Pathodynamics of intoxication in rats and mice by enterotoxin of Clostridium perfringens type A

The biology and pathogenicity of Clostridium perfringens type F: a common human enteropathogen with a new(ish) name

SUMMARYIn the 2018-revised Clostridium perfringens typing classification system, isolates carrying the enterotoxin (cpe) and alpha toxin genes but no other typing toxin genes are now designated as type F. Type F isolates cause food poisoning and nonfoodborne human gastrointestinal (GI) diseases, which most commonly involve type F isolates carrying, respectivefooly, a chromosomal or plasmid-borne cpe gene. Compared to spores of other C. perfringens isolates, spores of type F chromosomal cpe isolates often exhibit greater resistance to food environment stresses, likely facilitating their survival in improperly prepared or stored foods. Multiple factors contribute to this spore resistance phenotype, including the production of a variant small acid-soluble protein-4. The pathogenicity of type F isolates involves sporulation-dependent C. perfringens enterotoxin (CPE) production. C. perfringens sporulation is initiated by orphan histidine kinases and sporulation-associated sigma factors that drive cpe transcription. CPE-induced cytotoxicity starts when CPE binds to claudin receptors to form a small complex (which also includes nonreceptor claudins). Approximately six small complexes oligomerize on the host cell plasma membrane surface to form a prepore. CPE molecules in that prepore apparently extend β-hairpin loops to form a β-barrel pore, allowing a Ca2+ influx that activates calpain. With low-dose CPE treatment, caspase-3-dependent apoptosis develops, while high-CPE dose treatment induces necroptosis. Those effects cause histologic damage along with fluid and electrolyte losses from the colon and small intestine. Sialidases likely contribute to type F disease by enhancing CPE action and, for NanI-producing nonfoodborne human GI disease isolates, increasing intestinal growth and colonization.

NanJ Is the Major Sialidase for Clostridium perfringens Type F Food Poisoning Strain 01E809

Clostridium perfringens type F strains cause food poisoning (FP) when they sporulate and produce C. perfringens enterotoxin (CPE) in the intestines. Most type F FP strains carry a chromosomal cpe gene (c-cpe strains). C. perfringens produces up to three different sialidases, named NanH, NanI, and NanJ, but some c-cpe FP strains carry only nanJ and nanH genes. This study surveyed a collection of such strains and showed that they produce sialidase activity when cultured in Todd-Hewitt broth (TH) (vegetative cultures) or modified Duncan-Strong (MDS) medium (sporulating cultures). Sialidase null mutants were constructed in 01E809, a type F c-cpe FP strain carrying the nanJ and nanH genes. Characterization of those mutants identified NanJ as the major sialidase of 01E809 and showed that, in vegetative and sporulating cultures, nanH expression affects nanJ expression and vice versa; those regulatory effects may involve media-dependent changes in transcription of the codY or ccpA genes but not nanR. Additional characterization of these mutants demonstrated the following: (i) NanJ contributions to growth and vegetative cell survival are media dependent, with this sialidase increasing 01E809 growth in MDS but not TH; (ii) NanJ enhances 24-h vegetative cell viability in both TH and MDS cultures; and (iii) NanJ is important for 01E809 sporulation and, together with NanH, CPE production in MDS cultures. Lastly, NanJ was shown to increase CPE-induced cytotoxicity and CH-1 pore formation in Caco-2 cells. Collectively, these results suggest that NanJ may have a contributory role in FP caused by type F c-cpe strains that carry the nanH and nanJ genes.

Characterization of NanR Regulation of Sialidase Production, Sporulation and Enterotoxin Production by Clostridium perfringens Type F Strains Carrying a Chromosomal Enterotoxin Gene

Clostridium perfringens type F food poisoning (FP) strains produce C. perfringens enterotoxin (CPE) to cause a common bacterial food-borne illness in the United States. During FP, CPE is synthesized in the intestines when C. perfringens sporulates. Besides CPE, FP strains also produce sialidases. Most FP strains carry their cpe gene on the chromosome and all surveyed chromosomal cpe (c-cpe) FP strains produce NanH sialidase or both NanJ and NanH sialidases. NanR has been shown previously to regulate sialidase activity in non-FP strains. The current study investigated whether NanR also regulates sialidase activity or influences sporulation and CPE production for c-cpe FP strains SM101 and 01E809. In sporulation medium, the SM101 nanR null mutant showed lower sialidase activity, sporulation, and CPE production than its wild-type parent, while the 01E809 nanR null mutant showed roughly similar sialidase activity, sporulation, and CPE production as its parent. In vegetative medium, the nanR null mutants of both strains produced more spores than their parents while NanR repressed sialidase activity in SM101 but positively regulated sialidase activity in 01E809. These results demonstrate that NanR regulates important virulence functions of c-cpe strains, with this control varying depending on strain and culture conditions.

Characterizing the Contributions of Various Clostridium perfringens Enterotoxin Properties to In Vivo and In Vitro Permeability Effects

Clostridium perfringens enterotoxin (CPE) is thought to cause lethal enterotoxemia when absorbed from the intestinal lumen into the circulation. CPE action sequentially involves receptor-binding, oligomerization into a prepore, and pore formation. To explore the mechanistic basis by which CPE alters permeability, this study tested the permeability effects of several recombinant CPE (rCPE) species: rCPE and rCPE_C186A (which form pores), rC-CPE and rCPE_D48A (which bind to receptors but cannot oligomerize), rCPE_C186A/F91C (which binds and oligomerizes without pore formation), and rCPE_Y306A/L315A (which has poor receptor-binding ability). On Caco-2 cells, i) only rCPE and rCPE_C186A were cytotoxic; ii) rCPE and rCPE_C186A affected transepithelial resistance (TEER) and 4 kDa fluorescent dextran (FD4) transit more quickly than binding-capable, but noncytotoxic, rCPE variants; whereas iii) rCPE_Y306A/L315A did not affect TEER or FD4 transit. Using mouse intestinal loops, rCPE (but not noncytotoxic rC-CPE, rCPE_D48A or rCPE_Y306A/L315A) was lethal and caused intestinal histologic damage within 4 h. After 2 h of treatment, rCPE was more strongly absorbed into the serum than those noncytotoxic rCPE species but by 4 h rC-CPE and rCPE_D48A became absorbed similarly as rCPE, while rCPE_Y306A/L315A absorption remained low. This increased rC-CPE and rCPE_D48A absorption from 2 to 4 h did not involve a general intestinal permeability increase because Evans Blue absorption from the intestines did not increase between 2 and 4 h of treatment with rC-CPE or rCPE_D48A. Collectively, these results indicate that CPE receptor binding is sufficient to slowly affect permeability, but CPE-induced cytotoxicity is necessary for rapid permeability changes and lethality. IMPORTANCE Clostridium perfringens enterotoxin (CPE) causes lethal enterotoxemia when absorbed from the intestines into the bloodstream. Testing recombinant CPE (rCPE) or rCPE variants impaired for various specific steps in CPE action showed that full CPE-induced cytotoxicity causes rapid Caco-2 monolayer permeability alterations, as well as enterotoxemic lethality and rapid CPE absorption in mouse small intestinal loops. However, receptor binding-capable, but noncytotoxic, rCPE variants did cause slow-developing in vitro and in vivo permeability effects. Absorption of binding-capable, noncytotoxic rCPE variants from the intestines did not correlate with general intestinal permeability alterations, suggesting that CPE binding can induce its own uptake. These findings highlight the importance of binding and, especially, cytotoxicity for CPE absorption during enterotoxemia and may assist development of permeability-altering rCPE variants for translational purposes.

Potential Therapeutic Effects of Mepacrine against Clostridium perfringens Enterotoxin in a Mouse Model of Enterotoxemia

Clostridium perfringens enterotoxin (CPE) is a pore-forming toxin that causes the symptoms of common bacterial food poisoning and several non-foodborne human gastrointestinal diseases, including antibiotic-associated diarrhea and sporadic diarrhea. In some cases, CPE-mediated disease can be very severe or fatal due to the involvement of enterotoxemia. Therefore, the development of potential therapeutics against CPE action during enterotoxemia is warranted. Mepacrine, an acridine derivative drug with broad-spectrum effects on pores and channels in mammalian membranes, has been used to treat protozoal intestinal infections in human patients. A previous study showed that the presence of mepacrine inhibits CPE-induced pore formation and activity in enterocyte-like Caco-2 cells, reducing the cytotoxicity caused by this toxin in vitro Whether mepacrine is similarly protective against CPE action in vivo has not been tested. When the current study evaluated whether mepacrine protects against CPE-induced death and intestinal damage using a murine ligated intestinal loop model, mepacrine protected mice from the enterotoxemic lethality caused by CPE. This protection was accompanied by a reduction in the severity of intestinal lesions induced by the toxin. Mepacrine did not reduce CPE pore formation in the intestine but inhibited absorption of the toxin into the blood of some mice. Protection from enterotoxemic death correlated with the ability of this drug to reduce CPE-induced hyperpotassemia. These in vivo findings, coupled with previous in vitro studies, support mepacrine as a potential therapeutic against CPE-mediated enterotoxemic disease.

Development of Adjuvant-Free Bivalent Food Poisoning Vaccine by Augmenting the Antigenicity of Clostridium perfringens Enterotoxin

Clostridium perfringens enterotoxin (CPE) is a common cause of food poisoning and hyperkalemia-associated death. Previously, we reported that fusion of pneumococcal surface protein A (PspA) to C-terminal fragment of CPE (C-CPE) efficiently bound mucosal epithelium so that PspA-specific immune responses could be provoked. In this study, we found that fusion of C-CPE with PspA augmented the antigenicity of C-CPE itself. These findings allowed us to hypothesize that fusion of C-CPE and another food poisoning vaccine act as a bivalent food poisoning vaccine. Therefore, we constructed an adjuvant-free bivalent vaccine against CPE and cholera toxin (CT), which is a major food poisoning in developing country, by genetically fusing CT B subunit to C-CPE. Because of the low antigenicity of C-CPE, immunization of mice with C-CPE alone did not induce C-CPE-specific immune responses. However, immunization with our vaccine induced both C-CPE- and CT-specific neutralizing antibody. The underlying mechanism of the augmented antigenicity of C-CPE included the activation of T cells by CTB. Moreover, neutralizing antibodies lasted for at least 48 weeks and the quality of the antibody was dependent on the binding activity of CTB–C-CPE to its receptors. These findings suggest that our fusion protein is a potential platform for the development of an adjuvant-free bivalent vaccine against CPE and CT.

Animal models to study the pathogenesis of human and animal Clostridium perfringens infections

The most common animal models used to study Clostridium perfringens infections in humans and animals are reviewed here. The classical C. perfringens-mediated histotoxic disease of humans is clostridial myonecrosis or gas gangrene and the use of a mouse myonecrosis model coupled with genetic studies has contributed greatly to our understanding of disease pathogenesis. Similarly, the use of a chicken model has enhanced our understanding of type A-mediated necrotic enteritis in poultry and has led to the identification of NetB as the primary toxin involved in disease. C. perfringens type A food poisoning is a highly prevalent bacterial illness in the USA and elsewhere. Rabbits and mice are the species most commonly used to study the action of enterotoxin, the causative toxin. Other animal models used to study the effect of this toxin are rats, non-human primates, sheep and cattle. In rabbits and mice, CPE produces severe necrosis of the small intestinal epithelium along with fluid accumulation. C. perfringens type D infection has been studied by inoculating epsilon toxin (ETX) intravenously into mice, rats, sheep, goats and cattle, and by intraduodenal inoculation of whole cultures of this microorganism in mice, sheep, goats and cattle. Molecular Koch's postulates have been fulfilled for enterotoxigenic C. perfringens type A in rabbits and mice, for C. perfringens type A necrotic enteritis and gas gangrene in chickens and mice, respectively, for C. perfringens type C in mice, rabbits and goats, and for C. perfringens type D in mice, sheep and goats.

Animal models to study the pathogenesis of enterotoxigenic Clostridium perfringens infections

Rabbits, mice, rats, non-human primates, sheep and cattle have been used to study the effect of Clostridium perfringens enterotoxin (CPE). CPE produces mostly necrosis of the small intestinal epithelium along with fluid accumulation in rabbits and mice. In the latter, CPE can bind to internal organs such as the liver, which induces lethal potassium levels in blood.

Development and application of a mouse intestinal loop model to study the in vivo action of Clostridium perfringens enterotoxin

Clostridium perfringens enterotoxin (CPE) is responsible for causing the gastrointestinal symptoms of C. perfringens type A food poisoning, the second most commonly identified bacterial food-borne illness in the United States. CPE is produced by sporulating C. perfringens cells in the small intestinal lumen, where it then causes epithelial cell damage and villous blunting that leads to diarrhea and cramping. Those effects are typically self-limiting; however, severe outbreaks of this food poisoning, particularly two occurring in psychiatric institutions, have involved deaths. Since animal models are currently limited for the study of the CPE action, a mouse ligated intestinal loop model was developed. With this model, significant lethality was observed after 2 h in loops receiving an inoculum of 100 or 200 μg of CPE but not using a 50-μg toxin inoculum. A correlation was noted between the overall intestinal histological damage and lethality in mice. Serum analysis revealed a dose-dependent increase in serum CPE and potassium levels. CPE binding to the liver and kidney was detected, along with elevated levels of potassium in the serum. These data suggest that CPE can be absorbed from the intestine into the circulation, followed by the binding of the toxin to internal organs to induce potassium leakage, which can cause death. Finally, CPE pore complexes similar to those formed in tissue culture cells were detected in the intestine and liver, suggesting that (i) CPE actions are similar in vivo and in vitro and (ii) CPE-induced potassium release into blood may result from CPE pore formation in internal organs such as the liver.

Coronary vasoconstriction is the most probable cause of death of rats intoxicated with botulinolysin, a hemolysin produced by Clostridium botulinum

The pathophysiology of lethal intoxication by botulinolysin (Blyn) was studied using anesthetized rats and isolated rat organs. Intravenous injection of 10,000 and 1000 hemolytic units (HU) of Blyn killed rats rapidly while 100 HU of the toxin did not. Congestion and edema of lungs were observed at autopsies of the rats killed by intoxication. Hemoglobinemia was obvious in rats injected with 1000 HU of Blyn but not in rats with 10,000 HU. Electrocardiograms of the intoxicated rats showed depression of T waves but not changes characteristic of hyperpotassemia. All the rats injected with the above doses of Blyn showed a rapid fall in arterial blood pressure (BP) immediately after the toxin injection, and BP soon recovered in rats injected with 100 HU, partially and transiently in rats with 1000 HU, and not in rats with 10,000 HU of Blyn. Perfusion of Blyn (1 HU/ml) to isolated rat hearts caused a rapid and marked increase in perfusion pressure and cessation of spontaneous heart beat. Acetylsalicylic acid (10(-3) M) and quinacrine dihydrochloride (10(-5) M) did not essentially influence the effects of Blyn on the isolated hearts, but verapamil (10(-6) M) inhibited at least the initial increase in perfusion pressure elicited by Blyn. Spontaneous contractions of the isolated atria were little influenced by Blyn (60 HU/ml). Perfusion pressures of isolated kidneys, lungs and livers were also increased by Blyn (1 HU/ml). The results indicate that Blyn caused vasoconstriction but had little direct effect on myocardium. Based on the above findings, we conclude that coronary vasoconstriction elicited by direct action of Blyn causes acute cardiac dysfunction leading to systemic hypotension and death of the intoxicated animals.

Is cardiorespiratory failure induced by bacterial toxins the cause of sudden infant death syndrome? Studies with an animal model (the rabbit)

Recent studies have implicated various toxigenic bacteria and their toxins in the aetiology of sudden infant death syndrome (SIDS). Therefore the effect of six bacterial toxins on the cardiorespiratory system of the rabbit was studied as a model for SIDS. The toxins' effect on the heart rate, arterial blood pressure, and breathing of anaesthetized rabbits was determined and their action compared to that of endotoxin. Intravenous injection of Clostridium perfringens enterotoxin and alpha-toxin, Staphylococcus enterotoxin B, Escherichia coli heat-stable toxin (STa), Clostridium difficile toxin A and B reduced heart rate, blood pressure, respiration and increased, slowed and prolonged thorax expansion, and at higher concentrations caused sudden death without visible stress or trauma. A combination of a low concentration of enterotoxins caused a greater reduction of these activities and sudden death. These effects were generally similar to those produced by endotoxin. In non-anaesthetized rabbits, the toxins slowed metabolism until death occurred without agitation, spasms, visible distress or prolonged illness. Intestinal production of these toxins by toxigenic strains, when conditions are suitable, and their systemic absorption, could therefore cause SIDS by an endotoxin-like shock mechanism.

Inhibition of neuromuscular transmission in isolated mouse phrenic nerve-diaphragm by the enterotoxin of Clostridium perfringens type A

The enterotoxin of Clostridium perfringens type A, a channel forming protein toxin, inhibited neuromuscular transmission under conditions of low calcium. Twitch tension of isolated phrenic nerve-diaphragm preparations elicited by electrical stimulations to the phrenic nerve was recorded isometrically, and the preparations were exposed to the purified enterotoxin. In Krebs solution containing 0.5 mM calcium, the enterotoxin (20 micrograms/ml) reduced within 10 min the amplitude of the twitch tension to 34 +/- 7% (mean +/- S.D., n = 11) of that recorded before the treatment. The effects of the enterotoxin on the twitch tension were irreversible and proceeded independently of stimulation. The reduction of the twitch tension by the enterotoxin was apparent in Krebs solution containing less than 0.6 mM calcium and the degree of reduction was inversely related to the concentration of calcium. The reduction of the twitch tension by the enterotoxin was also dependent on temperature and concentration of the toxin. At temperatures below 20 degrees C, no obvious reduction of twitch tension was observed with 20 micrograms/ml of the enterotoxin. Enterotoxin at a concentration of 0.4 micrograms/ml caused 16 +/- 2% (mean +/- S.D., n = 4) reduction of twitch tension, and the degree of the reduction in twitch tension increased with toxin concentration, reaching a plateau of 65 +/- 4% (mean +/- S.D., n = 7) at 6.5 micrograms/ml of the enterotoxin. The effects of the enterotoxin were antagonized by 2 microM physostigmine. Unlike curare, pretreatment of the preparation with enterotoxin did not antagonize the neuromuscular block by decamethonium. Neither the tension of muscular twitch elicited by direct electrical stimulation to the muscle nor the resting membrane potentials of muscle fibers recorded intracellularly were affected by the enterotoxin. The enterotoxin (2.2 micrograms/ml) reduced the frequency, but not mean amplitude or amplitude distribution, of miniature end-plate potentials, from 0.91 +/- 0.07/sec to 0.72 +/- 0.07 (mean +/- S.E., n = 5). The results suggest that the enterotoxin will provide a novel tool for the studies on the mechanism of the neuromuscular transmission because of the unique characteristics of the inhibition and of the known mechanism of its action on the cell membrane.