Real-Time PCR Detection of Vibrio vulnificus in Oysters: Comparison of Oligonucleotide Primers and Probes Targeting vvhA

We compared three sets of oligonucleotide primers and two probes designed for Vibrio vulnificus hemolysin A gene (vvhA) for TaqMan-based real-time PCR method enabling specific detection of Vibrio vulnificus in oysters. Two of three sets of primers with a probe were specific for the detection of all 81 V. vulnificus isolates by TaqMan PCR. The 25 nonvibrio and 12 other vibrio isolates tested were negative. However, the third set of primers, F-vvh1059 and R-vvh1159, with the P-vvh1109 probe, although positive for all V. vulnificus isolates, also exhibited positive cycle threshold (C_T) values for other Vibrio spp. Optimization of the TaqMan PCR assay using F-vvh785/R-vvh990 or F-vvh731/R-vvh1113 primers and the P-vvh874 probe detected 1 pg of purified DNA and 10³ V. vulnificus CFU/ml in pure cultures. The enriched oyster tissue homogenate did not exhibit detectable inhibition to the TaqMan PCR amplification of vvhA. Detection of 3 × 10³ CFU V. vulnificus, resulting from a 5-h enrichment of an initial inoculum of 1 CFU/g of oyster tissue homogenate, was achieved with F-vvh785/R-vvh990 or F-vvh731/R-vvh1113 primers and P-vvh875 probe. The application of the TaqMan PCR using these primers and probe, exhibited detection of V. vulnificus on 5-h-enriched natural oysters harvested from the Gulf of Mexico. Selection of appropriate primers and a probe on vvhA for TaqMan-PCR-based detection of V. vulnificus in post-harvest-treated oysters would help avoid false-positive results, thus ensuring a steady supply of safe oysters to consumers and reducing V. vulnificus-related illnesses and deaths.     

Real-time PCR analysis of Vibrio vulnificus from oysters

Vibrio vulnificus is an opportunistic human pathogen commonly found in estuarine environments. Infections are associated with raw oyster consumption and can produce rapidly fatal septicemia in susceptible individuals. Standard enumeration of this organism in shellfish or seawater is laborious and inaccurate; therefore, more efficient assays are needed. An oligonucleotide probe derived from the cytolysin gene, vvhA, was previously used for colony hybridizations to enumerate V. vulnificus. However, this method requires overnight growth, and vibrios may lack culturability under certain conditions. In the present study, we targeted the same locus for development of a TaqMan real-time PCR assay. Probe specificity was confirmed by amplification of 28 V. vulnificus templates and by the lack of a PCR product with 22 non-V. vulnificus strains. Detection of V. vulnificus in pure cultures was observed over a 6-log-unit linear range of concentration (10(2) to 10(8) CFU ml(-1)), with a lower limit of 72 fg of genomic DNA micro l of PCR mixture(-1) or the equivalent of six cells. Similar sensitivity was observed in DNA extracted from mixtures of V. vulnificus and V. parahaemolyticus cells. Real-time PCR enumeration of artificially inoculated oyster homogenates correlated well with colony hybridization counts (r(2) = 0.97). Numbers of indigenous V. vulnificus cells in oysters by real-time PCR showed no significant differences from numbers from plate counts with probe (t test; P = 0.43). Viable but nonculturable cells were also enumerated by real-time PCR and confirmed by the BacLight viability assay. These data indicate that real-time PCR can provide sensitive species-specific detection and enumeration of V. vulnificus in seafood.     

Development of a quantitative real-time polymerase chain reaction targeted to the toxR for detection of Vibrio vulnificus

The TaqMan assay, a quantitative real-time polymerase chain reaction (PCR), was developed to target the ToxR gene (toxR) of Vibrio vulnificus. The toxR of V. vulnificus was cloned and sequenced. Based on these results, we designed specific primers and a probe for use in the quantitative PCR assay. Twenty-nine strains of V. vulnificus that were obtained from various sources produced a single PCR product. The amount of final amplification product and threshold cycle number were the same among the strains. We used the method to detect V. vulnificus in seawater and oyster samples. We developed standard curves to quantitate V. vulnificus numbers using the PCR from seawater and oyster samples. The standard curves were not different from that of the pure culture of V. vulnificus. We found the assay was very sensitive detecting as few as 10 microbes per milliliter of seawater and oyster homogenate. Moreover, we evaluated the TaqMan assay to detect V. vulnificus in seawater samples. The numbers of V. vulnificus counted by the TaqMan assay were similar to those by a culture method in almost samples. The TaqMan assay was performed within 2 h compared to days using the culture method. The results indicate the TaqMan assay method used in this study was rapid, effective and quantitative for monitoring V. vulnificus contamination in seawater and seafoods such as oysters.     

TaqMan PCR for detection of Vibrio cholerae O1, O139, non-O1, and non-O139 in pure cultures, raw oysters, and synthetic seawater

Vibrio cholerae is recognized as a leading human waterborne pathogen. Traditional diagnostic testing for Vibrio is not always reliable, because this bacterium can enter a viable but nonculturable state. Therefore, nucleic acid-based tests have emerged as a useful alternative to traditional enrichment testing. In this article, a TaqMan PCR assay is presented for quantitative detection of V. cholerae in pure cultures, oysters, and synthetic seawater. Primers and probe were designed from the nonclassical hemolysin (hlyA) sequence of V. cholerae strains. This probe was applied to DNA from 60 bacterial strains comprising 21 genera. The TaqMan PCR assay was positive for all of the strains of V. cholerae tested and negative for all other species of Vibrio tested. In addition, none of the other genera tested was amplified with the TaqMan primers and probe used in this study. The results of the TaqMan PCR with raw oysters and spiked with V. cholerae serotypes O1 and O139 were comparable to those of pure cultures. The sensitivity of the assay was in the range of 6 to 8 CFU g(-1) and 10 CFU ml(-1) in spiked raw oyster and synthetic seawater samples, respectively. The total assay could be completed in 3 h. Quantification of the Vibrio cells was linear over at least 6 log units. The TaqMan probe and primer set developed in this study can be used as a rapid screening tool for the presence of V. cholerae in oysters and seawater without prior isolation and characterization of the bacteria by traditional microbiological methods.     

Multiplex PCR detection of clinical and environmental strains of Vibrio vulnificus in shellfish

In this study, we developed a PCR-based rapid detection method for clinically important pathogenic strains of Vibrio vulnificus. Positive amplification of the 504-bp viuB fragment was seen in all 22 clinical isolates tested but only in 8 out of 33 environmental isolates. The combination of the species-specific 205-bp vvh fragment along with viuB in a multiplexed PCR enabled us to confirm the presence of potentially pathogenic strains of V. vulnificus. No amplification of other Vibrio spp. or non-Vibrio bacteria was evidenced, suggesting a high specificity of detection by this method. The sensitivity of detection for both targeted genes was 10 pg of purified DNA, which correlated with 10(3) V. vulnificus CFU in 1 mL of pure culture or 1 g un-enriched seeded oyster tissue homogenate. This sensitivity was improved to 1 CFU per gram of oyster tissue homogenate in overnight-enriched samples. A SYBR Green I based real-time PCR method was also developed that was shown to produce results consistent with the conventional PCR method. Application of the multiplexed real-time PCR to natural oyster tissue homogenates exhibited positive detection of vvh in 51% of the samples collected primarily during the summer months; however, only 15% of vvh positive samples exhibited viuB amplicons. The rapid, sensitive, and specific detection of clinically important pathogenic V. vulnificus in shellfish would be beneficial in reducing illnesses and deaths caused by this pathogen.     

Rapid detection of Vibrio vulnificus in shellfish and Gulf of Mexico water by real-time PCR

In this paper we describe optimization of SYBR Green I-based real-time PCR parameters and testing of a large number of microbial species with vvh-specific oligonucleotide primers to establish a rapid, specific, and sensitive method for detection of Vibrio vulnificus in oyster tissue homogenate and Gulf of Mexico water (gulf water). Selected oligonucleotide primers for the vvh gene were tested for PCR amplification of a 205-bp DNA fragment with a melting temperature of approximately 87 degrees C for 84 clinical and environmental strains of V. vulnificus. No amplification was observed with other vibrios or nonvibrio strains with these primers. The minimum level of detection by the real-time PCR method was 1 pg of purified genomic DNA or 10(2) V. vulnificus cells in 1 g of unenriched oyster tissue homogenate or 10 ml of gulf water. It was possible to improve the level of detection to one V. vulnificus cell in samples that were enriched for 5 h. The standard curves prepared from the real-time PCR cycle threshold values revealed that there was a strong correlation between the number of cells in unenriched samples and the number of cells in enriched samples. Detection of a single cell of V. vulnificus in 1 g of enriched oyster tissue homogenate is in compliance with the recent Interstate Shellfish Sanitation Conference guidelines. The entire detection method, including sample processing, enrichment, and real-time PCR amplification, was completed within 8 h, making it a rapid single-day assay. Rapid and sensitive detection of V. vulnificus would ensure a steady supply of postharvest treated oysters to consumers, which should help decrease the number of illnesses or outbreaks caused by this pathogen.     

用基于TaqMan探针的Real-time PCR技术定量检测副溶血弧菌

副溶血弧菌是一种引起食源性疾病的重要病原菌,传统的鉴定方法费时费力且容易出现假阴性,建立一种定量检测副溶血弧菌基因的方法尤为重要。根据GenBank公布的副溶血弧菌的gyrB基因序列设计一对引物和TaqMan探针,建立了基于TaqMan探针的RealtimePCR方法。通过对9种细菌(12株菌株)的DNA进行扩增,结果所有4株副溶血弧菌均可产生扩增曲线,其他8株非副溶血弧菌均不产生扩增曲线,证明了引物和探针具有很高的特异性。细菌纯培养物品和人工布菌的检测敏感度分别为1CFUPCR反应体系和10CFUPCR反应体系,相关系数均为0.99(r2=0.99),整个试验可在1h内完成。建立的方法可用于海产品中副溶血弧菌的快速定量检测。     

Detecting potentially virulent Vibrio vulnificus strains in raw oysters by quantitative loop-mediated isothermal amplification

Vibrio vulnificus is a leading cause of seafood-related deaths in the United States. Sequence variations in the virulence-correlated gene (vcg) have been used to distinguish between clinical and environmental V. vulnificus strains, with a strong association between clinical ones and the C sequence variant (vcgC). In this study, vcgC was selected as the target to design a loop-mediated isothermal amplification (LAMP) assay for the rapid, sensitive, specific, and quantitative detection of potentially virulent V. vulnificus strains in raw oysters. No false-positive or false-negative results were generated among the 125 bacterial strains used to evaluate assay specificity. The detection limit was 5.4 CFU per reaction for a virulent V. vulnificus strain (ATCC 33815) in pure culture, 100-fold more sensitive than that of PCR. In spiked raw oysters, the assay was capable of detecting 2.5 × 10(3) CFU/g of V. vulnificus ATCC 33815, while showing negative results for a nonvirulent V. vulnificus strain (515-4c2) spiked at 10(7) CFU/g. After 6 h of enrichment, the LAMP assay could detect 1 CFU/g of the virulent V. vulnificus strain ATCC 33815. Standard curves generated in pure culture and spiked oysters suggested a good linear relationship between cell numbers of the virulent V. vulnificus strain and turbidity signals. In conclusion, the LAMP assay developed in this study could quantitatively detect potentially virulent V. vulnificus in raw oysters with high speed, specificity, and sensitivity, which may facilitate better control of V. vulnificus risks associated with raw oyster consumption.     

Study of the occurrence of Vibrio vulnificus in oysters in India by polymerase chain reaction (PCR) and heterogeneity among V. vulnificus by randomly amplified polymorphic DNA PCR and gyrB sequence analysis

The pathogenic bacterium Vibrio vulnificus is widely distributed in estuarine waters throughout the world. In this study, the presence of V. vulnificus in oysters was studied both by conventional culture and DNA-based molecular technique. Following enrichment in alkaline peptone water (APW), the bacteria were lysed and a nested polymerase chain reaction (PCR) for vvhA gene was performed. The effect of duration of enrichment on the sensitivity of detection by PCR was evaluated. The organism was isolated from 43% of samples after 18 h enrichment in APW by conventional culture method. Nested PCR amplifying a fragment of vvhA gene detected the organism in 11%, 60% and 81% of samples following 0, 6 and 18 h of enrichment. All the biochemically identified V. vulnificus strains possessed vvhA gene and belonged to biotype 1. The genetic relatedness among the strains was studied by randomly amplified polymorphic DNA (RAPD) PCR and gyrB sequence analysis. The results suggest the presence of two distinct clonal groups of V. vulnificus in oysters in India. The study demonstrates, for the first time that gyrB sequence analysis could be used to study the genetic diversity of V. vulnificus.     

Detection of Vibrio parahaemolyticus in shellfish by use of multiplexed real-time PCR with TaqMan fluorescent probes

We developed a multiplexed real-time PCR assay using four sets of gene-specific oligonucleotide primers and four TaqMan probes labeled with four different fluorophores in a single reaction for detection of total and pathogenic Vibrio parahaemolyticus, including the pandemic O3:K6 serotype in oysters. V. parahaemolyticus has been associated with outbreaks of food-borne gastroenteritis caused by the consumption of raw or undercooked seafood and therefore is a concern to the seafood industry and consumers. We selected specific primers and probes targeting the thermostable direct hemolysin gene (tdh) and tdh-related hemolysin gene (trh) that have been reported to be associated with pathogenesis in this organism. In addition, we targeted open reading frame 8 of phage f237 (ORF8), which is associated with a newly emerged virulent pandemic serotype of V. parahameolyticus O3:K6. Total V. parahaemolyticus was targeted using the thermolabile hemolysin gene (tlh). The sensitivity of the combined four-locus multiplexed TaqMan PCR was found to be 200 pg of purified genomic DNA and 10(4) CFU per ml for pure cultures. Detection of an initial inoculum of 1 CFU V. parahaemolyticus per g of oyster tissue homogenate was possible after overnight enrichment, which resulted in a concentration of 3.3x10(9) CFU per ml. Use of this method with natural oysters resulted in 17/33 samples that were positive for tlh and 4/33 samples that were positive for tdh. This assay specifically and sensitively detected total and pathogenic V. parahaemolyticus and is expected to provide a rapid and reliable alternative to conventional detection methods by reducing the analysis time and obviating the need for multiple assays.     

Detection of pathogenic Vibrio spp. in shellfish by using multiplex PCR and DNA microarrays

This study describes the development of a gene-specific DNA microarray coupled with multiplex PCR for the comprehensive detection of pathogenic vibrios that are natural inhabitants of warm coastal waters and shellfish. Multiplex PCR with vvh and viuB for Vibrio vulnificus, with ompU, toxR, tcpI, and hlyA for V. cholerae, and with tlh, tdh, trh, and open reading frame 8 for V. parahaemolyticus helped to ensure that total and pathogenic strains, including subtypes of the three Vibrio spp., could be detected and discriminated. For DNA microarrays, oligonucleotide probes for these targeted genes were deposited onto epoxysilane-derivatized, 12-well, Teflon-masked slides by using a MicroGrid II arrayer. Amplified PCR products were hybridized to arrays at 50 degrees C and detected by using tyramide signal amplification with Alexa Fluor 546 fluorescent dye. Slides were imaged by using an arrayWoRx scanner. The detection sensitivity for pure cultures without enrichment was 10(2) to 10(3) CFU/ml, and the specificity was 100%. However, 5 h of sample enrichment followed by DNA extraction with Instagene matrix and multiplex PCR with microarray hybridization resulted in the detection of 1 CFU in 1 g of oyster tissue homogenate. Thus, enrichment of the bacterial pathogens permitted higher sensitivity in compliance with the Interstate Shellfish Sanitation Conference guideline. Application of the DNA microarray methodology to natural oysters revealed the presence of V. vulnificus (100%) and V. parahaemolyticus (83%). However, V. cholerae was not detected in natural oysters. An assay involving a combination of multiplex PCR and DNA microarray hybridization would help to ensure rapid and accurate detection of pathogenic vibrios in shellfish, thereby improving the microbiological safety of shellfish for consumers.     

Detection of pathogenic Vibrio parahaemolyticus in oyster enrichments by real time PCR

A real time polymerase chain reaction (PCR) assay was developed and evaluated to detect the presence of the thermostable direct hemolysin gene (tdh), a current marker of pathogenicity in Vibrio parahaemolyticus. The real time PCR fluorogenic probe and primer set was tested against a panel of numerous strains from 13 different bacterial species. Only V. parahaemolyticus strains possessing the tdh gene generated a fluorescent signal, and no cross-reaction was observed with tdh negative Vibrio or non-Vibrio spp. The assay detected a single colony forming unit (CFU) per reaction of a pure culture template. This sensitivity was achieved when the same template amount per reaction was tested in the presence of 2.5 microl of a tdh negative oyster:APW enrichment (oyster homogenate enriched in alkaline peptone water overnight at 35 degrees C). This real time technique was used to test 131 oyster:APW enrichments from an environmental survey of Alabama oysters collected between March 1999 and September 2000. The results were compared to those previously obtained using a streak plate procedure for culture isolation from the oyster:APW enrichment combined with use of a non-radioactive DNA probe for detection of the tdh gene. Real time PCR detected tdh in 61 samples, whereas the streak plate/probe method detected tdh in 15 samples. Only 24 h was required for detection of pathogenic V. parahaemolyticus in oyster:APW enrichments by real time PCR, whereas the streak plate/probe method required 3 days and was more resource intensive. This study demonstrated that real time PCR is a rapid and reliable technique for detecting V. parahaemolyticus possessing the tdh gene in pure cultures and in oyster enrichments.     

Detection of Vibrio vulnificus biotypes 1 and 2 in eels and oysters by PCR amplification.

DNA extraction procedures and PCR conditions to detect Vibrio vulnificus cells naturally occurring in oysters were developed. In addition, PCR amplification of V. vulnificus from oysters seeded with biotype 1 cells was demonstrated. By the methods described, V. vulnificus cells on a medium (colistin-polymyxin B-cellobiose agar) selective for this pathogen were detectable in oysters harvested in January and March, containing no culturable cells (< 67 CFU/g), as well as in oysters harvested in May and June, containing culturable cells. It was possible to complete DNA extraction, PCR, and gel electrophoresis within 10 h by using the protocol described for oysters. V. vulnificus biotype 2 cells were also detected in eel tissues that had been infected with this strain and subsequently preserved in formalin. The protocol used for detection of V. vulnificus cells in eels required less than 5 h to complete. Optimum MgCl2 concentrations for the PCR of V. vulnificus from oysters and eels were different, although the same primer pair was used for both. This is the first report on the detection of cells of V. vulnificus naturally present in shellfish and represents a potentially powerful method for monitoring this important human and eel pathogen.     

Lethal cold stress of Vibrio vulnificus in oysters.

Studies were conducted on the survival of Vibrio vulnificus, an estuarine human pathogen, in oyster homogenates held at 4 degrees C. Results indicated a rapid and dramatic decrease in viability not attributable to either cold shock or the oyster homogenate alone but to a combination of the two. Such a decline was not observed with Vibrio parahaemolyticus. Chilled V. vulnificus cells were unable to repair themselves in brain heart infusion broth at 37 degrees C. V. vulnificus cells incubated on whole raw oysters at 0.5 degrees C also exhibited a decline in viability, but of a lesser degree. The effects of various plating media were also investigated. The data reported here suggest that oysters kept on ice are not likely to be a major factor in the epidemiology of V. vulnificus infection. It is further suggested that the standard method of homogenizing oysters for examining bacteriological quality should not be followed because toxic compounds are released from the oysters during this process.     

Occurrence of pathogenic vibrios in coastal areas of France

AIMS: This study was carried out to investigate the occurrence of potentially pathogenic species of Vibrio in French marine and estuarine environments. METHODS AND RESULTS: Samples of coastal waters and mussels collected between July and September 1999 were analysed by culture, using selective media including thiosulphate-citrate-bile salts-sucrose and modified cellobiose-polymixin B-colistin agar. Presumptive Vibrio colonies were isolated and identified using selected biochemical tests. Specific primers based on flanking sequences of the cytolysin, vvhA gene, pR72H DNA fragment and 16S-23S rRNA intergenic spacer region (ISR) were used in a polymerase chain reaction (PCR) to confirm the identification of Vibrio vulnificus, V. parahaemolyticus and V. cholerae, respectively. In this study, V. alginolyticus (99 of 189) was the predominant species, followed by V. parahaemolyticus (41 of 189), V. vulnificus (20 of 189) and non-O1/non-O139 V. cholerae (three of 189). All 20 V. vulnificus isolates showed PCR amplification of the vvhA gene, 16 of which had been isolated from estuarine water. The PCR amplification of the pR72H DNA fragment in 41 V. parahaemolyticus isolates generated two unique amplicons of 387 and 320 bp. The latter, present in 24.4% of these isolates, had not previously been found in V. parahaemolyticus strains examined to date. Amplification of the trh gene in two of the isolates suggested these to be virulent strains. Three strains identified as V. cholerae by amplification of the 16S-23S rRNA ISR were confirmed to be non-cholera (non-O1/non-O139) strains. CONCLUSIONS: The results of this study demonstrated the presence of pathogenic Vibrio species in French coastal waters. Furthermore, the PCR approach proved useful for the rapid and reliable confirmation of species identification. SIGNIFICANCE AND IMPACT OF THE STUDY: These findings indicate the potential sanitary risk associated with the presence of pathogenic Vibrio spp. in cultivated mussels and in the aquatic environment. The PCR can be used to detect pathogenic vibrios directly in environmental samples.     

Analysis of Vibrio vulnificus from market oysters and septicemia cases for virulence markers

Representative encapsulated strains of Vibrio vulnificus from market oysters and oyster-associated primary septicemia cases (25 isolates each) were tested in a blinded fashion for potential virulence markers that may distinguish strains from these two sources. These isolates were analyzed for plasmid content, for the presence of a 460-bp amplicon by randomly amplified polymorphic DNA PCR, and for virulence in subcutaneously (s.c.) inoculated, iron-dextran-treated mice. Similar percentages of market oyster and clinical isolates possessed detectable plasmids (24 and 36%, respectively), produced the 460-bp amplicon (45 and 50%, respectively), and were judged to be virulent in the mouse s.c. inoculation-iron-dextran model (88% for each). Therefore, it appears that nearly all V. vulnificus strains in oysters are virulent and that genetic tests for plasmids and specific PCR size amplicons cannot distinguish between fully virulent and less virulent strains or between clinical and environmental isolates. The inability of these methods to distinguish food and clinical V. vulnificus isolates demonstrates the need for alternative subtyping approaches and virulence assays.     

Polymerase chain reaction identification of Vibrio vulnificus in artificially contaminated oysters.

DNAs extracted from Vibrio vulnificus seeded into oyster homogenates were evaluated as templates for the polymerase chain reaction. Several extraction procedures were examined, and it was determined that DNA recovered from cells lysed by guanidine isothiocyanate, extracted with chloroform, and precipitated with ethanol was most suitable for use as a polymerase chain reaction template. The region targeted was a 519-bp portion of the cytotoxin-hemolysin gene of V. vulnificus. This region was amplified only when DNA from this species was present in the homogenate. V. vulnificus seeded into oyster homogenates at an initial level of 10(2) CFU/g of oyster meat was consistently observed after 24 h of incubation in alkaline peptone water.     

Validation of a green fluorescent protein-labeled strain of Vibrio vulnificus for use in the evaluation of postharvest strategies for handling of raw oysters

In this paper we describe a biological indicator which can be used to study the behavior of Vibrio vulnificus, an important molluscan shellfish-associated human pathogen. A V. vulnificus ATCC 27562 derivative that expresses green fluorescent protein (GFP) and kanamycin resistance was constructed using conjugation. Strain validation was performed by comparing the GFP-expressing strain (Vv-GFP) and the wild-type strain (Vv-WT) with respect to growth characteristics, heat tolerance (45 degrees C), freeze-thaw tolerance (-20(o) and -80 degrees C), acid tolerance (pH 5.0, 4.0, and 3.5), cold storage tolerance (5 degrees C), cold adaptation (15 degrees C), and response to starvation. Levels of recovery were evaluated using nonselective medium (tryptic soy agar containing 2% NaCl) with and without sodium pyruvate. The indicator strain was subsequently used to evaluate the survival of V. vulnificus in oysters exposed to organic acids (citric and acetic acids) and various cooling regimens. In most cases, Vv-GFP was comparable to Vv-WT with respect to growth and survival upon exposure to various biological stressors; when differences between the GFP-expressing and parent strains occurred, they usually disappeared when sodium pyruvate was added to media. When V. vulnificus was inoculated into shellstock oysters, the counts dropped 2 log(10) after 11 to 12 days of refrigerated storage, regardless of the way in which the oysters were initially cooled. Steeper population declines after 12 days of refrigerated storage were observed for both iced and refrigerated products than for slowly cooled product and product held under conservative harvest conditions. By the end of the refrigeration storage study (22 days), the counts of Vv-GFP in iced and refrigerated oysters had reached the limit of detection (10(2) CFU/oyster), but slowly cooled oysters and oysters stored under conservative harvest conditions still contained approximately 10(3) and >10(4) CFU V. vulnificus/oyster by day 22, respectively. The Vv-GFP levels in the oyster meat remained stable for up to 24 h when the meat was exposed to acidic conditions at various pH values. Ease of detection and comparability to the wild-type parent make Vv-GFP a good candidate for use in studying the behavior of V. vulnificus upon exposure to sublethal stressors that might be encountered during postharvest handling of molluscan shellfish.     

Detection of pandemic Vibrio parahaemolyticus O3:K6 serovar in Gulf of Mexico water and shellfish using real-time PCR with Taqman fluorescent probes

We describe a real-time multiplexed PCR method using Taqman probes for the detection of total and pandemic Vibrio parahaemolyticus O3:K6 serovar in oysters and Gulf of Mexico water (gulf water). The specificity of these primers and probes was tested for amplification of a 450 bp thermolabile hemolysin (tlh) and a 369 bp ORF8 amplicon representing all V. parahaemolyticus and post-1996 clinical isolates of pandemic serovar O3:K6, respectively. The sensitivity of detection was 10 pg purified DNA or 10(3) CFU in 1 mL pure culture. Enrichment of this pathogen in oyster tissue homogenate or gulf water for 5 or 8 h resulted in the detection of an initial inoculum of 1 CFU in 1 mL or 1 g of samples. Application of the Taqman PCR assay on natural oysters exhibited a positive detection of V. parahaemolyticus, ranging from 16% to 100% of the samples collected primarily during the summer months. None of the samples exhibited a positive detection of O3:K6 serovar. Rapid and sensitive detection of this pathogen will help shellfish industry and Interstate Shellfish Sanitation Conference (ISSC) undertake appropriate measures to monitor this pathogen in oysters and oyster-growing waters, thereby preventing disease outbreaks and consequently protecting consumer health.     

Polymerase chain reaction identification of Vibrio vulnificus in artificially contaminated oysters

DNAs extracted from Vibrio vulnificus seeded into oyster homogenates were evaluated as templates for the polymerase chain reaction. Several extraction procedures were examined, and it was determined that DNA recovered from cells lysed by guanidine isothiocyanate, extracted with chloroform, and precipitated with ethanol was most suitable for use as a polymerase chain reaction template. The region targeted was a 519-bp portion of the cytotoxin-hemolysin gene of V. vulnificus. This region was amplified only when DNA from this species was present in the homogenate. V. vulnificus seeded into oyster homogenates at an initial level of 10(2) CFU/g of oyster meat was consistently observed after 24 h of incubation in alkaline peptone water.