitivity, specificity, and speed of the IMS-RPA-LF assay, this newly developed method opens a novel pathway for rapid diagnostic screening of V. parahaemolyticus in seafood, which is an increasingly important health issue worldwide. Graphical abstract.

Toxigenic V. cholerae, V. parahaemolyticus, and V. vulnificus in oysters from the Gulf of Mexico and sold in Mexico City

Oysters can accumulate potentially pathogenic bacteria, such as Vibrio cholerae, V. parahaemolyticus, and V. vulnificus. The aim of this study was to detect the presence of these Vibrio species and their toxigenic variants in oysters from the Gulf of Mexico sold in Mexico City. Oyster samples were studied using traditional culture and molecular polymerase chain reaction analysis. V. cholerae was present in 30.4% of the samples and its toxigenic variant chxA+ in 26.1%. It was isolated only in deshelled oysters, mainly in the dry season. V. parahaemolyticus was present in 95.7% of the samples and the toxigenic variant was found in 17.4%. V. vulnificus was identified in 60.9% of the samples, 38% of which corresponded to the environmental genotype and 21.7% to the clinical genotype, mainly in the cold season. Consumption of the oysters analyzed poses health risks due to the presence of Vibrio species, especially in deshelled oysters.

Whole-genome comparison between reference sequences and oyster Vibrio vulnificus C-genotype strains

Whole-genome sequences of Vibrio vulnificus clinical genotype (C-genotype) from the CICESE Culture Collection, isolated from oysters, were compared with reference sequences of CMCP6 and YJ016 V. vulnificus C-genotype strains of clinical origin. The RAST web server estimated the whole genome to be ~4.8 Mb in CICESE strain 316 and ~4.7 Mb in CICESE strain 325. No plasmids were detected in the CICESE strains. Based on a phylogenetic tree that was constructed with the whole-genome results, we observed high similarity between the reference sequences and oyster C-genotype isolates and a sharp contrast with environmental genotype (E-genotype) reference sequences, indicating that the differences between the C- and E-genotypes do not necessarily correspond to their isolation origin. The CICESE strains share 3488 genes (63.2%) with the YJ016 strain and 3500 genes (63.9%) with the CMCP6 strain. A total of 237 pathogenicity associated genes were selected from reference clinical strains, where—92 genes were from CMCP6, 126 genes from YJ016, and 19 from MO6-24/O; the presence or absence of these genes was recorded for the CICESE strains. Of the 92 genes that were selected for CMCP6, 67 were present in both CICESE strains, as were as 86 of the 126 YJ016 genes and 13 of the 19 MO6-24/O genes. The detection of elements that are related to virulence in CICESE strains—such as the RTX gene cluster, vvhA and vvpE, the type IV pili cluster, the XII genomic island, and the viuB genes, suggests that environmental isolates with the C-genotype, have significant potential for infection.

Modelling of Indicator Escherichia coli Contamination in Sentinel Oysters and Estuarine Water

This study was performed to improve the ability to predict the concentrations of Escherichia coli in oyster meat and estuarine waters by using environmental parameters, and microbiological and heavy metal contamination from shellfish growing area in southern Thailand. Oyster meat (n = 144) and estuarine waters (n = 96) were tested for microbiological and heavy metal contamination from March 2016 to February 2017. Prevalence and mean concentrations of E. coli were 93.1% and 4.6 × 10³ most probable number (MPN)/g in oyster meat, and 78.1% and 2.2 × 10² MPN/100 mL in estuarine water. Average 7-day precipitation, ambient air temperature, and the presence of Salmonella were associated with the concentrations of E. coli in oyster meat (p < 0.05). Raw data (MPN/g of oyster meat and MPN/100 mL of estuarine water) and log-transformed data (logMPN/g of oyster meat and logMPN/100 mL of estuarine water) of E. coli concentrations were examined within two contrasting regression models. However, the more valid predictions were conducted using non-log transformed values. These findings indicate that non-log transformed data can be used for building more accurate statistical models in microbiological food safety, and that significant environmental parameters can be used as a part of a rapid warning system to predict levels of E. coli before harvesting oysters.

Impact of Phaeobacter inhibens on marine eukaryote-associated microbial communities

Bacteria-host interactions are universal in nature and have significant effects on host functionality. Bacterial secondary metabolites are believed to play key roles in such interactions as well as in interactions within the host-associated microbial community. Hence, prominent secondary metabolite-producing bacteria may be strong drivers of microbial community composition in natural host-associated microbiomes. This has, however, not been rigorously tested, and the purpose of this study was to investigate how the secondary metabolite producer Phaeobacter inhibens affects the diversity and composition of microbiomes associated with the microalga Emiliania huxleyi and the European flat oyster, Ostrea edulis. Roseobacters were indigenous to both communities exhibiting relative abundances between 2.8% and 7.0%. Addition of P. inhibens caused substantial changes in the overall structure of the low-complexity microbiome of E. huxleyi, but did not shape microbial community structure to the same degree in the more complex oyster microbiomes. Species-specific interactions occurred in both microbiomes and specifically the abundances of other putative secondary metabolite-producers such as vibrios and pseudoalteromonads were reduced. Thus, the impact of a bioactive strain like P. inhibens on host-associated microbiomes depends on the complexity and composition of the existing microbiome.

Bacteriophages Against Pathogenic Vibrios in Delaware Bay Oysters (Crassostrea virginica) During a Period of High Levels of Pathogenic Vibrio parahaemolyticus

Eastern oysters (Crassostrea virginica) from three locations along the Delaware Bay were surveyed monthly from May to October 2017 for levels of total Vibrio parahaemolyticus, pathogenic strains of V. parahaemolyticus and Vibrio vulnificus, and for strain-specific bacteriophages against vibrios (vibriophages). The objectives were to determine (a) whether vibriophages against known strains or serotypes of clinical and environmental vibrios were detectable in oysters from the Delaware Bay and (b) whether vibriophage presence or absence corresponded with Vibrio abundances in oysters. Host cells for phage assays included pathogenic V. parahaemolyticus serotypes O3:K6, O1:KUT (untypable) and O1:K1, as well as clinical and environmental strains of V. vulnificus. Vibriophages against some, but not all, pathogenic V. parahaemolyticus serotypes were readily detected in Delaware Bay oysters. In July, abundances of total and pathogenic V. parahaemolyticus at one site spiked to levels exceeding regulatory guidelines. Phages against three V. parahaemolyticus host serotypes were detected in these same oysters, but also in oysters with low V. parahaemolyticus levels. Serotype-specific vibriophage presence or absence did not correspond with abundances of total or pathogenic V. parahaemolyticus. Vibriophages were not detected against three V. vulnificus host strains, even though V. vulnificus were readily detectable in oyster tissues. Selected phage isolates against V. parahaemolyticus showed high host specificity. Transmission electron micrographs revealed that most isolates were ~ 60-nm diameter, non-tailed phages. In conclusion, vibriophages were detected against pandemic V. parahaemolyticus O3:K6 and O1:KUT, suggesting that phage monitoring in specific host cells may be a useful technique to assess public health risks from oyster consumption.

Development and Evaluation of Polymorphic Locus Sequence Typing for Epidemiological Tracking of Vibrio parahaemolyticus

Vibrio parahaemolyticus is a common inhabitant of coastal estuaries, and can accumulate to high levels in the shellfish that populate those waters. Human gastrointestinal infection occasionally follows ingestion of raw oysters, and it can lead to extended closures of implicated oyster beds with serious economic consequences. To track down the source of human infection, and to monitor strain variation in the environment, a user-friendly and affordable typing method that provides sufficient resolution for epidemiological analysis is needed. Polymorphic locus sequence typing (PLST) is based on conventional PCR and dideoxynucleotide sequencing of the one or two most phylogenetically informative genomic loci. Bioinformatic analyses of GenBank databases identified the V. parahaemolyticus polymorphic tandem repeat-containing loci VpMT1 and VpMT2 on chromosomes 1 and 2, respectively, as promising PLST targets, yielding diversity indexes of 0.99. Phylogenetic analysis identified multiple clusters representing strains known or likely to be epidemiologically related. Correlations with serotype and multilocus sequence type were strong but resolution was higher; for example, North American ST36 strains yielded 16 VpMT1 alleles. In the laboratory, VpMT1 and VpMT2 were robust, resolving 16 of 17 strains following PCR and sequencing directly from heat-killed colonies. Finally, 4 of 13 retail oyster enrichments yielded VpMT sequences that were unique but closely related to previously characterized clinical or environmental V. parahaemolyticus isolates.

Snapshot of environmental condition in different tropical estuarine systems by using S. cucullata (an edible oyster) as bio-indicator

Accumulation of toxic metals and indigenous bacteria in oyster, (Saccostrea cucullata) and their impact on antioxidant enzyme activities in the biological system was studied and used to provide snapshot of environmental condition in different tropical estuarine systems. The sedimentary Cd, Pb, and Hg concentration varied from 0.1 to 1.8, 22.0 to 98.0, and 0.03 to 0.11 mg kg^-1 (dry wt.) respectively. The bioaccumulated Cd, Pb, and Hg concentration in the oysters ranged from 3.6 to 9.0, 0.03 to 8.0, and 0.06 to 0.1 mg kg^-1 (dry wt.) respectively. In the oyster, the Cd concentration was well above the safe limit whereas the Pb and Hg concentrations were below the safe limit recommended by the European Commission (EC No. 1881/2006) for human consumption. The MPN value in the raw oyster for fecal coliforms (33-110 × 10³/100 g) exceeded the United States Food and Drug Administration (USFDA) approved limits. Increase in antioxidant enzymes (catalase, superoxide dismutase, glutathione-s-transferase, and metallothionein) activities with increasing pollutants loading was observed. The activities of antioxidant enzymes in the oyster were found to be very useful tool for evaluating environmental condition in any tropical estuarine systems.

Characterisation of the Pacific Oyster Microbiome During a Summer Mortality Event

The Pacific oyster, Crassostrea gigas, is a key commercial species that is cultivated globally. In recent years, disease outbreaks have heavily impacted C. gigas stocks worldwide, with many losses incurred during summer. A number of infectious agents have been associated with these summer mortality events, including viruses (particularly Ostreid herpesvirus 1, OsHV-1) and bacteria; however, cases where no known aetiological agent can be identified are common. In this study, we examined the microbiome of disease-affected and disease-unaffected C. gigas during a 2013-2014 summer mortality event in Port Stephens (Australia) where known oyster pathogens including OsHV-1 were not detected. The adductor muscle microbiomes of 70 C. gigas samples across 12 study sites in the Port Stephens estuary were characterised using 16S rRNA (V1-V3 region) amplicon sequencing, with the aim of comparing the influence of spatial location and disease state on the oyster microbiome. Spatial location was found to be a significant determinant of the disease-affected oyster microbiome. Furthermore, microbiome comparisons between disease states identified a significant increase in rare operational taxonomic units (OTUs) belonging to Vibrio harveyi and an unidentified member of the Vibrio genus in the disease-affected microbiome. This is indicative of a potential role of Vibrio species in oyster disease and supportive of previous culture-based examination of this mortality event.

Cyclopropane-Containing Fatty Acids from the Marine Bacterium Labrenzia sp. 011 with Antimicrobial and GPR84 Activity

Bacteria of the family Rhodobacteraceae are widespread in marine environments and known to colonize surfaces, such as those of e.g., oysters and shells. The marine bacterium Labrenzia sp. 011 is here investigated and it was found to produce two cyclopropane-containing medium-chain fatty acids (1, 2), which inhibit the growth of a range of bacteria and fungi, most effectively that of a causative agent of Roseovarius oyster disease (ROD), Pseudoroseovarius crassostreae DSM 16950. Additionally, compound 2 acts as a potent partial, β-arrestin-biased agonist at the medium-chain fatty acid-activated orphan G-protein coupled receptor GPR84, which is highly expressed on immune cells. The genome of Labrenzia sp. 011 was sequenced and bioinformatically compared with those of other Labrenzia spp. This analysis revealed several cyclopropane fatty acid synthases (CFAS) conserved in all Labrenzia strains analyzed and a putative gene cluster encoding for two distinct CFASs is proposed as the biosynthetic origin of 1 and 2.

Antibiotic and heavy-metal resistance of Vibrio parahaemolyticus isolated from oysters in Korea

Vibrio parahaemolyticus, found frequently in oysters and other seafoods, is the most prevalent gastroenteritis-causing pathogen in Korea and other Asian countries. It is associated exclusively with the consumption of raw or improperly cooked contaminated seafood, especially oysters. In this study, we isolated and characterized 59 V. parahaemolyticus strains (toxR-positive) from May to October 2016 in shellfish-harvesting areas off the west coast of Korea. The results revealed that none of the isolates contained the tdh and trh toxicity genes. The multiple antibiotic resistance (MAR) value of most isolates was 0.32, but it was as high as 0.69 in one isolate strain. Moreover, when resistance to heavy metals was examined, the majority of the isolates displayed resistance to Ba²⁺ (98.3%), Co³⁺ (28.8%), Cd²⁺ (16.9%), and Cu²⁺ (13.6%). Interestingly our data revealed that tolerance to heavy metals was prevalent in the V. parahaemolyticus strains with more than two antibiotic resistance phenotypes.

Colorimetric Immunoassay for Rapid Detection of Vibrio parahemolyticus Based on Mn2+ Mediates the Assembly of Gold Nanoparticles

Vibrio parahemolyticus ( V. parahemolyticus) is an important food-borne pathogen that causes food poisoning and acute gastroenteritis in humans. Herein, a novel colorimetric immunoassay was presented for rapid detection of V. parahemolyticus using gold nanoparticles (18.1 nm diameter) as chromogenic substrate, whose combination of a magnetic bead-based sandwich immunoassay and an optical sensing system via Mn²⁺ ions mediated aggregation of gold nanoparticles. MnO₂ nanoparticles coated with polyclonal IgG antibodies (7.8 nm diameter) are used to recognize the target and can be etched to generate manganese ions by ascorbic acid. A color change ranging from red to purple to blue can be easily discerned by bare eye, corresponding to V. parahemolyticus concentration in the range between 10 and 10⁶ cfu·mL^-1. The proposed method possesses high specificity with a limit of detection of 10 cfu·mL^-1 and was successfully applied to determination of V. parahemolyticus in oyster samples without pre-enrichment. In our perception, it shows promise in rapid instrumental and on-site visual detection of V. parahemolyticus.

Assessment of Bacterial Accumulation and Environmental Factors in Sentinel Oysters and Estuarine Water Quality from the Phang Nga Estuary Area in Thailand

This study characterized microbiological and chemical contamination of oyster meat and estuarine water in Phang Nga, Thailand. Pooled oyster meats (n = 144), estuarine waters (n = 96) and environmental parameters were collected from March, 2016 to February, 2017, and assessed for levels of total coliforms (TC), fecal coliforms (FC), Escherichia coli (EC), and Vibrio parahaemolyticus (VP), presence of Salmonella and Shigella and levels of heavy metals (Mn, Pb and Cd). The prevalence of TC, FC and EC were in 99.3%, 94.4% and 93.1% of oyster meat and 94.8%, 79.2%, and 78.1% of water, respectively. The average VP levels was 8.5 × 10⁷ most probable number (MPN)/g oyster. Prevalence of Shigella and Salmonella in the pooled oysters were 7.6% and 30.6%, respectively. The dominant Salmonella serovars were Paratyphi B followed by Seremban, and Kentucky. In contrast, the prevalence of Shigella were 27.1%, but Salmonella was not detected in estuarine water. Factors statistically associated with EC accumulation in oyster were level of FC, 7-day average precipitation, temperature, relative humidity, and presence of Salmonella in the sample. The optimal cutoff value of EC to predict Salmonella in oyster was 420 MPN/g. Results indicate this area has relatively safe levels of heavy metals, whereas bacterial contamination was very high for oysters.

Ruegeria denitrificans sp. nov., a marine bacterium in the family Rhodobacteraceae with the potential ability for cyanophycin synthesis

Strain CECT 5091^T, an aerobic, marine, Gram-reaction- and Gram-stain-negative, chemoheterotrophic bacterium was isolated from oysters harvested off the Spanish Mediterranean coast. Analysis of the 16S rRNA gene sequence placed the strain within the genus Ruegeria, in the family Rhodobacteraceae, with 16S rRNA gene similarities of 98.7, 98.7 and 98.4 % to Ruegeria conchae, Ruegeria atlanticaand Ruegeria arenilitoris, respectively. Average nucleotide identities (ANI) and in silico DNA-DNA hybridization (DDH) were determined, comparing the genome sequence of CECT 5091^T with those of the type strains of 12 species of the genus Ruegeria: the values obtained were always below the thresholds (95-96 % ANI, 70 % in silico DDH) used to define genomic species, proving that CECT 5091^T represents a novel species of the genus Ruegeria. The strain was slightly halophilic and mesophilic, with optimum growth at 26 °C, pH 7.0 and 3 % salinity, it required sodium and magnesium ions for growth and was able to reduce nitrate to dinitrogen. Carbon sources for growth include some carbohydrates (d-ribose, d-glucose, l-rhamnose, N-acetyl-d-glucosamine) and multiple organic acids and amino acids. The major cellular fatty acid was summed feature 8 (C18 : 1ω7c and/or C18 : 1ω6c), representing 70 % of the total fatty acids. Carbon monoxide oxidation, cyanophycin synthetic ability and phosphatidylglycerol, diphosphatidylglycerol and phosphatidylcholine production are predicted from genome annotation, while bacteriochlorophyll a production was absent. The DNA G+C content of the genome was 56.7 mol%. We propose the name Ruegeriadenitrificans sp. nov. and strain CECT 5091^T (=5OM10^T=LMG 29896^T) as the type strain for the novel species.

Genotypic characterization and assessment of infectivity of human waterborne pathogens recovered from oysters and estuarine waters in Brazil

Waterborne, food-borne and sewage-borne pathogens are a major global concern, with the annual recurrence, most notably during the summer, of outbreaks of gastroenteritis of unconfirmed etiology associated with recreational activities in marine environments. The consumption of contaminated water-based foodstuffs is also related to outbreaks of human illness. The main goals of the present study were: i) to identify the genetic assemblages of Giardia duodenalis cysts in growing and depurated oysters destined for human consumption on the southern coast of São Paulo, Brazil; ii) to verify the main circulating G. duodenalis assemblages and their subtypes in different brackish waters used for the production of mollusks and for recreational purposes; iii) to track the contamination of growing and depurated oysters by the human adenovirus and identify the infectivity of adenoviral particles recovered from oysters before and after depuration; iv) to evaluate the occurrence and genotype of the free-living amoebae of the genus Acanthamoeba in brackish water and oysters from all the sites described above. Four sampling sites in the Cananeia estuary were selected to search for pathogenic and amphizoic protozoa (Giardia and Acanthamoeba respectively): site 1: oyster growth, site 2: catchment water (before UV depuration procedure), site 3: filter backwash (filtration stage of water treatment) and site 4: oyster depuration tank. Oysters at sites 1 and 4 were evaluated for the presence of adenovirus (HAdV). Analysis consisted of conventional microbiological as well as molecular methods. Giardia duodenalis were detected in all the water sites analyzed and the molecular analysis revealed that sub-assemblage AII was the most frequently distributed throughout the estuarine environment, although one sample was identified as belonging to the assemblage C. Acanthamoeba were also isolated from different locations of the estuarine area, and were detected at all the analyzed sites. The majority of isolates belonged to the T3 genotype, while the T4 genotype was identified once. The sequencing reaction of Giardia duodenalis revealed the contamination of three batches of depurated oysters by the sub-assemblage AII. With respect to viruses, seven batches of oysters (four growing and three depurated) were found to be harboring infectious HAdV particles when submitted to plaque assay. Overall, the results of the sequencing reactions combined with the plaque assay revealed that the isolates of Giardia duodenalis and the infectious HAdV particles identified in oyster tissues have the potential to infect humans and pose a threat if consumed raw or lightly cooked. This is the first report on the sub-assemblage AII identified in oysters which are submitted to a cleaning and disinfection procedure prior to human consumption in Brazil. Acanthamoeba specific genotypes were also identified for the first time in a recreational estuarine area in Brazil, contributing to knowledge of their molecular and environmental epidemiology, which is considered scarce even in marine and estuarine areas of the world.

A model for estimating pathogen variability in shellfish and predicting minimum depuration times

Norovirus is a major cause of viral gastroenteritis, with shellfish consumption being identified as one potential norovirus entry point into the human population. Minimising shellfish norovirus levels is therefore important for both the consumer’s protection and the shellfish industry’s reputation. One method used to reduce microbiological risks in shellfish is depuration; however, this process also presents additional costs to industry. Providing a mechanism to estimate norovirus levels during depuration would therefore be useful to stakeholders. This paper presents a mathematical model of the depuration process and its impact on norovirus levels found in shellfish. Two fundamental stages of norovirus depuration are considered: (i) the initial distribution of norovirus loads within a shellfish population and (ii) the way in which the initial norovirus loads evolve during depuration. Realistic assumptions are made about the dynamics of norovirus during depuration, and mathematical descriptions of both stages are derived and combined into a single model. Parameters to describe the depuration effect and norovirus load values are derived from existing norovirus data obtained from U.K. harvest sites. However, obtaining population estimates of norovirus variability is time-consuming and expensive; this model addresses the issue by assuming a ‘worst case scenario’ for variability of pathogens, which is independent of mean pathogen levels. The model is then used to predict minimum depuration times required to achieve norovirus levels which fall within possible risk management levels, as well as predictions of minimum depuration times for other water-borne pathogens found in shellfish. Times for Escherichia coli predicted by the model all fall within the minimum 42 hours required for class B harvest sites, whereas minimum depuration times for norovirus and FRNA+ bacteriophage are substantially longer. Thus this study provides relevant information and tools to assist norovirus risk managers with future control strategies.

Spatial and Temporal Distribution of Norovirus and E. coli in Sydney Rock Oysters Following a Sewage Overflow into an Estuary

This paper reports a study of norovirus (NoV) GII distribution and persistence in Sydney rock oysters (SRO) (Saccostrea glomerata) located in an estuary after a pump station sewage overflow. SRO were strategically placed at six sites spanning the length of the estuary from the pump station to the sea. The spatial and temporal distribution of NoV, hepatitis A virus (HAV) and Escherichia coli (E. coli) in oysters was mapped after the contamination event. NoV GI and GII, HAV and E. coli were quantified for up to 48 days in oysters placed at six sites ranging from 0.05 to 8.20 km from the sewage overflow. NoV GII was detected up to 5.29 km downstream and persisted in oysters for 42 days at the site closest to the overflow. NoV GII concentrations decreased significantly over time; a reduction rate of 8.5% per day was observed in oysters (p < 0.001). NoV GII concentrations decreased significantly as a function of distance at a rate of 5.8% per km (p < 0.001) and the decline in E. coli concentration with distance was 20.1% per km (p < 0.001). HAV and NoV GI were not detected. A comparison of NoV GII reduction rates from oysters over time, as observed in this study and other published research, collectively suggest that GII reduction rates from oysters may be broadly similar, regardless of environmental conditions, oyster species and genotype.

Characterizing the Adherence Profiles of Virulent Vibrio parahaemolyticus Isolates

The human pathogen Vibrio parahaemolyticus is a leading cause of seafood-borne illness in the USA, and infections with V. parahaemolyticus typically result from eating raw or undercooked oysters. V. parahaemolyticus has been shown to be highly resistant to oyster depuration, suggesting that the bacterium possesses specific mechanisms or factors for colonizing oysters and persisting during depuration. In this study, we characterized eight different V. parahaemolyticus strains for differences in resistance to oyster depuration, biofilm formation, and motility. While each strain exhibited distinct phenotypes in the various assays, we determined that biofilm formation on abiotic surfaces, such as glass or plastic, does not directly correlate with bacterial retention in oysters during depuration. However, we did observe that the motility phenotype of a strain appeared to be a better indicator for persistence in the oyster. Further studies examining the molecular mechanisms underlying the observed colonization differences by these and other V. parahaemolyticus strains may provide beneficial insights into what critical factors are required for proficient colonization of the Pacific oyster.

Comparison of bioaccumulation and elimination of Escherichia coli and male-specific bacteriophages by ascidians and bivalves

Levels of Escherichia coli and male-specific bacteriophages (MSBs) were determined in the filter feeders obtained from retail markets, commercial farms, and wild beds in Korea. The accumulation and elimination of E. coli and MSBs were compared between ascidians and bivalves (oysters and mussels) during relaying and depuration. E. coli concentrations in ascidians from retail markets ranged between < 20 and 460 most probable number/100 g while MSBs were not detected. E. coli levels in bivalves from commercial farms and wild beds were not significantly different but bacterial levels in ascidians were consistently lower. Ascidians exhibited much lower ability than bivalves to accumulate E. coli and MSBs during relaying in a polluted coastal area. This study also shows that an equilibrium was developed between levels of microbes in water and ascidians and shellfish during relaying. E. coli and MSBs in ascidians decreased quickly during depuration in a clean seawater tank. However, after 1 day, E. coli in bivalves decreased by only 1.1-1.6 logs, and the elimination of MSBs was negligible. Therefore, depuration is an effective means to reduce the health risk of contaminated ascidians.

Rare occurrence of heart lesions in Pacific oysters Crassostrea gigas caused by an unknown bacterial infection

On rare occasions, small cream-coloured cysts have been observed in the heart and pericardial cavity of Pacific oysters Crassostrea gigas from British Columbia, Canada. Histopathology revealed the presence of large colonies of bacteria (up to 800 µm in diameter) causing significant host response and hypertrophy of the heart epithelium. The causative bacteria were characterized as follows: Gram-negative, coccoid to small rod-shaped, typically <1.5 µm in size, cell walls highly endowed with surface fimbriae and division via binary fission. Although these bacteria shared some morphological characteristics with the order Rickettsiales, they did not require an intracellular existence for multiplication. Unfortunately, a cultured isolate was not available, and a retrospective attempt to further characterize the bacteria using DNA sequence analysis of a fragment from the 16S rDNA region proved to be uninformative.

Remote sensing measurements of sea surface temperature as an indicator of Vibrio parahaemolyticus in oyster meat and human illnesses

BACKGROUND

Vibrio parahaemolyticus (Vp) is a naturally occurring bacterium found in marine environments worldwide. It can cause gastrointestinal illness in humans, primarily through raw oyster consumption. Water temperatures, and potentially other environmental factors, play an important role in the growth and proliferation of Vp in the environment. Quantifying the relationships between environmental variables and indicators or incidence of Vp illness is valuable for public health surveillance to inform and enable suitable preventative measures. This study aimed to assess the relationship between environmental parameters and Vp in British Columbia (BC), Canada.

METHODS

The study used Vp counts in oyster meat from 2002-2015 and laboratory confirmed Vp illnesses from 2011-2015 for the province of BC. The data were matched to environmental parameters from publicly available sources, including remote sensing measurements of nighttime sea surface temperature (SST) obtained from satellite readings at a spatial resolution of 1 km. Using three separate models, this paper assessed the relationship between (1) daily SST and Vp counts in oyster meat, (2) weekly mean Vp counts in oysters and weekly Vp illnesses, and (3) weekly mean SST and weekly Vp illnesses. The effects of salinity and chlorophyll a were also evaluated. Linear regression was used to quantify the relationship between SST and Vp, and piecewise regression was used to identify SST thresholds of concern.

RESULTS

A total of 2327 oyster samples and 293 laboratory confirmed illnesses were included. In model 1, both SST and salinity were significant predictors of log(Vp) counts in oyster meat. In model 2, the mean log(Vp) count in oyster meat was a significant predictor of Vp illnesses. In model 3, weekly mean SST was a significant predictor of weekly Vp illnesses. The piecewise regression models identified a SST threshold of approximately 14^oC for both model 1 and 3, indicating increased risk of Vp in oyster meat and Vp illnesses at higher temperatures.

CONCLUSION

Monitoring of SST, particularly through readily accessible remote sensing data, could serve as a warning signal for Vp and help inform the introduction and cessation of preventative or control measures.

Characterization of Vibrio parahaemolyticus isolated from oysters in Korea: Resistance to various antibiotics and prevalence of virulence genes

Vibrio parahaemolyticus, found frequently in oysters, is the most prevalent gastroenteritis-causing pathogen in Korea and in several other Asian countries. This study monitored changes in the environmental parameters and occurrence of V. parahaemolyticus in oyster aquaculture sites. Of the 44 presumed V. parahaemolyticus isolates obtained, when tested against 16 antibiotics, 90.9, 86.4, and 75.0% of the 44 isolates exhibited resistance to vancomycin, ampicillin, and streptomycin, respectively. PCR analysis for the presence of the toxR gene confirmed 31 of the 44 isolates as being positive V. parahaemolyticus strains. The toxR positive isolates were tested for the presence of thermostable direct hemolysin (tdh) and tdh-related hemolysin (trh) virulence genes. Only 9.1% toxR positive isolate exhibit the trh gene and none of the isolates were tested positive for tdh. The occurrence of multi drug resistance strains in the environment could be an indication of excessive usage of antibiotics in agriculture and aquaculture fields.

[Norovirus infection surveillance in early warning of outbreaks in population in oyster farming areas]

OBJECTIVE

To have an insight into the prevalence tendency caused by Noroviruses( NoVs) in population of oyster farming areas, and evaluate the early warning signification of acute gastroenteritis( AGE) monitoring.

METHODS

Between January and December in 2014, a retrospective household survey of AGE during past four weeks was conducted to residents using multi-stage sampling in oyster farming areas. Norovirus capsid genome was detected using real-time RT-PCR and semi-nested PCR, sequenced and phylogenetic analyzed.

RESULTS

A total of 75 cases of AGE were reported. The incidence rate was 0. 10 per person-year, the detection rate of norovirus was 20. 0%( 15 /75). The dominant epidemic No Vs strain in oyster farming was still GII. 4 Sydney 2012. Furthermore, a newly GII. 17 variant was detected and early in March 2014.

CONCLUSION

The GII. 4 Sydney 2012 genotype is still prevalent strain that caused AGE currently in the community residents of oyster farming areas. NoVs GII. 17 variant was found in sporadic patients of sentinel hospital AGE monitoring in March 2014 that have an early warning effect to the outbreaks of winter in 2014.

Plesiomonas shigelloides Periprosthetic Knee Infection After Consumption of Raw Oysters

Periprosthetic infections are a leading cause of morbidity after total joint arthroplasty. Common pathogens include Staphylococcus aureus, streptococcus, enterococcus, Escherichia coli, and Pseudomonas aeruginosa. However, there are many cases in which rare bacteria are isolated. This case report describes a periprosthetic knee infection caused by Plesiomonas shigelloides. In the United States, P shigelloides and 2 other Vibrionaceae family members, Vibrio vulnificus and Vibrio parahaemolyticus, are most often contracted from eating raw oysters and shellfish. P shigelloides usually causes a self-limiting watery diarrhea, but in immunosuppressed people it can cause septicemia. In this case report, a chemically and biologically immunosuppressed man consumed raw oysters and developed P shigelloides septicemia and acute periprosthetic knee infection that required surgical intervention.

Integrated assessment of biomarker responses and microbiological analysis of oysters from São Luís Island, Brazil

This study was conducted to evaluate the use of biochemical biomarkers and microbiological analysis to identify levels of oyster contamination at different ports in São Luís Island (Maranhão), Brazil. Oysters were analyzed for total coliforms, thermotolerant coliforms, Escherichia coli and Aeromonas spp. In addition, tissue was removed from the digestive gland to determine the glutathione-S-transferase (GST) and catalase (CAT) activity. The highest percentage of microbiological contamination of oyster samples occurred during the rainy season. The activity of GST and catalase in oysters was also higher in the rainy season, coinciding with the greatest abundance of total and thermotolerant coliforms. Among the prospective biomarkers, GST showed the best results for identification of areas with higher levels of contamination.

Quantification of Vibrio species in oysters from the Gulf of Mexico with two procedures based on MPN and PCR

Oysters can accumulate potentially pathogenic water bacteria. The objective of this study was to compare two procedures to quantify Vibrio species present in oysters to determine the most sensitive method. We analyzed oyster samples from the Gulf of Mexico, commercialized in Mexico City. The samples were inoculated in tubes with alkaline peptone water (APW), based on three tubes and four dilutions (10^-1 to 10^-4). From these tubes, the first quantification of Vibrio species was performed (most probable number (MPN) from tubes) and bacteria were inoculated by streaking on thiosulfate-citrate-bile salts-sucrose (TCBS) petri dishes. Colonies were isolated for a second quantification (MPN from dishes). Polymerase chain reaction (PCR) was used to determine species with specific primers: ompW for Vibrio cholerae, tlh for Vibrio parahaemolyticus, and VvhA for Vibrio vulnificus. Simultaneously, the sanitary quality of oysters was determined. The quantification of V. parahaemolyticus was significantly higher in APW tubes than in TCBS dishes. Regarding V. vulnificus counts, the differences among both approaches were not significant. In contrast, the MPNs of V. cholerae obtained from dishes were higher than from tubes. The quantification of MPNs through PCR of V. parahaemolyticus and V. vulnificus obtained from APW was sensitive and recommendable for the detection of both species. In contrast, to quantify V. cholerae, it was necessary to isolate colonies on TCBS prior PCR. Culturing in APW at 42 °C could be an alternative to avoid colony isolation. The MPNs of V. cholerae from dishes was associated with the bad sanitary quality of the samples.

Antimicrobial susceptibility of Vibrio alginolyticus isolated from oyster in Korea

Pathogenic Vibrio alginolyticus, a cause of severe infection in shellfish, as well as in humans, has been found at high frequency around all coastal areas of Korea. The aim of this study was to determine the occurrence of V. alginolyticus, to identify the strains isolated from oysters in West Sea, and to investigate their antimicrobial resistance profiles. Biochemical analyses of the 90 initially recovered presumptive V. alginolyticus colonies indicated that 16 isolates were V. alginolyticus. PCR analysis to detect the presence of the gyrB gene confirmed that 15 (93.8 %) of the 16 isolates were V. alginolyticus. These 15 isolates had the following profiles of resistance against 16 antibiotics: all isolates were resistant to ampicillin and vancomycin, and 26.7 % of the isolates exhibited resistance to cephalothin. A large number of isolates showed intermediate resistance to erythromycin (100 %) and rifampin (73.3 %). Five (33.3 %) of the V. alginolyticus isolates demonstrated multiple resistance to at least three antimicrobials.

Bacteriological quality evaluation of seawater and oysters from the Jaranman-Saryangdo area, a designated shellfish growing area in Korea: Impact of inland pollution sources

From 2011 to 2013, we conducted a full sanitary survey of pollution sources in proximity to a designated shellfish growing area in Korea, and their impact on the sea area therein. From this area, 836 seawater samples and 93 oyster samples were examined to evaluate their bacteriological quality. There were 483 potential pollution sources in the drainage area of the Jaranman-Saryangdo area, including 38 sources discharging water. It demonstrates that while many pollution sources have been identified, no significant impact occurred within the designated shellfish growing area. Variations in fecal coliform (FC) levels in seawater were closely related to rainfall. The FC levels of seawater and oysters from the designated area met the regulation limits set by various countries. Our study indicates that the oysters produced in this area are apparently safe for raw consumption based on their bacterial quality.

Cloning, sequencing and molecular characterisation of a cryptic plasmid from a urease-positive thermophilic Campylobacter (UPTC) isolate

Cloning, sequencing and molecular characterisation of a cryptic plasmid, pUPTC237, from a urease-positive thermophilic Campylobacter (UPTC) isolate obtained from the natural environment in Northern Ireland is reported in this study. Based on the determined DNA sequence, the pUPTC237 DNA was identified as a circular molecule of 3828 bp with a G+C content of 29.5%. As with other plasmid DNAs from Gram-negative bacteria, pUPTC237 contained an A+T-rich region (A+T content: 95%), followed by multiple direct tandem repeat units of 22 bp, characteristic of a replication origin and iteron sequence. A possible open reading frame (ORF)-1 was located upstream of the A+T-rich region and the iteron sequence that encoded a 460 amino acid protein similar to the mobilisation (mob) protein and two putative promoter structure sequences at the -35 and -10 regions and a possible ribosome binding site occurred upstream of the start codon for the ORF-1. Moreover, three possible ORFs (a short ORF-2 encoding 26 amino acids, similar to repA; an ORF-3 encoding 341 amino acids, similar to repB; and an ORF-4 encoding 96 amino acids with unknown function) were also identified. There are also two putative promoter structures for these three ORFs at the -35 and -10 regions upstream of the possible ORF-2. A possible transcription termination region was identified downstream of ORF-4. Northern blot hybridisation analysis suggested that these four ORFs constitute an operon and generate a messenger RNA (mRNA) transcript.

Environmental Conditions Associated with Elevated Vibrio parahaemolyticus Concentrations in Great Bay Estuary, New Hampshire

Reports from state health departments and the Centers for Disease Control and Prevention indicate that the annual number of reported human vibriosis cases in New England has increased in the past decade. Concurrently, there has been a shift in both the spatial distribution and seasonal detection of Vibrio spp. throughout the region based on limited monitoring data. To determine environmental factors that may underlie these emerging conditions, this study focuses on a long-term database of Vibrio parahaemolyticus concentrations in oyster samples generated from data collected from the Great Bay Estuary, New Hampshire over a period of seven consecutive years. Oyster samples from two distinct sites were analyzed for V. parahaemolyticus abundance, noting significant relationships with various biotic and abiotic factors measured during the same period of study. We developed a predictive modeling tool capable of estimating the likelihood of V. parahaemolyticus presence in coastal New Hampshire oysters. Results show that the inclusion of chlorophyll a concentration to an empirical model otherwise employing only temperature and salinity variables, offers improved predictive capability for modeling the likelihood of V. parahaemolyticus in the Great Bay Estuary.

Vibrio bacteria in raw oysters: managing risks to human health

The human-pathogenic marine bacteria Vibrio vulnificus and V. parahaemolyticus are strongly correlated with water temperature, with concentrations increasing as waters warm seasonally. Both of these bacteria can be concentrated in filter-feeding shellfish, especially oysters. Because oysters are often consumed raw, this exposes people to large doses of potentially harmful bacteria. Various models are used to predict the abundance of these bacteria in oysters, which guide shellfish harvest policy meant to reduce human health risk. Vibrio abundance and behaviour varies from site to site, suggesting that location-specific studies are needed to establish targeted risk reduction strategies. Moreover, virulence potential, rather than simple abundance, should be also be included in future modeling efforts.

A cytokine-like factor astakine accelerates the hemocyte production in Pacific oyster Crassostrea gigas

Astakine has been reported to be a hematopoietic growth factor of prokineticin homolog firstly found in arthropods freshwater crayfish Pacifastacus leniusculus. In the present study, an astakine homologous gene was identified from Pacific oyster Crassostrea gigas (designated CgAstakine). The full length cDNA of CgAstakine encoded a polypeptide of 103 amino acids containing a prokineticin (PK) domain homologous to that in astakine from freshwater crayfish P. leniusculus. The deduced amino acid sequence of CgAstakine shared higher similarity with those of other invertebrate astakines than prokineticins from vertebrates. The mRNA of CgAstakine was highly expressed in hepatopancreas and adductor muscle of oyster, while the CgAstakine protein was mainly distributed in hepatopancreas, gill and hemocytes. The mRNA expression of CgAstakine in hemocytes was significantly increased (p < 0.01) and maintained at a high level from 3 h to 9 h after Vibrio anguillarum challenge. After the oyster hemocytes were incubated with 5 μg/mL recombinant CgAstakine protein (rCgAstakine) for 24 h in vitro, the proliferation of hemocytes was significantly increased to 1.89 fold of that in control group (p < 0.05). Moreover, the total count of oyster hemocytes was significantly upregulated (2.45 fold of that in control group, p < 0.05) at 12 h after the oysters were received an injection of rCgAstakine (0.5 μg/g). These results collectively indicated that CgAstakine could modulate the hemocytes proliferation both in vitro and in vivo, and probably involved in the hematopoietic process fighting against the invasion of foreign pathogens.

The gill microbiota of invasive and indigenous Spondylus oysters from the Mediterranean Sea and northern Red Sea

The gill tissue of bivalve mollusks hosts rich symbiotic microbial communities that may contribute to the animal's metabolism. Spondylus spinosus is an invasive oyster that has become highly abundant along the eastern Mediterranean Sea (EMS) coastline, but is scarce in the northern Red Sea (NRS), its indigenous region. The composition and seasonal dynamics of the gill microbial communities of S. spinosus were examined in both regions, using 16S rRNA gene amplicon sequencing. Additionally, two Red Sea Spondylus species, S. avramsingeri and S. pickeringae, were investigated using the same approach. Significant differences were found between microbial communities of the EMS S. spinosus and the three NRS species. Bacteria from the family Hahellaceae dominated the communities of the EMS S. spinosus and the NRS S. avramsingeri, oysters that are dominant in their habitat, yet were rare in the NRS S. spinosus and S. pickeringae, which are only seldom encountered. Bacterial communities of EMS S. spinosus were more similar to those of NRS S. spinosus than to those of other NRS Spondylus species, indicating that either part of the microbiota had co-invaded with their host into the Mediterranean Sea, or that there are species-specific selective constraints on microbial composition.

Factors other than metalloprotease are required for full virulence of French Vibrio tubiashii isolates in oyster larvae

Vibrio tubiashii is a marine pathogen isolated from larval and juvenile bivalve molluscs that causes bacillary necrosis. Recent studies demonstrated the isolation of this species in a French experimental hatchery/nursery affecting Crassostrea gigas spat in 2007. Here, using larvae of C. gigas as an interaction model, we showed that the French V. tubiashii is virulent to larvae and can cause bacillary necrosis symptoms with an LD50 of about 2.3 × 10(3) c.f.u. ml(-1) after 24 h. Moreover, complete or gel permeation HPLC fractionated extracellular products (ECPs) of this strain appeared toxic to larvae. MS-MS analysis of the different ECP fractions revealed the existence of an extracellular metalloprotease and other suspected virulence factors. This observation is also supported by the expression level of some potential virulence factors. The overall results suggest that the pathology caused by the French V. tubiashii in C. gigas oysters is caused by a group of toxic factors and not only the metalloprotease.

Environmental parameters influence on the dynamics of total and pathogenic Vibrio parahaemolyticus densities in Crassostrea virginica harvested from Mexico's Gulf coast

The influence of environmental parameters on the total and pathogenic Vibrio parahaemolyticus seasonal densities in American oysters (Crassostrea virginica) was evaluated for 1 year. Harvesting site A yielded the highest mean densities of V. parahaemolyticus tlh+, tdh+/trh-, tdh-/trh+ and tdh+/trh+ during spring season at 2.57, 1.74, 0.36, and -0.40 log10 MPN/g, respectively, and tdh+/orf8+ during winter season (0.90 log10 MPN/g). V. parahaemolyticus tlh+ densities were associated to salinity (R(2)=0.372, P<0.022), tdh+/trh+ to turbidity (R(2)=0.597, P<0.035), and orf8+ to temperature, salinity, and pH (R(2)=0.964, P<0.001). The exposure to salinity and temperature conditions during winter and spring seasons regulated the dynamics of V. parahaemolyticus harboring potentially pathogenic genotypes within the oyster. The adaptive response of V. parahaemolyticus to seasonal environmental changes may lead to an increase in survival and virulence, threatening the seafood safety and increasing the risk of illness.