Toxin production by Clostridium botulinum type A under various fermentation conditions

Endopeptidase activities of Clostridium botulinum toxins in the development of this bacterium

By-products like CO₂ and organic acids, produced during Clostridium botulinum growth, appear to inhibit its development and reduce ATP production. A decrease in ATP production creates an imbalance in the ATP/GTP ratio. GTP activates CodY, which regulates BoNT expression. This toxin is released into the extracellular medium. Its light chains act as a specific endopeptidase, targeting SNARE proteins. The specific amino acids released enter the cells and are metabolized by the Stickland reaction, resulting in the synthesis of ATP. This ATP might then be used by histidine kinases to activate Spo0A, the main regulator initiating sporulation, through phosphorylation.

Update on Non-Interchangeability of Botulinum Neurotoxin Products

The growing use of botulinum neurotoxins (BoNTs) for medical and aesthetic purposes has led to the development and marketing of an increasing number of BoNT products. Given that BoNTs are biological medications, their characteristics are heavily influenced by their manufacturing methods, leading to unique products with distinct clinical characteristics. The manufacturing and formulation processes for each BoNT are proprietary, including the potency determination of reference standards and other features of the assays used to measure unit potency. As a result of these differences, units of BoNT products are not interchangeable or convertible using dose ratios. The intrinsic, product-level differences among BoNTs are compounded by differences in the injected tissues, which are innervated by different nerve fiber types (e.g., motor, sensory, and/or autonomic nerves) and require unique dosing and injection sites that are particularly evident when treating complex therapeutic and aesthetic conditions. It is also difficult to compare across studies due to inherent differences in patient populations and trial methods, necessitating attention to study details underlying each outcome reported. Ultimately, each BoNT possesses a unique clinical profile for which unit doses and injection paradigms must be determined individually for each indication. This practice will help minimize unexpected adverse events and maximize efficacy, duration, and patient satisfaction. With this approach, BoNT is poised to continue as a unique tool for achieving individual goals for an increasing number of medical and aesthetic indications.

Regulatory Networks Controlling Neurotoxin Synthesis in Clostridium botulinum and Clostridium tetani

Clostridium botulinum and Clostridium tetani are Gram-positive, spore-forming, and anaerobic bacteria that produce the most potent neurotoxins, botulinum toxin (BoNT) and tetanus toxin (TeNT), responsible for flaccid and spastic paralysis, respectively. The main habitat of these toxigenic bacteria is the environment (soil, sediments, cadavers, decayed plants, intestinal content of healthy carrier animals). C. botulinum can grow and produce BoNT in food, leading to food-borne botulism, and in some circumstances, C. botulinum can colonize the intestinal tract and induce infant botulism or adult intestinal toxemia botulism. More rarely, C. botulinum colonizes wounds, whereas tetanus is always a result of wound contamination by C. tetani. The synthesis of neurotoxins is strictly regulated by complex regulatory networks. The highest levels of neurotoxins are produced at the end of the exponential growth and in the early stationary growth phase. Both microorganisms, except C. botulinum E, share an alternative sigma factor, BotR and TetR, respectively, the genes of which are located upstream of the neurotoxin genes. These factors are essential for neurotoxin gene expression. C. botulinum and C. tetani share also a two-component system (TCS) that negatively regulates neurotoxin synthesis, but each microorganism uses additional distinct sets of TCSs. Neurotoxin synthesis is interlocked with the general metabolism, and CodY, a master regulator of metabolism in Gram-positive bacteria, is involved in both clostridial species. The environmental and nutritional factors controlling neurotoxin synthesis are still poorly understood. The transition from amino acid to peptide metabolism seems to be an important factor. Moreover, a small non-coding RNA in C. tetani, and quorum-sensing systems in C. botulinum and possibly in C. tetani, also control toxin synthesis. However, both species use also distinct regulatory pathways; this reflects the adaptation of C. botulinum and C. tetani to different ecological niches.

Posttranslational Regulation of Botulinum Neurotoxin Production in Clostridium botulinum Hall A-hyper

Botulinum neurotoxins (BoNTs) are the most toxic substances known to humankind and are the causative agents of the neuroparalytic disease botulism. Despite the overall importance of BoNTs in public health and safety, as a bioterrorism concern, and in pharmaceutical development, little is known about the molecular mechanisms mediating BoNT stability and degradation in various environments. Previous studies using Clostridium botulinum strain ATCC 3502 revealed that high levels of arginine (20 g/liter) repressed BoNT production approximately 1,000-fold. In the present study, the mechanisms of toxin reduction in arginine-enriched cultures of C. botulinum strain Hall A-hyper, which we have previously genetically manipulated using ClosTron technology, were explored. Cultures were grown in toxin production medium (TPM) and TPM enriched with arginine. Cultures were analyzed for growth (optical density at 600 nm [OD₆₀₀]), changes in pH, and BoNT formation and stability. Our data indicate that arginine enrichment of C. botulinum strain Hall A-hyper cultures results in a pH shift that induces pH-dependent posttranslational control mechanisms. We further show that independent of arginine, maintenance of an acidic culture pH during growth of C. botulinum strain Hall A-hyper plays a central role in toxin stability and that an extracellular metalloprotease produced by the culture results in BoNT degradation at pH levels between ⁓6.5 and 8.0.

IMPORTANCE Botulinum neurotoxin (BoNT) is a public health and bioterrorism concern as well as an important and widely used pharmaceutical, yet the regulation of its synthesis by BoNT-producing clostridia is not well understood. This paper highlights the role of environmentally controlled posttranslational regulatory mechanisms influencing processing and stability of biologically active BoNTs produced by C. botulinum. The results of this work will help enhance public health and safety measures and our ability to evaluate safety risks of novel BoNTs and improve production and quality of BoNTs for pharmaceutical use.

Vaccine Production to Protect Animals Against Pathogenic Clostridia

Clostridium is a broad genus of anaerobic, spore-forming, rod-shaped, Gram-positive bacteria that can be found in different environments all around the world. The genus includes human and animal pathogens that produce potent exotoxins that cause rapid and potentially fatal diseases responsible for countless human casualties and billion-dollar annual loss to the agricultural sector. Diseases include botulism, tetanus, enterotoxemia, gas gangrene, necrotic enteritis, pseudomembranous colitis, blackleg, and black disease, which are caused by pathogenic Clostridium. Due to their ability to sporulate, they cannot be eradicated from the environment. As such, immunization with toxoid or bacterin-toxoid vaccines is the only protective method against infection. Toxins recovered from Clostridium cultures are inactivated to form toxoids, which are then formulated into multivalent vaccines. This review discusses the toxins, diseases, and toxoid production processes of the most common pathogenic Clostridium species, including Clostridiumbotulinum, Clostridiumtetani, Clostridiumperfringens, Clostridiumchauvoei, Clostridiumsepticum, Clostridiumnovyi and Clostridiumhemolyticum.

Heat shock and prolonged heat stress attenuate neurotoxin and sporulation gene expression in group I Clostridium botulinum strain ATCC 3502

Foodborne pathogenic bacteria are exposed to a number of environmental stresses during food processing, storage, and preparation, and in the human body. In order to improve the safety of food, the understanding of molecular stress response mechanisms foodborne pathogens employ is essential. Many response mechanisms that are activated during heat shock may cross-protect bacteria against other environmental stresses. To better understand the molecular mechanisms Clostridium botulinum, the causative agent of botulism, utilizes during acute heat stress and during adaptation to stressfully high temperature, the C. botulinum Group I strain ATCC 3502 was grown in continuous culture at 39°C and exposed to heat shock at 45°C, followed by prolonged heat stress at 45°C to allow adaptation of the culture to the high temperature. Growth in continuous culture was performed to exclude secondary growth phase effects or other environmental impacts on bacterial gene transcription. Changes in global gene expression profiles were studied using DNA microarray hybridization. During acute heat stress, Class I and III heat shock genes as well as members of the SOS regulon were activated. The neurotoxin gene botA and genes encoding the neurotoxin-associated proteins were suppressed throughout the study. Prolonged heat stress led to suppression of the sporulation machinery whereas genes related to chemotaxis and motility were activated. Induced expression of a large proportion of prophage genes was detected, suggesting an important role of acquired genes in the stress resistance of C. botulinum. Finally, changes in the expression of a large number of genes related to carbohydrate and amino acid metabolism indicated remodeling of the cellular metabolism.

Clostridium botulinum neurotoxin type B is heat-stable in milk and not inactivated by pasteurization

Foodborne botulism is caused by the ingestion of foods containing botulinum neurotoxins (BoNTs). To study the heat stability of Clostridium botulinum neurotoxins, we needed to measure and compare the activity of botulinum neurotoxins, serotypes A and B, under various pasteurization conditions. Currently, the only accepted assay to detect active C. botulinum neurotoxin is an in vivo mouse bioassay, which raises ethical concerns with regard to the use of experimental animals. In this study, noninvasive methods were used to simultaneously detect and distinguish between active BoNT serotypes A and B in one reaction and sample. We developed an enzymatic activity assay employing internally quenched fluorogenic peptides corresponding to SNAP-25, for BoNT-A, and VAMP2, for BoNT-B, as an alternative method to the mouse bioassay. Because each peptide is labeled with different fluorophores, we were able to distinguish between these two toxins. We used this method to analyze the heat stability of BoNT-A and BoNT-B. This study reports that conventional milk pasteurization (63 °C, 30 min) inactivated BoNT serotype A; however, serotype B is heat-stable in milk and not inactivated by pasteurization. Using this activity assay, we also showed that the commonly used food processes such as acidity and pasteurization, which are known to inhibit C. botulinum growth and toxin production, are more effective in inactivating BoNT serotype A than serotype B when conventional pasteurization (63 °C, 30 min) is used.

Effects of carbon dioxide on growth of proteolytic Clostridium botulinum, its ability to produce neurotoxin, and its transcriptome

The antimicrobial gas carbon dioxide is frequently used in modified atmosphere packaging. In the present study, the effects of CO2 (10 to 70%, vol/vol) on gene expression (measured using quantitative reverse transcription-PCR and a whole-genome DNA microarray) and neurotoxin formation (measured using an enzyme-linked immunosorbent assay [ELISA]) by proteolytic Clostridium botulinum type A1 strain ATCC 3502 were studied during the growth cycle. Interestingly, in marked contrast to the situation with nonproteolytic C. botulinum types B and E, CO2 had little effect on any of these parameters. At all CO2 concentrations, relative expression of neurotoxin cluster genes peaked in the transition between exponential and stationary phases, with evidence of a second rise in expression in late stationary phase. Microarray analysis enabled identification of coding sequences whose expression profiles matched those of the neurotoxin cluster. Further research is needed to determine whether these are connected to neurotoxin formation or are merely growth phase associated.

Substrate recognition of VAMP-2 by botulinum neurotoxin B and tetanus neurotoxin

Botulinum neurotoxin (BoNT; serotypes A-G) and tetanus neurotoxin elicit flaccid and spastic paralysis, respectively. These neurotoxins are zinc proteases that cleave SNARE proteins to inhibit synaptic vesicle fusion to the plasma membrane. Although BoNT/B and tetanus neurotoxin (TeNT) cleave VAMP-2 at the same scissile bond, their mechanism(s) of VAMP-2 recognition is not clear. Mapping experiments showed that residues 60-87 of VAMP-2 were sufficient for efficient cleavage by BoNT/B and that residues 40-87 of VAMP-2 were sufficient for efficient TeNT cleavage. Alanine-scanning mutagenesis and kinetic analysis identified three regions within VAMP-2 that were recognized by BoNT/B and TeNT: residues adjacent to the site of scissile bond cleavage (cleavage region) and residues located within N-terminal and C-terminal regions relative to the cleavage region. Analysis of residues within the cleavage region showed that mutations at the P7, P4, P2, and P1' residues of VAMP-2 had the greatest inhibition of LC/B cleavage (> or =32-fold), whereas mutations at P7, P4, P1', and P2' residues of VAMP-2 had the greatest inhibition of LC/TeNT cleavage (> or =64-fold). Residues within the cleavage region influenced catalysis, whereas residues N-terminal and C-terminal to the cleavage region influenced binding affinity. Thus, BoNT/B and TeNT possess similar organization but have unique residues to recognize and cleave VAMP-2. These studies provide new insights into how the clostridial neurotoxins recognize their substrates.

Regulation of neurotoxin complex expression in Clostridium botulinum strains 62A, Hall A-hyper, and NCTC 2916

The kinetics of botulinum toxin gene expression have been investigated in Clostridium botulinum type A strains 62A, Hall A-hyper, and type A(B) strain NCTC 2916 during the growth cycle. The analyses were performed in TPGY and type A Toxin Production Media (TPM). The mRNA transcript levels encoding the proteins of the neurotoxin complex were determined using Northern analyses. Neurotoxin concentrations in culture supernatants and lysed cell pellets were assayed using ELISA, Western blots, and mouse bioassay. Proteolytic activation of botulinum neurotoxin during the growth cycle was evaluated by Western blots. For all three strains, mRNA transcripts for the toxin complex genes were initially detected in early log phase, reached peak levels in early stationary phase, and rapidly decreased in mid-to-late stationary phase and during lysis. Toxin expression varied depending on the strain and growth medium. Toxin production was highest in strain Hall A-hyper, followed by NCTC 2916 and 62A. For C. botulinum strain Hall A-hyper, cell lysis and toxin release into the supernatant occurred rapidly for cells grown in TPM, while cells grown in TPGY remained in stationary phase with minimal lysis and toxin release through 96 h of growth. In contrast, strains 62A and NCTC 2916 lysed more extensively than Hall A-hyper in TPGY. TPM supported higher toxin production and activation than TPGY in strains 62A and Hall A-hyper. These data support that the genes of the botulinum neurotoxin complex are temporally expressed during late-log and early stationary phase and that toxin complex formation depends on the strain and growth medium. Botulinum toxin synthesis and activation appears to be a complex process that is highly regulated by nutritional and environmental conditions. Further research is needed to elucidate the sensing mechanisms and genetic regulatory factors controlling these processes.

Expression of botulinum neurotoxins A and E, and associated non-toxin genes, during the transition phase and stability at high temperature: analysis by quantitative reverse transcription-PCR

Production of botulinum neurotoxin A (BoNT/A) and associated non-toxic proteins (ANTPs), which include a non-toxic non-haemagglutinin (NTNH/A) as well as haemagglutinins (HAs), was found previously to be dependent upon an RNA polymerase alternative sigma factor (BotR/A). Expression of the botR/A, bont/A and antp genes, monitored by reverse transcription and real-time PCR analysis, occurred concomitantly at the transition between the exponential and stationary growth phases of Clostridium botulinum A. The botR/A expression level was about 100-fold less than those of the bont/A and antp genes. Therefore, BotR/A is an alternative sigma factor controlling the botulinum A locus genes during the transition phase. The highest toxin concentration was released into the culture supernatant 12 h after maximum expression of the botR/A, bont/A and antp genes, without any apparent bacterial lysis. Toxin levels were then stable over 5 days in cultures at 37 degrees C, whereas a dramatic decrease in lethal activity was observed between 24 and 48 h in cultures at 44 degrees C. High temperature did inhibit transcription, since expression levels of the botR/A, bont/A and antp genes were similar in cultures at 37 and 44 degrees C. However, incubation at 44 degrees C triggered a calcium-dependent protease that degraded BoNT/A and NTNH/A, but not HAs. In C. botulinum E, which contains no gene related to botR, the bont/E and p47 genes were also expressed during the transition phase, and no protease activation at 44 degrees C was evident.

Unique Substrate Recognition by Botulinum Neurotoxins Serotypes A and E

Botulinum neurotoxins (BoNTs) are zinc proteases that cleave SNARE proteins to elicit flaccid paralysis by inhibiting the fusion of neurotransmitter-carrying vesicles to the plasma membrane of peripheral neurons. There are seven serotypes of BoNT, termed A-G. BoNT serotype A and serotype E cleave SNAP25 at residues 197-198 and 180-181, respectively. Unlike other zinc proteases, the BoNTs recognize extended regions of SNAP25 for cleavage. The basis for this extended substrate recognition and specificity is unclear. Saturation mutagenesis and deletion mapping identified residues 156-202 of SNAP25 as the optimal cleavage domain for BoNT/A, whereas the optimal cleavage domain for BoNT/E was shorter, comprising residues 167-186 of SNAP25. Two sub-sites were resolved within each optimal cleavage domain, which included a recognition or active site (AS) domain that contained the site of cleavage and a binding (B) domain, which contributed to substrate affinity. Within the AS domains, the P1', P3, and P5 sites of SNAP25 contributed to scissile bond cleavage by LC/A, whereas the P1' and P2 sites of SNAP25 contributed to scissile bond cleavage by LC/E. These studies provide insight into the development of strategies for small molecule inhibitors of the BoNTs.

Relative neurotoxin gene expression in clostridium botulinum type B, determined using quantitative reverse transcription-PCR

A quantitative reverse transcription-PCR (qRT-PCR) method was developed to monitor the relative expression of the type B botulinum neurotoxin (BoNT/B) gene (cntB) in Clostridium botulinum. The levels of cntB mRNA in five type B strains were accurately monitored by using primers specific for cntB and for the reference gene encoding the 16S rRNA. The patterns and relative expression of cntB were different in the different strains. Except for one of the strains investigated, an increase in cntB expression was observed when the bacteria entered the early stationary growth phase. In the proteolytic strain C. botulinum ATCC 7949, the level of cntB mRNA was four- to fivefold higher than the corresponding levels in the other strains. This was confirmed when we quantified the production of extracellular BoNT/B by an enzyme-linked immunosorbent assay and measured the toxicity of BoNT/B by a mouse bioassay. When the effect of exposure to air on cntB expression was investigated, no decline in the relative expression was observed in spite of an 83% reduction in the viable count based on the initial cell number. Instead, the level of cntB mRNA remained the same. When there was an increase in the sodium nitrite concentration, the bacteria needed a longer adjustment time in the medium before exponential growth occurred. In addition, there was a reduction in the expression of cntB compared to the expression of the 16S rRNA gene at higher sodium nitrite concentrations. This was most obvious in the late exponential growth phase, but at the highest sodium nitrite concentration investigated, 45 ppm, a one- to threefold decline in the cntB mRNA level was observed in all growth phases.

Effect of ethanol on the growth of Clostridium botulinum

Model broth studies were carried out to investigate the effect of ethanol on the growth of proteolytic (group I) strains of Clostridium botulinum. Ethanol extended the pathogen's lag phase, decreased its exponential growth rate, and decreased its final level of growth in the stationary phase. In all cases, botulinum neurotoxin production was associated with growth. Micrographs of C. botulinum cultures grown at 37 degrees C in trypticase peptone glucose yeast extract (TPGY) broths containing 2 and 4% ethanol showed elongation of vegetative cells and interference with cell division. The inhibition of growth and toxin production at the ethanol level predicted (5.5%, wt/wt) was confirmed by microscopy and by the mouse bioassay. A subsequent study was carried out to determine the combined effect of ethanol (0 to 8% [wt/wt]), water activity (aw; 0.953 to 0.997), and pH (6.2 to 8.2) on the probability of the growth of and neurotoxin production by proteolytic strains of C. botulinum (10(3) spores per ml). Growth and neurotoxin production occurred in 1 to 3 days in TPGY broths without ethanol (0%) and in 2 to 4 days in broths containing 2% ethanol regardless of the aw or pH levels (P < 0.005). Growth and neurotoxin production were delayed by an ethanol concentration of 4% ethanol and completely inhibited by a concentration of 6%. At an ethanol concentration of 4%, the probability of growth and toxin production over 365 days (Pt) was influenced by aw and pH. After 365 days, the maximum probability of growth and toxin production (Pmax) was 1 for all but one combination. However, tau, the time it took for 50% of all eventually positive replicates for any given combination of barriers to show growth and/or turbidity, ranged from <3 to 229 days. All tubes of TPGY broths that showed no growth after 365 days were subcultured in fresh TPGY broths. In all cases, growth and toxin production occurred within 24 h at 37 degrees C, indicating the reversible (sporostatic and/or bacteriostatic) effect of ethanol on C. botulinum.

Clostridium botulinum and its neurotoxins: a metabolic and cellular perspective

Clostridium botulinum comprises a diverse assemblage of clostridia that have the common property of producing a distinctive protein neurotoxin (BoNT) of similar pharmacological activity and extraordinary potency. BoNTs are produced in culture as molecular complexes consisting of BoNT, hemagglutinin (HA) and associated subcomponent proteins, nontoxic nonhemagglutinin (NTNH), and RNA. The genes encoding the protein components reside as a cluster on the chromosome, on bacteriophages, or on plasmids depending on the C. botulinum serotype. A gene BotR coding for a regulatory protein has been detected in toxin gene clusters from certain strains, as well as ORFs coding for uncharacterized components. The gene encoding TeNT is located on a large plasmid, and expression of the structural gene is controlled by the regulatory gene, TetR, located immediately upstream of the TeNT structural gene. TeNT is not known to be assembled into a protein/nucleic acid complex in culture. Cellular synthesis of BoNT and TeNT have been demonstrated to be positively regulated by the homologous proteins, BotR/A and TetR. Evidence suggests that negative regulatory factors and general control cascades such as those involved in nitrogen regulation and carbon catabolite repression also regulate synthesis of BoNTs. Neurotoxigenic clostridia have attracted considerable attention from scientists and clinicians during the past decade, and many excellent reviews are available on various aspects of these organisms and their neurotoxins. However, certain areas have not been well-studied, including metabolic regulation of toxin formation and genetic tools to study neurotoxigenic clostridia. These topics are the focus of this review.

In situ characterization of Clostridium botulinum neurotoxin synthesis and export

A monoclonal antitoxin/colloidal gold probe and sequential centrifugation were used to study synthesis, translocation and export of Clostridium botulinum strain 62A neurotoxin (NT). Exponential growth occurred after 5 h of anaerobic incubation of spores and continued for 15-16 h. NT was detected at 15 h using the probe and transmission electron microscopy (TEM), 2 h earlier than the first detection by the mouse bioassay. During exponential growth, the probe localized NT primarily in the cytoplasm, on the inner side of the cytoplasmic membrane and in the cell wall. During stationary and death phases, the NT was located within the cytoplasm, cell wall and extracellularly. NT was released from the cell during cell wall exfoliation. Cells retained NT after repeated gelatin-phosphate washes and sequential centrifugations, consistent with the TEM observation that the NT is bound to the cell wall. These observations indicate that the process of Cl. botulinum type A NT production follows a sequence of synthesis, translocation across the cytoplasmic membrane and export through the cell wall.

Properties and use of botulinum toxin and other microbial neurotoxins in medicine

Crystalline botulinum toxin type A was licensed in December 1989 by the Food and Drug Administration for treatment of certain spasmodic muscle disorders following 10 or more years of experimental treatment on human volunteers. Botulinum toxin exerts its action on a muscle indirectly by blocking the release of the neurotransmitter acetylcholine at the nerve ending, resulting in reduced muscle activity or paralysis. The injection of only nanogram quantities (1 ng = 30 mouse 50% lethal doses [U]) of the toxin into a spastic muscle is required to bring about the desired muscle control. The type A toxin produced in anaerobic culture and purified in crystalline form has a specific toxicity in mice of 3 x 10(7) U/mg. The crystalline toxin is a high-molecular-weight protein of 900,000 Mr and is composed of two molecules of neurotoxin (ca. 150,000 Mr) noncovalently bound to nontoxic proteins that play an important role in the stability of the toxic unit and its effective toxicity. Because the toxin is administered by injection directly into neuromuscular tissue, the methods of culturing and purification are vital. Its chemical, physical, and biological properties as applied to its use in medicine are described. Dilution and drying of the toxin for dispensing causes some detoxification, and the mouse assay is the only means of evaluation for human treatment. Other microbial neurotoxins may have uses in medicine; these include serotypes of botulinum toxins and tetanus toxin. Certain neurotoxins produced by dinoflagellates, including saxitoxin and tetrodotoxin, cause muscle paralysis through their effect on the action potential at the voltage-gated sodium channel. Saxitoxin used with anaesthetics lengthens the effect of the anaesthetic and may enhance the effectiveness of other medical drugs. Combining toxins with drugs could increase their effectiveness in treatment of human disease.

Purification of type E botulinum neurotoxin by high-performance ion exchange chromatography

A purification procedure for type E botulinum neurotoxin has been developed, based solely on high-performance ion exchange chromatography. The method exploits the differential chromatographic behavior of the free neurotoxin versus the neurotoxin-protein 12S complex. The high purity of the product was demonstrated with sodium dodecyl sulfate-gel electrophoresis and amino acid sequencing. Beginning with dialyzed crude extract, at least 4 mg of pure neurotoxin could be obtained in two working days. The method has been adapted to user-prepared columns for processing large volumes of crude neurotoxin in one batch.

Effect of 3,4-diaminopyridine on the survival of mice injected with botulinum neurotoxin type A, B, E, or F

To determine the efficacy of 3,4-diaminopyridine (3,4-DAP) as a potential treatment for botulism, its effect on the survival times of mice injected with type A, B, E, or F botulinum toxin (Bo Tx) was examined. Mice were injected ip with 10, 20, or 40 LD50 of Bo Tx. Three hours later, when the mice displayed signs of botulism, half of each group of mice was treated with 3,4-DAP, an agent which increases nerve-evoked transmitter release. At each dose of type A Bo Tx tested, 3,4-DAP definitely prolonged survival. In contrast, treatment with the drug did not significantly increase the survival time of mice injected with type B, E, or F Bo Tx. The differences in efficacy of 3,4-DAP against the four serotypes of Bo Tx together with previously reported variations in specific toxicity and duration of paralysis may reflect differences in the pharmacological activity of these neurotoxins.

Comparison of the action of types A and F botulinum toxin at the rat neuromuscular junction

Blockade of neuromuscular transmission was produced in the lower hind limb of the rat by local injection of either type A or type F botulinum toxin (BoTx). At 1, 3, 7, and 10 days after injection, the extensor digitorum longus (edl) nerve-muscle preparation was excised and analyzed for alterations in muscle mechanical properties or spontaneous and nerve stimulus-evoked quantal transmitter release. Muscles receiving type A toxin were paralyzed up to and including 7 days after injection. Muscles treated with type F toxin, although completely paralyzed at 1 and 3 days after injection, twitched in response to nerve stimulation by 7 days. Both toxins induced a marked decrease in the frequency of miniature end-plate potentials, but type A did so to a greater extent. Between 1 and 3 days after toxin injection nerve impulse-evoked transmitter release was reduced in both type A- and type F-treated muscles. Evoked release was temperature sensitive in type A-treated muscles but not in those treated with type F. 3,4-Diaminopyridine (3,4-DAP), a compound which increases nerve-evoked transmitter release by increasing Ca2+ influx, was more effective in reversing the paralysis in type A than in type F-treated muscles. 3,4-DAP induced asynchronous end-plate potentials in response to nerve stimulation in type F-paralyzed muscles, but not in muscles treated with type A. Amidination of the amino groups (presumably lysine) on the toxin by treatment with ethylacetimidate increased the potency and efficacy of only type F BoTx. The results show that type F BoTx differs from type A, mainly by its lower potency, efficacy, shorter duration of action, and by being less effectively antagonized by 3,4-DAP.

Different effects of types A and B botulinum toxin on transmitter release at the rat neuromuscular junction

Blockade of neuromuscular transmission was produced in the lower hind limb of the rat by local injection of either crystalline type A botulinum toxin or purified type B botulinum neurotoxin. At 1, 3, 5 and 7 days after injection, the extensor digitorum longus nerve-muscle preparation was excised and analyzed in vitro for alterations in spontaneous and nerve stimulus-evoked quantal transmitter release. Muscles receiving type A toxin were paralyzed up to and including 7 days after injection. Muscles treated with type B toxin, although completely paralyzed at 1 and 3 days, twitched in response to nerve stimulation at 5 and 7 days after injection. Both toxins induced a marked decrease in the frequency of miniature endplate potentials but type A did so to a greater extent. The remaining population of miniature endplate potentials contained a greater frequency of potentials with small or large amplitudes and prolonged rise times compared to normal muscle. These changes were more pronounced with type A toxin than with type B toxin. In the presence of alpha-dinitrophenol (1 mM), high frequency, fast-rising miniature endplate potentials of uniform size reappeared. High K+ (20 mM) was less effective in this respect. At 3 days after toxin injection nerve impulse evoked transmitter release was reduced more for type A treated muscles than for type B. However, 3,4-diaminopyridine, an agent which increases nerve-evoked transmitter release by increasing Ca2+ influx, was more effective in reversing the paralysis in type A than in type B-treated muscles.(ABSTRACT TRUNCATED AT 250 WORDS)

Dependence of Clostridium botulinum gas and protease production on culture conditions

Reports that Clostridium botulinum toxin can sometimes be detected in the absence of indicators of overt spoilage led to a systematic study of this phenomenon in a model system. Media with various combinations of pH (5.0 to 7.0) and glucose (0.0 to 1.0%) were inoculated with vegetative cells of C. botulinum 62A and incubated anaerobically at 35 degrees C. Although growth and toxin production occurred at all pH and glucose combinations, accumulation of gas was delayed or absent in media with low pH, low glucose levels, or both. Other proteolytic C. botulinum strains gave similar results. Trypsin activation was required to detect toxin in some low pH cultures. The trypsinization requirement correlated with low proteolytic activity in the cultures. Proteolytic activity of the strains examined was 5- to 500-fold lower in botulinal assay medium than in cooked meat medium. The results indicate that the absence of gas accumulation does not preclude the presence of botulinal toxin and that proteolytic cultures grown under adverse conditions may require trypsinization for the detection of toxin.

Immunodiffusion method for detection of type A Clostridium botulinum

A simple gel immunodiffusion agar procedure was developed for detecting toxigenic strains of Clostridium botulinum type A. The method consisted of overlaying colonies grown on thin-layer tryptone-peptone-glucose-yeast extract agar with gel diffusion agar containing desired levels of C. botulinum type A antitoxin. Concentric precipitin zones formed around colonies of C. botulinum type A. Strains of C. botulinum type A were detected by this procedure. However, C. botulinum type B reacted to a lesser degree with this system. No reaction was noted with types E, F, Langeland, F8G, Clostridium perfringens, or with strains of nontoxigenic Clostridium sporogenes. Thickness of the plating medium, incubation time and temperature, environmental growth conditions, and levels of both agar an antitoxin were important factors affecting the efficiency of the procedure, whereas the age of the culture (used as inoculum) was not critical. Thin agar medium (5 ml per plate [15 by 100 mm]) containing 1.5% agar gave consistent results, but more agar limited diffusion, and lower levels encouraged spreaders. The optimal concentration of antitoxin incorporated in to the gel diffusion agar overlay was 1.2 IU/ml gel diffusion agar. Rabbit type A antitoxin prepared with purer immunizing agent gave similar reactions. The addition of type A antitoxin in tryptone-peptone-glucose-yeast extract agar medium before inoculation with type A C. botulinum showed promising results.

Effect of fermentation conditions on toxin production by Clostridium botulinum type B

To obtain high yields of toxin for the preparation of purified neurotoxoids, we examined the time of appearance and the quantity of toxin produced by the Bean strain of Clostridium botulinum type B under various conditions by using a fermentor system. The medium employed consisted of 2.0% casein hydrolylsate and 1.5% yeast extract plus an appropriate concentration of glucose. The maximum toxin concentration (4 x 10(5) to 5 x 10(5) mouse median lethal doses per ml) was attained within 48 h under the following fermentation conditions: an initial glucose concentration of 0.5 or 1.0%, a temperature of 35 degrees C, a nitrogen overlay at a rate of 5 liters/min, and an agitation rate of 50 rpm.