Methods for detection of Clostridium botulinum toxin in foods

Facile detection of botulinum neurotoxin using LSPR nanosensor based on Langmuir-Blodgett films of gold nanoparticles

In this exploratory study, Langmuir-Blodgett (LB) films of gold nanoparticles (Au NPs) were utilized for the first time to detect botulinum neurotoxin (BoNT) based on localized surface plasmon resonance (LSPR), acting as biosensors. Monolayers of Au NPs were initially transferred onto a transparent polymer substrate using the LB technique. This substrate was then used as the base material for subsequent depositions of capping ligands, and eventually, the BoNT at different concentrations. Upon each deposition, LSPR signals were recorded employing UV-Vis spectroscopy. As a result, it was demonstrated that the LB films transferred at a surface pressure of 35 mN m-1 were the optimal choice, capable of detecting BoNT at a concentration as low as 1 pg ml-1. Furthermore, it was discovered that the formation of Au NP clusters reduced the sensing capacity of the LB films. This sensor offers advantages such as easy fabrication and a quick detection process that utilizes visible light.

Simultaneous determination of BoNT/A and /E using an electrochemical sandwich immunoassay based on the nanomagnetic immunosensing platform

Developing new ultrasensitive assays for the detection of the presence, and determination of the serotype of the most poisonous material known i.e. botulinum neurotoxin (BoNT) is vital to human health and the wellbeing of the surrounding environment. Here, an electrochemical sandwich immunoassay with high sensitivity is adopted to achieve simultaneous determination of BoNT serotypes A and E based on polystyrene@polydopamine/Cd²⁺ and Ag nanoparticles acting as monoclonal antibody labels. Two well-separated peaks with strong electrochemical signals are generated by the labels, allowing for the simultaneous detection of two analytes existing on the electrode. To obtain well-oriented polyclonal antibodies immobilization, boronic acid is directly attached to the magnetic core/metal-organic framework (MOF) shell nanoagent surfaces without the requirement of a long and flexible spacer. Accordingly, it is possible to directly detect the metal ion labels through square wave voltammetry without the metal pre-concentration step. This results in distinct and well-defined voltammetric peaks, pertaining to each sandwich-type immunocomplexes. The limits of detection of BoNT/A and BoNT/E analyses were found to be 0.04 and 0.16 pg mL^-1 with the linear dynamic ranges of 0.1-1000 and 0.5-1000 pg mL^-1, respectively. Based on the obtained results, this immunosensor has the wide linear ranges, while also exhibiting low limits of detection along with good stability and reproducibility.

Use of Crystallography and Molecular Modeling for the Inhibition of the Botulinum Neurotoxin A Protease

Botulinum neurotoxins (BoNTs) are extremely toxic and have been deemed a Tier 1 potential bioterrorism agent. The most potent and persistent of the BoNTs is the "A" serotype, with strategies to counter its etiology focused on designing small-molecule inhibitors of its light chain (LC), a zinc-dependent metalloprotease. The successful structure-based drug design of inhibitors has been confounded as the LC is highly flexible with significant morphological changes occurring upon inhibitor binding. To achieve greater success, previous and new cocrystal structures were evaluated from the standpoint of inhibitor enantioselectivity and their effect on active-site morphology. Based upon these structural insights, we designed inhibitors that were predicted to take advantage of π-π stacking interactions present in a cryptic hydrophobic subpocket. Structure-activity relationships were defined, and X-ray crystal structures and docking models were examined to rationalize the observed potency differences between inhibitors.

Protein biomarker elucidation for the verification of biological agents in the taxonomic group of Gammaproteobacteria using tandem mass spectrometry

Some pathogenic microbes can be used for nefarious applications and instigate population-based fear. In a bio-threat scenario, rapid and accurate methods to detect biological agents in a wide range of complex environmental and clinical matrices, is of paramount importance for the implementation of mitigation protocols and medical countermeasures. This study describes targeted and shot-gun tandem MS based approaches for the verification of biological agents from the environmental samples. The marker proteins and peptides were elucidated by an exhaustive literature mining, in silico analysis of prioritized proteins, and MS/MS analysis of abundant proteins from selected bacterial species. For the shot-gun methodology, tandem MS analysis of abundant peptides was carried from spiked samples. The validation experiments employing a combination of shot-gun tandem MS analysis and a targeted search reported here is a proof of concept to show the applicability of the methodology for the unambiguous verification of biological agents at sub-species level, even with limited fractionation of crude protein extracts from environmental samples.

Effects of Citrus sinensis Essential Oil and Intrinsic and Extrinsic Factors on the Growth and ToxinProducing Ability of Clostridium botulinum Type A

Background: Considering the high fatality of botulism, the control of Clostridium botulinum and its neurotoxins has clinical importance. In this regard, using chemical preservatives, natural essential oils (Eos), and changes in the growth predisposing factors of bacteria are suitable methods to control the growth and toxin producing of C. botulinum in foods. Objective: The current survey was done to assess the effects of Citrus sinensis EO and intrinsic and extrinsic factors on the growth and toxin producing of C. botulinum type A. Materials and Methods: In this experiment with a factorial design, C. sinensis EO (0.0%, 0.015%, 0.03%, and 0.045%), nisin (0, 500, and 1500 IU/mL), nitrite (0, 20, and 60 ppm), pH (5.5 and 6.5), storage temperature (25 and 35° C), and sodium chloride (NaCl, 0.5% and 3%) were used to assess bacterial growth in the brain heart infusion medium. Finally, the mouse bioassay method was also used to assess toxicity. Results: Clostridium sinensis EO with a concentration of 0.045%, as well as the reduction of pH and temperature could significantly delay the growth of bacteria (P≤0.05) in contrast to the use of NaCl and nisin alone. However, all concentrations of sodium chloride (NaCl), nisin, and C. sinensis EO (< 0.045%) in interaction with each other, especially in combination with nitrite, showed good synergistic effects. Conclusion: These results suggested that using certain concentrations of C. sinensis EO and nisin, along with other suboptimal factors caused a significant decrease in the nitrite contents of foods with a significant reduction in the growth and toxin-producing ability of C. botulinum.

Elucidation of protein biomarkers for verification of selected biological warfare agents using tandem mass spectrometry

Some pathogens and toxins have the potential to be used as weapons of mass destruction and instigate population-based fear. Efforts to mitigate biothreat require development of efficient countermeasures which in turn relies on fast and accurate methods to detect the biological agents in a range of complex matrices including environmental and clinical samples. We report here an mass spectrometry (MS) based methodology, employing both targeted and shot-gun approaches for the verification of biological agents from the environmental samples. Our shot-gun methodology relied on tandem MS analysis of abundant peptides from the spiked samples, whereas, the targeted method was based on an extensive elucidation of marker proteins and unique peptides resulting in the generation of an inclusion list of masses reflecting relevant peptides for the unambiguous identification of nine bacterial species [listed as priority agents of bioterrorism by Centre for Disease Control and Prevention (CDC)] belonging to phylogenetically diverse genera. The marker peptides were elucidated by extensive literature mining, in silico analysis, and tandem MS (MS/MS) analysis of abundant proteins of the cultivated bacterial species in our laboratory. A combination of shot-gun MS/MS analysis and the targeted search using a panel of unique peptides is likely to provide unambiguous verification of biological agents at sub-species level, even with limited fractionation of crude protein extracts from environmental samples. The comprehensive list of peptides reflected in the inclusion list, makes a valuable resource for the multiplex analysis of select biothreat agents and further development of targeted MS/MS assays.

A simple and fast protocol for the synthesis of 2-amino-4-(4-formylphenyl)-4H-chromene-3-carbonitrile to develop an optical immunoassay for the quantification of botulinum neurotoxin type F

In this study, a novel optical immunoassay platform using (S)-2-amino-4-(4-formylphenyl)-4H-chromene-3-carbonitrile, which was synthesized by an ultra-sonication method, as an optical probe.

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.

Prevalence of C. Botulinum and C. Perfringens Spores in Food Products Available on Polish Market

Introduction

The aim of this study was to evaluate the prevalence of Clostridium botulinum and Clostridium perfringens in food samples purchased from Polish producers.

Material and Methods

The analyses were performed on 260 food samples collected in Lublin and Subcarpathian regions: 56 of smoked meat, 21 of pork meat, 20 of dairy products, 26 of vegetable and fruit preserves, 40 of ready-to-eat meals, 27 of fish preserves, and 70 of honey collected directly from apiaries.

Results

C. botulinum strains were isolated from 2.3% (6/260) of samples and the isolates were classified as toxin types A (4/260) and B (2/260). C. perfringens strains were isolated from 14% (37/260) of samples. All the isolates were classified as toxin type A, 28 of them were able also to produce α toxin and 9 – β2 toxin.

Conclusion

On the basis of the obtained results it could be suggested that risk assessment, especially regarding the entire honey harvesting process, should be provided in order to ensure the microbiological safety of the products to be consumed by infants and people with a weakened immune system.

Mass spectrometry for the detection of bioterrorism agents: from environmental to clinical applications

In the current context of international conflicts and localized terrorist actions, there is unfortunately a permanent threat of attacks with unconventional warfare agents. Among these, biological agents such as toxins, microorganisms, and viruses deserve particular attention owing to their ease of production and dissemination. Mass spectrometry (MS)-based techniques for the detection and quantification of biological agents have a decisive role to play for countermeasures in a scenario of biological attacks. The application of MS to every field of both organic and macromolecular species has in recent years been revolutionized by the development of soft ionization techniques (MALDI and ESI), and by the continuous development of MS technologies (high resolution, accurate mass HR/AM instruments, novel analyzers, hybrid configurations). New possibilities have emerged for exquisite specific and sensitive detection of biological warfare agents. MS-based strategies for clinical application can now address a wide range of analytical questions mainly including issues related to the complexity of biological samples and their available volume. Multiplexed toxin detection, discovery of new markers through omics approaches, and identification of untargeted microbiological or of novel molecular targets are examples of applications. In this paper, we will present these technological advances along with the novel perspectives offered by omics approaches to clinical detection and follow-up.

Centrifugal microfluidic platform for ultrasensitive detection of botulinum toxin

We present an innovative centrifugal microfluidic immunoassay platform (SpinDx) to address the urgent biodefense and public health need for ultrasensitive point-of-care/incident detection of botulinum toxin. The simple, sample-to-answer centrifugal microfluidic immunoassay approach is based on binding of toxins to antibody-laden capture particles followed by sedimentation of the particles through a density-media in a microfluidic disk and quantification by laser-induced fluorescence. A blind, head-to-head comparison study of SpinDx versus the gold-standard mouse bioassay demonstrates 100-fold improvement in sensitivity (limit of detection = 0.09 pg/mL), while achieving total sample-to-answer time of <30 min with 2-μL required volume of the unprocessed sample. We further demonstrate quantification of botulinum toxin in both exogeneous (human blood and serum spiked with toxins) and endogeneous (serum from mice intoxicated via oral, intranasal, and intravenous routes) samples. SpinDx can analyze, without any sample preparation, multiple sample types including whole blood, serum, and food. It is readily expandable to additional analytes as the assay reagents (i.e., the capture beads and detection antibodies) are disconnected from the disk architecture and the reader, facilitating rapid development of new assays. SpinDx can also serve as a general-purpose immunoassay platform applicable to diagnosis of other conditions and diseases.

Nanopore sensing of botulinum toxin type B by discriminating an enzymatically cleaved Peptide from a synaptic protein synaptobrevin 2 derivative

Botulinum neurotoxins (BoNTs) are the most lethal toxin known to human. Biodefense requires early and rapid detection of BoNTs. Traditionally, BoNTs can be detected by looking for signs of botulism in mice that receive an injection of human material, serum or stool. While the living animal assay remains the most sensitive approach, it is costly, slow and associated with legal and ethical constrains. Various biochemical, optical and mechanical methods have been developed for BoNTs detection with improved speed, but with lesser sensitivity. Here, we report a novel nanopore-based BoNT type B (BoNT-B) sensor that monitors the toxin's enzymatic activity on its substrate, a recombinant synaptic protein synaptobrevin 2 derivative. By analyzing the modulation of the pore current caused by the specific BoNT-B-digested peptide as a marker, the presence of BoNT-B at a subnanomolar concentration was identified within minutes. The nanopore detector would fill the niche for a much needed rapid and highly sensitive detection of neurotoxins, and provide an excellent system to explore biophysical mechanisms for biopolymer transportation.

Isolation and quantification of botulinum neurotoxin from complex matrices using the BoTest matrix assays

Accurate detection and quantification of botulinum neurotoxin (BoNT) in complex matrices is required for pharmaceutical, environmental, and food sample testing. Rapid BoNT testing of foodstuffs is needed during outbreak forensics, patient diagnosis, and food safety testing while accurate potency testing is required for BoNT-based drug product manufacturing and patient safety. The widely used mouse bioassay for BoNT testing is highly sensitive but lacks the precision and throughput needed for rapid and routine BoNT testing. Furthermore, the bioassay's use of animals has resulted in calls by drug product regulatory authorities and animal-rights proponents in the US and abroad to replace the mouse bioassay for BoNT testing. Several in vitro replacement assays have been developed that work well with purified BoNT in simple buffers, but most have not been shown to be applicable to testing in highly complex matrices. Here, a protocol for the detection of BoNT in complex matrices using the BoTest Matrix assays is presented. The assay consists of three parts: The first part involves preparation of the samples for testing, the second part is an immunoprecipitation step using anti-BoNT antibody-coated paramagnetic beads to purify BoNT from the matrix, and the third part quantifies the isolated BoNT's proteolytic activity using a fluorogenic reporter. The protocol is written for high throughput testing in 96-well plates using both liquid and solid matrices and requires about 2 hr of manual preparation with total assay times of 4-26 hr depending on the sample type, toxin load, and desired sensitivity. Data are presented for BoNT/A testing with phosphate-buffered saline, a drug product, culture supernatant, 2% milk, and fresh tomatoes and includes discussion of critical parameters for assay success.

Time-resolved botulinum neurotoxin A activity monitored using peptide-functionalized Au nanoparticle energy transfer sensors

A peptide mimicking SNAP-25 was immobilized on Au nanoparticles for the monitoring of botulinum neurotoxin light chain A activity.

Detection of botulinum neurotoxin serotypes A and B using a chemiluminescent versus electrochemiluminescent immunoassay in food and serum

Botulinum neurotoxins (BoNTs) are some of the most potent biological toxins. High-affinity monoclonal antibodies (mAbs) have been developed for the detection of BoNT serotypes A and B using a chemiluminescent capture enzyme-linked immunosorbent assay (ELISA). In an effort to improve toxin detection levels in complex matrices such as food and sera, we evaluated the performance of existing antitoxin mAbs using a new electrochemiluminescence (ECL) immunoassay platform developed by Meso Scale Discovery. In side-by-side comparisons, the limits of detection (LODs) observed for ELISA and the ECL immunoassay for BoNT/A were 12 and 3 pg/mL, and for BoNT/B, they were 17 and 13 pg/mL, respectively. Both the ELISA and the ECL method were more sensitive than the "gold standard" mouse bioassay. The ECL assay outperformed ELISA in detection sensitivity in most of the food matrices fortified with BoNT/A and in some foods spiked with BoNT/B. Both the ELISA and the ECL immunoassay platforms are fast, simple alternatives for use in the routine detection of BoNTs in food and animal sera.

Emerging opportunities for serotypes of botulinum neurotoxins

Background: Two decades ago, botulinum neurotoxin (BoNT) type A was introduced to the commercial market. Subsequently, the toxin was approved by the FDA to address several neurological syndromes, involving muscle, nerve, and gland hyperactivity. These syndromes have typically been associated with abnormalities in cholinergic transmission. Despite the multiplicity of botulinal serotypes (designated as types A through G), therapeutic preparations are currently only available for BoNT types A and B. However, other BoNT serotypes are under study for possible clinical use and new clinical indications; Objective: To review the current research on botulinum neurotoxin serotypes A-G, and to analyze potential applications within basic science and clinical settings; Conclusions: The increasing understanding of botulinal neurotoxin pathophysiology, including the neurotoxin’s effects on specific neuronal populations, will help us in tailoring treatments for specific diagnoses, symptoms and patients. Scientists and clinicians should be aware of the full range of available data involving neurotoxin subtypes A-G.

Ultrafiltration improves ELISA and Endopep MS analysis of botulinum neurotoxin type A in drinking water

The objective of this study was to adapt and evaluate two in vitro botulinum neurotoxin (BoNT) detection methods, including the Botulinum Toxin ELISA and the Endopep MS (a mass spectrometric-based endopeptidase method), for use with drinking water samples. The method detection limits (MDL) of the ELISA and Endopep MS were 260 pg/mL and 21 pg/mL of BoNT/A complex toxin, respectively. Since toxin could be present in water samples at highly dilute concentrations, large volume (100-L) samples of municipal tap water from five US municipalities having distinct water compositions were dechlorinated, spiked with 5 μg BoNT/A, and subjected to tangential-flow ultrafiltration (UF) using hollow fiber dialyzers. The recovery efficiency of BoNT/A using UF and quantified by ELISA ranged from 11% to 36% while efficiencies quantified by MS ranged from 26% to 55%. BoNT/A was shown to be stable in dechlorinated municipal tap water stored at 4°C for up to four weeks. In addition, toxin present in UF-concentrated water samples was also shown to be stable at 4°C for up to four weeks, allowing holding of samples prior to analysis. Finally, UF was used to concentrate a level of toxin (7 pg/mL) which is below the MDL for direct analysis by both ELISA and Endopep MS. Following UF, toxin was detectable in these samples using both in vitro analysis methods. These data demonstrate that UF-concentration of toxin from large volume water samples followed by use of existing analytical methods for detection of BoNT/A can be used in support of a monitoring program for contaminants in drinking water.

Detection of botulinum neurotoxin serotype A, B, and F proteolytic activity in complex matrices with picomolar to femtomolar sensitivity

Rapid, high-throughput assays that detect and quantify botulinum neurotoxin (BoNT) activity in diverse matrices are required for environmental, clinical, pharmaceutical, and food testing. The current standard, the mouse bioassay, is sensitive but is low in throughput and precision. In this study, we present three biochemical assays for the detection and quantification of BoNT serotype A, B, and F proteolytic activities in complex matrices that offer picomolar to femtomolar sensitivity with small assay volumes and total assay times of less than 24 h. These assays consist of magnetic beads conjugated with BoNT serotype-specific antibodies that are used to purify BoNT from complex matrices before the quantification of bound BoNT proteolytic activity using the previously described BoTest reporter substrates. The matrices tested include human serum, whole milk, carrot juice, and baby food, as well as buffers containing common pharmaceutical excipients. The limits of detection were below 1 pM for BoNT/A and BoNT/F and below 10 pM for BoNT/B in most tested matrices using 200-μl samples and as low as 10 fM for BoNT/A with an increased sample volume. Together, these data describe rapid, robust, and high-throughput assays for BoNT detection that are compatible with a wide range of matrices.

Botulinum neurotoxin: where are we with detection technologies?

Because of its high toxicity, botulinum neurotoxin (BoNT) poses a significant risk to humans and it represents a possible biological warfare agent. Nevertheless, BoNT serotypes A and B are considered an effective treatment for a variety of neurological disorders. The growing applicability of BoNT as a drug, and its potential use as a biological threat agent, highlight the urgent need to develop sensitive detection assays and therapeutic counter measures. In the last decade, significant progress has been made in BoNT detection technologies but none have fully replaced the mouse lethality assay, the current "gold standard". Recently, new advances in robotics and the availability of new reagents have allowed development of methods for rapid toxin analysis. These technologies while promising need further refinement.

Llama-derived single-domain antibodies for the detection of botulinum A neurotoxin

Single-domain antibodies (sdAb) specific for botulinum neurotoxin serotype A (BoNT A) were selected from an immune llama phage display library derived from a llama that was immunized with BoNT A toxoid. The constructed phage library was panned using two methods: panning on plates coated with BoNT A toxoid (BoNT A Td) and BoNT A complex toxoid (BoNT Ac Td) and panning on microspheres coupled to BoNT A Td and BoNT A toxin (BoNT A Tx). Both panning methods selected for binders that had identical sequences, suggesting that panning on toxoided material may be as effective as panning on bead-immobilized toxin for isolating specific binders. All of the isolated binders tested were observed to recognize bead-immobilized BoNT A Tx in direct binding assays, and showed very little cross-reactivity towards other BoNT serotypes and unrelated protein. Sandwich assays that incorporated selected sdAb as capture and tracer elements demonstrated that all of the sdAb were able to recognize soluble ("live") BoNT A Tx and BoNT Ac Tx with virtually no cross-reactivity with other BoNT serotypes. The isolated sdAb did not exhibit the high degree of thermal stability often associated with these reagents; after the first heating cycle most of the binding activity was lost, but the portion of the protein that did refold and recover antigen-binding activity showed only minimal loss on subsequent heating and cooling cycles. The binding kinetics of selected binders, assessed by both an equilibrium fluid array assay as well as surface plasmon resonance (SPR) using toxoided material, gave dissociation constants (K(D)) in the range 2.2 x 10(-11) to 1.6 x 10(-10) M. These high-affinity binders may prove beneficial to the development of recombinant reagents for the rapid detection of BoNT A, particularly in field screening and monitoring applications.

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.

Construction of a nontoxigenic Clostridium botulinum strain for food challenge studies

Clostridium botulinum produces the most poisonous natural toxin known and is a perennial concern to the food industry and to regulatory agencies due to the potential threat of food-borne botulism. To ensure the botulinal safety of foods, rigorous food challenge testing to validate food-processing conditions and food formulations has been routinely performed. Detection of the botulinum neurotoxin is performed by using a mouse bioassay and/or in vitro assays. There has been considerable interest by the food industry and regulatory agencies in minimizing or even replacing the use of animals in these challenge studies. In addition, due to stringent select-agent regulations, the testing of various foods using toxigenic C. botulinum strains requires facilities and personnel that are certified for work with this organism. For this purpose we propose to generate sets of nontoxigenic C. botulinum strains from proteolytic and nonproteolytic groups that differ from the wild-type strains only by their inability to produce botulinum neurotoxin. In this initial study we describe the generation of a nontoxigenic mutant of C. botulinum strain 62A using the ClosTron mutagenesis system by inserting a group II intron into the botulinum neurotoxin type A gene (bont/A). The mutant clones were nontoxigenic as determined by Western blots and mouse bioassays but showed physiological characteristics, including growth properties and sporulation, that were similar to those of the parent strain in laboratory media. Additional studies will be required to evaluate comparable characteristics in various food matrices. The availability of suitable nontoxigenic C. botulinum strains for food challenge studies will be beneficial for enhancing the botulinal safety of foods as well as increasing the biosafety of workers and may eliminate the use of laboratory animals.

Rapid multiplexed flow cytometric assay for botulinum neurotoxin detection using an automated fluidic microbead-trapping flow cell for enhanced sensitivity

A bead-based sandwich immunoassay for botulinum neurotoxin serotype A (BoNT/A) has been developed and demonstrated using a recombinant 50 kDa fragment (BoNT/A-HC-fragment) of the BoNT/A heavy chain (BoNT/A-HC) as a structurally valid simulant. Three different anti-BoNT/A antibodies were attached to three different fluorescent dye encoded flow cytometry beads for multiplexing. The assay was conducted in two formats: a manual microcentrifuge tube format and an automated fluidic system format. Flow cytometry detection was used for both formats. The fluidic system used a novel microbead-trapping flow cell to capture antibody-coupled beads with subsequent sequential perfusion of sample, wash, dye-labeled reporter antibody, and final wash solutions. After the reaction period, the beads were collected for analysis by flow cytometry. Sandwich assays performed on the fluidic system gave median fluorescence intensity signals on the flow cytometer that were 2-4 times higher than assays performed manually in the same amount of time. Limits of detection were estimated at 1 pM (approximately 50 pg/mL for BoNT/A-HC-fragment) for the 15 min fluidic assay in buffer.

Quantum dot immunoassays in renewable surface column and 96-well plate formats for the fluorescence detection of botulinum neurotoxin using high-affinity antibodies

A fluorescence sandwich immunoassay using high-affinity antibodies and quantum dot (QD) reporters has been developed for detection of botulinum neurotoxin serotype A (BoNT/A) using a nontoxic recombinant fragment of the holotoxin (BoNT/A-H(C)-fragment) as a structurally valid simulant for the full toxin molecule. The antibodies used, AR4 and RAZ1, bind to nonoverlapping epitopes present on both the full toxin and on the recombinant fragment. In one format, the immunoassay is carried out in a 96-well plate with detection in a standard plate reader using AR4 as the capture antibody and QD-coupled RAZ1 as the reporter. Detection to 31 pM with a total incubation time of 3 h was demonstrated. In a second format, the AR4 capture antibody was coupled to Sepharose beads, and the reactions were carried out in microcentrifuge tubes with an incubation time of 1 h. The beads were subsequently captured and concentrated in a rotating rod "renewable surface" flow cell equipped with a fiber optic system for fluorescence measurements. In PBS buffer, the BoNT/A-H(C)-fragment was detected to concentrations as low as 5 pM using the fluidic measurement approach.

Egg yolk antibodies for detection and neutralization of Clostridium botulinum type A neurotoxin

The objective of this research project was to determine the usefulness of an egg antibody platform for producing materials for the detection and neutralization of botulinum type A neurotoxin. Yield estimates for detection and neutralizing antibodies produced using methods described were calculated. Antibody specific to botulinum toxoid A (aToxoid) and toxin A (aBoNT/A) was produced by immunizing hens with botulinum toxoid A (toxoid) followed by increasing amounts of botulinum neurotoxin A (BoNT/A) in Freund incomplete adjuvant. Egg yolks were extracted with polyethylene glycol (PEG) for antibody detection and neutralization experiments. A model aToxoid/toxoid immunoassay using only egg yolk antibody was developed and had a detection limit of 1 pg/ml of toxoid. In an indirect enzyme-linked immunosorbent assay of BoNT/A-specific antibody, the aBoNT/A contained more BoNT/A-specific antibody than did the aToxoid, and aBoNT/A was as effective as commercial rabbit antibody. The aToxoid provided no protection against BoNT/A in a standard mouse neutralization assay; however, 1 mg of PEG-extracted aBoNT/A neutralized 4,000 lethal doses of BoNT/A injected intraperitoneally. Based on these results, we calculated that in 1 month one hen could produce more than 100 liters of antibody detection reagents or enough antibody to neutralize approximately 11.6 million mouse lethal doses of botulinum toxin. Utilization of an egg antibody platform is potentially rapid (28 to 70 days) and scalable to kilogram quantities using current egg production facilities with as few as 1,000 hens.

Epitope characterization and variable region sequence of f1-40, a high-affinity monoclonal antibody to botulinum neurotoxin type a (Hall strain)

BACKGROUND

Botulism, an often fatal neuroparalytic disease, is caused by botulinum neurotoxins (BoNT) which consist of a family of seven serotypes (A-H) produced by the anaerobic bacterium Clostridium botulinum. BoNT, considered the most potent biological toxin known, is a 150 kDa protein consisting of a 100 kDa heavy-chain (Hc) and a 50 kDa light-chain (Lc). F1-40 is a mouse-derived, IgG1 monoclonal antibody that binds the light chain of BoNT serotype A (BoNT/A) and is used in a sensitive immunoassay for toxin detection. We report the fine epitope mapping of F1-40 and the deduced amino acid sequence of the variable regions of the heavy and light chains of the antibody.

METHODS AND FINDINGS

To characterize the binding epitope of F1-40, three complementary experimental approaches were selected. Firstly, recombinant peptide fragments of BoNT/A light-chain were used in Western blots to identify the epitope domains. Secondly, a peptide phage-display library was used to identify the specific amino acid sequences. Thirdly, the three-dimensional structure of BoNT/A was examined in silico, and the amino acid sequences determined from the phage-display studies were mapped onto the three-dimensional structure in order to visualize the epitope. F1-40 was found to bind a peptide fragment of BoNT/A, designated L1-3, which spans from T125 to L200. The motif QPDRS was identified by phage-display, and was mapped to a region within L1-3. When the three amino acids Q138, P139 and D140 were all mutated to glycine, binding of F1-40 to the recombinant BoNT/A light chain peptide was abolished. Q-138, P-139 and D-140 form a loop on the external surface of BoNT/A, exposed to solvent and accessible to F1-40 binding.

CONCLUSIONS

The epitope of F1-40 was localized to a single exposed loop (ss4, ss5) on the Lc of BoNT. Furthermore amino acids Q138, P139 and D140 forming the tip of the loop appear critical for binding.

Renewable surface fluorescence sandwich immunoassay biosensor for rapid sensitive botulinum toxin detection in an automated fluidic format

A renewable surface biosensor for rapid detection of botulinum neurotoxin serotype A is described based on fluidic automation of a fluorescence sandwich immunoassay, using a recombinant protein fragment of the toxin heavy chain ( approximately 50 kDa) as a structurally valid simulant. Monoclonal antibodies AR4 and RAZ1 bind to separate non-overlapping epitopes of the full botulinum holotoxin ( approximately 150 kDa). Both of the targeted epitopes are located on the recombinant fragment. The AR4 antibody was covalently bound to Sepharose beads and used as the capture antibody. A rotating rod flow cell was used to capture these beads delivered as a suspension by a sequential injection flow system, creating a 3.6 microL column. After perfusing the bead column with sample and washing away the matrix, the column was perfused with Alexa 647 dye-labeled RAZ1 antibody as the reporter. Optical fibers coupled to the rotating rod flow cell at a 90 degrees angle to one another delivered excitation light from a HeNe laser (633 nm) using one fiber and collected fluorescent emission light for detection with the other. After each measurement, the used Sepharose beads are released and replaced with fresh beads. In a rapid screening approach to sample analysis, the toxin simulant was detected to concentrations of 10 pM in less than 20 minutes using this system.

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.

Botulism diagnostics: from clinical symptoms to in vitro assays

Botulinum neurotoxin (BoNT), which cause the deadly neuroparalytic disease, botulism, is the most toxic substance known to man. BoNT can be used as potential bioterrorism agents, and therefore, pose great threat to national security and public health. Rapid and sensitive detection of BoNTs using molecular and biochemical techniques is an essential component in the diagnosis of botulism, and is yet to be achieved. The most sensitive and widely accepted assay method for BoNTs is mouse bioassay, which takes 4 days to complete. This clearly can not meet the need for clinical diagnosis of botulism, botulinum detection in field conditions, and screening of large scale samples. Consequently, the clinical diagnosis of botulism relies on the clinical symptom development, thus limiting the effectiveness of antitoxin treatment. In response to this critical need, many in vitro methods for BoNT detection are under development. This review is focused on recently developed in vitro detection methods for BoNTs, and emerging new technologies with potential for sensitive and rapid in vitro diagnostics for botulism.

The 5th International Conference on Basic and Therapeutic Aspects of Botulinum and Tetanus Neurotoxins. Workshop review: assays and detection

The development of diagnostic tests for the botulinum neurotoxins is complicated by their extremely high potencies and the considerable diversity observed within the neurotoxin family. Current approaches for the detection of the toxins and the organism include amplified immunoassays and PCR techniques. Assays which exploit the biological activities within the botulinum toxins are also in development. These are based on both antibody and mass spectrometric techniques which measure the endopeptidase activities of the neurotoxins. This overview of the Assays and Detection Workshop of the 5th International Conference of on Basic and Therapeutic Aspects of Botulinum and Tetanus Neurotoxins discusses recent progress in the development of these assay systems and the issues that need to be overcome prior to their implementation.

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.

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.