Comparison of the effects of environmental parameters on growth rates of Vibrio vulnificus biotypes I, II, and III by culture and quantitative PCR analysis

Prevalence and risk factors of seafood-borne Vibrio vulnificus in Asia: a systematic review with meta-analysis and meta-regression

Vibrio vulnificus is a free-living marine bacterium associated with the contamination of fish and shellfish-the most consumed seafood in Asia. Owing to its potentially lethal clinical consequences, the consumption of seafood contaminated with V. vulnificus has become a growing public health concern. This systematic review with meta-analysis and meta-regression aimed to integrate data on the prevalence of seafood-borne V. vulnificus specifically in Asia and assess the potential risk factors that can influence the outcomes. A comprehensive literature search of four electronic databases yielded 279 relevant studies, among which 38 fulfilled the inclusion criteria. These selected studies were subjected to risk-of-bias assessment and data extraction by three independent researchers. A meta-analysis of the eligible studies estimated the overall prevalence of seafood-borne V. vulnificus in Asia to be 10.47% [95% confidence interval (CI): 6.8-15.8%], with bivalve shellfish, such as oysters, mussels, clams, and cockles being the most contaminated seafood. The highest prevalence was reported in Japan, where 47.6% of the seafood samples tested positive for V. vulnificus. The subgroup and meta-regression analyses identified three potential covariates-detection method, publication year, and country-associated with between-study heterogeneity. Furthermore, data visualization displayed the variations in V. vulnificus prevalence across the studies, associated with differences in sample type, sample size, and sampling stage. This study provides valuable insights into the prevalence of V. vulnificus in fish and shellfish across the entire Asian continent and highlights the potential factors that cause variation in the prevalence rates among the studies. These findings underscore the importance of enhancing hygiene measures throughout the seafood supply chain to mitigate V. vulnificus infection risks and ensure the safety of consumers.

Meteorological associations of Vibrio vulnificus clinical infections in tropical settings: Correlations with air pressure, wind speed, and temperature

V. vulnificus is one of the deadliest waterborne pathogens, yet little is known of the ecological and environmental forces that drive outbreaks. As a nationally notifiable disease, all cases of V. vulnificus diagnosed in the United States are reported to the state in which they occurred, as well as to the Centers for Disease Control (CDC) in Atlanta, Georgia. Given that the state of Florida is a 'hotspot' for V. vulnificus in the United States, we examined the prevalence and incidence of cases reported to the Florida Department of Health (2008-2020). Using a dataset comprised of 448 cases of disease caused by V. vulnificus infection, we identified meteorological variables that were associated with clinical cases and deaths. Combined with data from the National Oceanic and Atmospheric Administration (NOAA), we first utilized correlation analysis to examine the linear relationships between satellite meteorological measurements such as wind speed, air temperature, water temperature, and sea-level pressure. We then measured the correlation of those meteorological variables with coastal cases of V. vulnificus, including the outcome, survival, or death. We also constructed a series of logistic regression models to analyze the relationship between temporal and meteorological variables during months that V. vulnificus cases were reported versus months when V. vulnificus cases were not reported. We report that between 2008 and 2020, V. vulnificus cases generally increased over time, peaking in 2017. As water temperature and air temperature increased, so too did the likelihood that infection with V. vulnificus would lead to patient death. We also found that as mean wind speed and sea-level pressure decreased, the probability that a V. vulnificus case would be reported increased. In summary, we discuss the potential factors that may contribute to the observed correlations and speculate that meteorological variables may increase in their public health relevance in light of rising global temperatures.

Optimum environmental conditions controlling prevalence of vibrio parahaemolyticus in marine environment

This literature review presents major environmental indicators and their optimum variation ranges for the prevalence of Vibrio parahaemolyticus in the marine environment by critically reviewing and statistically analyzing more than one hundred studies from countries around the world. Results of this review indicated that the prevalence of Vibrio parahaemolyticus in the marine environment is primarily responsive to favorable environmental conditions that are described with environmental indicators. The importance of environmental indicators to the prevalence of Vibrio parahaemolyticus can be ranked from the highest to lowest as Sea Surface Temperature (SST), salinity, pH, chlorophyll a, and turbidity, respectively. It was also found in this study that each environmental indicator has an optimum variation range favoring the prevalence of Vibrio parahaemolyticus. Specifically, the SST range of 25.67 ± 2 °C, salinity range of 27.87 ± 3 ppt, and pH range of 7.96 ± 0.1 were found to be the optimum conditions for the prevalence of Vibrio parahaemolyticus. High vibrio concentrations were also observed in water samples with the chlorophyll a range of 16-25 μg/L. The findings provide new insights into the importance of environmental indicators and their optimum ranges, explaining not only the existence of both positive and negative associations reported in the literature but also the dynamic associations between the Vibrio presence and its environmental drivers.

Epidemiological and microbiological investigation of a large increase in vibriosis, northern Europe, 2018

BackgroundVibriosis cases in Northern European countries and countries bordering the Baltic Sea increased during heatwaves in 2014 and 2018.AimWe describe the epidemiology of vibriosis and the genetic diversity of Vibrio spp. isolates from Norway, Sweden, Denmark, Finland, Poland and Estonia in 2018, a year with an exceptionally warm summer.MethodsIn a retrospective study, we analysed demographics, geographical distribution, seasonality, causative species and severity of non-travel-related vibriosis cases in 2018. Data sources included surveillance systems, national laboratory notification databases and/or nationwide surveys to public health microbiology laboratories. Moreover, we performed whole genome sequencing and multilocus sequence typing of available isolates from 2014 to 2018 to map their genetic diversity.ResultsIn 2018, we identified 445 non-travel-related vibriosis cases in the study countries, considerably more than the median of 126 cases between 2014 and 2017 (range: 87-272). The main reported mode of transmission was exposure to seawater. We observed a species-specific geographical disparity of vibriosis cases across the Nordic-Baltic region. Severe vibriosis was associated with infections caused by Vibrio vulnificus (adjOR: 17.2; 95% CI: 3.3-90.5) or Vibrio parahaemolyticus (adjOR: 2.1; 95% CI: 1.0-4.5), age ≥ 65 years (65-79 years: adjOR: 3.9; 95% CI: 1.7-8.7; ≥ 80 years: adjOR: 15.5; 95% CI: 4.4-54.3) or acquiring infections during summer (adjOR: 5.1; 95% CI: 2.4-10.9). Although phylogenetic analysis revealed diversity between Vibrio spp. isolates, two V. vulnificus clusters were identified.ConclusionShared sentinel surveillance for vibriosis during summer may be valuable to monitor this emerging public health issue.

Depuration of live oysters to reduce Vibrio parahaemolyticus and Vibrio vulnificus: A review of ecology and processing parameters

Consumption of raw oysters, whether wild-caught or aquacultured, may increase health risks for humans. Vibrio vulnificus and Vibrio parahaemolyticus are two potentially pathogenic bacteria that can be concentrated in oysters during filter feeding. As Vibrio abundance increases in coastal waters worldwide, ingesting raw oysters contaminated with V. vulnificus and V. parahaemolyticus can possibly result in human illness and death in susceptible individuals. Depuration is a postharvest processing method that maintains oyster viability while they filter clean salt water that either continuously flows through a holding tank or is recirculated and replenished periodically. This process can reduce endogenous bacteria, including coliforms, thus providing a safer, live oyster product for human consumption; however, depuration of Vibrios has presented challenges. When considering the difficulty of removing endogenous Vibrios in oysters, a more standardized framework of effective depuration parameters is needed. Understanding Vibrio ecology and its relation to certain depuration parameters could help optimize the process for the reduction of Vibrio. In the past, researchers have manipulated key depuration parameters like depuration processing time, water salinity, water temperature, and water flow rate and explored the use of processing additives to enhance disinfection in oysters. In summation, depuration processing from 4 to 6 days, low temperature, high salinity, and flowing water effectively reduced V. vulnificus and V. parahaemolyticus in live oysters. This review aims to emphasize trends among the results of these past works and provide suggestions for future oyster depuration studies.

Variable freshwater influences on the abundance of Vibrio vulnificus in a tropical urban estuary

To better understand the controls on the opportunistic human pathogen Vibrio vulnificus in warm tropical waters, we conducted a year-long investigation in the Ala Wai Canal, a channelized estuary in Honolulu, HI. The abundance of V. vulnificus as determined by qPCR of the hemolysin gene (vvhA), varied spatially and temporally nearly four orders of magnitude (≤ 3 to 14,000 mL^-1). Unlike in temperate and subtropical systems, temperatures were persistently warm (19-31°C) and explained little of the variability in V. vulnificus abundance. Salinity (1-36 ppt) had a significant, but non-linear, relationship with V. vulnificus abundance with highest vvhA concentrations (> 2,500 mL^-1) observed only at salinities from 7 to 22 ppt. V. vulnificus abundances were lower on average in the summer dry season when waters were warmer but more saline. Highest canal-wide average abundances were observed during a time of modest rainfall when moderate salinities and elevated concentrations of reduced nitrogen species and silica suggested a groundwater influence. Distinguishing the abundances of two genotypes of V. vulnificus (C-type and E-type) suggest that C-type strains, which are responsible for most human infections, were usually less abundant (25% on average), but their relative contribution was greater at higher salinities, suggesting a broader salinity tolerance. Generalized regression models suggested up to 67% of sample-to-sample variation in log-transformed V. vulnificus abundance was explained (n = 202) using the measured environmental variables, and up to 97% of the monthly variation in canal-wide average concentrations (n = 13) was explained with the best subset of four variables. IMPORTANCE Our data illustrate that, in the absence of strong seasonal variation in water temperature in the tropics, variation in salinity driven by rainfall becomes a primary controlling variable on V. vulnificus abundance. There is thus a tendency for a rainfall-driven seasonal cycle in V. vulnificus abundance that is inverted from the temperature-driven seasonal cycle at higher latitudes. However, stochasticity in rainfall and its non-linear, indirect effects on V. vulnificus concentration means that high abundances can occur at any location in the canal at any time of year, making it challenging to predict concentrations of this pathogen at high temporal or spatial resolution. Much of the variability in canal-wide average concentrations, on the other hand, was explained by a few variables that reflect the magnitude of freshwater input to the system, suggesting that relative risk of exposure to this pathogen could be predicted as an average for the system.

Survivability of Alcaligenaceae and Chromatiaceae as palm oil mill effluent pollution bioindicators under fluctuations of temperature, pH and total suspended solid

Alcaligenaceae and Chromatiaceae were previously reported as the specific pollution bioindicators in the receiving river water contaminated by palm oil mill effluent (POME) final discharge. Considering the inevitable sensitivity of bacteria under environmental stresses, it is crucial to assess the survivability of both bacteria in the fluctuated environmental factors, proving their credibility as POME pollution bioindicators in the environment. In this study, the survivability of Alcaligenaceae and Chromatiaceae from facultative pond, algae (aerobic) pond and final discharge were evaluated under varying sets of temperature (25-40°C), pH (pH 7-9) and low/high total suspended solid (TSS) contents of POME collected during low/high crop seasons of oil palm, respectively. Following treatment, the viability status and compositions of the bacterial community were assessed using flow cytometry-based assay and high-throughput Illumina MiSeq, respectively, in correlation with the changes of physicochemical properties. The changes in temperature, pH and TSS indeed changed the physicochemical properties of POME. The functionality of bacterial cells was also shifted where the viable cells and high nucleic acid contents reduced at elevated levels of temperature and pH but increased at high TSS content. Interestingly, the Alcaligenaceae and Chromatiaceae continuously detected in the samples which accounted for more than 0.5% of relative abundance, with a positive correlation with biological oxygen demand (BOD₅) concentration. Therefore, either Alcaligenaceae or Chromatiaceae or both could be regarded as the reliable and specific bacterial indicators to indicate the pollution in river water due to POME final discharge despite the fluctuations in temperature, pH and TSS.

Assessment and Antibiotic Resistance Profiling in Vibrio Species Isolated from Wild Birds Captured in Danube Delta Biosphere Reserve, Romania

Antimicrobial and multidrug-resistant bacteria are a major problem worldwide and, consequently, the surveillance of antibiotic-resistant bacteria and assessment of the dissemination routes are essential. We hypothesized that migratory birds, coming from various environments, would carry more numerous Vibrio strains than sedentary species, with increased risk to be passed to their contacts or environment in habitats they transit or nest in. Similarly, we presumed that strains from migratory birds will show multidrug resistance. A total of 170 oral and rectal swabs were collected from wild birds captured in different locations of the Danube Delta (Malic, Sfantu-Gheorghe, Letea Forest) and processed using standardized selective media. V. cholerae strains were confirmed by serology and molecular methods and, subsequently, their susceptibility was evaluated. The prevalence of Vibrio species by host species, habitat type, and location was interpreted. The isolated Vibrio species were identified as Vibrio cholerae 14.33%, V. fluvialis 13.33%, V. alginolyticus 12%, V. mimicus 17.33%, V. vulnificus 10.88%, with V. parahaemolyticus and V. metschnikovii (16%) also being prevalent. Of the 76 Vibrio spp. isolates, 18.42% were resistant towards at least three antimicrobials, and 81.57% demonstrated a multidrug resistance phenotype, including mainly penicillins, aminoglycosides, and macrolides. The results of the present study indicate higher numbers of Vibrio strains in migratory (74.66%) than in sedentary birds (25.33%), confirming our hypothesis. Furthermore, the increased pathogenicity of Vibrio spp. strains, isolated from wild migratory and sedentary birds, was confirmed by their increased multiple antibiotic resistance (MAR) index (0.09–0.81).

Quantitative PCR enumeration of vcgC and 16S rRNA type A and B genes as virulence indicators for environmental and clinical strains of Vibrio vulnificus in Galveston Bay oysters

Oysters from a reef in Galveston Bay, Texas, USA, were screened for more virulent clinical strains versus less virulent environmental strains of Vibrio vulnificus using a combination of quantitative PCR assays for the virulence correlating gene (clinical variant, vcgC) and 16S rRNA types A and B (type A = environmental, type B = clinical). The combination of vcgC and 16S rRNA type B loci to determine clinical type strains was suitable, as indicated by the strong correlation (R² = 0.98; p < 0.001) between these gene counts over time and their relative proportion (up to 93.8% and 94.3%, respectively) to vvhA genes used to quantify all strains of V. vulnificus. A strong seasonal shift of V. vulnificus strain types was observed. Environmental strains (16S rRNA type A) predominated from April to mid-June as salinities increased from 22 to 27 PSU (practical salinity unit) and temperatures rose 20 to 28 °C, with peak gene quantities of 16 812 ± 56 CFU/g. As temperatures increased to ≥30 °C from mid-June to September and salinities rose above 27 PSU, clinical strains (16S rRNA type B; vcgC) predominated with peak quantities 31 868 ± 287 and 32 360 ± 178 CFU/g, respectively.

Unveiling the acid stress response of clinical genotype Vibrio vulnificus isolated from the marine environments of Mangaluru coast, India

Gastric acidity is one of the earliest host defences faced by ingested organisms, and successful pathogens need to overcome this hurdle. The objective of this study was the systematic assessment of acid-stress response of Vibrio vulnificus isolated from coastal regions of Mangaluru. Acid-shock experiments were carried out at pH 4.0 and pH 4.5, with different experimental conditions expected to produce a varied acid response. Exposure to mild acid before the acid shock was favourable to the bacteria but was dependent on cell population and pH of the media and was independent of the strains tested. Lysine-dependent acid response was demonstrated with reference to the previously identified lysine decarboxylase system. Additionally, the results showed that inoculation into oysters provided some level of protection against acid stress. Increased expression of lysine/cadaverine genes was observed upon the addition of ground oyster and was confirmed by quantitative real-time PCR. The potential role of ornithine was analyzed with regard to acid stress, but no change in the survival pattern was observed. These findings highlight the physiology of bacteria in acid stress.

Non-parametric estimation of the structural stability of non-equilibrium community dynamics

Environmental factors are important drivers of community dynamics. Yet, despite extensive research, it is still extremely challenging to predict the effect of environmental changes on the dynamics of ecological communities. Equilibrium- and model-based approaches have provided a theoretical framework with which to investigate this problem systematically. However, the applicability of this framework to empirical data has been limited because equilibrium dynamics of populations within communities are seldom observed in nature and exact equations for community dynamics are rarely known. To overcome these limitations, here we develop a data-driven non-parametric framework to estimate the tolerance of non-equilibrium community dynamics to environmental perturbations (that is, their structural stability). Following our approach, we show that in non-equilibrium systems, structural stability can vary significantly across time. As a case study, we investigate the structural stability of a rocky intertidal community with dynamics at the edge of chaos. The structural stability of the community as a whole exhibited a clear seasonal pattern, despite the persistent chaotic dynamics of individual populations. Importantly, we show that this seasonal pattern of structural stability is causally driven by sea temperature. Overall, our approach provides novel opportunities for estimating the tolerance of ecological communities to environmental changes within a non-parametric framework.

Impact of Climate Change on Vibrio vulnificus Abundance and Exposure Risk

Vibrio species are marine bacteria that occur in estuaries worldwide; many are virulent human pathogens with high levels of antibiotic resistance. The average annual incidence of all Vibrio infections has increased by 41% between 1996 and 2005. V. vulnificus (Vv), a species associated with shellfish and occurring in the US Southeast, has ranges of temperature (16-33 °C) and salinity (5-20 ppt) dependencies for optimal growth. Increased water temperatures caused by atmospheric warming and increased salinity gradients caused by sea level rise raise concerns for the effect of climate change on the geographic range of Vv and the potential for increased exposure risk. This research combined monthly field sampling, laboratory analysis, and modeling to identify the current occurrence of Vv in the Winyah Bay estuary (South Carolina, USA) and assess the possible effects of climate change on future geographic range and exposure risk in the estuary. Vv concentrations ranged from 0 to 58 colony forming units (CFU)/mL, salinities ranged from 0 to 28 ppt, and temperature from 18 to 31 °C. A significant empirical relationship was found between Vv concentration and salinity and temperature that fit well with published optimal ranges for growth for these environmental parameters. These results, when coupled with an existing model of future specific conductance, indicated that sea level rise has a greater impact on exposure risk than temperature increases in the estuary. Risk increased by as much as four times compared to current conditions with the largest temporally widespread increase at the most upriver site where currently there is minimal risk.

Vibrio parahaemolyticus and Vibrio vulnificus Recovered from Oysters during an Oyster Relay Study

Vibrio parahaemolyticus and Vibrio vulnificus are naturally occurring estuarine bacteria and are the leading causes of seafood-associated infections and mortality in the United States. Though multiple-antibiotic-resistant V. parahaemolyticus and V. vulnificus strains have been reported, resistance patterns in vibrios are not as well documented as those of other foodborne bacterial pathogens. Salinity relaying (SR) is a postharvest processing (PHP) treatment to reduce the abundances of these pathogens in shellfish harvested during the warmer months. The purpose of this study was to evaluate the antimicrobial susceptibility (AMS), pathogenicity, and genetic profiles of V. parahaemolyticus and V. vulnificus recovered from oysters during an oyster relay study. Isolates (V. parahaemolyticus [n = 296] and V. vulnificus [n = 94]) were recovered from oysters before and during the 21-day relaying study to detect virulence genes (tdh and trh) and genes correlated with virulence (vcgC) using multiplex quantitative PCR (qPCR). AMS to 20 different antibiotics was investigated using microbroth dilution, and pulsed-field gel electrophoresis (PFGE) was used to study the genetic profiles of the isolates. Twenty percent of V. vulnificus isolates were vcgC⁺, while 1 and 2% of V. parahaemolyticus were tdh⁺ and trh⁺, respectively. More than 77% of the V. vulnificus isolates and 30% of the V. parahaemolyticus isolates were resistant to at least one antimicrobial. Forty-eight percent of V. vulnificus and 8% of V. parahaemolyticus isolates were resistant to two or more antimicrobials. All isolates demonstrated a high genetic diversity, even among those isolated from the same site and having a similar AMS profile. No significant effects of the relaying process on AMS, virulence genes, or PFGE profiles of V. vulnificus and V. parahaemolyticus were observed.IMPORTANCE Analysis of the antibiotic resistance profiles of V. vulnificus and V. parahaemolyticus isolated from oysters during this study indicated that more than 48% of V. vulnificus isolates were resistant to two or more antimicrobials, including those recommended by the CDC for treating Vibrio infections. Also, the V. parahaemolyticus isolates showed high MICs for some of the Vibrio infection treatment antibiotics. Monitoring of AMS profiles of this bacterium is important to ensure optimal treatment of infections and improve food safety. Our study showed no significant differences in the AMS profiles of V. vulnificus (P = 0.26) and V. parahaemolyticus (P = 0.23) isolated from the oysters collected before versus after relaying. This suggests that the salinity of the relaying sites did not affect the AMS profiles of the Vibrio isolates, although it did reduce the numbers of these bacteria in oysters (S. Parveen et al., J Food Sci 82:484-491, 2017, https://doi.org/10.1111/1750-3841.13584).

Maximum specific growth rate of anammox bacteria revisited

Anammox bacteria have long been considered to be slow-growing bacteria. However, it has recently been reported that they could grow much faster than previously thought when they were cultivated in a membrane bioreactor (MBR) with a step-wise decrease in the solid retention time (SRT). Here, we reevaluated the maximum specific growth rates (μ_max) of three phylogenetically distant anammox bacterial species (i.e. "Ca. Brocadia sinica", "Ca. Jettenia caeni" and "Ca. Scalindua sp.") by directly measuring 16S rRNA gene copy numbers using newly developed quantitative polymerase chain reaction (qPCR) assays. When free-living planktonic "Ca. B. sinica" and "Ca. J. caeni" cells were immobilized in polyvinyl alcohol (PVA) and sodium alginate (SA) gel beads and cultivated in an up-flow column reactor with high substrate loading rates at 37 °C, the μ_max were determined to be 0.33 ± 0.02 d^-1 and 0.18 d^-1 (corresponding doubling time of 2.1 day and 3.9 day) from the exponential increases in 16S rRNA genes copy numbers, respectively. These values were faster than the fastest growth rates reported for these species so far. The cultivation of anammox bacteria in gel beads was achieved less than one month without special cultivation method and selection pressure, and the exponential increase in 16S rRNA gene numbers was directly measured by qPCR with high reproducibility; therefore, the resulting μ_max values were considered accurate. Taken together, the fast growth is, therefore, considered to be an intrinsic kinetic property of anammox bacteria.

Occurrence of clinical genotype Vibrio vulnificus in clam samples in Mangalore, Southwest coast of India

Vibrio vulnificus is an opportunistic human pathogen causing gastroenteritis, wound infection and primary septicemia. V. vulnificus population has been divided into subpopulations based on their phenotype and genotype characteristics. In this study, 38.5% (10/26) of clam (Meretrix meretrix) samples obtained from Mangalore markets were seen to harbor V. vulnificus. Biochemical characterization of V. vulnificus isolates showed the strains to belong to Biotype 1 phenotype. Genotyping of strains using the 16S rRNA and virulence correlated gene (vcg) typing methods identified the isolates to be of 16S rRNA typeB and vcgC type respectively. Analysis of representative 16S rRNA and vcg gene sequences further substantiated that the V. vulnificus associated with clams in the present study to be of clinical origin, implicated as virulent type responsible for causing infection in humans.

Influence of Environmental Factors on Vibrio spp. in Coastal Ecosystems

Various studies have examined the relationships between vibrios and the environmental conditions surrounding them. However, very few reviews have compiled these studies into cohesive points. This may be due to the fact that these studies examine different environmental parameters, use different sampling, detection, and enumeration methodologies, and occur in diverse geographic locations. The current article is one approach to compile these studies into a cohesive work that assesses the importance of environmental determinants on the abundance of vibrios in coastal ecosystems.

Sediment and vegetation as reservoirs of Vibrio vulnificus in the Tampa Bay Estuary and Gulf of Mexico

The opportunistic pathogen Vibrio vulnificus occurs naturally in estuarine habitats and is readily cultured from water and oysters under warm conditions but infrequently at ambient conditions of <15°C. The presence of V. vulnificus in other habitats, such as sediments and aquatic vegetation, has been explored much less frequently. This study investigated the ecology of V. vulnificus in water by culture and quantitative PCR (qPCR) and in sediment, oysters, and aquatic vegetation by culture. V. vulnificus samples were taken from five sites around Tampa Bay, FL. Levels determined by qPCR and culture were significantly correlated (P = 0.0006; r = 0.352); however, V. vulnificus was detected significantly more frequently by qPCR (85% of all samples) compared to culture (43%). Culturable V. vulnificus bacteria were recovered most frequently from oyster samples (70%), followed by vegetation and sediment (∼50%) and water (43%). Water temperature, which ranged from 18.5 to 33.4°C, was positively correlated with V. vulnificus concentrations in all matrices but sediments. Salinity, which ranged from 1 to 35 ppt, was negatively correlated with V. vulnificus levels in water and sediments but not in other matrices. Significant interaction effects between matrix and temperature support the hypothesis that temperature affects V. vulnificus concentrations differently in different matrices and that sediment habitats may serve as seasonal reservoirs for V. vulnificus. V. vulnificus levels in vegetation have not been previously measured and reveal an additional habitat for this autochthonous estuarine bacterium.

Microbes in Beach Sands: Integrating Environment, Ecology and Public Health

Beach sand is a habitat that supports many microbes, including viruses, bacteria, fungi and protozoa (micropsammon). The apparently inhospitable conditions of beach sand environments belie the thriving communities found there. Physical factors, such as water availability and protection from insolation; biological factors, such as competition, predation, and biofilm formation; and nutrient availability all contribute to the characteristics of the micropsammon. Sand microbial communities include autochthonous species/phylotypes indigenous to the environment. Allochthonous microbes, including fecal indicator bacteria (FIB) and waterborne pathogens, are deposited via waves, runoff, air, or animals. The fate of these microbes ranges from death, to transient persistence and/or replication, to establishment of thriving populations (naturalization) and integration in the autochthonous community. Transport of the micropsammon within the habitat occurs both horizontally across the beach, and vertically from the sand surface and ground water table, as well as at various scales including interstitial flow within sand pores, sediment transport for particle-associated microbes, and the large-scale processes of wave action and terrestrial runoff. The concept of beach sand as a microbial habitat and reservoir of FIB and pathogens has begun to influence our thinking about human health effects associated with sand exposure and recreational water use. A variety of pathogens have been reported from beach sands, and recent epidemiology studies have found some evidence of health risks associated with sand exposure. Persistent or replicating populations of FIB and enteric pathogens have consequences for watershed/beach management strategies and regulatory standards for safe beaches. This review summarizes our understanding of the community structure, ecology, fate, transport, and public health implications of microbes in beach sand. It concludes with recommendations for future work in this vastly under-studied area.

Vibrio vulnificus biotype 3 multifunctional autoprocessing RTX toxin is an adenylate cyclase toxin essential for virulence in mice

Vibrio vulnificus is an environmental organism that causes both food-borne and wound infections with high morbidity and mortality in humans. The annual incidence and global distribution of infections associated with this pathogen are increasing with climate change. In the late 1990s, an outbreak of tilapia-associated wound infections in Israel was linked to a previously unrecognized variant of V. vulnificus designated biotype 3. The sudden emergence and clonality of the outbreak suggest that this strain may be a true newly emergent pathogen with novel virulence properties compared to those of other V. vulnificus strains. In a subcutaneous infection model to mimic wound infection, the multifunctional autoprocessing RTX (MARTX) toxin of biotype 3 strains was shown to be an essential virulence factor contributing to highly inflammatory skin wounds with severe damage affecting every tissue layer. We conducted a sequencing-based analysis of the MARTX toxin and found that biotype 3 MARTX toxin has an effector domain structure distinct from that of either biotype 1 or biotype 2. Of the two new domains identified, a domain similar to Pseudomonas aeruginosa ExoY was shown to confer adenylate cyclase activity on the MARTX toxin. This is the first demonstration that the biotype 3 MARTX toxin is essential for virulence and that the ExoY-like MARTX effector domain is a catalytically active adenylate cyclase.

Differential expression of a sodium-phosphate cotransporter among Vibrio vulnificus strains

Vibrio vulnificus is an estuarine bacterium with pathogenic potential. Its three known biotypes differ in host distribution. We have found the nptA gene for a sodium-phosphate cotransporter, which is rare in bacteria, in each biotype. nptA transcript abundance differed significantly among biotypes, leading to the hypothesis that transcript levels differ under environmental conditions associated with estuarine and host environments. nptA transcript abundance was assessed in V. vulnificus biotypes 1 (C and E genotypes), 2 and 3 strains under varied salinity, phosphate concentration, and pH. Differences in transcript abundance separated strains into two groups. Type C and biotype 3 strains formed Group 1, while type E and biotype 2 strains formed Group 2. Group 2 strains had significantly greater nptA RNA transcript abundance than Group 1. Transcript abundance in the two groups also responded differently to pH and salinity, suggesting differential regulation of nptA in response to environmental conditions. Comparison of the deduced amino acid sequences of NptA among strains resulted in strain grouping similar to that based on transcript abundance. Variation in transcript abundance between groups may affect the ability of V. vulnificus strains to colonize hosts and/or to compete as free-living bacteria in various habitats.

Host-nonspecific iron acquisition systems and virulence in the zoonotic serovar of Vibrio vulnificus

The zoonotic serovar of Vibrio vulnificus (known as biotype 2 serovar E) is the etiological agent of human and fish vibriosis. The aim of the present work was to discover the role of the vulnibactin- and hemin-dependent iron acquisition systems in the pathogenicity of this zoonotic serovar under the hypothesis that both are host-nonspecific virulence factors. To this end, we selected three genes for three outer membrane receptors (vuuA, a receptor for ferric vulnibactin, and hupA and hutR, two hemin receptors), obtained single and multiple mutants as well as complemented strains, and tested them in a series of in vitro and in vivo assays, using eels and mice as animal models. The overall results confirm that hupA and vuuA, but not hutR, are host-nonspecific virulence genes and suggest that a third undescribed host-specific plasmid-encoded system could also be used by the zoonotic serovar in fish. hupA and vuuA were expressed in the internal organs of the animals in the first 24 h of infection, suggesting that they may be needed to achieve the population size required to trigger fatal septicemia. vuuA and hupA were sequenced in strains representative of the genetic diversity of this species, and their phylogenies were reconstructed by multilocus sequence analysis of selected housekeeping and virulence genes as a reference. Given the overall results, we suggest that both genes might form part of the core genes essential not only for disease development but also for the survival of this species in its natural reservoir, the aquatic environment.

Molecular characterization and antibiotic susceptibility of Vibrio vulnificus in retail shrimps in Hangzhou, People's Republic of China

Vibrio vulnificus is a gram-negative bacterium that occurs naturally in estuarine and marine water and is associated with wound infections or septicemia related to the consumption of raw shellfish in humans. The molecular characteristics and antibiotic susceptibilities of V. vulnificus strains in shrimps from retail markets in Hangzhou, People's Republic of China, were investigated in this study. Thirty-three samples were positive for V. vulnificus in 78 shrimp samples which were collected from 15 retail markets between July and August 2012; the most-probable-number values ranged from 3 to 1,600 g(-1) in these positive samples, with a median most-probable-number value of 72 g(-1). Twenty-five biotype 1 strains and eight biotype 2 strains were identified by biochemical tests, and all strains could be definitively genotyped. By 16S rRNA genotyping, 21.2% (7 of 33) were classified as genotype A, 63.6% (21 of 33) as genotype B, and 15.2% (5 of 33) as genotype AB, while by virulence-correlated gene (vcg) typing, 21.2% (7 of 33) were characterized as genotype E and 78.8% (26 of 33) were genotype C. More than 50% of those isolates were identified as the potentially virulent type vcg type C-16S rRNA B (CB). The antibiotic susceptibilities of the V. vulnificus strains to 21 antimicrobial agents were tested as well. Some strains showed resistance or intermediate resistance to cefepime (3.03%), tetracycline (6.06%), aztreonam (24.24%), streptomycin (45.45%), gentamicin (93.94%), tobramycin (100%), and cefazolin (100%). Multiple-locus variable-number tandem repeat-based fingerprinting analysis (MLVA) was successfully applied to these 33 isolates and yielded 30 patterns that clustered into two MLVA groups; with a calculated Simpson's index of diversity of 0.994, this revealed that MLVA had great discriminating power for V. vulnificus. To minimize the potential risk of V. vulnificus infections due to the consumption of raw shrimp, it is necessary to monitor the hygiene status of seafood.

Fitness factors in vibrios: a mini-review

Vibrios are Gram-negative curved bacilli that occur naturally in marine, estuarine, and freshwater systems. Some species include human and animal pathogens, and some vibrios are necessary for natural systems, including the carbon cycle and osmoregulation. Countless in vivo and in vitro studies have examined the interactions between vibrios and their environment, including molecules, cells, whole animals, and abiotic substrates. Many studies have characterized virulence factors, attachment factors, regulatory factors, and antimicrobial resistance factors, and most of these factors impact the organism's fitness regardless of its external environment. This review aims to identify common attributes among factors that increase fitness in various environments, regardless of whether the environment is an oyster, a rabbit, a flask of immortalized mammalian cells, or a planktonic chitin particle. This review aims to summarize findings published thus far to encapsulate some of the basic similarities among the many vibrio fitness factors and how they frame our understanding of vibrio ecology. Factors representing these similarities include hemolysins, capsular polysaccharides, flagella, proteases, attachment factors, type III secretion systems, chitin binding proteins, iron acquisition systems, and colonization factors.

Detection and differentiation of Vibrio vulnificus and V. sinaloensis in water and oysters of a Gulf of Mexico estuary

Vibrio vulnificus is a potentially lethal human pathogen that occurs naturally in estuarine waters and shellfish. Vibrio vulnificus was quantified in water and oysters from Florida's Gulf Coast by plating on mCPC agar, enrichment and plating, and quantitative PCR (qPCR). Vibrio vulnificus was detected in 19%, 29%, and 97% of samples respectively by direct plating, qPCR, and enrichment. Only 8% of typical colonies from direct plating were confirmed by PCR for vvhA; others yielded no or atypically sized amplicons. Sequencing of the 16S rDNA of 16 vvhA-negative isolates with colony morphology typical of V. vulnificus identified 75% as V. sinaloensis. In vitro growth curves showed that V. sinaloensis grew more rapidly than V. vulnificus in seawater at temperatures ≤ 30°C. In contrast, the growth rate of V. vulnificus in alkaline peptone water was greater than that of V. sinaloensis, suggesting that these species can outcompete one another under conditions that are relevant to environmental parameters or regulatory monitoring regimes respectively. The virulence potential and ecology of V. sinaloensis are poorly understood; however, its phenotypic resemblance to V. vulnificus and the possibility that it could outcompete the pathogen in warm, estuarine waters argue for the need for a better understanding of this newly described Vibrio species.

Prevalence and population structure of Vibrio vulnificus on fishes from the northern Gulf of Mexico

The prevalence of Vibrio vulnificus on the external surfaces of fish from the northern Gulf of Mexico was determined in this study. A collection of 242 fish comprising 28 species was analyzed during the course of 12 sampling trips over a 16-month period. The prevalence of V. vulnificus was 37% but increased up to 69% in summer. A positive correlation was found between the percentages of V. vulnificus-positive fish and water temperatures, while salinity and V. vulnificus-positive fish prevalence were inversely correlated. A general lineal model (percent V. vulnificus-positive fish = 0.5930 - 0.02818 × salinity + 0.01406 × water temperature) was applied to best fit the data. Analysis of the population structure was carried out using 244 isolates recovered from fish. Ascription to 16S rRNA gene types indicated that 157 isolates were type A (62%), 72 (29%) were type B, and 22 (9%) were type AB. The percentage of type B isolates, considered to have greater virulence potential, was higher than that previously reported in oyster samples from the northern Gulf of Mexico. Amplified fragment length polymorphism (AFLP) was used to resolve the genetic diversity within the species. One hundred twenty-one unique AFLP profiles were found among all analyzed isolates, resulting in a calculated Simpson's index of diversity of 0.991. AFLP profiles were not grouped on the basis of collection date, fish species, temperature, or salinity, but isolates were clustered into two main groups that correlated precisely with 16S rRNA gene type. The population of V. vulnificus associated with fishes from the northern Gulf of Mexico is heterogeneous and includes strains of great virulence potential.

Ecology of Vibrio parahaemolyticus and Vibrio vulnificus in the coastal and estuarine waters of Louisiana, Maryland, Mississippi, and Washington (United States)

Vibrio parahaemolyticus and Vibrio vulnificus, which are native to estuaries globally, are agents of seafood-borne or wound infections, both potentially fatal. Like all vibrios autochthonous to coastal regions, their abundance varies with changes in environmental parameters. Sea surface temperature (SST), sea surface height (SSH), and chlorophyll have been shown to be predictors of zooplankton and thus factors linked to vibrio populations. The contribution of salinity, conductivity, turbidity, and dissolved organic carbon to the incidence and distribution of Vibrio spp. has also been reported. Here, a multicoastal, 21-month study was conducted to determine relationships between environmental parameters and V. parahaemolyticus and V. vulnificus populations in water, oysters, and sediment in three coastal areas of the United States. Because ecologically unique sites were included in the study, it was possible to analyze individual parameters over wide ranges. Molecular methods were used to detect genes for thermolabile hemolysin (tlh), thermostable direct hemolysin (tdh), and tdh-related hemolysin (trh) as indicators of V. parahaemolyticus and the hemolysin gene vvhA for V. vulnificus. SST and suspended particulate matter were found to be strong predictors of total and potentially pathogenic V. parahaemolyticus and V. vulnificus. Other predictors included chlorophyll a, salinity, and dissolved organic carbon. For the ecologically unique sites included in the study, SST was confirmed as an effective predictor of annual variation in vibrio abundance, with other parameters explaining a portion of the variation not attributable to SST.

Development and validation of a predictive model for the growth of Vibrio vulnificus in postharvest shellstock oysters

Postharvest growth of Vibrio vulnificus in oysters can increase risk of human infection. Unfortunately, limited information is available regarding V. vulnificus growth and survival patterns over a wide range of storage temperatures in oysters harvested from different estuaries and in different oyster species. In this study, we developed a predictive model for V. vulnificus growth in Eastern oysters (Crassostrea virginica) harvested from Chesapeake Bay, MD, over a temperature range of 5 to 30°C and then validated the model against V. vulnificus growth rates (GRs) in Eastern and Asian oysters (Crassostrea ariakensis) harvested from Mobile Bay, AL, and Chesapeake Bay, VA, respectively. In the model development studies, V. vulnificus was slowly inactivated at 5 and 10°C with average GRs of -0.0045 and -0.0043 log most probable number (MPN)/h, respectively. Estimated average growth rates at 15, 20, 25, and 30°C were 0.022, 0.042, 0.087, and 0.093 log MPN/h, respectively. With respect to Eastern oysters, bias (B(f)) and accuracy (A(f)) factors for model-dependent and -independent data were 1.02 and 1.25 and 1.67 and 1.98, respectively. For Asian oysters, B(f) and A(f) were 0.29 and 3.40. Residual variations in growth rate about the fitted model were not explained by season, region, water temperature, or salinity at harvest. Growth rate estimates for Chesapeake Bay and Mobile Bay oysters stored at 25 and 30°C showed relatively high variability and were lower than Food and Agricultural Organization (FAO)/WHO V. vulnificus quantitative risk assessment model predictions. The model provides an improved tool for designing and implementing food safety plans that minimize the risk associated with V. vulnificus in oysters.