Distribution of virulence markers among Vibrio vulnificus isolates of clinical and environmental origin and regional characteristics in Japan

In vivo examination of pathogenicity and virulence in environmentally isolated Vibrio vulnificus

Human exposure to Vibrio vulnificus, a gram-negative, halophilic environmental pathogen, is increasing. Despite this, the mechanisms of its pathogenicity and virulence remain largely unknown. Each year, hundreds of infections related to V. vulnificus occur, leading to hospitalization in 92% of cases and a mortality rate of 35%. The infection is severe, typically contracted through the consumption of contaminated food or exposure of an open wound to contaminated water. This can result in necrotizing fasciitis and the need for amputation of the infected tissue. Although several genes (rtxA1, vvpE, and vvhA) have been implicated in the pathogenicity of this organism, a defined mechanism has not been discovered. In this study, we examine environmentally isolated V. vulnificus strains using a zebrafish model (Danio rerio) to investigate their virulence capabilities. We found significant variation in virulence between individual strains. The commonly used marker gene of disease-causing strains, vcgC, did not accurately predict the more virulent strains. Notably, the least virulent strain in the study, V. vulnificus Sept WR1-BW6, which tested positive for vcgC, vvhA, and rtxA1, did not cause severe disease in the fish and was the only strain that did not result in any mortality. Our study demonstrates that virulence varies greatly among different environmental strains and cannot be accurately predicted based solely on genotype.

Virulent properties and genomic diversity of Vibrio vulnificus isolated from environment, human, diseased fish

The incidence of Vibrio vulnificus infections, with high mortality rates in humans and aquatic animals, has escalated, highlighting a significant public health challenge. Currently, reliable markers to identify strains with high virulence potential are lacking, and the understanding of evolutionary drivers behind the emergence of pathogenic strains is limited. In this study, we analyzed the distribution of virulent genotypes and phenotypes to discern the infectious potential of V. vulnificus strains isolated from three distinct sources. Most isolates, traditionally classified as biotype 1, possessed the virulence-correlated gene-C type. Environmental isolates predominantly exhibited YJ-like alleles, while clinical and diseased fish isolates were significantly associated with the nanA gene and pathogenicity region XII. Hemolytic activity was primarily observed in the culture supernatants of clinical and diseased fish isolates. Genetic relationships, as determined by multiple-locus variable-number tandem repeat analysis, suggested that strains originating from the same source tended to cluster together. However, multilocus sequence typing revealed considerable genetic diversity across clusters and sources. A phylogenetic analysis using single nucleotide polymorphisms of diseased fish strains alongside publicly available genomes demonstrated a high degree of evolutionary relatedness within and across different isolation sources. Notably, our findings reveal no direct correlation between phylogenetic patterns, isolation sources, and virulence capabilities. This underscores the necessity for proactive risk management strategies to address pathogenic V. vulnificus strains emerging from environmental reservoirs.IMPORTANCEAs the global incidence of Vibrio vulnificus infections rises, impacting human health and marine aquacultures, understanding the pathogenicity of environmental strains remains critical yet underexplored. This study addresses this gap by evaluating the virulence potential and genetic relatedness of V. vulnificus strains, focusing on environmental origins. We conduct an extensive genotypic analysis and phenotypic assessment, including virulence testing in a wax moth model. Our findings aim to uncover genetic and evolutionary factors that drive pathogenic strain emergence in the environment. This research advances our ability to identify reliable virulence markers and understand the distribution of pathogenic strains, offering significant insights for public health and environmental risk management.

Vibrio vulnificus and Vibrio parahaemolyticus in Oysters under Low Tidal Range Conditions: Is Seawater Analysis Useful for Risk Assessment?

Human-pathogenic Vibrio bacteria are acquired by oysters through filtering seawater, however, the relationships between levels of these bacteria in measured in oysters and overlying waters are inconsistent across regions. The reasons for these discrepancies are unclear hindering our ability to assess if -or when- seawater samples can be used as a proxy for oysters to assess risk. We investigated whether concentrations of total and human pathogenic Vibrio vulnificus (vvhA and pilF genes) and Vibrio parahaemolyticus (tlh, tdh and trh genes) measured in seawater reflect concentrations of these bacteria in oysters (Crassostrea virginica) cultured within the US lower Chesapeake Bay region. We measured Vibrio spp. concentrations using an MPN-qPCR approach and analyzed the data using structural equation modeling (SEM). We found seawater concentrations of these bacteria to predictably respond to temperature and salinity over chlorophyll a, pheophytin or turbidity. We also inferred from the SEM results that Vibrio concentrations in seawater strongly predict their respective concentrations in oysters. We hypothesize that such seawater-oyster coupling can be observed in regions of low tidal range. Due to the ease of sampling and processing of seawater samples compared to oyster samples, we suggest that under low tidal range conditions, seawater samples can foster increased spatial and temporal coverage and complement data associated with oyster samples.

Investigating the Relationship between Nitrate, Total Dissolved Nitrogen, and Phosphate with Abundance of Pathogenic Vibrios and Harmful Algal Blooms in Rehoboth Bay, Delaware

Vibrio-associated illnesses have been expanding globally over the past several decades (A. Newton, M.

Prevalence, Genetic Diversity, Antimicrobial Resistance, and Toxigenic Profile of Vibrio vulnificus Isolated from Aquatic Environments in Taiwan

Vibrio vulnificus is a gram-negative, opportunistic human pathogen associated with life-threatening wound infections and is commonly found in warm coastal marine water environments, globally. In this study, two fishing harbors and three tributaries of the river basin were analyzed for the prevalence of V. vulnificus in the water bodies and shellfish that are under the pressure of external pollutions. The average detection rate of V. vulnificus in the river basins and fishing harbors was 8.3% and 4.2%, respectively, in all seasons. A total of nine strains of V. vulnificus were isolated in pure cultures from 160 samples belonging to river basins and fishing harbors to analyze the antibiotic susceptibility, virulence gene profiles, and enterobacterial repetitive intergenic consensus PCR (ERIC-PCR) fingerprinting. All isolates were susceptible to 10 tested antibiotics. The genotypic characterization revealed that 11.1% (n = 1/9) strain was nonvirulent, whereas 88.9% (n = 8/9) isolates were virulent strains, which possessed the four most prevalent toxin genes such as vcgC (88.9%), 16S B (88.9%), vvhA (88.9%), and manIIA (88.9%), followed by nanA (77.8%), CPS1 (66.7), and PRXII (44.4%). Additionally, ERIC-PCR fingerprinting grouped these nine isolates into two main clusters, among which the river basin isolates showed genetically diverse profiles, suggesting multiple sources of V. vulnificus. Ultimately, this study highlighted the virulent strains of V. vulnificus in the coastal aquatic environments of Taiwan, harboring a potential risk of infection to human health through water-borne transmission.

Exploring the Pathogenic Potential of Vibrio vulnificus Isolated from Seafood Harvested along the Mangaluru Coast, India

It has been observed that not all strains of Vibrio vulnificus are virulent. Determining the virulence of strains that are frequently present in seafood is of significance for ensuring seafood safety. This study is an attempt to predict the virulence of seafood-borne V. vulnificus isolated along the Mangaluru Coast, India. The isolates tested possessed a vcgC gene sequence with high similarity to that in the clinical strain. Transcriptional analysis of core virulence genes in seafood isolate E4010 showed the phenomenon of contact-mediated expression of rtxA1 which correlated well with the actin disintegration and cytotoxicity. These results suggest that the seafood isolates tested in this study possess a functional RtxA1 which could help in initiating the infection. However, other putative virulence genes such as vvpE encoding an extracellular protease, vvhA encoding hemolysin, flp encoding tad pilin and ompU encoding fibronectin-binding protein were also constitutively expressed. Virulence-associated attributes such as cytotoxicity and adherence matched the response of the clinical strain (p > 0.05). On the other hand, the environmental strains showed higher serum sensitivity compared with the clinical strain. These findings show that the part of virulence attributes required for the disease process might be intact in these isolates.

Different abundance and correlational patterns exist between total and presumed pathogenic Vibrio vulnificus and V. parahaemolyticus in shellfish and waters along the North Carolina coast

Monitoring of Vibrio vulnificus and V. parahaemolyticus abundance is pertinent due to the ability of these species to cause disease in humans through aquatic vectors. Previously, we performed a multiyear investigation tracking Vibrio spp. levels in five sites along the southeastern North Carolina coast. From February 2013 to October 2015, total V. vulnificus and V. parahaemolyticus abundance was measured in water, oysters and clams. In the current study, pathogenic subpopulations were identified in these isolates using molecular markers, revealing that 5.3% of V. vulnificus isolates possessed the virulence-correlated gene (vcgC), and 1.9% of V. parahaemolyticus isolates harbored one or both of the virulence-associated hemolysin genes (tdh and trh). Total V. parahaemolyticus abundance was not sufficient to predict the abundance of pathogenic subpopulations. Specifically, pathogenic V. parahaemolyticus isolates were more often isolated in cooler waters and were sometimes isolated when no other V. parahaemolyticus strains were detectable. Vibrio vulnificus clinical (C-) genotypes correlated with total V. vulnificus; however, salinity, water depth and total suspended solids influenced C- and E-genotypes differently. Lastly, we documented individual oysters harboring significantly higher V. vulnificus levels for which there was no ecological explanation, a phenomenon that deserves closer attention due to the potentially elevated health hazard associated with these 'hot' shellfish.

Virulence Profiles of Vibrio vulnificus in German Coastal Waters, a Comparison of North Sea and Baltic Sea Isolates

Vibrio vulnificus is a halophilic bacterium of coastal environments known for sporadically causing severe foodborne or wound infections. Global warming is expected to lead to a rising occurrence of V. vulnificus and an increasing incidence of human infections in Northern Europe. So far, infections in Germany were exclusively documented for the Baltic Sea coast, while no cases from the North Sea region have been reported. Regional variations in the prevalence of infections may be influenced by differences in the pathogenicity of V. vulnificus populations in both areas. This study aimed to compare the distribution of virulence-associated traits and genotypes among 101 V. vulnificus isolates from the Baltic Sea and North Sea in order to assess their pathogenicity potential. Furthermore, genetic relationships were examined by multilocus sequence typing (MLST). A high diversity of MLST sequences (74 sequence types) and differences regarding the presence of six potential pathogenicity markers were observed in the V. vulnificus populations of both areas. Strains with genotypes and markers associated with pathogenicity are not restricted to a particular geographic region. This indicates that lack of reported cases in the North Sea region is not caused by the absence of potentially pathogenic strains.

Genotypic Diversity and Population Structure of Vibrio vulnificus Strains Isolated in Taiwan and Korea as Determined by Multilocus Sequence Typing

The genetic diversity and population structure of Vibrio vulnificus isolates from Korea and Taiwan were investigated using PCR-based assays targeting putative virulence-related genes and multilocus sequence typing (MLST). BOX-PCR genomic fingerprinting identified 52 unique genotypes in 84 environmental and clinical V. vulnificus isolates. The majority (> 50%) of strains had pathogenic genotypes for all loci tested; moreover, many environmental strains had pathogenic genotypes. Although significant (p < 0.05) inter-relationships among the genotypes were observed, the association between genotype and strain source (environmental or clinical) was not significant, indicating that genotypic characteristics alone are not sufficient to predict the isolation source or the virulence of a given V. vulnificus strain and vice versa. MLST revealed 23–35 allelic types per locus analyzed, resulting in a total of 44 unique sequence types (STs). Two major monophyletic groups (lineages A and B) corresponding to the two known lineages of V. vulnificus were observed; lineage A had six STs that were exclusively environmental, whereas lineage B had STs from both environmental and clinical sources. Pathogenic and nonpathogenic genotypes predominated in MLST lineages B and A, respectively. In addition, V. vulnificus was shown to be in linkage disequilibrium (p < 0.05), although two different recombination tests (PHI and Sawyer’s tests) detected significant evidence of recombination. Tajima’s D test also indicated that V. vulnificus might be comprised of recently sub-divided lineages. These results suggested that the two lineages revealed by MLST correspond to two distinct ecotypes of V. vulnificus.

Detection and Antimicrobial Resistance of Vibrio Isolates in Aquaculture Environments: Implications for Public Health

The aim of this study was to evaluate the presence of Vibrio isolates recovered from four different fish pond facilities in Benin City, Nigeria, determine their antibiogram profiles, and evaluate the public health implications of these findings. Fish pond water samples were collected from four sampling sites between March and September 2014. A total of 56 samples were collected and screened for the isolation of Vibrio species using standard culture-based methods. Polymerase chain reaction (PCR) was used to confirm the identities of the Vibrio species using the genus-specific and species-specific primers. Vibrio species were detected at all the study sites at a concentration on the order of 10(3) and 10(6) CFU/100 ml. A total of 550 presumptive Vibrio isolates were subjected to PCR confirmation. Of these isolates, 334 isolates tested positive, giving an overall Vibrio prevalence rate of 60.7%. The speciation of the 334 Vibrio isolates from fish ponds yielded 32.63% Vibrio fluvialis, 20.65% Vibrio parahaemolyticus, 18.26% Vibrio vulnificus, and 28.44% other Vibrio species. In all, 167 confirmed Vibrio isolates were selected from a pool of 334 confirmed Vibrio isolates for antibiogram profiling. The susceptibility profiles of 20 antimicrobial agents on the isolates revealed a high level of resistance for AMP(R), ERY(R), NAL(R), SUL(R), TMP(R), SXT(R), TET(R), OTC(R), and CHL(R). The percentage of multiple drug resistance Vibrio isolates was 67.6%. The multiple antibiotic resistance index mean value of 0.365 for the Vibrio isolates found in this study indicated that the Vibrio isolates were exposed to high-risk sources of contamination when antibiotics were frequently used. The resistant Vibrio strains could be transmitted through the food chain to humans and therefore constitutes a risk to public health.

Hydrogen peroxide causes Vibrio vulnificus bacteriolysis accelerated by sulfonyl fluoride compounds

Induction of bacteriolysis of Vibrio vulnificus cells by 10 mM hydrogen peroxide (H(2)O(2)) was analyzed. All Vibrio species examined, except for Vibrio hollisae, were lysed by 10 mM H(2)O(2). Bacteriophage induction was not the cause of H(2)O(2)-induced bacteriolysis. Autolysis is also known to cause bacteriolysis. VvpS protein is a serine protease of V. vulnificus essential for autolysis. vvpS mutant underwent H(2)O(2)-induced bacteriolysis in the same manner as the wild type. Protease inhibitors including serine protease inhibitors did not inhibit H(2)O(2)-induced bacteriolysis, which means that bacteriolysis is not due to autolysis. Unexpectedly, H(2)O(2)-induced bacteriolysis was accelerated by adding 4-(2-aminoethyl) benzenesulfonyl fluoride hydrochloride (AEBSF) and phenylmethylsulfonyl fluoride which are serine protease inhibitors. The hydroxyl radical was generated by H(2)O(2)-AEBSF interaction. It was considered that H(2)O(2)-induced bacteriolysis was caused by the hydroxyl radical which was generated by Fenton reaction, and possibly mediated by AEBSF. Deferoxamine, an agent chelating ferric ion and Fenton reaction inhibitor, suppressed both H(2)O(2)-induced bacteriolysis and its acceleration by AEBSF. This suggests that both phenomena were Fenton reaction dependent, and hydroxyl radical generated by Fenton reaction caused bacteriolysis of V. vulnificus though the reason for high susceptibility of Vibrio species to hydroxyl radical is not known.

In vivo efficacy of the combination of ciprofloxacin and cefotaxime against Vibrio vulnificus sepsis

Objectives

The invivo efficacy of a cefotaxime-ciprofloxacin combination against Vibrio vulnificus and the effects on rtxA1 expression of commonly used antibiotics are unknown.

Methods

In vitro time-kill studies were performed to evaluate synergism. Female BALB/c mice were injected subcutaneously with 1×10⁷ or 1×10⁸ cfu of V. vulnificus. Antibiotic therapy was initiated at 2 h after inoculation in the following four therapy groups: cefotaxime; ciprofloxacin; cefotaxime-plus-ciprofloxacin; and cefotaxime-plus-minocycline. The cytotoxicity of V. vulnificus for HeLa cells was measured using the lactate dehydrogenase assay; rtxA1 transcription was measured in a transcriptional reporter strain using a β-galactosidase assay.

Results

In vitro time-kill assays exhibited synergism between cefotaxime and ciprofloxacin. In the animal experiments, the 96-h survival rate for the cefotaxime-plus-ciprofloxacin group (85%; 17/20) was significantly higher than that of the cefotaxime-plus-minocycline (35%; 7/20) and cefotaxime alone (0%; 0/20) groups (P<0.05 for both). Bacterial counts in the liver and spleen were significantly lower in the cefotaxime-plus-ciprofloxacin group 24 and 48 h after treatment, relative to the other groups. At sub-inhibitory concentrations, ciprofloxacin inhibited more effectively rtxA1 transcription and mammalian cell cytotoxicity than either minocycline or cefotaxime (P<0.05 for both).

Conclusions

Ciprofloxacin is more effective at reducing rtxA1 transcription and subsequent cytotoxicity than either minocycline or cefotaxime, and the combination of ciprofloxacin and cefotaxime was more effective in clearing V. vulnificus invivo than previously used regimens. These data suggest that the combination of ciprofloxacin and cefotaxime is an effective option for the treatment of V. vulnificus sepsis in humans.

Detection of Vibrio parahaemolyticus, Vibrio vulnificus and Vibrio cholerae with respect to seasonal fluctuations in temperature and plankton abundance

Over a 1-year period, bi-monthly estuarine surface water and plankton samples (63-200 and > 200 μm fractions) were assayed by polymerase chain reaction for the prevalence of total Vibrio parahaemolyticus, V. vulnificus and V. cholerae and select genes associated with clinical strains found in each species. Neither temperature nor plankton abundance was a significant correlate of total V. parahaemolyticus; however, the prevalence of genes commonly associated with clinical strains (trh, tdh, ORF8) increased with temperature and copepod abundance (P < 0.05). The prevalence of total V. vulnificus and the siderophore-related viuB gene also increased with temperature and copepod and decapod abundance (P < 0.001). Temperature and copepod abundance also covaried with the prevalence of V. cholerae (P < 0.05), but there was no significant relationship with ctxA or other genes commonly found in clinical strains. Results show that genes commonly associated with clinical Vibrio strains were more frequently detected in association with chitinous plankton. We conclude that V. parahaemolyticus, V. vulnificus, V. cholerae and subpopulations that harbour genes common to clinical strains respond distinctly to seasonal changes in temperature as well as shifts in the taxonomic composition of discrete plankton fractions.