Vibrio parahaemolyticus: a concern of seafood safety

Computational study of the Na+/H + antiporter from Vibrio parahaemolyticus

Sodium proton antiporters are ubiquitous membrane proteins that catalyze the exchange of Na(+) for protons throughout the biological world. The Escherichia coli NhaA is the archetypal Na(+)/H(+) antiporter and is absolutely essential for survival in high salt concentrations under alkaline conditions. Its crystal structure, accompanied by extensive molecular dynamics simulations, have provided an atomically detailed model of its mechanism. In this study, we utilized a combination of computational methodologies in order to construct a structural model for the Na(+)/H(+) antiporter from the gram-negative bacterium Vibrio parahaemolyticus. We explored its overall architecture by computational means and validated its stability and robustness. This protein belongs to a novel group of NhaA proteins that transports not only Na(+) and Li(+) as substrate ions, but K(+) as well, and was also found to miss a β-hairpin segment prevalent in other homologs of the Bacteria domain. We propose, for the first time, a structure of a prototype model of a β-hairpin-less NhaA that is selective to K(+). Better understanding of the Vibrio parahaemolyticus NhaA structure-function may assist in studies on ion transport, pH regulation and designing selective blockers.

Differences in stress response after UVC or UVA irradiation in Vibrio parahaemolyticus

The SOS response is a global regulatory network for repairing DNA damage induced by various environmental stresses such as UV irradiation. The Escherichia coli SOS response has been extensively studied. However, there are no reports on the SOS response in Vibrio parahaemolyticus. In this study, we examined the SOS response in V. parahaemolyticus and compared the differential expression of genes induced by UVC and UVA irradiation. In UVC-exposed wild-type cells, expression of several DNA repair genes was increased. However, expression of these genes was not increased in ΔrecA or lexA mutants. Cell filamentation was observed in wild-type cells, but not in ΔrecA and lexA mutant cells. Sensitivity to UVC was significantly increased in ΔrecA, lexA mutant and Δlon strains compared with wild type. In the case of UVA irradiation, LexA-controlled DNA repair genes were minimally induced and cell filamentation was not observed. Sensitivity to UVA was the same in the mutant and wild-type strains. These findings suggest that there is a RecA-LexA-mediated SOS response in V. parahaemolyticus, and that this response is important to UVC tolerance but does not contribute to UVA tolerance.

Proteomic analysis reveals responsive proteins of Vibrio parahaemolyticus on exposure to cationic antimicrobial peptides

AIMS

To investigate whether Vibrio parahaemolyticus can sense and directly respond to the presence of cationic antimicrobial peptides (AMPs).

METHODS AND RESULTS

We performed proteomic methodologies to investigate the responsive proteins of V. parahaemolyticus on exposure to AMP Q6. Differential expression patterns of the outer membrane, inner membrane and cytoplasmic proteins (OMPs, IMPs and CPs) from the bacteria with or without Q6 treatment were obtained using two-dimensional gel electrophoresis (2-DE). Three OMPs (maltoporin, flagellin and OmpV), two IMPs (ATP synthase F1, alpha subunit; and OmpV) and three CPs (pyruvate dehydrogenase subunit E1, glyceraldehyde-3-phosphate dehydrogenase and inositol-5-monophosphate dehydrogenase) were identified using LC-ESI-Q-TOF MS/MS and Mascot program. Real-time quantitative polymerase chain reaction was also performed to determine the mRNA expression level of the target genes.

CONCLUSIONS

Our results suggested that V. parahaemolyticus may directly respond to AMPs through the upregulation of the efflux channel, increased yield of energy, effective repair of damaged membranes and downregulation of carbohydrate and nucleotide metabolism for energy preservation.

SIGNIFICANCE AND IMPACT OF THE STUDY

AMP-responsive proteins identified in the current study could serve as attractive targets for developing more effective antimicrobial agents.

Population dynamics of Vibrio spp. associated with marine sponge microcosms

Vibrio is a diverse genus of marine-associated bacteria with at least 74 species and more expected as additional marine ecospheres are interrogated. This report describes a phylogenetic reconstruction of Vibrio isolates derived from one such unique ecosystem, marine sponges (Phylum Porifera) collected from depths of 150 to 1242 feet. 16S rRNA gene sequencing along with molecular typing of 16S-23S rRNA intergenic spacer regions clustered many sponge-associated Vibrio (spp) with current known species. That is, several benthic Vibrio species commensal with Porifera sponges seemed genetically linked to vibrios associated with coastal or shallow-water communities, signalling a panmictic population structure among seemingly ecologically disparate strains. Conversely, phylogenetic analysis provided evidence for at least two novel Vibrio speciation events within this specific sponge microcosm. Collectively, these findings earmark this still relatively unknown environment as a bastion of taxonomic and phylogenetic variability for the genus and probably other bacterial taxa.

Vibrio illness in Florida, 1998–2007

This study characterized the current epidemiology of vibrio infections in Florida and examined cases reported from 1998 to 2007. Logistic regression was used to determine risk of death. There were 834 vibrio infections in 825 individuals (average annual incidence rate 4·8/1 000 000). Common Vibrio species reported were Vibrio vulnificus (33%), V. parahaemolyticus (29%), and V. alginolyticus (16%). Most exposures were attributed to wounds (42%), and the most common clinical syndromes were wound infections (45%) and gastroenteritis (42%). Almost half of individuals reported an underlying health condition. Risk of death was associated with any underlying condition and increased with the number of conditions (P<0·0001). In Florida, incidence of vibriosis associated with raw oyster consumption has decreased while incidence associated with wound infections has increased. Most prevention efforts to date have focused on oyster consumption. New educational messages focusing on the risk of vibriosis from wound infections should target high-risk populations.

Refrigerated Seawater Depuration for Reducing Vibrio parahaemolyticus Contamination in Pacific Oyster (Crassostrea gigas)

The efficacy of refrigerated-seawater depuration for reducing Vibrio parahaemolyticus levels in Pacific oyster (Crassostrea gigas) was investigated. Raw Pacific oysters were inoculated with a mixed culture of five clinical strains of V. parahaemolyticus (105 to 106 most probable number [MPN] per g) and depurated with refrigerated seawater (5°C) in a laboratory-scale recirculation system equipped with a 15-W gamma UV sterilizer. Depuration with refrigerated seawater for 96 h reduced V. parahaemolyticus populations by &gt;3.0 log MPN/g in oysters harvested in the winter. However, 144 h of depuration at 5°C was required to achieve a 3-log reduction in oysters harvested in the summer. Depuration with refrigerated seawater at 5°C for up to 144 h caused no significant fatality in the Pacific oyster and could be applied as a postharvest treatment to reduce V. parahaemolyticus contamination in Pacific oysters. Further studies are needed to validate the efficacy of the depuration process for reducing naturally accumulated V. parahaemolyticus in oysters.

Modulation of responses of Vibrio parahaemolyticus O3:K6 to pH and temperature stresses by growth at different salt concentrations

Vibrio parahaemolyticus inhabits marine, brackish, and estuarine waters worldwide, where fluctuations in salinity pose a constant challenge to the osmotic stress response of the organism. Vibrio parahaemolyticus is a moderate halophile, having an absolute requirement for salt for survival, and is capable of growth at 1 to 9% NaCl. It is the leading cause of seafood-related bacterial gastroenteritis in the United States and much of Asia. We determined whether growth in differing NaCl concentrations alters the susceptibility of V. parahaemolyticus O3:K6 to other environmental stresses. Vibrio parahaemolyticus was grown at a 1% or 3% NaCl concentration, and the growth and survival of the organism were examined under acid or temperature stress conditions. Growth of V. parahaemolyticus in 3% NaCl versus that in 1% NaCl increased survival under both inorganic (HCl) and organic (acetic acid) acid conditions. In addition, at 42 degrees C and -20 degrees C, 1% NaCl had a detrimental effect on growth. The expression of lysine decarboxylase (encoded by cadA), the organism's main acid stress response system, was induced by both NaCl and acid conditions. To begin to address the mechanism of regulation of the stress response, we constructed a knockout mutation in rpoS, which encodes the alternative stress sigma factor, and in toxRS, a two-component regulator common to many Vibrio species. Both mutant strains had significantly reduced survival under acid stress conditions. The effect of V. parahaemolyticus growth in 1% or 3% NaCl was examined using a cytotoxicity assay, and we found that V. parahaemolyticus grown in 1% NaCl was significantly more toxic than that grown in 3% NaCl.

Enumeration of Vibrio parahaemolyticus in oyster tissues following artificial contamination and depuration

AIMS

To evaluate enumeration of Vibrio parahaemolyticus in oyster tissues following artificial contamination and depuration.

METHODS AND RESULTS

After inoculating with V. parahaemolyticus (ATCC 17802) and incubating for 24 h, the contaminated oysters were depurated with artificial seawater for 14 days. At each step, the tissue homogenate supernatants of oysters were spread-plated onto thiosulfate-citrate-bile salt-sucrose agar, followed by colony confirmation by the polymerase chain reaction. The pathogen was detected in the gills, digestive glands (including stomach, digestive ducts and digestive diverticula), adductor muscle and mantle cilia. After a 48-h depuration period at 17-19 degrees C, the retention rate of V. parahaemolyticus in the gills (28.1%) and digestive glands (13.5%) was higher than that in adductor muscle and mantle cilia (1.4 and 2.4%, respectively).

CONCLUSIONS

The population of V. parahaemolyticus in the digestive glands was the highest among all tissues tested, followed by the gills. The data indicate that digestive glands and gills are good sample candidates for direct monitoring of V. parahaemolyticus contamination in oysters.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first report on the dynamics of V. parahaemolyticus in various oyster tissues following artificial contamination and depuration. This study provides information to help in monitoring for V. parahaemolyticus in commercial oysters.

Development of a toxR-based loop-mediated isothermal amplification assay for detecting Vibrio parahaemolyticus

BACKGROUND

Vibrio parahaemolyticus is a leading cause of seafood-related bacterial gastroenteritis and outbreaks worldwide. Sensitive and specific detection methods are needed to better control V. parahaemolyticus infections. This study aimed at developing a highly specific and sensitive loop-mediated isothermal amplification (LAMP) assay for detecting V. parahaemolyticus in oysters. A set of five LAMP primers, two outer, two inner, and one loop were designed based on the published V. parahaemolyticus toxR sequence. Specificity of the assay was evaluated using a panel of 36 V. parahaemolyticus and 39 other strains. The assay sensitivity was determined using serial dilutions of V. parahaemolyticus ATCC 27969 culture ranging from 10(8) CFU/ml to extinction. The assay was also tested in experimentally inoculated oyster samples.

RESULTS

The toxR-based LAMP assay was able to specifically detect all of the 36 V. parahaemolyticus strains without amplification from 39 other strains. The detection limit was 47-470 cells per reaction in pure culture, up to 100-fold more sensitive than that of toxR-PCR. When applied in spiked oysters, the assay was able to detect 1.1 x 10(5) V. parahaemolyticus cells per gram of oyster without enrichment, up to 100-fold more sensitive than that of toxR-PCR. Standard curves generated for detecting V. parahaemolyticus in both pure culture and spiked oyster samples showed good linear relationship between cell numbers and the fluorescence or turbidity signals.

CONCLUSIONS

The toxR-based LAMP assay developed in this study was sensitive, specific, and quantitative, holding great potential for future field detection of V. parahaemolyticus in raw oysters.

Occurrence of Vibrio parahaemolyticus and its specific phages from shrimp ponds in east coast of India

Vibrio parahaemolyticus is a natural microflora of marine and coastal water bodies and associated with mortality of larval shrimp in penaeid shrimp in ponds. Bacteriophages occur virtually in all places where their hosts exist. In this study, total distribution of V. parahaemolyticus and its phages were examined in shrimp ponds, seawater, estuary, animal surface, and tissues. Total vibrio count in sediments of two ponds was found to be 2.6 × 10(3) and 5.6 × 10(3) cfu/g. Incidence of V. parahaemolyticus in the ponds was close, while it was markedly higher in the animal surface and tissue samples. Biochemically identified eight strains of V. parahaemolyticus (V1, V3-V6, V9, V11, and V12) were taken for further infection studies with bacteriophage. Totally five bacteriophages capable of infecting V. parahaemolyticus MTCC-451 strain were isolated from all the samples. One of the isolated bacteriophage Vp1 from estuary was able to lyse all the isolated V. parahaemolyticus strains we used. Therefore, the morphology of Vp1 was estimated in TEM. Vp1 phage head measuring approximately about 50-60 nm diameter with icosahedral outline and a contractile tails of diameter 7 nm and length 100 nm and it was identified as Myoviridae. Therefore, the phages have the potential application in destroying bacterial pathogens.

Prevalence, serotyping and molecular characterization of Vibrio parahaemolyticus in mussels from Italian growing areas, Adriatic Sea

The aims of this study were to investigate the prevalence of total and pathogenic Vibrio parahaemolyticus strains in Italian mussels from different geographical areas of the Adriatic Sea and to determine their serotypes, toxigenic profiles and pandemic potential. Out of 559 samples analysed during 2007, 65 (11.6%) were positive for V. parahaemolyticus. None of the isolates had the genes for thermostable direct haemolysin (tdh) and pandemic marker (toxRS), while five strains (7.7%) had that for TDH-related haemolysin (trh). Regarding geographical location of the toxigenic strains, three were from the Adriatic coast of Puglia, one from Veneto, and one from the Marches. The trh-positive V. parahaemolyticus isolates from Puglia belonged to O1:KUT (2/3) and O1:K37(1/3) serotypes, the trh-positive isolate from the Marches to OUT(O untypeable):KUT serotype, and that from Veneto to O3:KUT. The prevalence of trh-positive V. parahaemolyticus obtained from mussels in this study was higher respect to that reported in previous studies from other European and Extraeuropean countries. The Health Authorities should be more aware of the epidemiological role of environmental V. parahaemolyticus in local food-borne diseases, and increase the microbial surveillance on these microorganisms isolated from shellfish.

Chlorophyll a might structure a community of potentially pathogenic culturable Vibrionaceae. Insights from a one-year study of water and mussels surveyed on the French Atlantic coast

The present study focused on the isolation of culturable bacteria from mussels and sea water to identify Vibrionaceae potentially pathogenic for humans. Three sites located on the French Atlantic coast were monitored monthly (twice each month during summer) for 1 year. Environmental parameters were surveyed (water temperature, salinity, turbidity, chlorophyll a) and bacteria were detected by culture and identified by API 20E(®) systems (BioMérieux) and PCR. A total of seven species were detected (Grimontia hollisae, Photobacterium damselae, Vibrio alginolyticus, V. cholerae, V. fluvialis, V. vulnificus and V. parahaemolyticus) and species diversity was higher at the end of summer. Surprisingly, V. cholerae non-O1/non-O139 was detected in spring. No site effect was detected. Using Sørensen similarity indices and statistical analyses, we showed that chlorophyll a had a significant influence on the bacterial community detected in mussels and assemblages were more similar to one another when chlorophyll a values were above 20 µg l(-1) . No significant effect of any parameter was found on the community detected in water samples. Such surveys are essential for the understanding of sanitary crises and detection of emerging pathogens.

Correlation between environmental factors and prevalence of Vibrio parahaemolyticus in oysters harvested in the southern coastal area of Sao Paulo State, Brazil

The presence of Vibrio parahaemolyticus in 123 oyster samples collected from an estuary on the southern coast of Sao Paulo state, Brazil, was investigated. Of the 123 samples, 99.2% were positive with densities ranging from < 3 to 10(5) most probable number (MPN)/g. Densities correlated significantly with water temperature (r = 0.48; P < 0.001) but not with salinity (r = -0.09; P = 0.34). The effect of harvest site on counts was not significant (P > 0.05). These data provide information for the assessment of exposure of V. parahaemolyticus in oysters at harvest.

Diversity and pathogenecity of Vibrio species in cultured bivalve molluscs

Shellfish production is seriously affected by bacterial pathogens that cause high losses in hatcheries and in the aquaculture sector. A number of Vibrio species are considered important pathogens and have provoked severe mortality outbreaks. The pathologies caused by vibrios in bivalves have been described since the 1960s; however, over recent years, successive episodes of high mortality have been recorded due to these microorganisms. The present work provides an updated overview of the different studies performed in relation with the diversity of Vibrio spp. associated to bivalves. Special attention is given to the main Vibrio diseases and implicated species affecting the different life stages of cultured bivalves.

Ecology of pathogenic and non-pathogenic Vibrio parahaemolyticus on the French Atlantic coast. Effects of temperature, salinity, turbidity and chlorophyll a

Vibrio parahaemolyticus is one of the principal bacterial causes for seafood-borne gastroenteritis in the world. In the present study, three sites located on the French Atlantic coast were monitored monthly for environmental parameters over 1 year. The presence of total and pathogenic V. parahaemolyticus in sediment, water and mussel samples was detected following enrichment by culture and real-time PCR (toxR gene, tdh, trh1 and trh2 virulence genes). Using generalized linear models, we showed that the presence of V. parahaemolyticus in water could be explained by a combination of mean temperature over the 7 days before the day of sampling (P < 0.001) and turbidity (P = 0.058). In mussels, an effect of chlorophyll a (P = 0.005) was detected when an effect of the mean salinity over the 7 days before sampling was significant for the sediment (P < 0.001). We did not detect any significant effect of phytoplanktonic blooms or of the number of culturable bacteria on V. parahaemolyticus presence. No sample was revealed positive for tdh. The presence of trh1 and trh2 was positively influenced by the mean temperature during the 2 days before the day of sampling (P < 0.001 and P = 0.032). The importance of these ecological parameters is discussed in relation to the biology of V. parahaemolyticus.

Enteric bacterial pathogen detection in southern sea otters (Enhydra lutris nereis) is associated with coastal urbanization and freshwater runoff

Although protected for nearly a century, California's sea otters have been slow to recover, in part due to exposure to fecally-associated protozoal pathogens like Toxoplasma gondii and Sarcocystis neurona. However, potential impacts from exposure to fecal bacteria have not been systematically explored. Using selective media, we examined feces from live and dead sea otters from California for specific enteric bacterial pathogens (Campylobacter, Salmonella, Clostridium perfringens, C. difficile and Escherichia coli O157:H7), and pathogens endemic to the marine environment (Vibrio cholerae, V. parahaemolyticus and Plesiomonas shigelloides). We evaluated statistical associations between detection of these pathogens in otter feces and demographic or environmental risk factors for otter exposure, and found that dead otters were more likely to test positive for C. perfringens, Campylobacter and V. parahaemolyticus than were live otters. Otters from more urbanized coastlines and areas with high freshwater runoff (near outflows of rivers or streams) were more likely to test positive for one or more of these bacterial pathogens. Other risk factors for bacterial detection in otters included male gender and fecal samples collected during the rainy season when surface runoff is maximal. Similar risk factors were reported in prior studies of pathogen exposure for California otters and their invertebrate prey, suggesting that land-sea transfer and/or facilitation of pathogen survival in degraded coastal marine habitat may be impacting sea otter recovery. Because otters and humans share many of the same foods, our findings may also have implications for human health.

Effect of temperature on uptake and survival of Vibrio parahaemolyticus in oysters (Crassostrea plicatula)

This study investigated accumulation of Vibrio parahaemolyticus in Zhe oyster (Crassostrea plicatula) from culture water and effectiveness of frozen and chilled storage on reducing V. parahaemolyticus in oysters. Freshly harvested oysters were placed in artificial seawater containing V. parahaemolyticus (10(4)CFU/mL) at 16, 20, 26, and 32 degrees C for 96 h. Contaminated oysters were stored at chilled temperatures (0, 5, and 15 degrees C) and frozen at -18 and -30 degrees C and changes of V. parahaemolyticus populations in oysters were determined using the most probable number (MPN) method. Accumulations of V. parahaemolyticus in C. plicatula reached the peaks at 6.66 (32 degrees C), 5.72 (26 degrees C), 5.04 (20 degrees C), 4.72 (16 degrees C) log MPN/g after 32 h in contaminated artificial seawater. Holding contaminated Zhe oysters at 5 and 0 degrees C reduced V. parahaemolyticus populations in both shell stock and shucked oysters. Populations of V. parahaemolyticus in shell stock and shucked oysters declined by 1.42 and 2.0 log MPN/g, respectively, after 96 h of storage at 5 degrees C and by 2.11 and 2.38 log MPN/g, respectively, after 96 h of storage at 0 degrees C. However, populations of V. parahaemolyticus increased by 2.44 log MPN/g in shell stock oysters and by 1.64 og MPN/g in shucked oysters when stored at 15 degrees C for 60 h. Frozen storage was effective in inactivating V. parahaemolyticus. Populations of V. parahaemolyticus in shell stock and shucked oysters decreased from 5.46log MPN/g to 1.66 and 0.38 log MPN/g, respectively, after 75 days of storage at -30 degrees C. No V. parahaemolyticus cells were detected (<3 log MPN/g) in the shucked oysters after 60 days of storage at -18 degrees C. These results demonstrated that accumulation of V. parahaemolyticus in cultured C. plicatula increases as water temperature increases. Harvested C. plicatula should be stored at 5 degrees C or lower to control the hazard of V. parahaemolyticus.

Simultaneous identification of seven foodborne pathogens and Escherichia coli (pathogenic and nonpathogenic) using capillary electrophoresis-based single-strand conformation polymorphism coupled with multiplex PCR

The objective of this study was to develop a novel technique for parallel analysis of eight important foodborne microbes using capillary electrophoresis-based single-strand conformation polymorphism (CE-SSCP) coupled with multiplex PCR. Specific primers for multiplex PCR amplification of the 16S rRNA gene were designed, corresponding to eight species of bacteria, including Escherichia coli, Clostridium perfringens, Campylobacter jejuni, Salmonella enterica, Listeria monocytogenes, Vibrio parahaemolyticus, Staphylococcus aureus, and Bacillus cereus, for the species-specific identification and optimal separation of their PCR products in subsequent analysis by CE-SSCP. Multiplex PCR conditions including annealing temperature, extension time, the number of PCR cycles, and primer concentrations were then optimized for simultaneous detection of all target foodborne bacteria. The diagnostic system using CE-SSCP combined with multiplex PCR developed here can be used for rapid investigation of causative agents of foodborne illness. The simplicity and high sensitivity of the method may lead to improved management of safety and illness related to food.

Risks of recreational exposure to waterborne pathogens among persons with HIV/AIDS in Baltimore, Maryland

OBJECTIVES

We assessed the prevalence of recreational activities in the waterways of Baltimore, MD, and the risk of exposure to Cryptosporidium among persons with HIV/AIDS.

METHODS

We studied patients at the Johns Hopkins Moore Outpatient AIDS Clinic. We conducted oral interviews with a convenience sample of 157 HIV/AIDS patients to ascertain the sites used for recreational water contact within Baltimore waters and assess risk behaviors.

RESULTS

Approximately 48% of respondents reported participating in recreational water activities (fishing, crabbing, boating, and swimming). Men and women were almost equally likely to engage in recreational water activities (53.3% versus 51.3%). Approximately 67% (105 of 157) ate their own catch or that of friends or family members, and a majority (61%, or 46 of 75) of respondents who reported recreational water contact reported consumption of their own catch.

CONCLUSIONS

Baltimoreans with HIV/AIDS are engaging in recreational water activities in urban waters that may expose them to waterborne pathogens and recreational water illnesses. Susceptible persons, such as patients with HIV/AIDS, should be cautioned regarding potential microbial risks from recreational water contact with surface waters.

Psychrotrophic lactic acid bacteria used to improve the safety and quality of vacuum-packaged cooked and peeled tropical shrimp and cold-smoked salmon

Previously isolated lactic acid bacteria (LAB) from seafood products have been investigated for their capacity to increase the sensory shelf life of vacuum-packaged shrimp and cold-smoked salmon and to inhibit the growth of three pathogenic bacteria. Two different manufactured batches of cooked, peeled, and vacuum-packaged shrimp were inoculated with seven LAB strains separately at an initial level of 5 log CFU g-t, and the spoilage was estimated by sensory analysis after 7 and 28 days of storage at 8 degrees C. Two Leuconostoc gelidum strains greatly extended the shelf life of both batches, two Lactococcus piscium strains had a moderate effect, two bacteria were spoilers (Lactobacillus fuchuensis and Carnobacterium alterfunditum), and the last one (another Leuconostoc gelidum strain) showed highly variable results depending on the batch considered. The four strains showing the best results (two Leuconostoc gelidum and two Lactococcus piscium strains) were selected for the same experiment in cold-smoked salmon. In this product, Lactococcus piscium strains showed better inhibiting capacities, improving the sensory quality significantly at 14 and 28 days of storage. Finally, the inhibiting capacities of two strains (one Leuconostoc gelidum strain and one Lactococcus piscium strain) were tested against three pathogenic bacteria (Vibrio cholerae, Listeria monocytogenes, and Staphylococcus aureus) by challenge tests in shrimp. LAB and pathogenic bacteria were coinoculated in vacuum-packaged shrimp and enumerated during 5 weeks. Lactococcus piscium strain EU2241 was able to reduce significantly the number of Listeria monocytogenes and S. aureus organisms in the product by 2 log throughout the study for Listeria monocytogenes and up to 4 weeks for S. aureus.

Detection of Vibrio parahaemolyticus in tropical shellfish by SYBR green real-time PCR and evaluation of three enrichment media

A rapid, sensitive and highly reproducible SYBR green based real-time PCR assay was developed for detection of tdh positive pathogenic Vibrio parahaemolyticus. Minimum detection limit was 0.1 pg of pure V. parahaemolyticus genomic DNA with typical R(2) values >0.99 and coefficient of variation (CV) values ranging from 1.2 to 4.2 on three different days. The method was also used to evaluate the effect of three different enrichment media alkaline peptone water (APW), sodium taurocholate (ST) broth and salt polymyxin broth (SPB) on detection of V. parahaemolyticus. Crude lysates were directly used for real-time PCR. Without enrichment, the detection limit of pure cultures was 10(1) CFU/ml for ST broth and 10(2) CFU/ml in APW and SPB but for shrimp homogenates spiked with pure culture, the minimum detection limit was 10(2) CFU/ml for all three broths with a linear detection range of 10(2)-10(6). Without enrichment, detection in ST broth was more efficient than APW and SPB. After 6 h enrichment, limit of detection was found to be 1 CFU in all three media. However, for iced shrimp, the limit of detection was 10(2) after 6 h enrichment. No significant difference was seen between different enrichment media with respect to tdh gene detection of V. parahaemolyticus. The methodology developed here can be useful for rapid detection of tdh positive V. parahaemolyticus by laboratories involved in monitoring programmes for pathogenic V. parahaemolyticus.

Immunomagnetic separation and coagglutination of Vibrio parahaemolyticus with anti-flagellar protein monoclonal antibody

Mice were immunized by injection of Vibrio parahaemolyticus ATCC 17802 polar flagellin in order to produce monoclonal antibodies (mAbs). mAbs were analyzed by anti-H enzyme-linked immunosorbent assay using V. parahaemolyticus polar flagellar cores. The mAb exhibiting the highest anti-H titer was coated onto Cowan I Staphylococcus aureus cells at a concentration of 75 microg/ml cell suspension and used for slide coagglutination. Of 41 isolates identified genetically as V. parahaemolyticus, 100% coagglutinated with the anti-H mAb within 30 s, and the mAb did not react with 30 isolates identified as Vibrio vulnificus. A strong coagglutination reaction with V. parahaemolyticus ATCC 17802 was still observed when the S. aureus cells were armed with as little as 15 microg of mAb/ml S. aureus cell suspension. At this concentration, the mAb cross-reacted with three other Vibrio species, suggesting that they share an identical H antigen or antigens. The anti-H mAb was then used to optimize an immunomagnetic separation protocol which exhibited from 35% to about 45% binding of 10(2) to 10(3) V. parahaemolyticus cells in phosphate-buffered saline. The mAb would be useful for the rapid and selective isolation, concentration, and detection of V. parahaemolyticus cells from environmental sources.

A model of the effect of temperature on the growth of pathogenic and nonpathogenic Vibrio parahaemolyticus isolated from oysters in Korea

Vibrio parahaemolyticus is recognized as the leading cause of human gastroenteritis associated with the consumption of seafood. The objective of this study was to model the growth kinetics of pathogenic and nonpathogenic V. parahaemolyticus in broth and oyster slurry. Primary growth models of V. parahaemolyticus in broth and oyster slurry fit well to a modified Gomperz equation (broth R(2)=0.99; oyster slurry R(2)=0.96). The lag time (LT), specific growth rate (SGR), and maximum population density (MPD) of each primary model were compared. The growth of nonpathogenic V. parahaemolyticus was found to be more rapid than that of pathogenic V. parahaemolyticus, regardless of the model medium. In addition, significant (P<0.05) differences in the growth kinetics between pathogenic and nonpathogenic V. parahaemolyticus in broth were observed at 10 degrees C. When compared to growth in broth, the growth of V. parahaemolyticus was delayed in oyster slurry, and growth was not observed at 10 or 15 degrees C. The Davey and square root models were identified as appropriate secondary models for predicting the LT and SGR, respectively. For the broth model, the average B(f) and A(f) values for LT were found to be 0.97 and 1.3, respectively, whereas the average B(f) and A(f) values for SGR were 1.05 and 1.11, respectively. The model generated in this study predicted an LT that was shorter and an SGR that was similar to those that were actually observed, which indicates that these models provide a reliable and safe prediction of V. parahaemolyticus growth.

Development of a multiplex real-time PCR assay with an internal amplification control for the detection of total and pathogenic Vibrio parahaemolyticus bacteria in oysters

Vibrio parahaemolyticus is an estuarine bacterium that is the leading cause of shellfish-associated cases of bacterial gastroenteritis in the United States. Our laboratory developed a real-time multiplex PCR assay for the simultaneous detection of the thermolabile hemolysin (tlh), thermostable direct hemolysin (tdh), and thermostable-related hemolysin (trh) genes of V. parahaemolyticus. The tlh gene is a species-specific marker, while the tdh and trh genes are pathogenicity markers. An internal amplification control (IAC) was incorporated to ensure PCR integrity and eliminate false-negative reporting. The assay was tested for specificity against >150 strains representing eight bacterial species. Only V. parahaemolyticus strains possessing the appropriate target genes generated a fluorescent signal, except for a late tdh signal generated by three strains of V. hollisae. The multiplex assay detected <10 CFU/reaction of pathogenic V. parahaemolyticus in the presence of >10(4) CFU/reaction of total V. parahaemolyticus bacteria. The real-time PCR assay was utilized with a most-probable-number format, and its results were compared to standard V. parahaemolyticus isolation methodology during an environmental survey of Alaskan oysters. The IAC was occasionally inhibited by the oyster matrix, and this usually corresponded to negative results for V. parahaemolyticus targets. V. parahaemolyticus tlh, tdh, and trh were detected in 44, 44, and 52% of the oyster samples, respectively. V. parahaemolyticus was isolated from 33% of the samples, and tdh(+) and trh(+) strains were isolated from 19 and 26%, respectively. These results demonstrate the utility of the real-time PCR assay in environmental surveys and its possible application to outbreak investigations for the detection of total and pathogenic V. parahaemolyticus.