Endophthalmitis caused by Vibrio alginolyticus

Genomic analysis and biological characterization of a novel Schitoviridae phage infecting Vibrio alginolyticus

Vibrio alginolyticus is a Gram-negative bacterium commonly associated with mackerel poisoning. A bacteriophage that specifically targets and lyses this bacterium could be employed as a biocontrol agent for treating the bacterial infection or improving the shelf-life of mackerel products. However, only a few well-characterized V. alginolyticus phages have been reported in the literature. In this study, a novel lytic phage, named ΦImVa-1, specifically infecting V. alginolyticus strain ATCC 17749, was isolated from Indian mackerel. The phage has a short latent period of 15 min and a burst size of approximately 66 particles per infected bacterium. ΦImVa-1 remained stable for 2 h at a wide temperature (27-75 °C) and within a pH range of 5 to 10. Transmission electron microscopy revealed that ΦImVa-1 has an icosahedral head of approximately 60 nm in diameter with a short tail, resembling those in the Schitoviridae family. High throughput sequencing and bioinformatics analysis elucidated that ΦImVa-1 has a linear dsDNA genome of 77,479 base pairs (bp), with a G + C content of ~ 38.72% and 110 predicted gene coding regions (106 open reading frames and four tRNAs). The genome contains an extremely large virion-associated RNA polymerase gene and two smaller non-virion-associated RNA polymerase genes, which are hallmarks of schitoviruses. No antibiotic genes were found in the ΦImVa-1 genome. This is the first paper describing the biological properties, morphology, and the complete genome of a V. alginolyticus-infecting schitovirus. When raw mackerel fish flesh slices were treated with ΦImVa-1, the pathogen loads reduced significantly, demonstrating the potential of the phage as a biocontrol agent for V. alginolyticus strain ATCC 17749 in the food. KEY POINTS: • A novel schitovirus infecting Vibrio alginolyticus ATCC 17749 was isolated from Indian mackerel. • The complete genome of the phage was determined, analyzed, and compared with other phages. • The phage is heat stable making it a potential biocontrol agent in extreme environments.

GcvB Regulon Revealed by Transcriptomic and Proteomic Analysis in Vibrio alginolyticus

Vibrio alginolyticus is a widely distributed marine bacterium that is a threat to the aquaculture industry as well as human health. Evidence has revealed critical roles for small RNAs (sRNAs) in bacterial physiology and cellular processes by modulating gene expression post-transcriptionally. GcvB is one of the most conserved sRNAs that is regarded as the master regulator of amino acid uptake and metabolism in a wide range of Gram-negative bacteria. However, little information about GcvB-mediated regulation in V. alginolyticus is available. Here we first characterized GcvB in V. alginolyticus ZJ-T and determined its regulon by integrated transcriptome and quantitative proteome analysis. Transcriptome analysis revealed 40 genes differentially expressed (DEGs) between wild-type ZJ-T and gcvB mutant ZJ-T-ΔgcvB, while proteome analysis identified 50 differentially expressed proteins (DEPs) between them, but only 4 of them displayed transcriptional differences, indicating that most DEPs are the result of post-transcriptional regulation of gcvB. Among the differently expressed proteins, 21 are supposed to be involved in amino acid biosynthesis and transport, and 11 are associated with type three secretion system (T3SS), suggesting that GcvB may play a role in the virulence besides amino acid metabolism. RNA-EMSA showed that Hfq binds to GcvB, which promotes its stability.

Characteristic and Otopathogenic Analysis of a Vibrio alginolyticus Strain Responsible for Chronic Otitis Externa in China

Vibrio alginolyticus, a Gram-negative rod bacterium found in marine environments, is known to cause opportunistic infections in humans, including ear infections, which can be difficult to diagnose. We investigated the microbiological and otopathogenic characteristics of a V. alginolyticus strain isolated from an ear exudate specimen obtained from a patient with chronic otitis externa to provide a basis for the future diagnosis of V. alginolyticus-associated infections. The identification of V. alginolyticus was accomplished using a combination of matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF MS), classical biochemical identification methods, and the use of Vibrio-selective media and advanced molecular identification methodologies. Antimicrobial susceptibility testing revealed that the strain was resistant to ampicillin and sensitive to β-lactam, aminoglycosides, fluoroquinolones, and sulfonamide antibiotics. The potential otopathogenic effects of V. alginolyticus were determined through the performance of cell viability, cell apoptosis, and cell death assays in tympanic membrane (TM) keratinocytes and HEI-OC1 cells treated with V. alginolyticus-conditioned medium using cell-counting kit (CCK)-8 assay, a wound-healing migration assay, Annexin V/propidium iodide (PI) flow cytometric analysis, and terminal deoxynucleotidyl transferase deoxyuridine triphosphate (dUTP) nick-end labeling (TUNEL staining). The results indicated that the identified V. alginolyticus strain exerts cytotoxic effects on keratinocytes and HEI-OC1 cells by inhibiting cell proliferation and migration and inducing apoptosis and cell death. To evaluate the ototoxicity of V. alginolyticus, the cell density and morphological integrity of hair cells (HCs) and spiral ganglion neurons (SGNs) were analyzed after exposing cochlear organotypic explants to the bacterial supernatant, which revealed the pre-dominant susceptibility and vulnerability of HCs and SGNs in the basal cochlear region to the ototoxic insults exerted by V. alginolyticus. Our investigation highlights the challenges associated with the identification and characteristic analysis of the Vibrio strain isolated in this case and ultimately aims to increase the understanding and awareness of clinicians and microbiologists for the improved diagnosis of V. alginolyticus-associated ear infections and the recognition of its potential otopathogenic and ototoxic effects.

CsrA Regulates Swarming Motility and Carbohydrate and Amino Acid Metabolism in Vibrio alginolyticus

Vibrio alginolyticus, like other vibrio species, is a widely distributed marine bacterium that is able to outcompete other species in variable niches where diverse organic matters are supplied. However, it remains unclear how these cells sense and adjust metabolic flux in response to the changing environment. CsrA is a conserved RNA-binding protein that modulates critical cellular processes such as growth ability, central metabolism, virulence, and the stress response in gamma-proteobacteria. Here, we first characterize the csrA homolog in V. alginolyticus. The results show that CsrA activates swarming but not swimming motility, possibly by enhancing the expression of lateral flagellar associated genes. It is also revealed that CsrA modulates the carbon and nitrogen metabolism of V. alginolyticus, as evidenced by a change in the growth kinetics of various carbon and nitrogen sources when CsrA is altered. Quantitative RT-PCR shows that the transcripts of the genes encoding key enzymes involved in the TCA cycle and amino acid metabolism change significantly, which is probably due to the variation in mRNA stability given by CsrA binding. This may suggest that CsrA plays an important role in sensing and responding to environmental changes.

Antibiotic resistance and determination of resistant genes among cockle (Anadara granosa) isolates of Vibrio alginolyticus

A total of 24 strains of Vibrio alginolyticus were isolated from cockles (Anadara granosa) and identified for VibA and gyrB genes. All V. alginolyticus isolates were then tested against nine different antibiotics. In this study, the highest percentage of antibiotic resistance was obtained against penicillin (37.50%), followed by ampicillin, vancomycin (12.50%) and erythromycin (8.33%). All of V. alginolyticus isolates were susceptible against streptomycin, kanamycin, tetracycline, chloramphenicol and sulfamethoxazole. Polymerase chain reaction (PCR) assay has confirmed the presence of four antibiotic resistance genes of penicillin (pbp2a), ampicillin (blaOXA), erythromycin (ermB) and vancomycin (vanB). Out of 24 V. alginolyticus isolates, 2 isolates possessed the tdh-related hemolysin (trh) (strains VA15 and VA16) and none for the thermostable direct hemolysin (tdh) gene. Both strains of the tdh-related hemolysin (trh) were susceptible to all antibiotics tested. The multiple antibiotic resistance (MAR) index ranging between 0.2 and 0.3 with 5 antibiograms (A1-A5) was observed. Combination of enterobacterial repetitive intergenic consensus-polymerase chain reaction (ERIC-PCR) and antibiotic resistance indicated 18 genome types which showed genetic heterogeneity of those V. alginolyticus isolates. The results demonstrated the presence of V. alginolyticus strain found in cockles can be a potential risk to consumers and can contribute to the deterioration of human health in the study area. Thus, it is essential for local authority to provide the preventive measures in ensuring the cockles are safe for consumption.

Assessment of seawater bacterial infection in rabbit tibia by Illumina MiSeq sequencing and bacterial culture

Objectives

We aimed to explore the bacterial community composition following ocean bacterial infection using an animal model.

Methods

This animal-based experiment was conducted from September 2019 to November 2019. Eighteen seawater filter membranes were collected from Changle City, Fujiian Province, China, on September 8, 2019. Ten filter membranes were used for implantation. Eight filter membranes that were used in the bacterial culture for the exploration of seawater bacteria were assigned to the seawater group (SG). Fourteen healthy adult New Zealand rabbits were randomly divided into the experimental group (EG) and control group (CG). Seawater filter membranes and asepsis membranes were implanted into the tibia in the EG and CG, respectively. One week after surgery, tibial bone pathology tissues were collected and assessed using light microscopy and scanning electron microscopy (SEM). Medullary cavity tissues were collected for the performance of Illumina MiSeq sequencing and bacterial culture. The differences between EG and CG were assessed by pathological observation under light microscopy and SEM, high-throughput bacterial sequencing, and bacterial culture.

Results

Compared with the CG, the infection rate was 100%, and the mortality value was 20% after the implantation of the filter membranes in the EG. Both light microscopy and SEM showed that a large number of bacteria were distributed in the bone marrow cavity after ocean bacterial infection. No bacterial growth was found in the CG. Illumina MiSeq sequencing found that Firmicutes, Proteobacteria, Thermotogae, Fusobacteria, Bacteroidetes, and Actinobacteria were the dominant bacteria at the phylum level and Clostridium_sensu_stricto_7, Haloimpatiens, Clostridium_sensu_stricto_15, Clostridiaceae_1, Clostridium_sensu_stricto_18, and Oceanotoga were the dominant bacteria in genus level among the EG. In the bacterial culture of the medullary cavity tissues, Klebsiella pneumoniae, Shewanella algae, Staphylococcus aureus, Escherichia coli, Enterobacter cloacae, and Vibrio vulnificus were the predominant infective species. Moreover, compared with the SG, the EG showed a higher detection rate of E. coli and S. aureus (P = 0.008 and P = 0.001, respectively). The detection rates of V. alginolyticus, V. parahaemolyticus, and V. fluvialis were higher in the SG than the EG (P = 0.007, P = 0.03, and P = 0.03, respectively).

Conclusions

Our model, which was comprehensively evaluated using four techniques: histopathology and SEM observation, gene detection, and bacteria culture, provides a scientific basis for the clinical diagnosis and treatment of patients in such settings.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13018-021-02553-9.

Identification of Vibrio alginolyticus virulent strain-specific DNA regions by suppression subtractive hybridization and PCR

AIMS

Vibrio alginolyticus was frequently isolated from diseased farmed fish in the coaster waters of Hainan Island over the past two decades. In this study, we attempted to identify candidates of virulent strain-specific DNA regions for this pathogen.

METHODS AND RESULTS

Suppression subtractive hybridization (SSH) and PCR were successively performed between the typical virulent strain and avirulent strain of V. alginolyticus, in which they shared 99·54% homology of 16S rDNAs. Out of 2873 subtracted clones, nine clones were finally indicated to harbour virulent strain-specific DNA fragments. The receivable functions of the major fragments in the nine clones were believed to encode methyl-accepting chemotaxis protein (n = 1), type VI secretion system-associated FHA domain protein TagH (n = 1), diguanylate cyclase (n = 1), AraC family transcriptional regulator (n = 1), ABC-type uncharacterized transport system permease component (n = 1) and hypothetical proteins (n = 4). Two hypothetical proteins contain several disordered regions.

CONCLUSIONS

Some specific DNA regions existed in the virulent strain of V. alginolyticus, and the SSH assay could be a highly sensitive method for identifying virulent regions in pathogens.

SIGNIFICANCE AND IMPACT OF THE STUDY

This report is the first to describe the identification of virulent strain-specific DNA regions in the V. alginolyticus genome, which is helpful in developing virulent strain-specific rapid detection methods and is a pivotal precondition for clarifying the molecular virulence mechanism of V. alginolyticus.

A T3SS Regulator Mutant of Vibrio alginolyticus Affects Antibiotic Susceptibilities and Provides Significant Protection to Danio rerio as a Live Attenuated Vaccine

Vibrio alginolyticus is a major cause of Vibriosis in farmed marine aquatic animals and has caused large economic losses to the Asian aquaculture industry in recent years. Therefore, it is necessary to control V. alginolyticus effectively. The virulence mechanism of V. alginolyticus, the Type III secretion system (T3SS), is closely related to its pathogenicity. In this study, the T3SS gene tyeA was cloned from V. alginolyticus wild-type strain HY9901 and the results showed that the deduced amino acid sequence of V. alginolyticus tyeA shared 75–83% homology with other Vibrio spp. The mutant strain HY9901ΔtyeA was constructed by Overlap-PCR and homologous recombination techniques. The HY9901ΔtyeA mutant exhibited an attenuated swarming phenotype and an ~40-fold reduction in virulence to zebrafish. However, the HY9901ΔtyeA mutant showed no difference in growth, biofilm formation and ECPase activity. Antibiotic susceptibility test was observed that wild and mutant strains were extremely susceptible to Amikacin, Minocycline, Gentamicin, Cefperazone; and resistant to oxacillin, clindamycin, ceftazidime. In contrast wild strains are sensitive to tetracycline, chloramphenicol, kanamycin, doxycycline, while mutant strains are resistant to them. qRT-PCR was employed to analyze the transcription levels of T3SS-related genes, the results showed that compared with HY9901 wild type, ΔtyeA had increased expression of vscL, vscK, vscO, vopS, vopN, vscN, and hop. Following vaccination with the mutant strain, zebrafish had significantly higher survival than controls following infection with the wild-type HY9901 (71.2% relative percent survival; RPS). Analysis of immune gene expression by qPCR showed that vaccination with HY9901ΔtyeA increased the expression of IgM, IL-1β, IL-6, and TNF-α in zebrafish. This study provides evidence of protective efficacy of a live attenuated vaccine targeting the T3SS of V. alginolyticus which may be facilitated by up-regulated pro-inflammatory and immunoglobulin-related genes.

Outer membrane protein A (OmpA) is a potential virulence factor of Vibrio alginolyticus strains isolated from diseased fish

Vibrio alginolyticus is one of the most serious causative agents of diseases in cultured marine fish and shellfish. However, the characteristics of virulence factors in pathogenic V. alginolyticus are poorly known. To gain insight into fish diseases caused by V. alginolyticus, we carried out two-dimensional gel electrophoresis (2-DE) combined with MALDI-TOF mass spectrometry to identify uniquely expressed proteins in the disease-causing V. alginolyticus. V. alginolyticus strains were isolated from marine environments and diseased fish obtained from southern Thailand. We identified seven unique proteins in the disease-causing V. alginolyticus strain. Among those, the outer membrane protein A (OmpA) had the strongest expression. Therefore, the function of this protein was further analysed. To investigate the role of OmpA protein, an in-frame deletion mutant of ompA was constructed using the homologous recombination method. Although the ompA mutant V. alginolyticus strain (ΔompA) grew normally, the mutant exhibited a significant defect in the swarming ability and the biofilm formation. Furthermore, Galleria mellonella larvae injected with the mutant bacteria had a significantly greater survival percentage than those injected with the wild-type strain, demonstrating that OmpA protein is required for the pathogenicity of V. alginolyticus. Together, this study suggests a potential target for vaccine development against pathogenic V. alginolyticus strain.

Superoxide dismutase B (sodB), an important virulence factor of Vibrio alginolyticus, contributes to antioxidative stress and its potential application for live attenuated vaccine

Vibrio alginolyticus is an opportunistic and halophilic Gram-negative pathogen in limiting the development of aquatic industry and affecting human health. SODs are oxidative enzymes that play a critical role in oxidative defense. In this study, an in-frame deleted mutant strain (ΔsodB) was constructed by allelic exchange mutagenesis to investigate physiological role of sodB in pathogenicity of V. alginolyticus. The results exhibited that ΔsodB showed no differences in growth compared with wild-type strain HY9901 (WT), but led to increasing in biofilm formation, ECPase activity and sensitivity to hydrogen peroxide, decreasing in swarming motility, adherence to CIK cells, SOD activity and virulence. In addition, ΔsodB induced a high antibody titer and provided a valid protection with a relative percent survival value of 86.5% without inducing clinical symptoms after challenging with WT. These results suggest that sodB is important for normal physiological function, oxidation resistance and virulence in V. alginolyticus, and ΔsodB may be considered as an effective live attenuated vaccine against V. alginolyticus.

Phage Endolysins as Potential Antimicrobials against Multidrug Resistant Vibrio alginolyticus and Vibrio parahaemolyticus: Current Status of Research and Challenges Ahead

Vibrio alginolyticus and V. parahaemolyticus, the causative agents of Vibriosis in marine vertebrates and invertebrates, are also responsible for fatal illnesses such as gastroenteritis, septicemia, and necrotizing fasciitis in humans via the ingestion of contaminated seafood. Aquaculture farmers often rely on extensive prophylactic use of antibiotics in farmed fish to mitigate Vibrios and their biofilms. This has been postulated as being of serious concern in the escalation of antibiotic resistant Vibrios. For this reason, alternative strategies to combat aquaculture pathogens are in high demand. Bacteriophage-derived lytic enzymes and proteins are of interest to the scientific community as promising tools with which to diminish our dependency on antibiotics. Lysqdvp001 is the best-characterized endolysin with lytic activity against multiple species of Vibrios. Various homologues of Vibrio phage endolysins have also been studied for their antibacterial potential. These novel endolysins are the major focus of this mini review.

Construction of a Vibrio alginolyticus hopPmaJ (hop) mutant and evaluation of its potential as a live attenuated vaccine in orange-spotted grouper (Epinephelus coioides)

Vibrio alginolyticus, a bacterial pathogen in fish and humans, expresses a type III secretion system (T3SS) that is critical for pathogen virulence and disease development. However, little is known about the associated effectors (T3SEs) and their physiological role. In this study, the T3SE gene hopPmaJ (hop) was cloned from V. alginolyticus wild-type strain HY9901 and the mutant strain HY9901Δhop was constructed by the in-frame deletion method. The results showed that the deduced amino acid sequence of V. alginolyticus HopPmaJ shared 78-98% homology with other Vibrio spp. In addition, the HY9901Δhop mutant showed an attenuated swarming phenotype and a 2600-fold decrease in the virulence to grouper. However, the HY9901Δhop mutant showed no difference in morphology, growth, biofilm formation and ECPase activity. Finally, grouper vaccinated via intraperitoneal (IP) injection with HY9901Δhop induced a high antibody titer with a relative percent survival (RPS) value of 84% after challenging with the wild-type HY9901. Real-time PCR assays showed that vaccination with HY9901Δhop enhanced the expression of immune-related genes, including MHC-Iα, MHC-IIα, IgM, and IL-1β after vaccination, indicating that it is able to induce humoral and cell-mediated immune response in grouper. These results demonstrate that the HY9901Δhop mutant could be used as an effective live vaccine to combat V. alginolyticus in grouper.

Genetic heterogeneity among Vibrio alginolyticus strains, and design of a PCR-based identification method using gyrB gene sequence

Vibrio alginolyticus, a pathogen among humans and marine animals, is ubiquitous in marine environments. The aims of this study were to analyze the relationships between genetic diversity and origins, and to develop new primers based on the gyrB sequence to identify V. alginolyticus isolated from various sources. To determine the genetic diversity of this bacterium, an arbitrarily primed polymerase chain reaction (AP-PCR) technique was performed on 36 strains of V. alginolyticus isolated from diarrhea patients and from diseased marine animals and environments in southern Thailand. The results showed distinct DNA fingerprints of all strains, indicating that they are genetically heterogeneous. For species-specific identification of V. alginolyticus, primers targeting the gyrB gene of V. alginolyticus were developed. Thirty reference Vibrio spp., 13 non-Vibrio spp., and 160 strains of V. alginolyticus isolated from various sources in southern Thailand were used to evaluate the specificity of these primers. Our results showed that the gyrB primers could specifically identify V. alginolyticus from all sample types. In addition, the detection limit of the PCR was at least 95 pg of DNA template. Therefore, we concluded that the newly designed gyrB primers are rapid, highly sensitive, and specific to identify V. alginolyticus isolated from various sources.

Vibrio alginolyticus infections in the USA, 1988-2012

Vibrio alginolyticus causes soft tissue and bloodstream infection; little systematically collected clinical and epidemiological information is available. In the USA, V. alginolyticus infections are reported to the Cholera and Other Vibrio Illness Surveillance system. Using data from 1988 to 2012, we categorised infections using specimen source and exposure history, analysed case characteristics, and calculated incidence rates using US Census Bureau data. Most (96%) of the 1331 V. alginolyticus infections were from coastal states. Infections of the skin and ear were most frequent (87%); ear infections occurred more commonly in children, lower extremity infections more commonly in older adults. Most (86%) infections involved water activity. Reported incidence of infections increased 12-fold over the study period, although the extent of diagnostic or surveillance bias is unclear. Prevention efforts should target waterborne transmission in coastal areas and provider education to promote more rapid diagnosis and prevent complications.

Prevalence of Biofilm Formation and Wide Distribution of Virulence Associated Genes among Vibrio spp. Strains Isolated from the Monastir Lagoon, Tunisia

In the current study, 65 Vibrio spp. were isolated from the Monastir lagoon water, were characterized phenotypically and genotypically. In addition, we looked for the presence of three Vibrio parahaemolyticus virulence genes (tlh, trh and tdh) and ten Vibrio cholerae virulence genes (ctxA, vpi, zot, ace, toxR, toxT, tosS, toxRS, tcpA and cpP). We also investigated the antibiotic susceptibilities and the adherence ability of the identified strains to abiotic material and to biotic surfaces. The cytotoxicity activity against HeLa and Vero cell lines were also carried out for all tested strains. All Vibrio isolates were identified to the species level and produced several hydrolytic exoenzymes. The results also revealed that all strains were expressing high rates of resistance to tested antibiotics. The minimum inhibitory concentration (MIC) values showed that tetracycline and chloramphenicol were the most effective antibiotics against the tested bacteria. Vibrio alginolyticus and V. cholerae species were the most adhesive strains to both biotic and abiotic surfaces. Besides, V. alginolyticus isolates has the high levels of recombination of genes encoding V. cholerae and V. parahaemolyticus virulence factors. In vitro cytotoxic activities of several Vibrio extracellular product were also observed among HeLa and Vero cells.

An Innovative Method for Rapid Identification and Detection of Vibrio alginolyticus in Different Infection Models

Vibrio alginolyticus is one of the most common pathogenic marine Vibrio species, and has been found to cause serious seafood-poisoning or fatal extra-intestinal infections in humans, such as necrotizing soft-tissue infections, bacteremia, septic shock, and multiple organ failures. Delayed accurate diagnosis and treatment of most Vibrio infections usually result to high mortality rates. The objective of this study was to establish a rapid diagnostic method to detect and identify the presence of V. alginolyticus in different samples, so as to facilitate timely treatment. The widely employed conventional methods for detection of V. alginolyticus include biochemical identification and a variety of PCR methods. The former is of low specificity and time-consuming (2–3 days), while the latter has improved accuracy and processing time. Despite such advancements, these methods are still complicated, time-consuming, expensive, require expertise and advanced laboratory systems, and are not optimal for field use. With the goal of providing a simple and efficient way to detect V. alginolyticus, we established a rapid diagnostic method based on loop-mediated Isothermal amplification (LAMP) technology that is feasible to use in both experimental and field environments. Three primer pairs targeting the toxR gene of V. alginolyticus were designed, and amplification was carried out in an ESE tube scanner and Real-Time PCR device. We successfully identified 93 V. alginolyticus strains from a total of 105 different bacterial isolates and confirmed their identity by 16s rDNA sequencing. We also applied this method on infected mouse blood and contaminated scallop samples, and accurate results were both easily and rapidly (20–60 min) obtained. Therefore, the RT-LAMP assay we developed can be conveniently used to detect the presence of V. alginolyticus in different samples. Furthermore, this method will also fulfill the gap for real-time screening of V. alginolyticus infections especially while on field.

Multiplex PCR assays for the detection of Vibrio alginolyticus, Vibrio parahaemolyticus, Vibrio vulnificus, and Vibrio cholerae with an internal amplification control

A multiplex polymerase chain reaction (PCR) assay that can simultaneously detect 4 major Vibrio spp., Vibrio alginolyticus, Vibrio parahaemolyticus, Vibrio vulnificus, and Vibrio cholerae, in the presence of an internal amplification control (IAC) was developed. Species-specific PCR primers were designed based on the gyrB gene for V. alginolyticus, the collagenase gene for V. parahaemolyticus, the vvhA gene for V. vulnificus, and the ompW gene for V. cholerae. Additionally, an IAC primer pair was designed in conserved regions of the bacterial 16S rRNA gene that is used to indicate false-negative results. A multiplex PCR method was developed after optimization of the reaction conditions. The specificity of the PCR was validated by using 83 Vibrio strains and 10 other non-Vibrio bacterial species. The detection limit of the PCR was 10 CFU per tube for V. alginolyticus, V. parahaemolyticus, V. vulnificus, and 10(5) CFU per tube for V. cholerae in mixed conditions. This method was used to identify 69 suspicious Vibrio isolates, and the results were consistent with physiological and biochemical tests. This multiplex PCR method proved to be rapid, sensitive, and specific. The existence of IAC could successfully eliminate false-negative results for the detection of V. alginolyticus, V. parahaemolyticus, V. vulnificus, and V. cholerae.

Distribution of Vibrio alginolyticus-like species in Shenzhen coastal waters, China

We investigated the distribution of vibrios in Shenzhen coastal waters in order to obtain valuable information for the aquaculture industry and a health warning system. Quantities of vibrios from surface waters ranged from 0 to 4.40×10(4) CFUs mL(-1) in April (spring), while from 0 to 2.57×10(3) CFUs mL(-1) in September (autumn); the abundance of V. alginolyticus-like species from surface water ranged from 0 to 6.72×10(3) CFUs mL(-1) in April (spring) and from 0 to 1.28×10(3) CFUs mL(-1) in September (autumn); higher counts were observed in spring. The V. alginolyticus-like species was dominant in Shenzhen coastal waters, with the highest abundance in the clean region (stations YMK001 and GDN064) in April, suggesting that Vibrio spp. were naturally occurring bacteria in marine environments. The correlation between the abundance of vibrios (including V. alginolyticus-like species) and environmental factors varied in different regions and different seasons. There were no vibrios detected when the salinity was less than 11.15‰ in the Zhujiang River estuary, which indicated that salinity played a key role in the distribution of vibrios and V. alginolyticus-like species.

SYBR Green I-based real-time PCR targeting the rpoX gene for sensitive and rapid detection of Vibrio alginolyticus

rpoX, a Vibrio alginolyticus specific stress regulating gene, was used to detect this fish pathogen by SYBR Green I-based real-time PCR. The specificity of the detection was confirmed in different samples. The minimum level of detection was 10(3) cells from pure culture and 10(2) cells from seawater.