A Rapid, Sensitive, and Portable Biosensor Assay for the Detection of Botulinum Neurotoxin Serotype A in Complex Food Matrices

Botulinum neurotoxin (BoNT) intoxication can lead to the disease botulism, characterized by flaccid muscle paralysis that can cause respiratory failure and death. Due to the significant morbidity and mortality costs associated with BoNTs high toxicity, developing highly sensitive, rapid, and field-deployable assays are critically important to protect the nation’s food supply against either accidental or intentional contamination. We report here that the B-cell based biosensor assay CANARY^® (Cellular Analysis and Notification of Antigen Risks and Yields) Zephyr detects BoNT/A holotoxin at limits of detection (LOD) of 10.0 ± 2.5 ng/mL in assay buffer. Milk matrices (whole milk, 2% milk and non-fat milk) with BoNT/A holotoxin were detected at similar levels (7.4–7.9 ng/mL). BoNT/A complex was positive in carrot, orange, and apple juices at LODs of 32.5–75.0 ng/mL. The detection of BoNT/A complex in solid complex foods (ground beef, smoked salmon, green bean baby puree) ranged from 14.8 ng/mL to 62.5 ng/mL. Detection of BoNT/A complex in the viscous liquid egg matrix required dilution in assay buffer and gave a LOD of 171.9 ± 64.7 ng/mL. These results show that the CANARY^® Zephyr assay can be a highly useful qualitative tool in environmental and food safety surveillance programs.

Use of Monoclonal Antibodies in the Sensitive Detection and Neutralization of Botulinum Neurotoxin Serotype B

Botulinum neurotoxins (BoNT) are some of nature’s most potent toxins. Due to potential food contamination, and bioterrorism concerns, the development of detection reagents, therapeutics and countermeasures are of urgent interest. Recently, we have developed a sensitive electrochemiluminescent (ECL) immunoassay for BoNT/B, using monoclonal antibodies (mAbs) MCS6-27 and anti-BoNT/B rabbit polyclonal antibodies as the capture and detector. The ECL assay detected as little as 1 pg/mL BoNT/B in the buffer matrix, surpassing the detection sensitivities of the gold standard mouse bioassays. The ECL assay also allowed detection of BoNT/B in sera matrices of up to 100% sera with negligible matrix effects. This highly-sensitive assay allowed the determination of the biological half-lives of BoNT/B holotoxin in vivo. We further tested the toxin neutralization potential of our monoclonal antibodies using the mouse systemic and oral intoxication models. A combination of mAbs protected mice in both pre- and post-exposure models to lethal doses of BoNT/B. MAbs were capable of increasing survival of animals when administered even 10 h post-intoxication in an oral model, suggesting a likely time for BoNT/B complexes to reach the blood stream. More sensitive detection assays and treatments against BoNT intoxication will greatly enhance efforts to combat botulism.

Recommended Immunological Strategies to Screen for Botulinum Neurotoxin-Containing Samples

Botulinum neurotoxins (BoNTs) cause the life-threatening neurological illness botulism in humans and animals and are divided into seven serotypes (BoNT/A–G), of which serotypes A, B, E, and F cause the disease in humans. BoNTs are classified as “category A” bioterrorism threat agents and are relevant in the context of the Biological Weapons Convention. An international proficiency test (PT) was conducted to evaluate detection, quantification and discrimination capabilities of 23 expert laboratories from the health, food and security areas. Here we describe three immunological strategies that proved to be successful for the detection and quantification of BoNT/A, B, and E considering the restricted sample volume (1 mL) distributed. To analyze the samples qualitatively and quantitatively, the first strategy was based on sensitive immunoenzymatic and immunochromatographic assays for fast qualitative and quantitative analyses. In the second approach, a bead-based suspension array was used for screening followed by conventional ELISA for quantification. In the third approach, an ELISA plate format assay was used for serotype specific immunodetection of BoNT-cleaved substrates, detecting the activity of the light chain, rather than the toxin protein. The results provide guidance for further steps in quality assurance and highlight problems to address in the future.

Mass Spectrometric Detection of Bacterial Protein Toxins and Their Enzymatic Activity

Mass spectrometry has recently become a powerful technique for bacterial identification. Mass spectrometry approaches generally rely upon introduction of the bacteria into a matrix-assisted laser-desorption time-of-flight (MALDI-TOF) mass spectrometer with mass spectrometric recognition of proteins specific to that organism that form a reliable fingerprint. With some bacteria, such as Bacillus anthracis and Clostridium botulinum, the health threat posed by these organisms is not the organism itself, but rather the protein toxins produced by the organisms. One such example is botulinum neurotoxin (BoNT), a potent neurotoxin produced by C. botulinum. There are seven known serotypes of BoNT, A–G, and many of the serotypes can be further differentiated into toxin variants, which are up to 99.9% identical in some cases. Mass spectrometric proteomic techniques have been established to differentiate the serotype or toxin variant of BoNT produced by varied strains of C. botulinum. Detection of potent biological toxins requires high analytical sensitivity and mass spectrometry based methods have been developed to determine the enzymatic activity of BoNT and the anthrax lethal toxins produced by B. anthracis. This enzymatic activity, unique for each toxin, is assessed with detection of the toxin-induced cleavage of strategically designed peptide substrates by MALDI-TOF mass spectrometry offering unparalleled specificity. Furthermore, activity assays allow for the assessment of the biological activity of a toxin and its potential health risk. Such methods have become important diagnostics for botulism and anthrax. Here, we review mass spectrometry based methods for the enzymatic activity of BoNT and the anthrax lethal factor toxin.

Evaluation of an enzyme-linked immunosorbent assay (ELISA) kit for the detection of botulinum neurotoxins A, B, E, and F in selected food matrices

The mouse bioassay (MBA) is the only accepted standard method for detection of botulinum neurotoxins (BoNTs) in foods. The ELISA method has several advantages over the MBA and is therefore widely used for in vitro detection of BoNTs. The US Food and Drug Administration (FDA) and the Centers for Disease Control and Prevention (CDC) conducted a precollaborative study to evaluate the applicability of Botulinum Toxin ELISA kits for the detection of BoNT serotypes A, B, E, and F in a variety of food matrices. In this study, food samples (e.g., broccoli, salami, smoked salmon, green beans, orange juice, tomato juice, low-fat plain yogurt, whole milk, liquid infant formula milk, and liquid eggs) were spiked with high, medium, and low concentration BoNT serotypes A, B, E, and F. Samples (unspiked and spiked) were tested at both laboratories by the ELISA kits. All food samples were positive for BoNTs by ELISA in both laboratories at medium and high spiking levels; a positive ELISA result in low spiked samples was both serotype and laboratory dependent. Overall, the ELISA method appears to be an effective preliminary screening method for BoNT detection in food matrices.

A simple, rapid and sensitive FRET assay for botulinum neurotoxin serotype B detection

Botulinum neurotoxins (BoNTs), the most potent naturally-occurring neurotoxins known to humans, comprise seven distinct serotypes (BoNT/A-G), each of which exhibits unique substrate specificity. Many methods have been developed for BoNT detection, in particular for BoNT/A, with various complexity and sensitivity, while substrate based FRET assay is considered as the most widely used approach due to its simplicity and sensitivity. In this study, we designed a vesicle-associated membrane protein 2 (VAMP2) based FRET assay based on the understanding of the VAMP2 and light chain/B (LC/B) interactions in our previous studies. The current design constituted the shortest peptide, VAMP2 (63–85), with FRET dyes (EDAN and Dabcyl) labelled at position 76 and 85, respectively, which showed minimal effect on VAMP2 substrate catalysis by LC/B and therefore enhanced the sensitivity of the assay. The FRET peptide, designated as FVP-B, was specific to LC/B, with a detection sensitivity as low as ∼20 pM in 2 h. Importantly, FVP-B showed the potential to be scaled up and used in high throughput screening of LC/B inhibitor. The currently developed FRET assay is one of the most economic and rapid FRET assays for LC/B detection.

A graphene oxide based fluorescence resonance energy transfer (FRET) biosensor for ultrasensitive detection of botulinum neurotoxin A (BoNT/A) enzymatic activity

Botulinum neurotoxins (BoNTs) are among the most potent toxic bacterial proteins for humans, which make them potential agents for bioterrorism. Therefore, an ultrasensitive detection of BoNTs and their active states is in great need as field-deployable systems for anti-terrorism applications. We report the construction of a novel graphene oxide (GO)-peptide based fluorescence resonance energy transfer (FRET) biosensor for ultrasensitive detection of the BoNT serotype A light chain (BoNT-LcA) protease activity. A green fluorescence protein (GFP) modified SNAP-25 peptide substrate (SNAP-25-GFP) was optimally designed and synthesized with the centralized recognition/cleavage sites. This FRET platform was constructed by covalent immobilization of peptide substrate on GO with BSA passivation which have advantages of low non-specific adsorption and high stability in protein abundant solution. BoNT-LcA can specifically cleave SNAP-25-GFP substrate covalently immobilized on GO to release the fragment with GFP. Based on fluorescence signal recovery measurement, the target BoNT-LcA was detected sensitively and selectively with the linear detection range from 1fg/mL to 1pg/mL. The limit of detection (LOD) for BoNT-LcA is around 1fg/mL.

An electrochemiluminescence assay for the detection of bio threat agents in selected food matrices and in the screening of Clostridium botulinum outbreak strains associated with type A botulism

BACKGROUND

Specific screening methods for complex food matrices are needed that enable unambiguous and sensitive detection of bio threat agents (BTAs) such as Bacillus anthracis spores and microbial toxins (e.g. staphylococcal enterotoxin B (SEB) and clostridial botulinum neurotoxins (BoNTs)). The present study describes an image-based 96-well Meso Scale Discovery (MSD) electrochemiluminescence (ECL) assay for simultaneous detection of BTAs in dairy milk products.

RESULTS

The limit of detection of this ECL assay is 40 pg mL⁻¹ for BoNT/A complex, 10 pg mL⁻¹ for SEB and 40000 CFU mL⁻¹ for Bacillus anthracis spores in dairy milk products. The ECL assay was successfully applied to screen type A Clostridium botulinum outbreak strains.

CONCLUSION

The results of the study indicate that this ECL assay is very sensitive, rapid (<6 h) and multiplex in nature. The ECL assay has potential for use as an in vitro screening method for BTAs over other comparable immunoassays.

Infant botulism with prolonged faecal excretion of botulinum neurotoxin and Clostridium botulinum for 7 months

In Finland in April 2010, a 3-month old baby was diagnosed with type A infant botulism. He excreted botulinum neurotoxin and/or Clostridium botulinum in his faeces until November 2010. Five months of excretion was after clinical recovery and discharge from hospital. C. botulinum isolates recovered from the household dust in the patient's home were genetically identical to those found in the infant's stool samples. Long-term faecal excretion of C. botulinum may pose a possible health risk for the parents and others in close contact with the infant.

Application of Real-Time PCR for Quantitative Detection ofClostridium botulinumType A Toxin Gene in Food

The TaqMan real-time PCR method for the quantitative detection of C. botulinum type A was developed based on sequence-specific hybridization probes. The validity of this assay was verified by using 10 genera of 20 strains, including reference strains of C. botulinum types A, B, C, D, E and F. The detection limit of this assay was evaluated on C. botulinum type A, using a 10-fold dilution series of DNA and spores . The DNA and spores were detected up to level of 0.1 ng/ml and 10(2)spores/ml, respectively. Spore spiked food sample preparation prior to the real-time PCR was performed by two methods, heat treatment and GuSCN. The detection limits after heat treatment showed 10(2) spores/ml for spiked sausage slurry, and 10(3) spores/ml for spiked canned corn slurry, while detection limits after GuSCN precipitation showed 10(2) spores/ml in both sausage and canned corn. Therefore the real-time PCR assay after GuSCN precipitation is useful for the quantification of C. botulinum type A because it showed identical CT values in both pure spore solutions and food slurries. We suggest that quantitative analysis of C. botulinum type A by TaqMan real-time PCR can be a rapid and accurate assessment method for botulinal risk in food samples.

Botulinum toxin field assays evaluated using cosmetic botox preparations

Several quick tests for identifying botulinum toxins (BoNTs) are commercially available, but generally these tests have not been evaluated by independent laboratories. This study presents data on the evaluation of a number of commercial tests and demonstrates the use of cosmetic preparations of BoNT A and B as positive controls. For reference we used an in-house ELISA procedure. The cosmetic toxins, Botox(®) and Neurobloc(®), were found to be useful-that is, they had a sufficiently high toxin content to be used in test evaluation studies. Some commercial kits based on columns (ABICAP(®)) or lateral flow technology were tested for their detection limits. The ABICAP column system was found to be a useful alternative to an in-house ELISA method. In general, the lateral flow-based test systems evaluated here were not able to detect BoNT, and a large proportion of the tests showed construction failures. In conclusion, this study showed that cosmetic BoNT products have enough toxin content to be used as convenient and accessible means of testing commercially available quick tests. The lateral flow tests used in this study were not satisfactory, while the ABICAP system was found to be a good alternative to an ELISA.

Charged-coupled device (CCD) detectors for Lab-on-a Chip (LOC) optical analysis

A critical element of any Lab-on-a-Chip (LOC) is a detector; among the many detection approaches, optical detection is very widely used for biodetection. One challenge for advancing the development of LOC for biodetection has been to enhance the portability and lower the cost for Point-of-Care diagnostics, which has the potential to enhance the quality of healthcare delivery for underserved populations and for global health. We describe a simple and relatively low cost charged-coupled device (CCD)-based detector that can be integrated with a conventional microtiter plate or a portable LOC assay for various optical detection modalities including fluorescence, chemiluminescence, densitometry, and colorimetric assays. In general, the portable battery-operated CCD-based detection system consists of four modules: (1) a cooled CCD digital camera to monitor light emission, (2) a LOC or microtiter plate to perform assays, (3) a light source to illuminate the assay (such as electroluminescence (EL) or light emitting diode (LED)), and (4) a portable computer to acquire and analyze images. The configuration of the fluorescence detector presented here was designed to measure fluorogenic excitation at 490 nm and to monitor emission at 523 nm used for FITC detection.The LOC used for this detection system was fabricated with laminated object manufacturing (LOM) technology, and was designed to detection activity of botulinum neurotoxin serotype A (BoNT-A) using a fluorogenic peptide substrate (SNAP-25) for botulinum neurotoxin serotype A (BoNT-A) labeled with FITC. The limit of detection (LOD) for the CCD detector is 0.5 nM (25 ng/ml). The portable system is small and is powered by a 12 V source. The modular detector was designed with easily interchangeable LEDs, ELs, filters, lenses, and LOC, and can be used and adapted for a wide variety of densitometry, florescence and colorimetric assays.

[Development and optimization of immunoassays for the detection of botulinum toxins]

Monoparametric immunoassay tests for detecting botulinum toxins types A and B and multiparametric assays for simultaneous detection of botulinum toxins type A and B have been developed. It is shown that the sensitivity of assays is affected by the size of nanoparticles of colloidal gold used as a marker of antibodies, load intensity of antibodies of colloidal gold in conjugates, the type of analytical membranes, as well as the chemical composition of buffer solutions used for the storage of conjugates and immunoassay analysis. The detection limit of monoparametric immunoassay tests is 0.5 ng/ml; that of multiparametric assays, 5.0 ng/ml. The developed immunoassay can be used for rapid assay of product quality, for grade control of botulinum toxins in pharmaceuticals, and environmental monitoring.

Improved detection of botulinum neurotoxin type A in stool by mass spectrometry

Botulinum neurotoxins (BoNTs) are the most toxic substances known to humankind. Rapid and sensitive detection of BoNTs is necessary for timely clinical confirmation of the disease state in botulism. BoNTs cleave proteins and peptide mimics at specific sites. A mass spectrometry (MS)-based method, Endopep-MS, can detect these cleavages and has detection limits of 0.05-0.5 mouse LD(50) (U) in serum, depending on the BoNT serotypes. In this method, the products generated from cleavage of peptide substrates using antibody affinity-purified toxins are detected by MS. Nonspecific bound endogenous proteases or peptidases in stool can coextract with the toxin, cleaving the peptide substrates and reducing the sensitivity of the method. Here we report a method to reduce nonspecific substrate cleavage by reducing stool protease coextraction in the Endopep-MS assay.

Ultrasensitive detection of botulinum neurotoxins and anthrax lethal factor in biological samples by ALISSA

Both botulinum neurotoxins (BoNTs) and anthrax lethal factor, a component of anthrax toxin, exhibit zinc metalloprotease activity. The assay detailed here is capable of quantitatively detecting these proteins by measuring their enzymatic functions with high sensitivity. The detection method encompasses two steps: (1) specific target capture and enrichment and (2) cleavage of a fluorogenic substrate by the immobilized active target, the extent of which is quantitatively determined by differential fluorometry. Because a critical ingredient for the target enrichment is an immobilization matrix made out of hundreds of thousands of microscopic, antibody-coated beads, we have termed this detection method an assay with a large immuno-sorbent surface area (ALISSA). The binding and reaction surface area in the ALISSA is approximately 30-fold larger than in most microtiter plate-based enzyme-linked immunosorbent assays (ELISAs). ALISSA reaches atto (10(-18)) to femto (10(-15)) molar sensitivities for the detection of BoNT serotypes A and E and anthrax lethal factor. In addition, ALISSA provides high specificity in complex biological matrices, such as serum and liquid foods, which may contain various other proteases and hydrolytic enzymes. This methodology can potentially be expanded to many other enzyme targets by selecting appropriate fluorogenic substrates and capture antibodies. Important requirements are that the enzyme remains active after being immobilized by the capture antibody and that the substrate is specifically converted by the immobilized enzyme target at a fast conversion rate.A detailed protocol to conduct ALISSA for the detection and quantification of BoNT serotypes A and E and anthrax lethal factor is described.

Extraction of BoNT/A, /B, /E, and /F with a single, high affinity monoclonal antibody for detection of botulinum neurotoxin by Endopep-MS

Botulinum neurotoxins (BoNTs) are extremely potent toxins that are capable of causing respiratory failure leading to long-term intensive care or death. The best treatment for botulism includes serotype-specific antitoxins, which are most effective when administered early in the course of the intoxication. Early confirmation of human exposure to any serotype of BoNT is an important public health goal. In previous work, we focused on developing Endopep-MS, a mass spectrometry-based endopeptidase method for detecting and differentiating the seven serotypes (BoNT/A-G) in buffer and BoNT/A, /B, /E, and /F (the four serotypes that commonly affect humans) in clinical samples. We have previously reported the success of antibody-capture to purify and concentrate BoNTs from complex matrices, such as clinical samples. However, to check for any one of the four serotypes of BoNT/A, /B, /E, or /F, each sample is split into 4 aliquots, and tested for the specific serotypes separately. The discovery of a unique monoclonal antibody that recognizes all four serotypes of BoNT/A, /B, /E and /F allows us to perform simultaneous detection of all of them. When applied in conjunction with the Endopep-MS assay, the detection limit for each serotype of BoNT with this multi-specific monoclonal antibody is similar to that obtained when using other serotype-specific antibodies.

Lab-on-a-chip for botulinum neurotoxin a (BoNT-A) activity analysis

A Lab-on-a-chip (LOC) was designed, fabricated and tested for the in vitro detection of botulinum neurotoxin serotype A (BoNT-A) activity using an assay that measures cleavage of a fluorophore-tagged peptide substrate specific for BoNT-A (SNAP-25) by the toxin light chain (LcA). LcA cleavage was detected by Förster Resonance Energy Transfer (FRET) fluorescence. FRET fluorescence was measured by a newly developed portable charge-coupled device (CCD) fluorescent detector equipped with multi-wavelength light-emitting diodes (LED) illumination. An eight V-junction microchannel device for BoNTs activity assays was constructed using Laminated Object Manufacturing (LOM) technology. The six-layer device was fabricated with a Poly(methyl methacrylate (PMMA) core and five polycarbonate (PC) layers micromachined by CO2 laser. The LOC is operated by syringe and is equipped with reagents, sample wells, reaction wells, diffusion traps (to avoid cross contamination among channels) and waste reservoirs. The system was detected LcA at concentrations as low as 0.5 nM, which is the reported sensitivity of the SNAP-25 in vitro cleavage assay. Combined with our CCD detector, the simple point of care system enables the detection of BoNTs activity and may be useful for the performance of other complex medical assays without a laboratory. This approach may realize the potential to enhance the quality of health care delivery for underserved populations.

Linden flower (Tilia spp.) as potential vehicle of Clostridium botulinum spores in the transmission of infant botulism

Infant botulism is an intestinal toxemia caused principally by Clostridium botulinum. Since the infection occurs in the intestinal tract, numerous food products have been investigated for the presence of C. botulinum and its neurotoxins. In many countries, people use linden flower (Tilia spp) tea as a household remedy and give it to infants as a sedative. Therefore, to help provide a clear picture of this disease transmission, we investigated the presence of botulinum spores in linden flowers. In this study, we analyzed 100 samples of unwrapped linden flowers and 100 samples of linden flowers in tea bags to determine the prevalence and spore-load of C. botulinum. Results were analyzed by the Fisher test. We detected a prevalence of 3% of botulinum spores in the unwrapped linden flowers analyzed and a spore load of 30 spores per 100 grams. None of the industrialized linden flowers analyzed were contaminated with botulinum spores. C. botulinum type A was identified in two samples and type B in one sample. Linden flowers must be considered a potential vehicle of C. botulinum, and the ingestion of linden flower tea can represent a risk factor for infant botulism.

Self-assembled peptide monolayers as a toxin sensing mechanism within arrayed microchannels

A sensor for the lethal bacterial enzyme, botulinum neurotoxin type A (BoNT/A), was developed using self-assembled monolayers (SAMs). SAMs consisting of an immobilized synthetic peptide that mimicked the toxin's in vivo SNAP-25 protein substrate were formed on Au and interfaced with arrayed microfluidic channels. Efforts to optimize SAM composition and assay conditions for greatest reaction efficiency and sensitivity are described in detail. Channel design provided facile fluid manipulation, sample incubation, analyte concentration, and fluorescence detection all within a single microfluidic channel, thus avoiding sample transfer and loss. Peptide SAMs were exposed to varying concentrations of BoNT/A or its catalytic light chain (ALC), resulting in enzymatic cleavage of the peptide substrate from the surface. Fluorescence detection was achieved down to 20 pg/mL ALC and 3 pg/mL BoNT/A in 3 h. Toxin sensing was also accomplished in vegetable soup, demonstrating practicality of the method. The modular design of this microfluidic SAM platform allows for extension to sensing other toxins that operate via enzymatic cleavage, such as the remaining BoNT serotypes B-G, anthrax, and tetanus toxin.

Aptamer-based electrochemical biosensor for Botulinum neurotoxin

We have developed an aptamer-based electrochemical sensor for detection of Botulinum neurotoxin, where steric hindrance is applied to achieve specific signal amplification via conformational change of the aptamer. The incubation time and potassium concentration of the reaction buffer were found to be key parameters affecting the sensitivity of detection of the recognition of Botulinum neurotoxin by the aptamer. Under optimized experimental conditions, a high signal-to-noise ratio was obtained within 24 h with a limit of detection (LOD) of 40 pg/ml by two standard deviation cutoffs above the noise level.

Bead-based microfluidic toxin sensor integrating evaporative signal amplification

We have devised a microfluidic platform that incorporates substrate-laden silica beads for sensing the proteolytic activity of botulinum neurotoxin type A (BoNT/A)-one of the most poisonous substances known and a significant biological threat. The sensor relies on toxin-mediated cleavage of a fluorophore-tagged peptide substrate specific for only BoNT/A. Peptide immobilized on beads is recognized and cleaved by the toxin, releasing fluorescent fragments into solution that can be concentrated at an isolated port via evaporation and detected using microscopy. Evaporative concentration in combination with a specific channel geometry provides up to a 3-fold signal amplification in 35 min, allowing for detection of low levels of fluorophore-labeled peptide-a task not easily accomplished using traditional channel designs. Our bead-based microfluidic platform can sense BoNT/A down to 10 pg of toxin per mL buffer solution in 3.5 h and can be adapted to sensing other toxins that operate via enzymatic cleavage of a known substrate.

Attomolar detection of botulinum toxin type A in complex biological matrices

BACKGROUND

A highly sensitive, rapid and cost efficient method that can detect active botulinum neurotoxin (BoNT) in complex biological samples such as foods or serum is desired in order to 1) counter the potential bioterrorist threat 2) enhance food safety 3) enable future pharmacokinetic studies in medical applications that utilize BoNTs.

METHODOLOGY/PRINCIPAL FINDINGS

Here we describe a botulinum neurotoxin serotype A assay with a large immuno-sorbent surface area (BoNT/A ALISSA) that captures a low number of toxin molecules and measures their intrinsic metalloprotease activity with a fluorogenic substrate. In direct comparison with the "gold standard" mouse bioassay, the ALISSA is four to five orders of magnitudes more sensitive and considerably faster. Our method reaches attomolar sensitivities in serum, milk, carrot juice, and in the diluent fluid used in the mouse assay. ALISSA has high specificity for the targeted type A toxin when tested against alternative proteases including other BoNT serotypes and trypsin, and it detects the holotoxin as well as the multi-protein complex form of BoNT/A. The assay was optimized for temperature, substrate concentration, size and volume proportions of the immuno-sorbent matrix, enrichment and reaction times. Finally, a kinetic model is presented that is consistent with the observed improvement in sensitivity.

CONCLUSIONS/SIGNIFICANCE

The sensitivity, specificity, speed and simplicity of the BoNT ALISSA should make this method attractive for diagnostic, biodefense and pharmacological applications.

Liposome polymerase chain reaction assay for the sub-attomolar detection of cholera toxin and botulinum neurotoxin type A

We describe an ultrasensitive immunoassay for detecting biotoxins that uses a liposome with encapsulated DNA reporters, and ganglioside receptors embedded in the bilayer, as the detection reagent. After immobilization of the target biotoxin by a capture antibody and co-binding of the detection reagent, the liposomes are ruptured to release the reporters, which are quantified by real-time polymerase chain reaction. The new assays for cholera and botulinum toxins are several orders of magnitude more sensitive than current detection methods. A single 96-well microtiter plate can analyze approximately 20 specimens, including calibration standards and controls, with all measurements conducted in triplicate. Using pre-coated and blocked microtiter plates, and pre-prepared liposome reagents, a liposome polymerase chain reaction assay can be carried out in about 6 h.

Development and comparison of two immunoassay formats for rapid detection of botulinum neurotoxin type A

We have evaluated two formats of immunoassays for the rapid detection of Clostridium botulinum neurotoxin type A (BoNT/A), in assay buffer and various matrices (human serum and nasal swabs, fresh milk, sugar, flour and talcum). The two formats, a vertical-flow strip immunochromatography (ICT) and a small disposable immunoaffinity column (IAC), were selected because they are both rapid and readily usable in the field without sophisticated equipment. We utilised the same critical reagents to develop and optimise both assays, making it possible to compare the corresponding technologies on the same toxin preparations, without interference due to the properties of the antibodies. Results were interpreted using a standard statistical test (ANOVA) and showed little difference of sensitivity between matrices. Though both assays were completed in 40 min, the sensitivity of the IAC, evaluated at 0.45 pM (5 mouse LD50 units/ml), was 40 to 80 times better than that of the ICT. Furthermore, the sensitivity of the IAC assay was improved to 0.09 pM (1 mouse LD50 unit/ml) when performed on a 5-ml volume of human serum. Thus, the IAC appears to be one of the most sensitive and rapid assays for the detection of BoNT/A reported to date and, because it is also highly transportable, it is amongst the best suited for field diagnosis of BoNT/A poisoning.

Avian eyelid assay, a new diagnostic method for detecting botulinum neurotoxin serotypes A, B and E

Based upon botulinum neurotoxins' (BoNT) mechanism of action, a novel, rapid, and sensitive avian eyelid assay was developed to detect Clostridium botulinum neurotoxin serotypes A, B and E in assay buffer and mimic samples. It showed that chick was the most optimal model of 20-selected laboratory, non-laboratory animals. The eyelid closure of chick was the indicator symptom for positive results. The detection limits achieved range from 5 to 250 mouse LD(50) for toxin types A, B, and E in a buffer system and mimic samples. No cross reactivity occurred when using staphylococcal enterotoxin B, diphtheria toxin and nerve agent sarin, but cross reactivity was obtained in more than 6h for using high dose of tetanus toxin. This cross reactivity can be differentiated by BoNT neutralization tests with a serotype-specific antiserum in parallel. The avian eyelid assay can be performed within as short a time as 0.4-6 h. We report here the development of avian eyelid assay is the second animal bioassay for the detection of toxin types A, B, and E which approaches the sensitivity of the mouse bioassay, and is simple to perform as well as rapid to yield results.

Plastic enzyme-linked immunosorbent assays (ELISA)-on-a-chip biosensor for botulinum neurotoxin A

A plastic ELISA-on-a-chip (EOC) employing the concept of cross-flow immuno-chromatographic analysis was applied to the measurement of botulinum neurotoxin A (BoNT/A) as agent for bio-terrorism. Two monoclonal antibodies specific to the heavy chain of the toxin were raised and identified to form sandwich binding complexes as the pair with the analyte. For the construction of an immuno-strip, one was utilized as the capture antibody immobilized onto nitrocellulose membrane and the other as the detection coupled to an enzyme, horseradish peroxidase. The two plates of EOC used in this study were fabricated by injection molding of polycarbonate to improve the reproducibility of manufacture and, after inclusion of the immuno-strip, bonded using a UV-sensitive adhesive. Under optimal conditions of analysis, the chip produced a color signal in proportion to the analyte dose and the signal was quantified using a detector equipped with a digital camera. From the dose-response curve, the detection limit of BoNT/A was 2.0 ng mL(-1), approximately five times more sensitive than a commercial-version detection kit employing colloidal gold tracer.

Centers for Disease Control and Prevention (CDC). Foodborne botulism from home-prepared fermented tofu--California, 2006

In December 2006, the Orange County Health Care Agency (OCHCA) and California Department of Health Services (CDHS) were notified of two potential cases of foodborne botulism in an older Asian couple. This report summarizes the subsequent investigation, which identified home-prepared fermented tofu (soybean curd) as the source. The public should be aware of the risk for botulism when preparing fermented tofu at home.

Quantitative Duplex PCR of Clostridium botulinum Types A and B Neurotoxin Genes

A duplex quantitative polymerase chain reaction (PCR) assay for Clostridium botulinum types A and B was developed. The sensitivity and specificity of the assay were verified by using 6 strains of type A, 7 strains of type B, and 14 genera of 42 non-C. botulinum types A and B strains, including C. botulinum types C, D, E, F, and G. In pure culture, the detection limit was 10(2) CFU/ mL for type A and 10(3) CFU/mL for type B. In mushroom broth, increases in the amounts of C. botulinum types A and B could be monitored separately (the quantifiable range was 10(2) to 10(6) for type A and 10(2) to 10(7) for type B) from each sample that contained a large number of background bacteria, and toxin could be detected much earlier than with mouse assay. These results suggest that duplex quantitative PCR methods are useful to detect and quantify C. botulinum types A and/ or B toxin genes.

Evaluation of lateral flow assays for the detection of botulinum neurotoxin type A and their application in laboratory diagnosis of botulism

Four lateral flow assays (LFAs) were evaluated for the detection of purified botulinum neurotoxin A, toxin complex, and unpurified culture supernatant. They included the BioThreat (Tetracore, Rockville, MD), SMART (New Horizons Diagnostics, Columbia, MD), BADD (ADVNT Biotechnologies, Phoenix, AZ), and RAMP (Response Biomedical, Burnaby, BC, Canada) assays. BioThreat and SMART did not detect the purified toxin. The best sensitivity was achieved with the RAMP test (50 ng mL(-1)). BioThreat and SMART measured as low as 10 ng mL(-1) of the toxin complex. Specificity data differed among the tests. BADD gave false-positive signals with uninoculated bacterial culture medium. BioThreat and RAMP were further evaluated with clinical sample matrices (serum, gastric, and rectum contents from pigs). Because of matrix effects and a generally low positive response, the assays are unsuitable for the direct detection of the toxin. However, the LFAs can be a helpful tool in screening bacterial cultures for toxigenic Clostridium botulinum, if further validated according to the laboratory needs.

Capillary electrophoresis laser-induced fluorescence for screening combinatorial peptide libraries in assays of botulinum neurotoxin A

Botulinum neurotoxin serotype A (BoNT/A) is a proteolytic enzyme that induces muscle paralysis. It is a cause of food poisoning, a potential bioterrorist threat and, in low doses an emerging pharmaceutical product. No effective treatment is currently available for BoNT intoxication. Previously we developed a BoNT/A light chain enzyme assay using a peptide substrate based on the SNAP-25 protein target, with HPLC separation and UV detection of assay products, and applied the method to screen combinatorial peptide libraries for inhibitory activity to BoNT/A. We now report on development of a capillary electrophoresis laser-induced fluorescence (CE-LIF) method for measuring BoNT/A activity. The enzyme assay products were labeled with CBQCA dye followed by CE separation on a bare fused silica column in a HEPES-based buffer and LIF detection. All assay products were separated in CE within 8 min compared to incomplete separation of assay products within 1h by HPLC. The labeled products showed linear dependence of intensity versus concentration, and quantitative mole-fraction assignments. We used the CE-LIF method to screen combinatorial peptide libraries for potential modulating effects on BoNT/A peptidase activity. With some of the libraries, peptides co-migrated with assay products and interfered with quantitation. In such cases, interference was reduced by substituting sodium dodecyl sulfate (SDS) for Tween-20 in the running buffer. Separation in the capillaries then occurred by micellar electrokinetic chromatography (MEKC). The CE-LIF method is quick and lends itself to high-throughput or microfluidic formats.

A cyclic peptide–polymer probe for the detection of Clostridium botulinum neurotoxin serotype A

A Botulinum neurotoxin serotype A (BoNT/A) ELISA detection system was developed based upon an 11-mer cyclic peptide, termed C11-019, that was identified through peptide phage display technology. The assay employs a sandwich format using the C11-019 cyclic peptide attached to a PEMA (poly(ethylene maleic anhydride)) matrix as the capture phase and anti-BoNT/A polyclonal antibodies as the detection phase. Results reported demonstrate that the C11-019 peptide-polymer can specifically bind to BoNT/A with no cross-reactivity to other serotypes examined in assay buffers and a variety of body fluids and foodstuffs. When a highly sensitive chemiluminescent substrate was engaged, the detection of 1 pg/mL could be readily achieved within 3h with a linear range of 0.1-1 ng/mL. These results demonstrate that an inexpensive peptide-polymer-based capture ELISA system can be used for rapid, sensitive and highly specific BoNT detection.

Rapid detection of Clostridium botulinum toxins A, B, E, and F in clinical samples, selected food matrices, and buffer using paramagnetic bead-based electrochemiluminescence detection

Sensitive and specific electrochemiluminescence (ECL) assays were used to detect Clostridium botulinum neurotoxins serotypes A, B, E, and F in undiluted human serum, undiluted human urine, assay buffer, and selected food matrices (whole milk, apple juice, ground beef, pastry, and raw eggs). These novel assays used paramagnetic bead-based electrochemiluminescent technology in which biotinylated serotype-specific antibodies were bound to streptavidin-coated paramagnetic beads. The beads acted as the solid support and captured analyte from solution. Electrochemiluminescent detection relied on the use of ruthenium chelate-labeled anti-serotype antibodies and analysis with a BioVeris M-Series M1R analyzer. The sensitivities of the assays in clinically relevant matrices were 50 pg/ml for serotypes A and E, 100 pg/ml for serotype B, and 400 pg/ml for serotype F. The detection limits in selected food matrices ranged from 50 pg/ml for serotype A to 50 to 100 pg/ml for serotypes B, E, and F. The antibodies used for capture and detection exhibited no cross-reactivity when tested with the other serotypes. When purified native toxin was compared with toxins complexed to neurotoxin-associated proteins, no significant differences in assay response were noted for serotypes A, B, and F. Interestingly, the native form of serotype E exhibited reduced signal and limit of detection compared with the complexed form of the protein. We suspect that this difference may be due to trypsin activation of this particular serotype. The assays described in this article demonstrate limits of detection similar in range to the gold standard mouse bioassay, but with greatly reduced time to data. These rapid sensitive assays may have potential use in clinical settings, research studies, and screening of food products for botulinum toxins.

Biosensor detection of botulinum toxoid A and staphylococcal enterotoxin B in food

Immunoassays were developed for the simultaneous detection of staphylococcal enterotoxin B and botulinum toxoid A in buffer, with limits of detection of 0.1 ng/ml and 20 ng/ml, respectively. The toxins were also spiked and measured in a variety of food samples, including canned tomatoes, sweet corn, green beans, mushrooms, and tuna.

Integrated bioassays in microfluidic devices: botulinum toxin assays

A microfluidic assay was developed for screening botulinum neurotoxin serotype A (BoNT-A) by using a fluorescent resonance energy transfer (FRET) assay. Molded silicone microdevices with integral valves, pumps, and reagent reservoirs were designed and fabricated. Electrical and pneumatic control hardware were constructed, and software was written to automate the assay protocol and data acquisition. Detection was accomplished by fluorescence microscopy. The system was validated with a peptide inhibitor, running 2 parallel assays, as a feasibility demonstration. The small footprint of each bioreactor cell (0.5 cm2) and scalable fluidic architecture enabled many parallel assays on a single chip. The chip is programmable to run a dilution series in each lane, generating concentration-response data for multiple inhibitors. The assay results showed good agreement with the corresponding experiments done at a macroscale level. Although the system has been developed for BoNT-A screening, a wide variety of assays can be performed on the microfluidic chip with little or no modification.

Detection of Botulinum Neurotoxin A in a Spiked Milk Sample with Subtype Identification through Toxin Proteomics

Botulinum neurotoxin (BoNT) causes the disease botulism, which can be lethal if untreated. Rapid determination of exposure to BoNT is an important public health goal. Previous work in our laboratory focused on the development of Endopep-MS, a mass spectrometry-based endopeptidase method for detecting and differentiating BoNT in buffer. This method can rapidly determine the presence of BoNT in a sample and differentiate the toxin type of BoNT present but does not yield additional information about the subtype. We now describe here the application of Endopep-MS to detect BoNT A in a spiked milk sample. This work also describes subtype identification achieved through mass spectrometric analysis of the protein toxin itself and does not require the presence of DNA from the toxin-producing bacteria. Tryptic digests of A1 and A2 subtypes of BoNT were analyzed by mass spectrometry, and peptides unique to either the A1 or A2 subtype were subjected to tandem mass spectrometry analysis to confirm their identities. Finally, subtype identification through mass spectrometric analysis was performed on BoNT A isolated from spiked milk. In its entirety, this method would allow for analysis of BoNT with toxin type identification in a few hours and subtype identification within 24 h.

Molecular Evolution of Antibody Affinity for Sensitive Detection of Botulinum Neurotoxin Type A

Botulism is caused by botulinum neurotoxin (BoNT), the most poisonous substance known. Potential use of BoNT as a biothreat agent has made development of sensitive assays for toxin detection and potent antitoxin for treatment of intoxication a high priority. To improve detection and treatment of botulism, molecular evolution and yeast display were used to increase the affinity of two neutralizing single chain Fv (scFv) antibodies binding BoNT serotype A (BoNT/A). Selection of yeast displayed scFv libraries was performed using methods to select for both increased association rate constant (k(on)) and decreased dissociation rate constants (k(off)). A single cycle of error prone mutagenesis increased the affinity of the 3D12 scFv 45-fold from a K(D) of 9.43x10(-10)M to a K(D) of 2.1x10(-11)M. Affinity of the HuC25 scFv was increased 37-fold from 8.44x10(-10)M to 2.26x10(-11)M using libraries constructed by both random and site directed mutagenesis. scFv variable region genes were used to construct IgG for use in detection assays and in vivo neutralization studies. While IgG had the same relative increases in affinity as scFv, (35-fold and 81-fold, respectively, for 3D12 and HuC25) higher solution equilibrium binding constants were observed for the IgG, with the 3D12 K(D) increasing from 6.07x10(-11)M to 1.71x10(-12)M and the HuC25 K(D) increasing from 4.51x10(-11)M to 5.54x10(-13)M. Affinity increased due to both an increase in k(on), as well as slowing of k(off). Higher affinity antibodies had increased sensitivity, allowing detection of BoNT/A at concentrations as low as 1x10(-13)M. The antibodies will also allow testing of the role of affinity in in vivo toxin neutralization and could lead to the generation of more potent antitoxin.

Role for standards in assays of botulinum toxins: international collaborative study of three preparations of botulinum type A toxin

The biological activity of therapeutic preparations of botulinum type A toxin is currently expressed in units defined on the basis of the median lethal intraperitoneal dose of that preparation in mice at 72 h, the LD50 dose. In this study we describe the comparison, by ten laboratories in five countries, of three different formulations of botulinum type A toxin using the mouse lethality test, and also using the relative activities of the preparations. The results of this study show that use of a standard preparation and expression of relative potency gives substantially greater consistency between and within laboratories than when mouse LD50 unit is used to define activity of botulinum toxin.

Comparison of the mouse bioassay and enzyme-linked immunosorbent assay procedures for the detection of type A botulinal toxin in food

Samples of chili linked to a foodborne illness outbreak of type A botulism were examined for preformed type A botulinal toxin using two enzyme-linked immunosorbent assay (ELISA) procedures and the mouse bioassay. One of the samples was positive for type A botulinal toxin and three of the samples were negative for type A, B, E, and F botulinal toxins using the three methods. The mouse bioassay indicated that type A toxin was present at the 10,000 minimal lethal dose per gram (MLD per g) of product. The ELISA tests indicated a toxicity of 7,650 MLD per g with one method and 8,350 MLD per g with the other method. The sample toxicity determined by the ELISA was estimated by comparing samples to a standard curve generated with standard type A neurotoxin in casein buffer. The ELISA methods are more rapid than the mouse bioassay, since the toxin type can be determined in 1 day. The mouse bioassay is more sensitive than the ELISA but usually requires multiple assays to obtain the toxin type and toxicity. Type A culture isolates from the sample were also verified using one ELISA method.

Generation and characterization of monoclonal antibodies against botulinum neurotoxin type A (BoNT/A)

AIM

To generate the monoclonal antibodies(mAbs) against botulinum neurotoxin type A (BoNT/A).

METHODS

BALB/c mice were intraperitoneally immunized with purified BoNT/A-Hc, and the splenocytes of immunized mice were fused with myeloma cells Sp2/0. Hybridoma cells were screened by indirect ELISA and monoclonal hybridoma cells was obtained using limited dilution.

RESULTS

Three hybridomas, named 4A8, 2F7 and 4F2, producing the mAbs against BoNT/A, were successfully established, and the titer of ascitic mAbs ranged from 1x10(-4) to 1x10(-6). Identification of subclass showed that all the produced mAbs belonged to IgG1. 4A8 and 4F2 were stable in secreting anti-BoNT/A mAbs through three-month continuous culture and showed high specificity to recombinant BoNT/A-Hc and native BoNT/A.

CONCLUSION

Anti-BoNT/A mAbs we generated have high specificity, which laid the foundation for the immunological detection of BoNT/A and clinical treatment of botulism in the future.

A highly sensitive immuno-polymerase chain reaction assay for Clostridium botulinum neurotoxin type A

Our goal was to develop a sensitive method for detecting Clostridium botulinum neurotoxin type A (BoNT/A). We were able to detect BoNT/A in the femtogram (10(-15)g) range using an indirect immuno-polymerase chain reaction (immuno-PCR) assay and an indirect sandwich immuno-PCR assay. For the indirect immuno-PCR assay, enzyme-linked immunosorbent assay (ELISA) plates were coated with BoNT/A that was recognized by anti-BoNT/A monoclonal antibody. For the indirect sandwich immuno-PCR assay, the monoclonal antibody was immobilized on ELISA plates for detecting BoNT/A that was recognized by its polyclonal antibodies. Reporter DNA was prepared by PCR amplification using biotinylated 5'-primers, and it was coupled with biotinylated antibodies through streptavidin. In order to increase sensitivity and reduce background noise, the amounts of reporter DNA (ranging from 50 fg to 50 ng) and streptavidin (ranging from 0.125 ng to 8 ng) were optimized. Using the optimized concentration of reporter DNA and streptavidin, both indirect and indirect sandwich immuno-PCR assays detected BoNT/A as low as 50 fg. These results are a 10(5)-fold improvement over conventional indirect ELISA and indirect sandwich ELISA methods. The assays we developed are currently the most sensitive methods for detecting BoNT/A.

Detection of botulinal neurotoxins A, B, E, and F by amplified enzyme-linked immunosorbent assay: collaborative study

An amplified enzyme-linked immunosorbent assay (amp-ELISA) was compared with the AOAC Official Method 977.26 for detection of Clostridium botulinum and its toxins in foods. Eleven laboratories participated and the results of 10 laboratories were used in the study. Two anaerobic culture media, tryptone peptone glucose yeast extract (TPGY) and cooked meat medium (CMM) were used to generate toxic samples with types A, B, E, and F botulinal strains. Nonbotulinal clostridia were also tested. The toxicity of each botulinal culture was determined by the AOAC method, and the cultures were then diluted, if necessary, to high (about 10,000 minimal lethal dose [MLD]/mL) and low (about 100 MLD/mL) test samples. The overall sensitivity of detection in TPGY and CMM cultures with the amp-ELISA was 94.7% at about 100 MLD/mL and 99.6% for samples with > or = 10,000 MLD/mL toxicity. The amp-ELISA detection sensitivity for low toxin samples was 92.3% in TPGY and 99.4% in CMM. The false-positive rate ranged from 1.5% for type A to 28.6% for type F in TPGY, and from 2.4% for type A to 11.4% for type F in CMM. Most of the cross-reactivity was due to detection of other botulinal types, especially in high toxin samples. The amp-ELISA could be used to screen suspect cultures for botulinal toxins. Positive amp-ELISA samples would be confirmed by the AOAC reference method.

Rapid and sensitive detection of biological warfare agents using time-resolved fluorescence assays

We have achieved sensitive, rapid and reproducible detection of three biological threat agents in a variety of biological and environmental matrices using the DELFIA time-resolved fluorometry (TRF) assay system (Perkin-Elmer Life Sciences, Akron, OH). Existing ELISA assays for the detection of Francisella tularensis, Clostridium botulinum A/B neurotoxin (BotNT A/B), and Staphylococcus aureus enterotoxin B (SEB) were converted to TRF assays. They use 100 microl of positive control or unknown per test well and require just over 2 h to run. Fluorescent signal read time is a fraction of a second per well. The assay format consists of a capture ELISA utilizing a biotinylated capture antibody, prebound to a streptavidin-coated 96-well plate and a lanthanide (Europium, Eu3+)-labeled detector antibody. The bound Eu-labeled detector antibody produces a fluorescent signal upon the addition of an enhancement solution. The signal results from the dissociation of the Europium from the antibody, creating a micelle, thus amplifying the signal nearly one million-fold. Sensitivities achieved by these assays were between 4 and 20 pg/ml in buffer. Additionally, we have tested this system in different matrices such as serum, urine, dirt, and sewage. Concentration curves generated from standard solutions produced a wide linear range making serial dilutions of unknown samples unnecessary. DELFIA TRF assays are significantly better in terms of sensitivity, linear range, and run time than standard capture ELISAs and should facilitate early detection of potential biological warfare agents in clinical and environmental samples.

Detection of preformed type A botulinal toxin in hash brown potatoes by using the mouse bioasssay and a modified ELISA test

A foodborne illness caused by type A toxin-producing Clostridium botulinum was investigated by using the standard mouse bioassay and a rapid invitro test for toxin detection. The patient, who consumed improperly stored hash brown potatoes that contained the preformed toxin, was diagnosed with type A botulism. C. botulinum type A toxin was detected in the hash brown potatoes as well as in the tryptone-peptone-glucose-yeast extract (TPGY) medium subcultures of this food using the mouse bioassay and an amplified ELISA technique. The mouse bioassay revealed preformed toxin at 10,000 minimum lethal dose (MLD)/g uncooked product and the amplified ELISA an equivalent 50,000 MLD/g. The cultural toxin from the uncooked product killed mice at the 10(6) dilution and a modification of the ELISA procedure was positive at the 10(3) dilution. Cooked food obtained from the consumer's waste can contained 100 MLD/g and the ELISA was also positive at the same dilution of the product. The culture of the cooked product obtained from the waste can was lethal for mice at the 10(7) dilution and positive using the modified ELISA at the 10(4) dilution. The unmodified amplified ELISA method indicated a toxin level of approximately 1 ng/mL (equivalent to 5 x 10(5) MLD/mL) in diluted culture fluid from the uncooked food and the culture of cooked food obtained from the waste can. The hash brown potatoes were negative for types B, E, and F preformed and cultural botulinal toxins using both assays.

Prevalence of Clostridium difficile-associated diarrhoea among hospitalized Jordanian patients

We investigated stool specimens of 400 patients at Jordan University Hospital (300 patients with clinical diarrhoea and 100 controls without diarrhoea) for the presence of Clostridium difficile or its toxin. We found a 9.7% prevalence rate of C. difficile or its toxin in stools of patients with diarrhoea. The prevalence of other potential enteric pathogens, such as Salmonella spp. (2.3%), Shigella spp. (1.0%) and Entamoeba histolytica (2.7%), was significantly less. Prevalence of C. difficile or its toxin in controls was 3.0%. Toxin A was detected in 93.1% of C. difficile-associated diarrhoea cases using an enzyme immunoassay. Our study indicates that C. difficile-associated diarrhoea is mostly observed among hospitalized patients aged > or = 50 years, in association with antimicrobial treatment.

Comparison of amplified ELISA and mouse bioassay procedures for determination of botulinal toxins A, B, E, and F

The amplified enzyme-linked immunosorbent assay (amp-ELISA) was compared to the mouse bioassay for determination of botulinal neurotoxin types A, B, E, and F. Twelve different toxin-producing type A, 13 proteolytic type B, 9 nonproteolytic type B, 16 type E, 8 proteolytic type F, 5 nonproteolytic type F, and 6 nontoxigenic clostridial strains were tested. The cultures were inoculated into cooked meat medium (CMM) and tryptone-peptone-glucose-yeast extract (TPGY) medium, incubated for 5 days, and then examined for biological toxicity in mice and amp-ELISA endpoints. The amp-ELISA was less sensitive in detecting toxins produced by nonproteolytic than proteolytic strains of type B and F organisms. All of the toxin-producing strains tested were positive by the AOAC method and the amp-ELISA in either undiluted TPGY or CMM culture fluids regardless of mouse toxicity level, source, or strain. Cross-reactivity was observed between some but not all of the botulinal strains tested. None of the nontoxigenic strains were positive by the amp-ELISA. Purified botulinal toxins were also assayed using these 2 methods. The sensitivity of the amp-ELISA using purified neurotoxins was about 0.1 ng/mL for types A, B, and E and about 1.0 ng/mL for type F.

Development of sensitive colorimetric capture elisas for Clostridium botulinum neurotoxin serotypes A and B

Sensitive and specific enzyme-linked immunosorbent assays were developed to detect Clostridium botulinum neurotoxin serotypes A (BoNT A) and B (BoNT B) in assay buffer and human serum. The assay is based upon affinity-purified horse polyclonal antibodies directed against the approximately 50 kDa C-fragments of each toxin. Standard curves were linear over the range of 0.1-10 ng mL. Detection was possible at 0.2 ng mL (20 pg/well) and accurate quantitation at 0.5 ng/mL (50 pg well) in assay buffer and 10% human serum. Variations between triplicates was typically 5-10%. Less than 1% cross reactivity occurred between other serotypes when each assay was performed against serotypes A, B and E. When tested against toxins complexed to their associated nontoxic proteins, interference was absent (BoNT B) or < 25% (BoNT A). These assays demonstrate sensitivity close to that of the mouse bioassay without the use of animals and in a much simpler format than other reported assays of similar sensitivity.

Validation of in vitro assays for botulinum toxin: a case study

Ensuring the reliability and precision of assay results requires careful attention to assay design. In this case study we describe validation studies of an in vitro assay for botulinum neurotoxin type A based on its endopeptidase activity towards immobilised synthetic substrate. This assay, in common with many in vitro assays, is sensitive to changes in reagents and assay conditions and is time dependent. In addition, the toxin is not stable in solution. Differences in estimates of potency, resulting from positional factors, which are not significant in individual assays, are shown to be consistent and statistically significant over a longer series of assays. This study emphasizes that assay validation should not be viewed as a single step in assay development but must be considered as a continuing process if assay results are to be reliable and reproducible.

Clostridium botulinum spores and toxin in mascarpone cheese and other milk products

A total of 1,017 mascarpone cheese samples, collected at retail, were analyzed for Clostridium botulinum spores and toxin, aerobic mesophilic spore counts, as well as pH, a(w) (water activity), and Eh (oxidation-reduction potential). In addition 260 samples from other dairy products were also analyzed for spores and botulinum toxin. Experiments were carried out on naturally and artificially contaminated mascarpone to investigate the influence of different temperature conditions on toxin production by C. botulinum. Three hundred and thirty-one samples (32.5%) of mascarpone were positive for botulinal spores, and 7 (0.8%) of the 878 samples produced at the plant involved in an outbreak of foodborne botulism also contained toxin type A. The chemical-physical parameters (pH, a(w), Eh) of all samples were compatible with C. botulinum growth and toxinogenesis. Of the other milk products, 2.7% were positive for C. botulinum spores. Growth and toxin formation occurred in naturally and experimentally contaminated mascarpone samples after 3 and 4 days of incubation at 28 degrees C, respectively.

A large outbreak of botulism: the hazardous baked potato

In April 1994, the largest outbreak of botulism in the United States since 1978 occurred in El Paso, Texas. Thirty persons were affected; 4 required mechanical ventilation. All ate food from a Greek restaurant. The attack rate among persons who ate a potato-based dip was 86% (19/22) compared with 6% (11/176) among persons who did not eat the dip (relative risk [RR] = 13.8; 95% confidence interval [CI], 7.6-25.1). The attack rate among persons who ate an eggplant-based dip was 67% (6/9) compared with 13% (241189) among persons who did not (RR = 5.2; 95% CI, 2.9-9.5). Botulism toxin type A was detected from patients and in both dips. Toxin formation resulted from holding aluminum foil-wrapped baked potatoes at room temperature, apparently for several days, before they were used in the dips. Consumers should be informed of the potential hazards caused by holding foil-wrapped potatoes at ambient temperatures after cooking.