Detection of pathogenic bacteria in shellfish using multiplex PCR followed by CovaLink NH microwell plate sandwich hybridization

First Data on Campylobacter spp. Presence in Shellfish in Croatia

This study aimed to assess the presence of thermotolerant Campylobacter spp., as one of the most important foodborne zoonotic pathogens, in three shellfish species: mussels (Mytilus galloprovincialis), oysters (Ostrea edulis) and queen scallops (Aequipecten opercularis). The samples were collected from nine locations in the Istrian aquatory, Croatia. Isolation of Campylobacter was done according to standard ISO method, and species were identified using multiplex PCR. Isolates identified as C. jejuni and C. lari were genotyped using multilocus sequence typing (MLST) to determine the potential source of contamination. Among 108 examined samples of bivalve molluscs, mussels dominated and were the only ones found positive for the presence of Campylobacter (25.6%). In total, 19 C. lari and 1 C. jejuni strains were isolated. C. lari isolates found in this study belong to 13 sequence types (STs), and 9 of them are newly described in this paper. Two out of the four previously described C. lari STs that were found in this study were previously found in human stool. The only C. jejuni isolate was found to be sequence type 1268, which belongs to ST-1275 clonal complex that is almost exclusively found in seabirds and can sporadically cause infection in humans. Regarding the obtained results, introducing surveillance of thermotolerant Campylobacter in shellfish in the Republic of Croatia is advised as an improvement for public health safety.

Atypical Salmonella Typhimurium persistence in the pacific oyster, Crassostrea gigas, and its effect on the variation of gene expression involved in the oyster's immune system

Salmonella is one of the most important pathogens involved in food intoxication outbreaks, and in many cases, the intoxication has been linked to shellfish which is typically consumed raw. While much is understood about the interactions between Salmonella and vertebrates, much less is known about its relationships with invertebrates, which could be an overlooked and important aspect to better understand the Salmonella interaction with its diversified hosts. The aim of this study was to investigate the effect of preadaptation in seawater microcosms during 12 months on Salmonella Typhimurium by determining its survival capacity within this mollusk over a period of 30 days. The results showed that the stressed bacteria are able to survive in this mollusk at a higher concentration even after thirty days of infection compared to bacteria in the normal state. In order to minimize the effect of an experimental device for one month on the survival of Salmonella, we carried out an in vitro study to determine the number of viable Salmonella in the hemocytes of oysters. Interestingly, we evaluated the effect of the antibacterial activity of different extracts of C. gigas using the solvents (Methanol, Ethanol and acetic acid) specifically against stressed and unstressed Salmonella. Furthermore, we compared the expression of three genes in the oyster Cg-big-def1, timp and sod in response to experimental infections of this mollusk with Vibrio splendidus kb133 and S. Typhimurium LT2DT104 in normal and stressed states. These findings are very important to contribute to explaining several questions about the persistence of S. Typhimurium for a long time in C. gigas and the host's immune response to this microorganism which is considered to be non-virulent for molluscs.

Factors Influencing the Concentration of Fecal Coliforms in Oysters in the River Blackwater Estuary, UK

Contamination of water systems can not only entail high risks to human health but can also result in economic losses due to closure of beaches and shellfish harvesting areas. Understanding the origin of fecal pollution at locations where shellfish are grown is essential in assessing associated health risks—as well as the determining actions necessary to remedy the problem. The aim of this work is to identify the species-specific source(s) of fecal contamination impacting waters overlying the shellfisheries in the Blackwater Estuary, East Anglia, UK. Over a twelve-month period, water samples were taken from above the oysters and from a variety of upstream points considered to be likely sources of fecal microorganism, together with oyster samples, and the number of fecal streptococci and E. coli were determined. Transition from low to high tide significantly decreased the concentration of fecal streptococci in waters overlying the oyster beds, indicative of a freshwater input of fecal pollution in oyster bed waters. In 12 months, the number of E. coli remained constant throughout, while fecal streptococci numbers were generally higher in the winter months. Analyses of upstream samples identified a sewage outfall to be the main source of E. coli to the oyster beds, with additional fecal streptococci from agricultural sources. The findings may assist in developing approaches for assessing the risks to shellfishery industries of various fecal inputs into an estuary, which could then help local governmental authorities address the problem.

Multiplex PCR assay for simultaneous detection and differentiation of Entamoeba histolytica, Giardia lamblia, and Salmonella spp. in the municipality-supplied drinking water

BACKGROUND

The contamination with Entamoeba histolytica, Giardia lamblia, and Salmonella spp. in drinking water is the most prevalent in Indian subcontinent, but often difficult to detect all these pathogens from the drinking water.

MATERIALS AND METHODS

A multiplex polymerase chain reaction (mPCR) method was developed to detect contamination of municipality-supplied drinking water with E. histolytica, G. lamblia, and Salmonella spp. The primers were designed to target small subunit of 16S rRNA type gene of E. histolytica and G. lamblia, and invasive A gene of Salmonella typhimurium. The optimized mPCR assay was applied on 158 municipality-supplied drinking water samples collected from Delhi.

RESULTS

Out of total 158 water samples, 89 (56.32%) were found positive for the targeted pathogens by mPCR while conventional methods could be detected only in 11 (6.96%) samples. The mPCR assay showed 100% sensitivity and specificity for these pathogens in comparison with culture and microscopic detection. Of the 89 mPCR-positive samples, G. lamblia, E. histolytica, and Salmonella spp. were present in 35 (22.15%), 26 (16.45%), and 28 (17.72%), respectively. Nine (5.69%) samples were positive for both E. histolytica and G. lamblia, 10 (6.32%) were positive for G. lamblia and Salmonella spp., and 8 (5.06%) had Salmonella spp. and E. histolytica. Nonetheless, 3 (1.89%) samples were positive for all three pathogens.

CONCLUSIONS

The present assay is an alternative to conventional methods to serve as highly sensitive, specific, and economical means for water quality surveillance to detect the outbreak caused by E. histolytica, G. lamblia, and Salmonella spp. pathogens.

W. Vieira C, Parveen S. Genotypic and phenotypic characterization of Escherichia coli isolated from mollusks in Brazil and the United States

The aim of this study was to determine the serogroups, antimicrobial resistance and genetic diversity of Escherichia coli isolates from samples of bivalve mollusks collected along Santa Catarina coast, Brazil, and from the Chesapeake Bay, Maryland, USA. One hundred forty-one E. coli isolates were characterized for serogroups with 181 specific O antisera and antimicrobial susceptibility using the disk diffusion method. The genetic diversity was assessed using pulsed-field gel electrophoresis (PFGE). The results showed that among the isolates, 19.9% were classified as multi-drug resistant (MDR) and resistance was most frequently observed to cephalothin, nitrofurantoin, and ampicillin. The predominant serogroups were O6, O8, and O38. Some serogroups were recognized as pathogenic E. coli. PFGE dendrograms indicated extensive genetic diversity among the isolates. Although characteristics of the E. coli isolates were highly variable, it is important to note that E. coli belonging to pathogenic serogroups and MDR isolates are present in mollusks of both study areas. This is the first report on the phenotypic and genotypic characterization of E. coli from mollusks from Santa Catarina and the Chesapeake Bay that should encourage studies focusing on comparison of isolates across countries.

Cryptosporidium spp. Contamination in Perna perna Mussels Destined for Human Consumption in Southeastern Rio de Janeiro, Brazil

Cryptosporidium spp. has been recognized as an important pathogen. As bivalve mollusks are noted as potential sources of several pathogens due to their consumption as foodstuffs, the aim of this study was to investigate the occurrence of Cryptosporidium spp. oocysts in Perna perna mussels and in seawater samples from a mussel farm in Southeastern Brazil, where mussels are grown directly in the sea, attached to ropes. Oocysts were observed by microscopy and confirmed by an enzyme-linked immunosorbent assay. Oocysts were present in mussel gills and GI tracts, as well as in the seawater. Of the 100 females, 10% and 11% showed contaminated GI tracts and gills, respectively, while this rate was lower in males, at 5% and 8.9%. Oocysts were present in higher amounts in the GI tract compared to gills and water. Contamination of the study area is apparent, leading to public health risks. More in-depth studies are needed, including molecular investigations, to identify Cryptosporidium species in mussels, as well as the implementation of monitoring actions in animals destined for human consumption.

Parasites in the mangrove oyster Crassostrea rhizophorae cultivated in the estuary of the Graciosa River in Taperoá, Bahia

In this work, parasites associated with the mangrove oyster Crassostrea rhizophorae were studied at a cultivation unit in the estuary of the Graciosa River in Taperoá, Bahia. On a monthly basis, between April 2011 and March 2012, 20 oysters were collected, measured and fixed in 10% formaldehyde. In order to identify the parasites, routine histological techniques were used. The specimens were embedded in paraffin and sections, 7 µm thick, were cut. These were then stained with Harris hematoxylin and eosin and were examined using an optical microscope. The parameters analyzed to investigate water quality showed that the temperature ranged from 23.9 °C to 29.3 °C, water salinity from 0.4 to 24.2 Practical Salinity Units PSU and recorded rainfall from 80 mm to 406.4 mm/month. During the parasitological analyses, infestation of the polychaete Neanthes succinea was observed in 41% of the oysters. Through histological techniques, the following parasites were identified: colonies of Rickettsia-like organisms (RLOs); the protozoa Nematopsis sp. and Ancistrocoma sp.; the turbellarian Urastoma sp.; the metacestode Tylocephalum sp. and an unidentified tapeworm. The data collected showed that there was low-intensity infection with and prevalence of parasites, except for Nematopsis sp., thus attesting that these cultivated oysters were in a healthy condition.

Comparative inactivation of murine norovirus, human adenovirus, and human JC polyomavirus by chlorine in seawater

Viruses excreted by humans affect the commercial and recreational use of coastal water. Shellfish produced in contaminated waters have been linked to many episodes and outbreaks of viral gastroenteritis, as well as other food-borne diseases worldwide. The risk can be reduced by appropriate treatment following harvesting and by depuration. The kinetics of inactivation of murine norovirus 1 and human adenovirus 2 in natural and artificial seawater by free available chlorine was studied by quantifying genomic copies (GC) using quantitative PCR and infectious viral particles (PFU). Human JC polyomavirus Mad4 kinetics were evaluated by quantitative PCR. DNase or RNase were used to eliminate free genomes and assess potential viral infectivity when molecular detection was performed. At 30 min of assay, human adenovirus 2 showed 2.6- and 2.7-log(10) GC reductions and a 2.3- and 2.4-log(10) PFU reductions in natural and artificial seawater, respectively, and infectious viral particles were still observed at the end of the assay. When DNase was used prior to the nucleic acid extraction the kinetic of inactivation obtained by quantitative PCR was statistically equivalent to the one observed by infectivity assays. For murine norovirus 1, 2.5, and 3.5-log(10) GC reductions were observed in natural and artificial seawater, respectively, while no viruses remained infectious after 30 min of contact with chlorine. Regarding JC polyomavirus Mad4, 1.5- and 1.1-log(10) GC reductions were observed after 30 min of contact time. No infectivity assays were conducted for this virus. The results obtained provide data that might be applicable to seawater used in shellfish depuration.

Development of loop-mediated isothermal amplification method for rapid detection of Streptococcus iniae, the causative agent of streptococcicosis in fish

Streptococcus iniae is a major pathogen that causes sever economic losses in tilapia aquaculture. A set of four specific primers was designed by targeting lctO gene. With Bst DNA polymerase, the target DNA can be clearly amplified for 60 min at 64 °C in a simple water bath. The sensitivity of the LAMP assay for the detection of S. iniae is about 12.4 cells per reaction in both of pure cultures and added fish tissues cultures. LAMP products could be judged with agar gel or naked eye after addition of SYBR Green I. There were no cross-reactions with other bacterial strains indicating high specificity of the LAMP. The LAMP method was also applied to detect S. iniae-infected tilapia tissues effectively. The LAMP assay reported here indicates the potential usefulness of the technique as a valuable simple, rapid alternative procedure for the detection of S. iniae during streptococcicosis monitoring of cultured fish.

Evaluation of a loop-mediated isothermal amplification assay for detecting Vibrio vulnificus in raw oysters

Human consumption of raw or undercooked seafood, particularly oysters, may lead to severe infections due to the presence of Vibrio vulnificus. In this study, a sensitive and specific loop-mediated isothermal amplification (LAMP) assay was developed to detect this pathogen in raw oysters. Two outer and two inner primers were designed to specifically recognize the V. vulnificus cytolysin/hemolysin gene (vvhA), and the reaction could be completed in 1 hour at 63 degrees C. Direct visual observation of the LAMP amplicons was achieved with the aid of SYBR Green I fluorescent dye. The assay specificity was determined using 50 bacterial strains, including multiple Vibrio spp. and bacteria of other genera. No false-positive or false-negative results were observed. The detection limit of the LAMP assay was approximately 20 colony-forming units (CFU) in pure cultures, 10-fold more sensitive than a conventional polymerase chain reaction (PCR). When directly applied in oyster homogenate, the LAMP assay had a detection limit of approximately 10(7) CFU/g. After 5-hour enrichment, LAMP was capable of detecting 7 CFU of V. vulnificus per gram of oyster tissue without lengthy DNA extraction steps. This level of detection was 1000-fold more sensitive than PCRs included for comparison. Because of its isothermal format and unique amplicon detection technique, this rapid and sensitive LAMP assay holds potential for future field applications.

Depuration dynamics of oysters (Crassostrea gigas) artificially contaminated by Salmonella enterica serovar Typhimurium

The State of Santa Catarina produces the greatest quantity of edible mollusks in Brazil. To guarantee sanitary qualify, mollusk cultures should be monitored for contamination by pathogenic microorganisms. A self-purification or "depuration" system that eliminates Salmonella enterica serovar Typhimurium contamination from oysters has been developed and evaluated. The depuration process occurred within a closed system, in which 1000 L of water was recirculated for 24 h. The water was sterilized with ultraviolet (UV) light, chlorine, or both together. Oysters (Crassostrea gigas) artificially contaminated with S. typhimurium were harvested every 6 h. Samples of oyster tissue were excised and both the presence and numbers of bacteria were determined. Combined UV light and chlorine treatments resulted in total elimination of bacteria within 12 h. Polymerase chain reaction detected bacteria in water exposed to the three treatments. This pioneering study is the first of its kind in Brazil and represents a major contribution to commercial mollusk culture in this country.

Detection and characterization of Salmonella associated with tropical seafood

The prevalence of Salmonella in seafood samples collected from the southwest coast of India was studied by conventional culture and by a DNA based molecular technique, polymerase chain reaction (PCR). While conventional culture techniques detected Salmonella in only 20 out of the 100 samples analyzed, direct enrichment lysate PCR detected 52 as positive for Salmonella. A set of three different PCR primers viz., hns, invA and invE were used. It was observed that hns primer detected Salmonella in a significantly higher number of samples. Fourteen out of nineteen isolates belonged to serovar S. enterica Weltevreden. S. Weltevreden isolates were genotyped yielding 4 different patterns both by RAPD and ERIC-PCR but when combined, the overall results discriminated the isolates of S. Weltevreden into 6 different types. This suggests that genetically diverse Salmonella Weltevreden are prevalent in seafood.

Fiber-optic microarray for simultaneous detection of multiple harmful algal bloom species

Harmful algal blooms (HABs) are a serious threat to coastal resources, causing a variety of impacts on public health, regional economies, and ecosystems. Plankton analysis is a valuable component of many HAB monitoring and research programs, but the diversity of plankton poses a problem in discriminating toxic from nontoxic species using conventional detection methods. Here we describe a sensitive and specific sandwich hybridization assay that combines fiber-optic microarrays with oligonucleotide probes to detect and enumerate the HAB species Alexandrium fundyense, Alexandrium ostenfeldii, and Pseudo-nitzschia australis. Microarrays were prepared by loading oligonucleotide probe-coupled microspheres (diameter, 3 mum) onto the distal ends of chemically etched imaging fiber bundles. Hybridization of target rRNA from HAB cells to immobilized probes on the microspheres was visualized using Cy3-labeled secondary probes in a sandwich-type assay format. We applied these microarrays to the detection and enumeration of HAB cells in both cultured and field samples. Our study demonstrated a detection limit of approximately 5 cells for all three target organisms within 45 min, without a separate amplification step, in both sample types. We also developed a multiplexed microarray to detect the three HAB species simultaneously, which successfully detected the target organisms, alone and in combination, without cross-reactivity. Our study suggests that fiber-optic microarrays can be used for rapid and sensitive detection and potential enumeration of HAB species in the environment.

Development of a PCR assay followed by nonradioactive hybridization using oligonucleotides covalently bound to CovaLink NH microwells for detection of four Plasmodium species in blood samples from humans

We developed and evaluated a PCR-based assay to detect four Plasmodium species in 79 blood samples from 56 travelers returning from areas where malaria is endemic. DNA amplification targeting a small region of the 18S rRNA gene was performed with Plasmodium genus-specific primers. The biotinylated PCR products were then identified by PCR-colorimetric Covalink NH microwell plate hybridization (CMPH) using species-specific phosphorylated probes covalently bound to a pretreated polystyrene surface. The results from PCR-CMPH showed high specificity, and for 47 of the 56 patients (84%), microscopy and PCR-CMPH results were in agreement. Discordant results were reevaluated with microscopy examination, other molecular methods, and DNA sequencing. Except for one patient, discrepancies were resolved in favor of PCR-CMPH: three mixed infections were detected, four species identification errors were corrected, and two negative results were shown to be positive. Our results indicate that PCR-CMPH is a simple, rapid, and specific method for malaria diagnosis. It employs stable reagents and inexpensive equipment, making it suitable for routine epidemiological use.

Waterborne pathogen detection by use of oligonucleotide-based microarrays

A small-oligonucleotide microarray prototype was designed with probes specific for the universal 16S rRNA and cpn60 genes of several pathogens that are usually encountered in wastewaters. In addition to these two targets, wecE-specific oligonucleotide probes were included in the microarray to enhance its discriminating power within the Enterobacteriaceae family. Universal PCR primers were used to amplify variable regions of 16S rRNA, cpn60, and wecE genes directly in Escherichia coli and Salmonella enterica serovar Typhimurium genomic DNA mixtures (binary); E. coli, S. enterica serovar Typhimurium, and Yersinia enterocolitica genomic DNA mixtures (ternary); or wastewater total DNA. Amplified products were fluorescently labeled and hybridized on the prototype chip. The detection sensitivity for S. enterica serovar Typhimurium was estimated to be on the order of 0.1% (10(4) S. enterica genomes) of the total DNA for the combination of PCR followed by microarray hybridization. The sensitivity of the prototype could be increased by hybridizing amplicons generated by PCR targeting genes specific for a bacterial subgroup, such as wecE genes, instead of universal taxonomic amplicons. However, there was evidence of PCR bias affecting the detection limits of a given pathogen as increasing amounts of a different pathogen were spiked into the test samples. These results demonstrate the feasibility of using DNA microarrays in the detection of waterborne pathogens within mixed populations but also raise the problem of PCR bias in such experiments.

Nucleic acid-based methods for the detection of bacterial pathogens: Present and future considerations for the clinical laboratory

BACKGROUND

Recent advances in nucleic acid-based methods to detect bacteria offer increased sensitivity and specificity over traditional microbiological techniques. The potential benefit of nucleic acid-based testing to the clinical laboratory is reduced time to diagnosis, high throughput, and accurate and reliable results.

METHODS

Several PCR and hybridization tests are commercially available for specific organism detection. Furthermore, hundreds of nucleic acid-based bacterial detection tests have been published in the literature and could be adapted for use in the clinical setting. Contamination potential, lack of standardization or validation for some assays, complex interpretation of results, and increased cost are possible limitations of these tests, however, and must be carefully considered before implementing them in the clinical laboratory.

CONCLUSIONS

A major area of advancement in nucleic acid-based assay development has been for specific and broad-range detection of bacterial pathogens.

Influence of water temperature and salinity on seasonal occurrences of Vibrio cholerae and enteric bacteria in oyster-producing areas of Veracruz, México

The influence of temperature and salinity on the occurrence of Vibrio cholerae, Escherichia coli and Salmonella spp. associated with water and oyster samples was investigated in two lagoons on the Atlantic Coast of Veracruz, Mexico over a 1-year period. The results indicated that seasonal salinity variability and warm temperatures, as well as nutrient influx, may influence the occurrence of V. cholera. non-O1 and O1. The conditions found in the Alvarado (31.12 degrees C, 6.27 per thousand, pH=8.74) and La Mancha lagoons (31.38 degrees C, 24.18 per thousand, pH=9.15) during the rainy season 2002 favored the occurrence of V. cholera O1 Inaba enterotoxin positive traced in oysters. Vibrio alginolyticus was detected in Alvarado lagoon water samples during the winter season. E. coli and Salmonella spp. were isolated from water samples from the La Mancha (90-96.7% and 86.7-96.7%) and Alvarado (88.6-97.1% and 88.6-100%) lagoons. Occurrence of bacteria may be due to effluents from urban, agricultural and industrial areas.

Bacillus anthracis: toxicology, epidemiology and current rapid-detection methods

B. anthracis, the causative agent for anthrax, has been well studied for over 150 years. Due to the genetic similarities among various Bacillus species, as well as its existence in both a spore form and a vegetative state, the detection and specific identification of B. anthracis have been proven to require complex techniques and/or laborious methods. With the heightened interest in the organism as a potential biological threat agent, a large number of interesting detection technologies have recently been developed, including methods involving immunological and nucleic acid-based assay formats. The technologies range from culture-based methods to portable Total Analysis Systems based on real-time PCR. This review with 170 references provides a brief background on the toxicology and epidemiology of B. anthracis, discusses challenges associated with its detection related to genetic similarities to other species, and reviews immunological and, with greater emphasis, nucleic acid-based detection systems.

Genotypes and Antibiotic Resistance ofSalmonellaNewport Isolates from U.S. Market Oysters

The consumption of raw oysters contributes to food-borne diseases such as salmonellosis. Prevalence studies in our laboratory have shown that Salmonella spp. were present in 7.4% of U.S. market oysters, with the majority (78/101) of isolates being of the Salmonella enterica Newport serovar. E-tests were performed to assess the susceptibility of the S. Newport oyster isolates to antibiotics used for treatment of Salmonella infections. The oyster isolates were susceptible to Gentamicin, Trimethoprim/Sulphamethoxazole, and Ciprofloxacin, while for the most part they were resistant to Ampicillin and Tetracycline. Consistent with the uniform antibiotic susceptibility profile of these isolates, only three pulsed-field gel electrophoresis (PFGE) profiles were identified among the isolates. Of these three profiles, one was present in 63 of the 78 isolates, indicating not only the presence of S. Newport in oysters, but the predominance of a single PFGE type.

Prevalence of Salmonella spp. in oysters in the United States

Food-borne diseases such as salmonellosis can be attributed, in part, to the consumption of raw oysters. To determine the prevalence of Salmonella spp. in oysters, oysters harvested from 36 U.S. bays (12 each from the West, East, and Gulf coasts in the summer of 2002, and 12 bays, four per coast, in the winter of 2002-2003) were tested. Salmonella was isolated from oysters from each coast of the United States, and 7.4% of all oysters tested contained Salmonella. Isolation tended to be bay specific, with some bays having a high prevalence of Salmonella, while other bays had none. Differences in the percentage of oysters from which Salmonella was isolated were observed between the summer and winter months, with winter numbers much lower probably due to a variety of weather-related events. The vast majority (78/101) of Salmonella isolates from oysters were Salmonella enterica serovar Newport, a major human pathogen, confirming the human health hazard of raw oyster consumption. Contrary to previous findings, no relationship was found between the isolation of fecal coliforms and Salmonella from oysters, indicating a necessity for specific monitoring for Salmonella and other pathogens rather than the current reliance on fecal coliform testing.

Methods for isolation and confirmation of Vibrio vulnificus from oysters and environmental sources: a review

The gram-negative bacterium Vibrio vulnificus is a natural inhabitant of estuarine waters and poses a significant health threat to humans who suffer from immune disorders, liver disease, or hemochromatosis (iron overload). V. vulnificus enters human hosts via wound infections or consumption of raw shellfish (primarily oysters), and infections frequently progress to septicemia and death in susceptible individuals. Prevalence in waters and shellfish is not correlated with fecal indicator organisms; therefore, species-specific detection and enumeration of V. vulnificus in the environment has become a priority for agencies that are responsible for shellfish safety. The many selective-differential media developed for isolation of Vibrio spp., and specifically for V. vulnificus detection, are reviewed here; however, none of the media developed to date combines the sensitivity to low numbers with the specificity necessary to inhibit growth of other organisms. Therefore, immunological and molecular protocols are needed for confirmation of the identity of the organism and are discussed in detail. Methods under development that hold promise for rapid, accurate, and sensitive detection and enumeration of the organism include multiplex and real-time PCR. Developing technologies that have proven useful for detection and investigation of other pathogens such as biosensors, spectroscopy and microarrays may provide the next generation of tools for investigation of the prevalence and ecology of V. vulnificus.

Multiplex PCR detection of clinical and environmental strains ofVibrio vulnificusin 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 103V. 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.Key words: Vibrio, multiplex PCR, shellfish, SYBR Green I, real-time PCR.

Development of a multiplex PCR technique for detection and epidemiological typing of salmonella in human clinical samples

We have developed a multiplex PCR assay for Salmonella detection and epidemiological typing. Six sets of primers were designed to detect the major Salmonella serotypes and phage types in Spain. An internal amplification control was designed in order to detect PCR inhibition. The different amplification profiles obtained allowed us to detect Salmonella bacteria and to distinguish the clinically prevalent Salmonella enterica serotypes Enteritidis, Typhimurium and subspecies I serotype 4,5,12:i:-. Using this method, we could detect a specific band for DT104 and U302 phage types in Salmonella serotype Typhimurium. Salmonella enterica serotype Hadar and other C2 serogroup strains showed two specific band profiles. In the validation stage, the assay was reproducible for all serotypes studied, apart from some C2 serogroup strains. When the technique was applied to clinical stool specimens, the prevalent serotypes Enteritidis and Typhimurium were detected with a sensitivity of 93%, specificity of 100%, and efficiency of 98%. Also, a low PCR inhibition rate (8%) was obtained. The overall agreement of the multiplex PCR with conventional culture-based techniques was 95% for Salmonella typing using Cohen's kappa index.

Application Of The Multiplex Polymerase Chain Reaction (M-PCR) For The Screening Of Vibrio Spp. From Rivers In Kuching, Sarawak

The present study was conducted to investigate the occurrence of Vibrio spp. from selected rivers in Kuching,Sarawak (Malaysia) using Multiplex Polymerase Chain Reaction (m-PCR). During the 6-month study period,19 samples were collected monthly from 7 rivers, followed by simultaneous detection of three Vibrio spp.,Vibrio parahaemolyticus, Vibrio cholerae and Vibrio vulnificus, in a single tube PCR reaction. Three sets ofprimers targeting the thermolabile (tl), outer membrane protein (ompW) and hemolysin/cytolysin genes(vulCulsl) of V. parahaemolyticus, V. cholerae and V. vulnificus, respectively, were used. The results indicatedthat V. parahaemolyticus was the predominant species, occurring approximately 60.9% throughout thesampling period, followed by V. cholerae (23.1%) and V. vulnificus (16.0%). The months of July andDecember were found to be the months where all three Vibrio spp. were found to be at higher frequencies inthe river samples. Results analyzed also indicated that the rivers with the highest prevalence of the three Vibriospp. were Tambak Sejingkat, followed by Sungai Jernang and Sungai Tabuan. We conclude that m-PCR is apowerful and useful tool for the rapid and simultaneous detection of V. parahaemolyticus, V. cholerae and V.vulnificus from the riverine environments without the need for isolation and culturing. Furthermore, thismethod is highly specific, and could be applied in diagnostic laboratories for larger scale epidemiologicalinvestigations of Vibrio spp.