A sensitive and useful radioimmunoassay for neurotoxin and its haemagglutinin complex from Clostridium botulinum

Proteomic Methods of Detection and Quantification of Protein Toxins

Biological toxins are a heterogeneous group of compounds that share commonalities with biological and chemical agents. Among them, protein toxins represent a considerable, diverse set. They cover a broad range of molecular weights from less than 1000 Da to more than 150 kDa. This review aims to compare conventional detection methods of protein toxins such as in vitro bioassays with proteomic methods, including immunoassays and mass spectrometry-based techniques and their combination. Special emphasis is given to toxins falling into a group of selected agents, according to the Centers for Disease Control and Prevention, such as Staphylococcal enterotoxins, Bacillus anthracis toxins, Clostridium botulinum toxins, Clostridium perfringens epsilon toxin, ricin from Ricinus communis, Abrin from Abrus precatorius or control of trade in dual-use items in the European Union, including lesser known protein toxins such as Viscumin from Viscum album. The analysis of protein toxins and monitoring for biological threats, i.e., the deliberate spread of infectious microorganisms or toxins through water, food, or the air, requires rapid and reliable methods for the early identification of these agents.

Methods and difficulties in detection of Clostridium botulinum and its toxins

The aim of this work was to present selected data regarding traditional and modern methods for C. botulinum and its toxins detection. In this article, methods based on culturing techniques, mouse bioassay, immunological techniques, chromatography and PCR, PFGE, RFLP, AFLP are described. The mentioned techniques were evaluated considering their usefulness in the samples examination, genotyping of strains and the diagnostics of botulism.

Sensing the deadliest toxin: technologies for botulinum neurotoxin detection

Sensitive and rapid detection of botulinum neurotoxins (BoNTs), the most poisonous substances known to date, is essential for studies of medical applications of BoNTs and detection of poisoned food, as well as for response to potential bioterrorist threats. Currently, the most common method of BoNT detection is the mouse bioassay. While this assay is sensitive, it is slow, quite expensive, has limited throughput and requires sacrificing animals. Herein, we discuss and compare recently developed alternative in vitro detection methods and assess their ability to supplement or replace the mouse bioassay in the analysis of complex matrix samples.

Sensing the deadliest toxin: technologies for botulinum neurotoxin detection

Sensitive and rapid detection of botulinum neurotoxins (BoNTs), the most poisonous substances known to date, is essential for studies of medical applications of BoNTs and detection of poisoned food, as well as for response to potential bioterrorist threats. Currently, the most common method of BoNT detection is the mouse bioassay. While this assay is sensitive, it is slow, quite expensive, has limited throughput and requires sacrificing animals. Herein, we discuss and compare recently developed alternative in vitro detection methods and assess their ability to supplement or replace the mouse bioassay in the analysis of complex matrix samples.

Monoclonal antibody-based enzyme immunoassay for detection of botulinum neurotoxin type A

A sensitive and specific ELISA was developed to detect BoNT/A in biological fluids. The assay is based on the sandwich format using monoclonal antibodies (MAb) of two distinct specificities. An affinity-purified anti-BoNT/A heavy chain MAb (150-3) is utilized to adsorb BoNT/A from solution; the second anti-BoNT/A heavy chain MAb (44-1A) conjugated with peroxidase is then used to form a sandwich. Peroxidase allows color development and measurement of optical density at 450 nm. Standard curves were linear over the range of 2.5 to 100 ng/mL BoNT/A. The limit of detection was below 5 ng/mL in assay buffer, as well as in a 1:10 dilution of urine or 1:50 dilution of human serum spiked with BoNT/A. The developed BoNT/A assay also showed no cross-reaction to type B neurotoxin (BoNT/B) and type E neurotoxin (BoNT/E).

Laboratory diagnostics of botulism

Botulism is a potentially lethal paralytic disease caused by botulinum neurotoxin. Human pathogenic neurotoxins of types A, B, E, and F are produced by a diverse group of anaerobic spore-forming bacteria, including Clostridium botulinum groups I and II, Clostridium butyricum, and Clostridium baratii. The routine laboratory diagnostics of botulism is based on the detection of botulinum neurotoxin in the patient. Detection of toxin-producing clostridia in the patient and/or the vehicle confirms the diagnosis. The neurotoxin detection is based on the mouse lethality assay. Sensitive and rapid in vitro assays have been developed, but they have not yet been appropriately validated on clinical and food matrices. Culture methods for C. botulinum are poorly developed, and efficient isolation and identification tools are lacking. Molecular techniques targeted to the neurotoxin genes are ideal for the detection and identification of C. botulinum, but they do not detect biologically active neurotoxin and should not be used alone. Apart from rapid diagnosis, the laboratory diagnostics of botulism should aim at increasing our understanding of the epidemiology and prevention of the disease. Therefore, the toxin-producing organisms should be routinely isolated from the patient and the vehicle. The physiological group and genetic traits of the isolates should be determined.

Colloidal gold-based immunochromatographic assay for detection of botulinum neurotoxin type B

A rapid immunochromatographic assay was developed to detect botulinum neurotoxin type B (BoNT/B). The assay was based on the sandwich format using polyclonal antibody (Pab). The thiophilic gel purified anti-BoNT/B Pab was immobilized to a defined detection zone on a porous nitrocellulose membrane and conjugated to colloidal gold particles that served as a detection reagent. The BoNT/B-containing sample was added to the membrane and allowed to react with Pab-coated particles. The mixture was then passed along the porous membrane by capillary action past the Pab in the detection zone, which will bind the particles that had BoNT/B bound to their surface, giving a red colour within this detection zone with an intensity proportional to BoNT/B concentration. In the absence of BoNT/B, no immunogold was bound to the solid-phase antibody. With this method, 50 ng/ml of BoNT/B was detected in less than 10 min. The assay sensitivity can be increased by silver enhancement to 50 pg/ml. The developed BoNT/B assay also showed no cross reaction to type A neurotoxin (BoNT/A) and type E neurotoxin (BoNT/E).

Pharmacologic characterization of botulinum toxin for basic science and medicine

The use of Botulinum neurotoxin (BoNT) is increasing in both clinical and basic science. Clinically, intramuscular injection of nanogram quantities of BoNT is fast becoming the treatment of choice for a spectrum of disorders including movement disorders such as torticollis, blepharospasm, Meige Disease, and hemifacial spasm (Borodic et al., 1991, 1994a; Jankovic and Brin, 1991; Clarke, 1992). Neuroscientists are using BoNTs as tools to develop a better understanding of the mechanisms underlying the neurotransmitter release process. Consequently, our ability to accurately and reliably quantify the biologic activity of botulinum toxin has become more important than ever. The accurate measurement of the pharmacologic activity of BoNTs has become somewhat problematic with the most significant problems occurring with the clinical use of the toxins. The biologic activity of BoNTs has been measured using a variety of techniques including assessment of whole animal responses to in vitro effects on neurotransmitter release. The purpose of this review is to examine the approaches employed to characterize, quantify and investigate the actions of the BoNTs and to provide a guide to aid investigators in determining which of these methods is most appropriate for their particular application or use.

Immunological detection of Clostridium botulinum toxin type A in therapeutic preparations

The potent neurotoxins produced by strains of Clostridium botulinum act by blocking the release of acetylcholine from peripheral nerve junctions. This specific action of the botulinum neurotoxins is now being exploited therapeutically to treat a variety of conditions involving involuntary muscle spasms. We aimed to develop a sensitive and specific enzyme-linked immunosorbent assay (ELISA) which may be used in parallel with the currently accepted mouse bioassay test for the determination of botulinum neurotoxin type A in therapeutic preparations. High titre polyclonal antitoxins and their biotin derivatives, highly labelled horseradish peroxidase (HRP)-antibody conjugates, and streptavidin-biotin-HRP complexes were prepared and used in a sandwich ELISA for the detection of pure neurotoxin and neurotoxin in therapeutic material. The ELISA utilized either a monoclonal or polyclonal antibody as capture agent and HRP-labelled IgG or F(ab')2 fragment as second antibody. The limit of detection was 4-8 pg of purified toxin/ml (gcv < 13%), equivalent to 1-2 mouse bioassay units/ml. The assay was used to evaluate therapeutic preparations and the results compared with the mouse bioassay. The lower limit of detection for a therapeutic preparation of BoTxA was 2-5 mouse bioassay units/ml. Although across different manufacturers and bulk products there was no correlation between immunologically detected neurotoxin and its biological activity in different therapeutic preparations (r = -0.44, p = 0.34, n = 8), the assay could be used to quantify neurotoxin in therapeutic preparations derived from the same bulk concentrate and manufacturer. The assay is relatively simple, and may be readily adapted to routine monitoring of BoTxA content in therapeutic preparations.

Detection of botulinum toxin using an evanescent wave immunosensor

Using fluorescein isothiocyanate (FITC)-streptavidin, quartz fibre-immobilized antibody (FiAb) and the evanescent wave component of a light beam, detection of Botulinum Toxin-B (BoTX) is described. Exposure of 3-aminopropyltriethoxysilane/glutaraldehyde (APTS/GA) treated quartz fibres to increasing amounts of anti-BoTX Ab indicated toxin binding to increase in a linear fashion up to approximately 125 ng added Ab. Quantitation of bound BoTX and FiAb by Dot-Blot analysis using avidin-Horseradish peroxidase (HRP) conjugation indicated the presence of 0.27 and 0.67 pmoles, respectively. Inclusion of nonbiotinylated BoTX in sampling mixtures reduced fluorescence in a dose-dependent manner over a narrow concentration range (0-300 ng). Exposure of FiAb to a variety of venoms resulted in no reduction of BoTX binding suggesting detection of BoTX via immobilized anti-BoTX Ab to be very specific.

Detection of the genes encoding botulinum neurotoxin types A to E by the polymerase chain reaction

The polymerase chain reaction (PCR) was used as the basis for the development of highly sensitive and specific diagnostic tests for organisms harboring botulinum neurotoxin type A through E genes. Synthetic DNA primers were selected from nucleic acid sequence data for Clostridium botulinum neurotoxins. Individual components of the PCR for each serotype (serotypes A through E) were adjusted for optimal amplification of the target fragment. Each PCR assay was tested with organisms expressing each of the botulinum neurotoxin types (types A through G), Clostridium tetani, genetically related nontoxigenic organisms, and unrelated strains. Each assay was specific for the intended target. The PCR reliably identified multiple strains having the same neurotoxin type. The sensitivity of the test was determined with different concentrations of genomic DNA from strains producing each toxin type. As little as 10 fg of DNA (approximately three clostridial cells) was detected. C. botulinum neurotoxin types A, B, and E, which are most commonly associated with human botulism, could be amplified from crude DNA extracts, from vegetative cells, and from spore preparations. This suggests that there is great potential for the PCR in the identification and detection of botulinum neurotoxin-producing strains.

Specific detection of Clostridium botulinum type B by using the polymerase chain reaction

The polymerase chain reaction (PCR) and a radiolabeled oligonucleotide probe were used to specifically detect proteolytic and nonproteolytic Clostridium botulinum type B. Two synthetic primers deduced from the amino acid sequence data of type B neurotoxin were used to amplify a 1.5-kbp fragment corresponding to the light chain of the toxin. Although, nonspecific priming was observed when the PCR protocol was tested with other clostridial species, only the PCR product from C. botulinum type B isolates reacted with the radiolabeled internal probe. As little as 100 fg of DNA (approximately 35 clostridial cells) could be detected after only 25 amplification cycles.

Application of immunoassay in the food industry

Immunoassay techniques using the highly specific and sensitive nature of immunological reactions have been developed and applied in the food industry for detecting the naturally occurring constituents, antibiotics, pesticide residues, microorganisms, and fragments of microbial constituents related to food analysis, food production, food processing, and food safety. Both polyclonal and monoclonal antibodies are employed for the development of the various immunoassay systems, including enzyme-linked immunoassay (ELISA) and radioimmunoassay (RIA). Immunoassay techniques provide complementary and/or alternate approaches in reducing the use of costly, sophisticated equipment and analysis time, but still maintaining reliability and improved sensitivity. Immunoassay techniques in their most simple forms provide excellent screening tools to detect adulteration and contaminations qualitatively. The application of immunoassay techniques contributes tremendously to the quality control and safety of our food supply.

Assay in mice for low levels of Clostridium botulinum toxin

When botulinum toxin at a low level such as 0.1 to 1.0 mouse intraperitoneal LD50 was injected subcutaneously into a mouse at the inguinocrual region, abdominal ptosis with local palsy developed. If this symptom is taken as a marker, 1.0 mouse intraperitoneal LD50 can be detected within 6 h and 0.1 LD50 within 24 h. The severity of symptoms and the time-to-death in days after injection of toxin were converted into scores to quantify the toxic activity. Over a wide range of dose, between 0.075 and 38.4 mouse intraperitoneal LD50, a linear relationship was obtained between the log dose and the score. By use of this method, low levels of toxin such as 0.1 mouse intraperitoneal LD50 can be titrated accurately and easily.

Ca2(+)-dependent noradrenaline release from permeabilised PC12 cells is blocked by botulinum neurotoxin A or its light chain

Permeabilisation of PC12 cells with digitonin allowed a direct study of the intracellular action of botulinum neurotoxin A, one of a group of dichain proteins produced by Clostridium botulinum that causes the fatal neuroparalytic condition, botulism. Release of [3H]noradrenaline from these permeabilised cells could be evoked by Ca2+ and this was inhibited specifically by the neurotoxin in a dose-dependent manner (half-maximal dose approximately 2 nM under the conditions used). Inclusion of the reducing agent dithiothreitol (up to 10 mM) had no effect on the level of inhibition. Moreover, electrophoretic analysis showed that this treatment of the toxin in the native state caused negligible reduction of inter-chain disulphide bonds. Toxin-induced blockade of neurotransmitter release was incomplete and could not be overcome by increased Ca2+ concentration (100 microM). The observed toxin-insensitivity of the release from intact PC12 cells must result from inefficient toxin uptake, relative to that in peripheral cholinergic neurones. Refolded light chain alone inhibited exocytosis to the same degree and with similar potency to that of the intact neurotoxin, an effect not altered by the heavy chain. This inhibitory activity of the light chain in PC12 cells accords with observations made in permeabilised chromaffin cells [(1989) J. Biol. Chem. 264, 10354-10360; (1989) FEBS Lett. 255, 391-394] but contrasts with invertebrate neurones, where intracellular injection of the same preparations of both chains were necessary for inhibition of quantal release of acetylcholine [(1988) Proc. Natl. Acad. Sci. USA 85, 4090-4094]. These collective findings may signify an interesting difference in the release process in such diverse systems or denote a dissimilarity in the transport or processing of the toxin when applied into intact neurones or cells permeabilised by detergent or streptolysin.

Botulinum neurotoxin type B. Its purification, radioiodination and interaction with rat-brain synaptosomal membranes

Neurotoxin from Clostridium botulinum type B was purified to homogeneity by by affinity and ion-exchange chromatography; specific neurotoxicity of this protein (Mr of approximately equal to 155 000) following trypsinisation attained a level of 2 X 10(8) mouse LD50 units/mg protein. 125I-iodination of the toxin to high specific radioactivities (19-63 TBq/mmol) yielded typically greater than 65% of its original toxicity; dodecyl sulphate gel electrophoresis under reducing conditions, after trypsinisation, showed that the larger polypeptide (Mr of approximately equal to 101 000) was labelled preferentially. Saturable binding of the 125I-labelled neurotoxin to rat cerebrocortical synaptosomes was observed and Scatchard analysis showed a low content of acceptors with high affinity (Kd = 0.3-0.5 nM;Bmax approximately equal to 30-60 fmol/mg protein, together with a much larger population of weak-affinity sites. No significant differences in binding affinity were seen in competition experiments using native or fully activated (trypsinized) neurotoxin, indicating that chain cleavage is not essential for acceptor-toxin interaction. Type A botulinum neurotoxin showed a limited capacity to inhibit the synaptosomal binding of labelled type B toxin, even at high concentrations (1 muM), and other neurotoxins were without effect, emphasising the acceptor selectivity. Near-complete loss of specific toxin binding was produced by preincubation of synaptosomes with neuraminidase whereas inhibition of the low-affinity sites with wheat-germ agglutinin was less pronounced; such inactivation was prevented by inclusion of selective inhibitors (2,3-dehydro-2-deoxy-N-acetylneuraminic acid and N-acetylglucosamine, respectively). These observations implicate N-acetylneuraminic acid and, possibly, other sugar moieties as constituents of the toxin acceptors. Trypsinisation of synaptosomes gave incomplete inhibition of binding when assayed with 1 nM or 10 nM 125I-iodinated toxin. Detailed analysis of the actions of neuraminidase, trypsin and heat treatment on the concentration dependence of toxin binding suggest the existence of at least two distinguishable populations of sites that contain N-acetylneuraminic acid, with a protein component being associated with the acceptors of lower affinity. These findings are discussed in relation to those previously reported for type A neurotoxin and to the possible physiological significance of such membrane acceptors.