Rapid Extraction and Identification of Maitotoxin and Ciguatoxin-Like Toxins from Caribbean and Pacific Gambierdiscus Using a New Functional Bioassay

Background

Ciguatera is a circumtropical disease produced by polyether sodium channel toxins (ciguatoxins) that enter the marine food chain and accumulate in otherwise edible fish. Ciguatoxins, as well as potent water-soluble polyethers known as maitotoxins, are produced by certain dinoflagellate species in the genus Gambierdiscus and Fukuyoa spp. in the Pacific but little is known of the potential of related Caribbean species to produce these toxins.

Methods

We established a simplified procedure for extracting polyether toxins from Gambierdiscus and Fukuyoa spp. based on the ciguatoxin rapid extraction method (CREM). Fractionated extracts from identified Pacific and Caribbean isolates were analysed using a functional bioassay that recorded intracellular calcium changes (Ca²⁺) in response to sample addition in SH-SY5Y cells. Maitotoxin directly elevated Ca²⁺_i, while low levels of ciguatoxin-like toxins were detected using veratridine to enhance responses.

Results

We identified significant maitotoxin production in 11 of 12 isolates analysed, with 6 of 12 producing at least two forms of maitotoxin. In contrast, only 2 Caribbean isolates produced detectable levels of ciguatoxin-like activity despite a detection limit of >30 pM. Significant strain-dependent differences in the levels and types of ciguatoxins and maitotoxins produced by the same Gambierdiscus spp. were also identified.

Conclusions

The ability to rapidly identify polyether toxins produced by Gambierdiscus spp. in culture has the potential to distinguish ciguatoxin-producing species prior to large-scale culture and in naturally occurring blooms of Gambierdiscus and Fukuyoa spp. Our results have implications for the evaluation of ciguatera risk associated with Gambierdiscus and related species.

New scenario for speciation in the benthic dinoflagellate genus Coolia (Dinophyceae)

In this study, inter- and intraspecific genetic diversity within the marine harmful dinoflagellate genus Coolia Meunier was evaluated using isolates obtained from the tropics to subtropics in both Pacific and Atlantic Ocean basins. The aim was to assess the phylogeographic history of the genus and to clarify the validity of established species including Coolia malayensis. Phylogenetic analysis of the D1-D2 LSU rDNA sequences identified six major lineages (L1-L6) corresponding to the morphospecies Coolia malayensis (L1), C. monotis (L2), C. santacroce (L3), C. palmyrensis (L4), C. tropicalis (L5), and C. canariensis (L6). A median joining network (MJN) of C. malayensis ITS2 rDNA sequences revealed a total of 16 haplotypes; however, no spatial genetic differentiation among populations was observed. These MJN results in conjunction with CBC analysis, rDNA phylogenies and geographical distribution analyses confirm C. malayensis as a distinct species which is globally distributed in the tropical to warm-temperate regions. A molecular clock analysis using ITS2 rDNA revealed the evolutionary history of Coolia dated back to the Mesozoic, and supports the hypothesis that historical vicariant events in the early Cenozoic drove the allopatric differentiation of C. malayensis and C. monotis.

Fluorescent Receptor Binding Assay for Detecting Ciguatoxins in Fish

Ciguatera fish poisoning is an illness suffered by > 50,000 people yearly after consumption of fish containing ciguatoxins (CTXs). One of the current methodologies to detect ciguatoxins in fish is a radiolabeled receptor binding assay (RBA_(R)). However, the license requirements and regulations pertaining to radioisotope utilization can limit the applicability of the RBA_(R) in certain labs. A fluorescence based receptor binding assay (RBA_(F)) was developed to provide an alternative method of screening fish samples for CTXs in facilities not certified to use radioisotopes. The new assay is based on competition binding between CTXs and fluorescently labeled brevetoxin-2 (BODIPY^®- PbTx-2) for voltage-gated sodium channel receptors at site 5 instead of a radiolabeled brevetoxin. Responses were linear in fish tissues spiked from 0.1 to 1.0 ppb with Pacific ciguatoxin-3C (P-CTX-3C) with a detection limit of 0.075 ppb. Carribean ciguatoxins were confirmed in Caribbean fish by LC-MS/MS analysis of the regional biomarker (C-CTX-1). Fish (N = 61) of six different species were screened using the RBA_(F). Results for corresponding samples analyzed using the neuroblastoma cell-based assay (CBA-N2a) correlated well (R² = 0.71) with those of the RBA_(F), given the low levels of CTX present in positive fish. Data analyses also showed the resulting toxicity levels of P-CTX-3C equivalents determined by CBA-N2a were consistently lower than the RBA_(F) affinities expressed as % binding equivalents, indicating that a given amount of toxin bound to the site 5 receptors translates into corresponding lower cytotoxicity. Consequently, the RBA_(F), which takes approximately two hours to perform, provides a generous estimate relative to the widely used CBA-N2a which requires 2.5 days to complete. Other RBA_(F) advantages include the long-term (> 5 years) stability of the BODIPY^®- PbTx-2 and having similar results as the commonly used RBA_(R). The RBA_(F) is cost-effective, allows high sample throughput, and is well-suited for routine CTX monitoring programs.

Identification of Parabodo caudatus (class Kinetoplastea) in urine voided from a dog with hematuria

A voided urine sample, obtained from a 13-year-old intact male dog residing in a laboratory animal research facility, was observed to contain biflagellate protozoa 5 days following an episode of gross hematuria. The protozoa were identified as belonging to the class Kinetoplastea on the basis of light microscopic observation of Wright-Giemsa-stained urine sediment in which the kinetoplast was observed basal to 2 anterior flagella. A polymerase chain reaction (PCR) assay using primers corresponding with conserved regions within the 18S ribosomal RNA gene of representative kinetoplastid species identified nucleotide sequences with 100% identity to Parabodo caudatus. Parabodo caudatus organisms were unable to be demonstrated cytologically or by means of PCR in samples collected from the dog's environment. The dog had a history of 50 complete urinalyses performed over the 12-year period preceding detection of P. caudatus, and none of these were noted to contain protozoa. Moreover, the gross hematuria that was documented 5 days prior to detection of P. caudatus had never before been observed in this dog. Over the ensuing 2.5 years of the dog's life, 16 additional complete urinalyses were performed, none of which revealed the presence of protozoa. Bodonids are commonly found in soil as well as in freshwater and marine environments. However, P. caudatus, in particular, has a 150-year-long, interesting, and largely unresolved history in people as either an inhabitant or contaminant of urine. This historical conundrum is revisited in the current description of P. caudatus as recovered from the urine of a dog.

Formal revision of the Alexandrium tamarense species complex (Dinophyceae) taxonomy: the introduction of five species with emphasis on molecular-based (rDNA) classification

The Alexandrium tamarense species complex is one of the most studied marine dinoflagellate groups due to its ecological, toxicological and economic importance. Several members of this complex produce saxitoxin and its congeners - potent neurotoxins that cause paralytic shellfish poisoning. Isolates from this complex are assigned to A. tamarense, A. fundyense, or A. catenella based on two main morphological characters: the ability to form chains and the presence/absence of a ventral pore between Plates 1' and 4'. However, studies have shown that these characters are not consistent and/or distinctive. Further, phylogenies based on multiple regions in the rDNA operon indicate that the sequences from morphologically indistinguishable isolates partition into five clades. These clades were initially named based on their presumed geographic distribution, but recently were renamed as Groups I-V following the discovery of sympatry among some groups. In this study we present data on morphology, ITS/5.8S genetic distances, ITS2 compensatory base changes, mating incompatibilities, toxicity, the sxtA toxin synthesis gene, and rDNA phylogenies. All results were consistent with each group representing a distinct cryptic species. Accordingly, the groups were assigned species names as follows: Group I, A. fundyense; Group II, A. mediterraneum; Group III, A. tamarense; Group IV, A. pacificum; Group V, A. australiense.

Development, comparison, and validation using ELISAs for the determination of domoic acid in California sea lion body fluids

Mortalities of California sea lions (Zalophus californianus) attributed to the neurotoxin domoic acid (DA) produced by the diatom Pseudo-nitzschia have occurred repeatedly along the U.S. west coast since the late 1990s. Quantifying the amount of DA in these animals and correlating this information with the presence of DA in phytoplankton and the local food web has become a research focus for many scientists. However, differences in materials, equipment, technical capability, budgets, and objectives of the various groups and/or agencies involved in this work have influenced the DA quantification platforms used. The goal of the present study was to compare the performance of two commercially available ELISAs for the determination of DA in a spectrum of California sea lion body fluids and to compare the results with LC/MS of the same samples. The results indicated differences among these approaches, presumably owing to matrix effects (particularly urine) and antibody reactivities. This information implies that care should be taken in attempting to compare datasets generated using different analytical platforms and interpreting the results of published studies.

Differences in the toxicity of six Gambierdiscus (Dinophyceae) species measured using an in vitro human erythrocyte lysis assay

This study examined the toxicity of six Gambierdiscus species (Gambierdiscus belizeanus, Gambierdiscus caribaeus, Gambierdiscus carolinianus, Gambierdiscus carpenteri, Gambierdiscus ribotype 2 and Gambierdiscus ruetzleri) using a human erythrocyte lysis assay. In all, 56 isolates were tested. The results showed certain species were significantly more toxic than others. Depending on the species, hemolytic activity consistently increased by ∼7-40% from log phase growth to late log - early stationary growth phase and then declined in mid-stationary growth phase. Increasing growth temperatures from 20 to 31 °C for clones of G. caribaeus showed only a slight increase in hemolytic activity between 20 and 27 °C. Hemolytic activity in the G. carolinianus isolates from different regions grown over the same 20-31 °C range remained constant. These data suggest that growth temperature is not a significant factor in modulating the inter-isolate and interspecific differences in hemolytic activity. The hemolytic activity of various isolates measured repeatedly over a 2 year period remained constant, consistent with the hemolytic compounds being constitutively produced and under strong genetic control. Depending on species, greater than 60-90% of the total hemolytic activity was initially associated with the cell membranes but diffused into solution over a 24 h assay incubation period at 4 °C. These findings suggest that hemolytic compounds produced by Gambierdiscus isolates were held in membrane bound vesicles as reported for brevetoxins produced by Karenia brevis. Gambierdiscus isolates obtained from other parts of the world exhibited hemolytic activities comparable to those found in the Caribbean and Gulf of Mexico confirming the range of toxicities is similar among Gambierdiscus species worldwide. Experiments using specific inhibitors of the MTX pathway and purified MTX, Gambierdiscus whole cell extracts, and hydrophilic cell extracts containing MTX, were consistent with MTX as the primary hemolytic compound produced by Gambierdiscus species. While the results from inhibition studies require validation by LC-MS analysis, the available data strongly suggest differences in hemolytic activity observed in this study reflect maitotoxicity.

NITROGEN LIMITATION INCREASES BREVETOXINS IN KARENIA BREVIS (DINOPHYCEAE): IMPLICATIONS FOR BLOOM TOXICITY(1)

Laboratory and field measurements of the toxin content in Karenia brevis cells vary by >4-fold. These differences have been largely attributed to genotypic variations in toxin production among strains. We hypothesized that nutrient limitation of growth rate is equally or more important in controlling the toxicity of K. brevis, as has been documented for other toxic algae. To test this hypothesis, we measured cellular growth rate, chlorophyll a, cellular carbon and nitrogen, cell volume, and brevetoxins in four strains of K. brevis grown in nutrient-replete and nitrogen (N)-limited semi-continuous cultures. N-limitation resulted in reductions of chlorophyll a, growth rate, volume per cell and nirtogen:carbon (N:C) ratios as well as a two-fold increase (1%-4% to 5%-9%) in the percentage of cellular carbon present as brevetoxins. The increase in cellular brevetoxin concentrations was consistent among genetically distinct strains. Normalizing brevetoxins to cellular volume instead of per cell eliminated much of the commonly reported toxin variability among strains. These results suggest that genetically linked differences in cellular volume may affect the toxin content of K. brevis cells as much or more than innate genotypic differences in cellular toxin content per unit of biomass. Our data suggest at least some of the >4-fold difference in toxicity per cell reported from field studies can be explained by limitation by nitrogen or other nutrients and by differences in cell size. The observed increase in brevetoxins in nitrogen limited cells is consistent with the carbon:nutrient balance hypothesis for increases in toxins and other plant defenses under nutrient limitation.

DEVELOPMENT OF SEMI-QUANTITATIVE PCR ASSAYS FOR THE DETECTION AND ENUMERATION OF GAMBIERDISCUS SPECIES (GONYAULACALES, DINOPHYCEAE)(1)

Ciguatera fish poisoning (CFP) is a serious health problem in tropical regions and is caused by the bioaccumulation of lipophilic toxins produced by dinoflagellates in the genus Gambierdiscus. Gambierdiscus species are morphologically similar and are difficult to distinguish from one another even when using scanning electron microscopy. Improved identification and detection methods that are sensitive and rapid are needed to identify toxic species and investigate potential distribution and abundance patterns in relation to incidences of CFP. This study presents the first species-specific, semi-quantitative polymerase chain reaction (qPCR) assays that can be used to address these questions. These assays are specific for five Gambierdiscus species and one undescribed ribotype. The assays utilized a SYBR green format and targeted unique sequences found within the SSU, ITS, and the D1/D3 LSU ribosomal domains. Standard curves were constructed using known concentrations of cultured cells and 10-fold serial dilutions of rDNA PCR amplicons containing the target sequence for each specific assay. Assay sensitivity and accuracy were tested using DNA extracts purified from known concentrations of multiple Gambierdiscus species. The qPCR assays were used to assess Gambierdiscus species diversity and abundance in samples collected from nearshore areas adjacent to Ft. Pierce and Jupiter, Florida USA. The results indicated that the practical limit of detection for each assay was 10 cells per sample. Most interestingly, the qPCR analysis revealed that as many as four species of Gambierdiscus were present in a single macrophyte sample.

Global distribution of ciguatera causing dinoflagellates in the genus Gambierdiscus

Dinoflagellates in the genus Gambierdiscus produce toxins that bioaccumulate in tropical and sub-tropical fishes causing ciguatera fish poisoning (CFP). Little is known about the diversity and distribution of Gambierdiscus species, the degree to which individual species vary in toxicity, and the role each plays in causing CFP. This paper presents the first global distribution of Gambierdiscus species. Phylogenetic analyses of the existing isolates indicate that five species are endemic to the Atlantic (including the Caribbean/West Indies and Gulf of Mexico), five are endemic to the tropical Pacific, and that two species, Gambierdiscus carpenteri and Gambierdiscus caribaeus are globally distributed. The differences in Gambierdiscus species composition in the Atlantic and Pacific correlated with structural differences in the ciguatoxins reported from Atlantic and Pacific fish. This correlation supports the hypothesis that Gambierdiscus species in each region produce different toxin suites. A literature survey indicated a >100-fold variation in toxicity among species compared with a 2 to 9-fold within species variation due to changing growth conditions. These observations suggest that CFP events are driven more by inherent differences in species toxicity than by environmental modulation. How variations in species toxicity may affect the development of an early warning system for CFP is discussed.

Ciguatera fish poisoning and sea surface temperatures in the Caribbean Sea and the West Indies

Ciguatera fish poisoning (CFP) is a circumtropical disease caused by ingestion of a variety of reef fish that bioaccumulate algal toxins. Distribution and abundance of the organisms that produce these toxins, chiefly dinoflagellates of the genus Gambierdiscus, are reported to correlate positively with water temperature. Consequently, there is growing concern that increasing temperatures associated with climate change could increase the incidence of CFP. This concern prompted experiments on the growth rates of six Gambierdiscus species at temperatures between 18 degrees C and 33 degrees C and the examination of sea surface temperatures in the Caribbean and West Indies for areas that could sustain rapid Gambierdiscus growth rates year-round. The thermal optimum for five of six Gambierdiscus species tested was >/=29 degrees C. Long-term SST data from the southern Gulf of Mexico indicate the number of days with sea surface temperatures >/=29 degrees C has nearly doubled (44 to 86) in the last three decades. To determine how the sea surface temperatures and Gambierdiscus growth data correlate with CFP incidences in the Caribbean, a literature review and a uniform, region-wide survey (1996-2006) of CFP cases were conducted. The highest CFP incidence rates were in the eastern Caribbean where water temperatures are warmest and least variable.

Microcystin concentrations and genetic diversity of Microcystis in the lower Great Lakes

The resurgence of Microcystis blooms in the lower Great Lakes region is of great concern to public and ecosystem health due to the potential for these colonial cyanobacteria to produce hepatotoxic microcystins. A survey of Microcystis cell densities and microcystin concentrations during August 2004 showed particularly high concentrations of both cells and toxin in the nearshore regions of Saginaw Bay (Lake Huron) and western Lake Erie, often exceeding the World Health Organization's recommended drinking water limit of 1 microg L(-1). The dominant congener of microcystin in both basins was microcystin-LR (MC-LR), whereas the second most abundant congeners, accounting for up to 20-25% of the total microcystin concentrations, were MC-LA in Saginaw Bay and MC-RR in western Lake Erie. Multiplex PCR assays of Microcystis colonies isolated from these two regions showed that a much greater percentage of the Microcystis colonies from Saginaw Bay carried the mcyB gene necessary for microcystin production, in comparison with those from western Lake Erie. The mcyB genotypes sequenced separated into two distinct phylogenetic clusters, with Microcystis originating from Lake Erie predominantly in one branch and from Saginaw Bay present in both branches. These results indicate that the genetic composition of the bloom could impact the concentrations and congeners of microcystin produced and that the cell count methods currently being used to gauge public health threats posed by Microcystis blooms may not sufficiently assess actual bloom toxicity.

Antimicrobial peptides derived from hemoglobin are expressed in epithelium of channel catfish (Ictalurus punctatus, Rafinesque)

The beta-chain of the respiratory protein hemoglobin (Hbbeta), has recently been identified in novel sites, including mammalian macrophages and alveolar epithelium, as well as in gill microsomes of fish. However, the functional significance of extra-erythrocytically expressed hemoglobin has been unclear. Here we show inducible expression and upregulation of antimicrobial peptides (AMPs) homologous to Hbbeta in the gill epithelium of channel catfish (Ictalurus punctatus) in response to parasitic (Ichthyophthirius multifiliis, ich) infection. One peptide (HbbetaP-1), while having activity against some fish bacterial pathogens (e.g., Aeromonas hydrophila), had especially potent antiparasitic activity that was specifically lethal (lytic) to the feeding (trophont) stage of ich and also appeared to accelerate the differentiation of trophonts. However, it had no apparent effect on either the disseminative (theront) or reproductive (tomont) stages, nor was it lytic to channel catfish erythrocytes. Fish experimentally challenged with ich confirmed that the HbbetaP-1 sequence was both transcribed and translated in skin and gill epithelium, the target tissues for ich. The Hb AMP concentration expressed in vivo appeared to be well within the antiparasitic concentrations measured in vitro. Our findings suggest that hemoglobin-derived AMPs might play a significant role in the non-specific immune response.

PROROCENTRUM LEVIS, A NEW BENTHIC SPECIES (DINOPHYCEAE) FROM A MANGROVE ISLAND, TWIN CAYS, BELIZE(1)

As part of a long-term study of benthic dinoflagellates from the Belizean barrier reef system, we report a new species: Prorocentrum levis M. A. Faust, Kibler, Vandersea, P. A. Tester et Litaker sp. nov. P. levis cells are oval in valve view and range in size from 40 to 44 μm long and 37 to 40 μm wide. Each valve surface is smooth, with 221-238 valve pores and 99-130 marginal pores. These pores are uniformly small and range in diameter from 0.13 to 0.19 μm. Asexual reproduction in P. levis is atypical, occurring within a hyaline envelope, and produces long branching chains of adherent cells. A phylogenetic analysis of SSU rDNA indicated that of the Prorocentrum species sequenced so far, P. levis was most closely related to P. concavum. P. levis produces okadaic acid and dinophysis toxin-2 (DTX2). Further, SEM observations and SSU rDNA sequence for P. belizeanum M. A. Faust, which was isolated at the same time, are also presented.

Aphanomyces invadans and ulcerative mycosis in estuarine and freshwater fish in Florida

In the spring of 1998, the Florida Fish and Wildlife Research Institute received numerous reports of lesioned or ulcerated fish primarily from the St. Lucie Estuary on the southeast coast of Florida, an area known since the late 1970s for lesions of the ulcerative mycosis (UM) type. From these and archived reports, as well as others received from different areas of Florida, we documented that diseased specimens had randomly distributed skin ulcers (usually reddened or hemorrhagic) with raised irregular margins and, in some cases, deeply penetrating hyphae in the surrounding muscle tissue. Since 1998, 256 fish (comprising 18 species) with ulcerative lesions (from 15 different locations) were confirmed with hyphae in fresh squash preparation or by histological evaluation. Squash preparations revealed nonseptate, sparsely branching, thick-walled hyphae; histological sections revealed mycotic granulomas in the dermis that occasionally penetrated into the skeletal muscle. These pathological characteristics were consistent with UM caused by the oomycete Aphanomyces invadans in Southeast Asia, Japan, Australia, and the United States. For specific identification, six isolates from ulcerated fish were cultured and prepared for molecular characterization using established diagnostic methods. Ribosomal RNA gene sequence analysis identified three isolates as Aphanomyces invadans, one as the oomycete Achlya bisexualis, and two as the ascomycete Phialemonium dimorphosporum. A more extensive survey of 67 ulcerated skin samples from fish collected between 1998 and 2003 was performed using a polymerase chain reaction assay specific for Aphanomyces invadans. Of these, 26 (38.8%) samples from seven fish species and nine collection locations were positive. Confirmation of UM associated with Aphanomyces invadans represents new host records in Florida for the sheepshead Archosargus probatocephalus, striped mullet Mugil cephalus, white mullet Mugil curema, silver perch Bairdiella chrysoura, black drum Pogonias cromis, largemouth bass Micropterus salmoides, and American shad Alosa sapidissima.

Pathogenicity studies with the fungi Aphanomyces invadans, Achlya bisexualis, and Phialemonium dimorphosporum: induction of skin ulcers in striped mullet

Based on isolations from naturally infected fish in Florida, we investigated the role of the fungi Aphanomyces invadans, Achlya bisexualis, and Phialemonium dimorphosporum in the etiology of ulcerative mycosis (UM) in striped mullet Mugil cephalus. We injected healthy striped mullet subcutaneously with secondary zoospores of four oomycete isolates: two concentrations (50 and 115 zoospores/mL) of SJR (an endemic isolate of Aphanomyces invadans in American shad Alosa sapidissima from the St. Johns River); two concentrations each of CAL (25 and 65 zoospores/mL) and ACH (1,400 and 2,000 zoospores/mL; endemic isolates of Aphanomyces invadans and Achlyva bisexualis, respectively, in striped mullet from the Caloosahatchee River); and two concentrations of the ascomycete culture MTZ (2,500 and 3,500 zoospores/mL; endemic isolate of P. dimorphosporum from whirligig mullet M. gyrans in the Matanzas Inlet). All fish injected with either concentration of SJR developed granulomatous ulcers after 8 d and died within 21 d. Eighty percent (8/10) of fish injected with the high dose of CAL developed ulcers after 13 d and died within 28 d, but only 30% (3/10) of fish injected with the low dose of CAL developed ulcers. Four of the ulcerated fish died within 28 d, and the remaining fish were terminated after 32 d. Fish injected with zoospores of Aphanomyces invadans developed ulcers that were grossly and histologically similar to those observed in naturally infected striped mullet with UM from several estuaries or rivers in Florida. These hemorrhagic skin ulcers were characterized by myonecrosis and the presence of mycotic granulomas. None of the fish injected with ACH, MTZ, or sterile water developed ulcers. This study fulfilled Koch's postulates and demonstrated that ulcers could be experimentally induced in striped mullet after exposure via injection to secondary zoospores of an endemic Florida strain of Aphanomyces invadans.

A highly specific PCR assay for detecting the fish ectoparasite Amyloodinium ocellatum

Amyloodiniosis, caused by the dinoflagellate ectoparasite Amyloodinium ocellatum, is one of the most serious diseases affecting marine fish in warm and temperate waters. Current diagnostic methods rely entirely on the microscopic identification of parasites on the skin or gills of infested fish. However, subclinical infestations usually go undetected, while no method of detecting the free-swimming, infective (dinospore) stage has been devised. Targeting the parasite's ribosomal DNA region, we have developed a sensitive and specific PCR assay that can detect as little as a single cell from any of the 3 stages of the parasite's life cycle (trophont, tomont, dinospore). This assay performs equally well in a simple artificial seawater medium and in natural seawater containing a plankton community assemblage. The assay is also not inhibited by gill tissue. Sequence analysis of the internal transcribed spacer region of 5 A. ocellatum isolates, obtained from fish in the Red Sea (Israel), eastern Mediterranean Sea (Israel), Adriatic Sea (Italy), Gulf of Mexico (Florida), and from an unknown origin, revealed insignificant variation, indicating that all isolates were the same species. However, 3 of these isolates propagated in cell culture varied in behavior and morphology, and these differences were consistent during at least 2 yr in culture. Thus, our findings do not eliminate the possibility that different strains are in fact 'subspecies' or lower taxa, which may also differ in pathogenic and immunogenic characteristics, environmental tolerance, and other features.

Morphologic, Pathologic, and Genetic Investigations of Bolbophorus Species Affecting Cultured Channel Catfish in the Mississippi Delta

Trematodes belonging to the genus Bolbophorus have recently been reported as the cause of substantial morbidity and mortality in cultured channel catfish Ictalurus punctatus in Mississippi and Louisiana. Previous investigators identified only a single species, B. confusus. In this investigation, genetic techniques were used to identify all stages of the parasite in all of its hosts. The 18s rRNA genes from specimens collected in Mississippi were sequenced and compared; this analysis revealed that there are two distinct species, B. damnificus (previously identified as B. confusus) and another, undescribed species. (Phylogenetic analysis indicated that a third species, B. levantinus, is also closely related to the Mississippi species.) Species-specific polymerase chain reaction assays capable of identifying and differentiating between these two parasites were developed. Both species were found to infect the first intermediate host (the ram's horn snail Planorbella trivolvis) in commercial channel catfish ponds, but only B. damnificus was recovered from the fish themselves. The new, unidentified Bolbophorus species was determined to be highly pathogenic to a number of fish species. The contribution of B. damnificus to disease in cultured channel catfish remains undetermined. Future investigations of these parasites must now take into account the presence of two distinct species.

Rapid one-step quantitative reverse transcriptase PCR assay with competitive internal positive control for detection of enteroviruses in environmental samples

Human enteroviruses can serve as a more accurate indicator of human fecal contamination than conventional bacteriological fecal indicators. We describe here a quantitative reverse transcriptase PCR (qRT-PCR) assay specifically tailored to detect these viruses in environmental waters. The assay included a competitive internal positive control (CIPC) that allowed the inhibition of qRT-PCRs to be quantitatively assessed. Coamplification of the CIPC with enteroviral genetic material did not affect the sensitivity, specificity, or reproducibility of the enteroviral qRT-PCR assay. The assay is rapid (less than 5 h from sample to result), has a wide dynamic range (>3 logs), and is capable of detecting as few as 25 enteroviral genomes with an average amplification efficiency of 0.91. In samples with low or moderate inhibition, the delay in CIPC amplification was used to adjust enterovirus qRT-PCR concentrations to account for losses due to inhibition. Samples exhibiting significant inhibition were not corrected but instead diluted twofold and immediately assayed again. Using significantly inhibited samples, it was found that dilution relieved inhibition in 93% (25 of 27) of the samples. In addition, 15% (4 of 27) of these previously negative samples contained enteroviral genomes. The high-throughput format of the assay compared to conventional culture-based methods offers a fast, reliable, and specific method for detecting enteroviruses in environmental water samples. The ability of the assay to identify false negatives and provide improved quantitative assessments of enterovirus concentrations will facilitate the tracking of human fecal contamination and the assessment of potential public health risk due to enteroviruses in recreational and shellfish harvesting waters.

Molecular assays for detecting Aphanomyces invadans in ulcerative mycotic fish lesions

The pathogenic oomycete Aphanomyces invadans is the primary etiological agent in ulcerative mycosis, an ulcerative skin disease caused by a fungus-like agent of wild and cultured fish. We developed sensitive PCR and fluorescent peptide nucleic acid in situ hybridization (FISH) assays to detect A. invadans. Laboratory-challenged killifish (Fundulus heteroclitus) were first tested to optimize and validate the assays. Skin ulcers of Atlantic menhaden (Brevoortia tyrannus) from populations found in the Pamlico and Neuse River estuaries in North Carolina were then surveyed. Results from both assays indicated that all of the lesioned menhaden (n = 50) collected in September 2004 were positive for A. invadans. Neither the FISH assay nor the PCR assay cross-reacted with other closely related oomycetes. These results provided strong evidence that A. invadans is the primary oomycete pathogen in ulcerative mycosis and demonstrated the utility of the assays. The FISH assay is the first molecular assay to provide unambiguous visual confirmation that hyphae in the ulcerated lesions were exclusively A. invadans.

Molecular assays for detecting Aphanomyces invadans in ulcerative mycotic fish lesions

The pathogenic oomycete Aphanomyces invadans is the primary etiological agent in ulcerative mycosis, an ulcerative skin disease caused by a fungus-like agent of wild and cultured fish. We developed sensitive PCR and fluorescent peptide nucleic acid in situ hybridization (FISH) assays to detect A. invadans. Laboratory-challenged killifish (Fundulus heteroclitus) were first tested to optimize and validate the assays. Skin ulcers of Atlantic menhaden (Brevoortia tyrannus) from populations found in the Pamlico and Neuse River estuaries in North Carolina were then surveyed. Results from both assays indicated that all of the lesioned menhaden (n = 50) collected in September 2004 were positive for A. invadans. Neither the FISH assay nor the PCR assay cross-reacted with other closely related oomycetes. These results provided strong evidence that A. invadans is the primary oomycete pathogen in ulcerative mycosis and demonstrated the utility of the assays. The FISH assay is the first molecular assay to provide unambiguous visual confirmation that hyphae in the ulcerated lesions were exclusively A. invadans.