Correlation between the resistance genotype determined by multiplex PCR assays and the antibiotic susceptibility patterns of Staphylococcus aureus and Staphylococcus epidermidis

Clinical isolates of Staphylococcus aureus (a total of 206) and S. epidermidis (a total of 188) from various countries were tested with multiplex PCR assays to detect clinically relevant antibiotic resistance genes associated with staphylococci. The targeted genes are implicated in resistance to oxacillin (mecA), gentamicin ¿aac(6')-aph(2"), and erythromycin (ermA, ermB, ermC, and msrA). We found a nearly perfect correlation between genotypic and phenotypic analysis for most of these 394 strains, showing the following correlations: 98% for oxacillin resistance, 100% for gentamicin resistance, and 98.5% for erythromycin resistance. The discrepant results were (i) eight strains found to be positive by PCR for mecA or ermC but susceptible to the corresponding antibiotic based on disk diffusion and (ii) six strains of S. aureus found to be negative by PCR for mecA or for the four erythromycin resistance genes targeted but resistant to the corresponding antibiotic. In order to demonstrate in vitro that the eight susceptible strains harboring the resistance gene may become resistant, we subcultured the susceptible strains on media with increasing gradients of the antibiotic. We were able to select cells demonstrating a resistant phenotype for all of these eight strains carrying the resistance gene based on disk diffusion and MIC determinations. The four oxacillin-resistant strains negative for mecA were PCR positive for blaZ and had the phenotype of beta-lactamase hyperproducers, which could explain their borderline oxacillin resistance phenotype. The erythromycin resistance for the two strains found to be negative by PCR is probably associated with a novel mechanism. This study reiterates the usefulness of DNA-based assays for the detection of antibiotic resistance genes associated with staphylococcal infections.

Identification of mutans and other oral streptococci by random amplified polymorphic DNA analysis

The identification and classification of the non-haemolytic or viridans group of streptococci have long been recognised as difficult and unsatisfactory. Phenotypic and genotypic heterogeneity have resulted in ambiguous speciation, particularly with mutans streptococci and other oral streptococci. This study was done to determine whether random amplified polymorphic DNA (RAPD) analysis is useful to identify and even classify oral and other streptococci. DNA was prepared and purified from 25 strains of mutans streptococci including 11 reference strains of Streptococcus mutans, seven of S. sobrinus, three of S. rattus and one each of the four other species of the mutans group, together with 20 other reference species, mostly streptococci, and from 49 fresh isolates of mutans streptococci and of S. mutans from human saliva and dental plaque. DNA amplification was primed with each of three arbitrarily selected primers nine or 10 nucleotides in length. The amplified DNA fragments (amplicons) obtained were compared by agarose gel electrophoresis. Species- and strain-specific RAPD fingerprints were obtained not only from pure genomic DNA, but also from the supernates of crude cellular or colony extracts. Pending the analysis of numerous other strains, the data suggest that RAPD may be of value: (i) to distinguish the species S. mutans and S. sobrinus from each other and potentially from other species of oral streptococci, (ii) to differentiate and possibly classify oral streptococci and (iii) as a valuable tool in mutans streptococci epidemiology and transmission studies, by virtue of its rapidity, efficiency and reproducibility in generating genetic fingerprints of streptococcal isolates.

Development of a PCR assay for rapid detection of enterococci

Enterococci are becoming major nosocomial pathogens, and increasing resistance to vancomycin has been well documented. Conventional identification methods, which are based on culturing, require 2 to 3 days to provide results. PCR has provided a means for the culture-independent detection of enterococci in a variety of clinical specimens and is capable of yielding results in just a few hours. However, all PCR-based assays developed so far are species specific only for clinically important enterococci. We have developed a PCR-based assay which allows the detection of enterococci at the genus level by targeting the tuf gene, which encodes elongation factor EF-Tu. Initially, we compared the nucleotide sequences of the tuf gene from several bacterial species (available in public databases) and designed degenerate PCR primers derived from conserved regions. These primers were used to amplify a target region of 803 bp from four enterococcal species (Enterococcus avium, E. faecalis, E. faecium, and E. gallinarum). Subsequently, the complete nucleotide sequences of these amplicons were determined. The analysis of a multiple alignment of these sequences revealed regions conserved among enterococci but distinct from those of other bacteria. PCR primers complementary to these regions allowed amplification of genomic DNAs from 14 of 15 species of enterococci tested (E. solitarius DNA could not be amplified). There was no amplification with a majority of 79 nonenterococcal bacterial species, except for 2 Abiotrophia species and several Listeria species. Furthermore, this assay efficiently amplified all 159 clinical isolates of enterococci tested (61 E. faecium, 77 E. faecalis, 9 E. gallinarum, and 12 E. casseliflavus isolates). Interestingly, the preliminary sequence comparison of the amplicons for four enterococcal species demonstrated that there were some sequence variations which may be used to generate species-specific internal probes. In conclusion, this rapid PCR-based assay is capable of detecting all clinically important enterococci and has potential for use in clinical microbiology laboratories.

MHC class Ia molecules alone control NK-mediated bone marrow graft rejection

Mice with functionally deleted genes encoding MHC class I heavy (H-2K(b), H-2D(b)) and light (beta2-microglobulin) chains were used in bone marrow cell transfer experiments to study the role of class Ia and Ib molecules in NK cell function. Absence of H-2K(b) and absence of H-2D(b) on bone marrow cells resulted in complete and in almost complete NK-mediated rejection, respectively. Absence of either H-2 class Ib (at least when expressed in H-2 class Ia-deficient mice) or cell surface class Ia free heavy chains did not result in bone marrow rejection. Thus, in C57BL/6 adult mice, the inactivation of NK cells required for bone marrow cell engraftment relies entirely upon-H-2 class Ia molecules. These results imply the existence of an inhibitory receptor which recognizes either directly or indirectly H-2D(b) molecules and further suggest that in C57BL/6 mice the NK cells which do not express a H-2K(b) specific inhibitory receptor necessarily express an H-2D(b)-specific one.

Modulation of L-type calcium channel expression during retinoic acid-induced differentiation of H9C2 cardiac cells

The molecular mechanisms underlying the developmental regulation of L-type voltage-dependent Ca(2+) channels (VDCCs) are still unknown. In this study, we have characterized the expression patterns of skeletal (alpha(1S)) and cardiac (alpha(1C)) L-type VDCCs during cardiogenic differentiation in H9C2 cells that derived from embryonic rat heart. We report that chronic treatment of H9C2 cells with 10 nM all-trans-retinoic acid (all-trans-RA) enhanced cardiac Ca(2+) channel expression, as demonstrated by reverse transcription-polymerase chain reaction, immunoblotting, and indirect immunofluorescence studies, as well as patch-clamp experiments. In addition, RA treatment prevented expression of functional skeletal L-type VDCCs, which were restricted to myotubes that spontaneously appear in control H9C2 cultures undergoing myogenic transdifferentiation. The use of specific skeletal and cardiac markers indicated that RA, by preventing myogenic transdifferentiation, preserves cardiac differentiation of this cell line. Altogether, we provide evidence that cardiac and skeletal subtype-specific L-type Ca(2+) channels are relevant functional markers of differentiated cardiac and skeletal myocytes, respectively. In conclusion, our data demonstrate that in vitro RA stimulates cardiac (alpha(1C)) L-type Ca(2+) channel expression, therefore supporting the hypothesis that the RA pathway might be involved in the tissue specific expression of Ca(2+) channels in mature cardiac cells.

Rapid identification of essential and nonessential herpesvirus genes by direct transposon mutagenesis

Herpesviruses are important pathogens in animals and humans. The large DNA genomes of several herpesviruses have been sequenced, but the function of the majority of putative genes is elusive. Determining which genes are essential for their replication is important for identifying potential chemotherapy targets, designing herpesvirus vectors, and generating attenuated vaccines. For this purpose, we recently reported that herpesvirus genomes can be maintained as infectious bacterial artificial chromosomes (BAC) in Escherichia coli. Here we describe a one-step procedure for random-insertion mutagenesis of a herpesvirus BAC using a Tn1721-based transposon system. Transposon insertion sites were determined by direct sequencing, and infectious virus was recovered by transfecting cultured cells with the mutant genomes. Lethal mutations were rescued by cotransfecting cells containing noninfectious genomes with the corresponding wild-type subgenomic fragments. We also constructed revertant genomes by allelic exchange in bacteria. These methods, which are generally applicable to any cloned herpesvirus genome, will facilitate analysis of gene function for this virus family.

Adherence of Porphyromonas gingivalis to epithelial cells: analysis by flow cytometry

Porphyromonas gingivalis, implicated in the pathogenesis of periodontitis, can adhere to epithelial cells and gingival fibroblasts. This study employed flow cytometry to evaluate the adherence of P. gingivalis to epithelial cells under various conditions. The cell lines SK-MES and KB were used in the first experiments. The P. gingivalis strains employed were ATCC 33277, ATCC 49417 and W83. Different adherence conditions were tested (contact time, bacteria/cell ratio, contact temperature). In later experiments, adherence of P. gingivalis to human gingival epithelial cells (GEC) obtained by explant was studied under various conditions. Results showed that P. gingivalis had a high affinity for buccal keratinocytes compared with SK-MES. Adherence showed a level of saturation. The number of receptors may be limited for each epithelial cell line, and there may be more receptors for gingival keratinocytes. Depending on contact time, P. gingivalis showed a higher affinity for GEC, compared with the other two lines. P. gingivalis thus showed specific adherence for a host cell type from a site associated with periodontal disease.

Beta2-microglobulin-deficient NK cells show increased sensitivity to MHC class I-mediated inhibition, but self tolerance does not depend upon target cell expression of H-2Kb and Db heavy chains

Mice lacking beta2-microglobulin (beta2m- mice) express greatly reduced levels of MHC class I molecules, and cells from beta2m- mice are therefore highly sensitive to NK cells. However, NK cells from beta2m- mice fail to kill beta2m- normal cells, showing that they are self tolerant. In a first attempt to understand better the basis of this tolerance, we have analyzed more extensively the target cell specificity of beta2m- NK cells. In a comparison between several MHC class I-deficient and positive target cell pairs for sensitivity to beta2m- NK cells, we made the following observations: First, beta2m- NK cells displayed a close to normal ability to kill a panel of MHC class I-deficient tumor cells, despite their nonresponsiveness to beta2m- concanavalin A (Con A)-activated T cell blasts. Secondly, beta2m- NK cells were highly sensitive to MHC class I-mediated inhibition, in fact more so than beta2m+ NK cells. Thirdly beta2m- NK cells were not only tolerant to beta2m- Con A blasts but also to Con A blasts from H-2Kb-/Db- double deficient mice in vitro. We conclude that NK cell tolerance against MHC class I-deficient targets is restricted to nontransformed cells and independent of target cell expression of MHC class I free heavy chains. The enhanced ability of beta2m- NK cells to distinguish between MHC class I-negative and -positive target cells may be explained by increased expression of Ly49 receptors, as described previously. However, the mechanisms for enhanced inhibition by MHC class I molecules appear to be unrelated to self tolerance in beta2m- mice, which may instead operate through mechanisms involving triggering pathways.

Determination of clenbuterol in beef liver and muscle tissue using immunoaffinity chromatographic cleanup and liquid chromatography with ultraviolet absorbance detection

Clenbuterol, a beta-agonist, was determined in samples of beef liver and muscle. The method employed an acidic aqueous extraction followed by protein precipitation. The supernatant liquid was passed through a weak cation-exchange cartridge and then through a commercially available immunoaffinity cartridge. Clenbuterol was eluted from the immunoaffinity cartridge with 80% ethanol in water. The eluate was concentrated and analysed directly by reversed-phase liquid chromatography using gradient elution and UV detection at 245 nm. Detection limits were estimated to be 0.3 ng g-1 clenbuterol. A single immunoaffinity cartridge was used for ten sample extracts with no significant loss in capacity. No organic solvents other than ethanol and methanol were employed in the procedure. Recoveries of clenbuterol from samples of beef liver and muscle spiked at 2 and 5 ng g-1 carried through the entire procedure were 63 +/- 11% (range, 53-74%) compared to pure standards. Absolute recoveries of pure standards (30 ng clenbuterol) carried through the same analytical steps were 70 +/- 5% (n = 6), the losses being primarily due to the ion-exchange step.

Anal reeducation for postoperative fecal incontinence in congenital diseases of the rectum and anus

From October 1993 to March 1996, 14 patients with anorectal disease were referred to an anal reeducation clinic. Initial evaluation allowed the authors to identify three classes of defects: lack of proprioception in the sphincters, use of synergistic muscles (gluteal) to compensate for anal dysfunction, and inversion of command by contraction, rather than relaxation, of abdominal muscles. Patients were treated by electrostimulation through an anal probe as well as biofeedback therapy coupled with home exercises. This therapy resulted in rapid correction of the abnormal motor commands and erroneous use of accessory muscles. All patients became able to isolate their continence muscles with success, with documented increase in strength, rapidity of response, and duration of contraction. The mean Kelly score went from 1.46 (range, 0 to 4.5) to 3.07 (range, 0.5 to 5.5). This physiological improvement also increased patient motivation and discipline toward continence and subsequently their quality of life.

Effect of Porphyromonas gingivalis on epithelial cell MMP-9 type IV collagenase production

Porphyromonas gingivalis is reportedly capable of stimulating the expression of host cell matrix metalloproteinases (MMP), contributing to tissue destruction. However, the impact of this bacterium on specific molecules remains to be determined. In this study, we evaluate the effect of P. gingivalis on regulation of MMP-9 expression in human gingival epithelial cells (HGEC). Various inocula of P. gingivalis were added to cultures of HGEC. The effects of live bacteria, heat-killed bacteria, and outer membrane extract were analyzed. MMP-9 secretion by HGEC was evaluated by enzyme-linked immunosorbent assay. For inocula smaller than one bacterium per cell, the quantity of MMP-9 secreted by HGEC was increased in comparison to control conditions. For inocula from 2.5 to 250 bacteria per cell, an inhibition of MMP-9 secretion in a dose-response fashion was observed, with a maximum reduction (ranging from 80 to 95% in five experiments) at 50 bacteria per cell. Gelatin zymograms confirmed the decrease in MMP-9 secretion. A band of 83 kDa, corresponding to activated enzyme, was present for inocula of 0.5 to 50 bacteria. Inhibition took place without any alteration of epithelial cell viability. Heat-killed bacteria and outer membrane extract also provoked proenzyme activation but did not inhibit MMP-9 secretion. These results demonstrate a direct effect of P. gingivalis on HGEC, suggesting a specific action on the collagen renewal process at the interface between the epithelium and connective tissue.

Determination of decarbamoyl saxitoxin and its analogues in shellfish by prechromatographic oxidation and liquid chromatography with fluorescence detection

Oxidation and chromatographic conditions for detecting the decarbamoyl analogues of several paralytic shellfish poison (PSP) toxins were studied. Prechromatographic oxidation with periodate or hydrogen peroxide under slightly alkaline conditions was used as previously reported for the parent PSP toxins. Both periodate and hydrogen peroxide oxidations produced 2 fluorescent products separable by liquid chromatography for each decarbamoyl (dc) toxin (dc-saxitoxin, dc-neosaxatoxin and dc-gonyautoxins 2 and 3). Decarbamoyl saxitoxin produced the same 2 products as did dc-neosaxitoxin but in different ratios. One of these products was the same as the one obtained with neosaxitoxin after periodate oxidation. Decarbamoyl gonyautoxins 2 and 3 (together) produced 2 products, one of which was the same as the major product obtained with gonyautoxins 1 and 4 (together) after periodate oxidation. Decarbamoyl gonyautoxins 1 and 4 were not available for study. The method was used to detect dc-saxitoxin and dc-gonyautoxins 2 and 3 in shellfish extracts.

Liquid chromatographic determination of okadaic acid and dinophysistoxin-1 in shellfish after derivatization with 9-chloromethylanthracene

The reagent 9-chloromethylanthracene was evaluated for derivatization of the diarrhetic shellfish poisons, okadaic acid and dinophysistoxin-1 (DTX-1), to form fluorescent products separable by liquid chromatography. The toxins were reacted with the reagent in acetonitrile in the presence of tetramethylammonium hydroxide for 1 h at 90 degrees C. The products were purified by using two silica solid-phase extraction cartridges before being determined by reversed-phase liquid chromatography with fluorescence detection. The results are comparable to those obtained using 9-anthryldiazomethane (ADAM) for okadaic acid and DTX-1 in mussel tissue. Detection limits were estimated to be about 70-100 ng/g hepatopancreas (equivalent to 12-20 ng/g whole tissue) for each toxin.

Isolation of Porphyromonas gingivalis strain from tubal-ovarian abscess

An unusual case of involvement of Porphyromonas gingivalis is described. Two anaerobic isolates, identified as Fusobacterium nucleatum and P. gingivalis, were recovered from the pus of a tubal-ovarian abscess in a 35-year-old woman. Identification of the P. gingivalis isolate was confirmed by randomly amplified polymorphic DNA fingerprinting.

Clonal diversity of the taxon Porphyromonas gingivalis assessed by random amplified polymorphic DNA fingerprinting

A total of 97 strains of the periopathogen Porphyromonas gingivalis were collected. This collection included laboratory strains and clinical isolates of human origin with diverse clinical and geographical origins. Biological diversity was further increased by including 32 strains isolated from the oral cavities of nine different animal species. Genomic fingerprints of the 129 strains were generated as random amplified polymorphic DNAs (RAPDs) by the technique of PCR amplification with a single primer of arbitrary sequence. Four nonameric oligonucleotides were used as single primers, and the banding patterns of the DNA products separated on agarose gels were compared after ethidium ethidium bromide staining. Distance coeffients based on the positions of the major DNA fragments were calculated, and dendrograms were generated. We identified 102 clonal types (CTs) that could be assembled into three main groups by cluster analysis by the unweighted pair group method with mathematic averages. Group I (n = 79 CTs) included all 97 human strains and 6 monkey isolates. The strains in group II (n = 22 CTs) and III (n = 1 CT) were strongly differentiated from those in group I and included only strains of animal origin; they likely represent two cryptic species within the present P. gingivalis taxon. We observed that strains from Old World monkeys clustered together with the human genotype, whereas strains from New World monkeys clustered with the animal genotype. Our results with human strains also indicated that (i) the population structure is basically clonal, (ii) no dominant or widespread CT could be observed, and (iii) no relationship could be established between specific clusters of CTs and the periodontal status of the host. Our results corroborate previous findings by B. G. Loos, D. W. Dyer, T. S. Whittam, and R. K. Selander (Infect. Immun. 61:204-212, 1993) and suggest that P. gingivalis should be considered a commensal of the oral cavity acting as an opportunistic pathogen. Our results are not consistent with the hypothesis that only a few virulent clones of P. gingivalis are associated with disease.

Evaluation of prechromatographic oxidation for liquid chromatographic determination of paralytic shellfish poisons in shellfish

A liquid chromatographic (LC) method employing prechromatographic oxidation for the determination of paralytic shellfish poison (PSP) toxins was evaluated. A number of changes to an earlier method resulted in improved separation and quantitation of most PSP analogues. Modification of the periodate oxidation reaction for the N-hydroxy-containing toxins led to improved sensitivity and stability of the products, enabling automated overnight analyses. These changes also enabled quantitation of gonyautoxins 1 and 4 (together) in the presence of gonyautoxins 2 and 3. Decarbamoylsaxitoxin can be identified and quantitated after peroxide oxidation. A cleanup step using a strong-anion-exchange column removed the C toxins and B-2 from the extracts and enabled a more accurate quantitation of gonyautoxins 1 and 4 and neosaxitoxin. Chiral chromatography, employing a reversed-phase column and chiral mobile-phase additives (copper-proline complex), was briefly evaluated for the separation of the oxidation products of the isomer pairs, gonyautoxins 1 and 4 and gonyautoxins 2 and 3. A comparison of the method with the mouse bioassay for the determination of PSP in lobster hepatopancreas (58 samples) showed a reasonable correlation (0.90) over a concentration range of 40-500 micrograms/100 g (saxitoxin equivalents), although the LC results were consistently higher than the mouse bioassay values by about 40%.

Polymerase chain reaction using arbitrary primer for the design and construction of a DNA probe specific for Porphyromonas gingivalis

In this work, we used a novel approach for the design and construction of DNA probes which requires no knowledge of target DNA sequence. We demonstrated that species-specific genetic markers, identified as such among monomorphic, randomly amplified DNA segments generated by the polymerase chain reaction with arbitrary primer can be labelled to yield so-called "anonymous probes". We report here on the construction of such an anonymous probe, 1146 bp long, specific for the Gram-negative anaerobe Porphyromonas gingivalis, a suspected major etiologic agent of chronic periodontitis in adults.

Randomly amplified polymorphic DNA analysis confirms the biotyping scheme of Porphyromonas gingivalis

The application of the arbitrarily primed PCR (AP-PCR) procedure to generate randomly amplified polymorphic DNA (RAPD) fingerprints for the study of the taxon Porphyromonas gingivalis was investigated. Nine human strains and seven animal strains of P. gingivalis as well as eighteen strains other than P. gingivalis were analysed. Four nanomer primers of random sequence were evaluated for their ability to distinguish genetic diversity. Three primers generated RAPD fingerprints that allowed the sixteen strains to be differentiated; two of the primers yielded species-specific markers, and two of the primers permitted biotype distinction. Cluster analysis of the RAPD fingerprints revealed two major phenetic groups that matched the human and animal biotypes. Our results indicate that AP-PCR (i) can generate strain-specific fingerprints, (ii) confirms genetic heterogeneity and the biotype grouping of the P. gingivalis taxon, and (iii) enables identification of potential genetic markers at the species, biotype and subtype levels and is thus a promising tool for bacterial systematics. Our results also underline the potential of AP-PCR for epidemiological studies of periodontal pathogens.

Application of polymerase chain reaction with arbitrary primer (AP-PCR) to strain identification of Porphyromonas (Bacteroides) gingivalis

Several molecular methods are currently available for identification and discrimination of bacterial strains within the same species, which vary in efficiency and required labour. Here we applied a novel method for fingerprinting genomes, called arbitrarily primed PCR (AP-PCR), to the delineation of strains within the species Porphyromonas gingivalis. Using a single primer on a set of nine strains, nine simple distinct banding patterns, indicative of genetic polymorphism, were observed. Common amplicons and amplicons shared by only some strains were also observed, the latter suggesting that AP-PCR can be used to generate polymorphic markers. Genomic fingerprinting obtained by AP-PCR was independent of the quality of DNA. Assays performed directly using whole cells as a source of DNA template indicated that AP-PCR from colony is a quick, simple and accurate procedure.

Human neutrophils produce high levels of the interleukin 1 receptor antagonist in response to granulocyte/macrophage colony-stimulating factor and tumor necrosis factor alpha

Neutrophils, an abundant cell type at sites of inflammation, have the ability to produce a number of cytokines, including interleukin 1 (IL-1), IL-8, granulocyte-macrophage colony-stimulating factor (GM-CSF), and tumor necrosis factor alpha (TNF-alpha). In this study, we have examined the ability of human neutrophils to produce the IL-1 receptor antagonist (IL-1Ra), a 17-23-kD protein recently isolated and cloned from macrophages. Since IL-1Ra has been shown to inhibit both the in vitro and in vivo effects of IL-1, its production by large numbers of tissue-invading neutrophils might provide a mechanism by which the effects of IL-1 are regulated in inflammation. Using antibodies that are specific for IL-1Ra and a cDNA probe encoding for this protein, we were able to show that neutrophils constitutively produce IL-1Ra. However, after activation by GM-CSF and TNF-alpha, IL-1Ra was secreted into the extracellular milieu where it constituted the major de novo synthesized product of activated neutrophils. None of a large array of other potent neutrophil agonists were found to affect the production of IL-1Ra by neutrophils. Quantitative measurements by enzyme-linked immunosorbent assay revealed that intracellular IL-1Ra is in eightfold excess of the amount secreted in supernatants when studying nonactivated neutrophils. However, in GM-CSF- and TNF-alpha-activated cells, this difference was reduced to values between four- and fivefold, as virtually all of the de novo synthesized IL-1Ra was secreted. In activated cells, the intracellular content of IL-1Ra was found to be in the 2-2.5-ng/ml range per 10(6) neutrophils, whereas levels reached the 0.5-ng/ml range in supernatants. This would imply that IL-1Ra is produced in excess of IL-1 by a factor of at least 100, an observation that is in agreement with the reported amounts of IL-1Ra needed to inhibit the proinflammatory effects of IL-1. Neutrophils isolated from an inflammatory milieu, the synovial fluid of patients with rheumatoid arthritis, were found to respond to GM-CSF and TNF-alpha in terms of IL-1Ra synthesis, indicating that the in vitro observations made in this study are likely to occur in an inflammatory setting in vivo.

Liquid chromatographic determination of paralytic shellfish poisons in shellfish after prechromatographic oxidation

A liquid chromatographic method for quantitating paralytic shellfish poison toxins in shellfish has been developed in which the toxins are converted to fluorescent purines by prechromatographic oxidation under mildly basic conditions with hydrogen peroxide or periodate. The addition of ammonium formate to the periodate oxidation reaction greatly improved the yield of fluorescent derivatives for neosaxitoxin, gonyautoxin-1, B-2, and C-3 compared to the same reaction without ammonium formate. As little as 3-6 ng of each of the nonhydroxylated toxins and 7-12 ng of the hydroxylated compounds per gram of shellfish could be detected. Reversed-phase chromatography using ammonium formate in the mobile phase improved the chromatography of neosaxitoxin and B-2 compared to results obtained earlier. Because the oxidation products of neosaxitoxin and B-2 could not be separated, parent compounds were separated before oxidation by using an SPE-COOH ion exchange cartridge. The repeatability coefficient of variation for the oxidation reactions ranged from 3 to 8% for the peroxide reaction, and from 4 to 11% for the periodate reaction, depending upon the individual toxin determined and its concentration in the extract (0.04-0.55 micrograms/g). The method was compared to the mouse bioassay and the postcolumn oxidation method. In most cases, results were comparable.

Confirmation of domoic acid in shellfish using butyl isothiocyanate and reversed-phase liquid chromatography

A simple chemical confirmatory technique has been developed for domoic acid, a neurotoxic amino acid of marine origin. After extraction with water-methanol, the domoic acid-containing extract is analysed directly by reversed-phase liquid chromatography with UV absorption detection at 242 nm. For confirmation of positive results an aliquot of the extract is evaporated to dryness and reacted with butyl isothiocyanate to form a thiourea derivative which elutes later than underivatized domoic acid. No additional sample cleanup is required in order to carry out the derivatization for conformation of domoic acid at the Canadian 20 micrograms/g guideline level in shellfish. In mussel extract, domoic acid was converted to the thiourea derivative with a yield of 86-91% compared to a pure standard carried through the same reaction. The detection limit for the derivative was about 5-10 micrograms/g of equivalent domoic acid in extracts of mussels, clams or oysters.