Host cell-induced signaling causes Clostridium perfringens to upregulate production of toxins important for intestinal infections

Enteritis necroticans and Clostridium perfringens type C; Epidemiological and pathological findings over the past 20 years

Enteritis necroticans (EN) in humans caused by infection with Clostridium perfringens type C, once thought limited to the highlands of Papua New Guinea has been identified sporadically worldwide. Outbreaks still occur among children in low-income countries and isolated cases occur among children and adults in other countries. Here the disease seems to be associated with diabetes mellitus and other risk factors. C. perfringens type C is also an important cause of necrotizing enteritis among animals, particularly pigs. Research into the pathogenesis of this disease has confirmed the central role of beta toxin and its target, the endothelial cell. Unlike most bacterial enteric infections, the primary anatomic location of EN is the proximal small intestine, reasons for which are not completely understood. Ongoing surveillance for C. perfringens type C infection is warranted as well as public health measures of prevention in locations where environmental and food hygiene is poor.

Clostridium perfringens in the Intestine: Innocent Bystander or Serious Threat?

The Clostridium perfringens epidemic threatens biosecurity and causes significant economic losses. C. perfringens infections are linked to more than one hundred million cases of food poisoning annually, and 8-60% of susceptible animals are vulnerable to infection, resulting in an economic loss of more than 6 hundred million USD. The enzymes and toxins (>20 species) produced by C. perfringens play a role in intestinal colonization, immunological evasion, intestinal micro-ecosystem imbalance, and intestinal mucosal disruption, all influencing host health. In recent decades, there has been an increase in drug resistance in C. perfringens due to antibiotic misuse and bacterial evolution. At the same time, traditional control interventions have proven ineffective, highlighting the urgent need to develop and implement new strategies and approaches to improve intervention targeting. Therefore, an in-depth understanding of the spatial and temporal evolutionary characteristics, transmission routes, colonization dynamics, and pathogenic mechanisms of C. perfringens will aid in the development of optimal therapeutic strategies and vaccines for C. perfringens management. Here, we review the global epidemiology of C. perfringens, as well as the molecular features and roles of various virulence factors in C. perfringens pathogenicity. In addition, we emphasize measures to prevent and control this zoonotic disease to reduce the transmission and infection of C. perfringens.

Targeting microbial quorum sensing: the next frontier to hinder bacterial driven gastrointestinal infections

Bacteria synchronize social behaviors via a cell-cell communication and interaction mechanism termed as quorum sensing (QS). QS has been extensively studied in monocultures and proved to be intensively involved in bacterial virulence and infection. Despite the role QS plays in pathogens during laboratory engineered infections has been proved, the potential functions of QS related to pathogenesis in context of microbial consortia remain poorly understood. In this review, we summarize the basic molecular mechanisms of QS, primarily focusing on pathogenic microbes driving gastrointestinal (GI) infections. We further discuss how GI pathogens disequilibrate the homeostasis of the indigenous microbial consortia, rebuild a realm dominated by pathogens, and interact with host under worsening infectious conditions via pathogen-biased QS signaling. Additionally, we present recent applications and main challenges of manipulating QS network in microbial consortia with the goal of better understanding GI bacterial sociality and facilitating novel therapies targeting bacterial infections.

Genomic Insights into Virulence Factors and Multi-Drug Resistance in Clostridium perfringens IRMC2505A

Clostridium perfringens is a spore-forming, Gram-positive anaerobic pathogen that causes several disorders in humans and animals. A multidrug-resistant Clostridium strain was isolated from the fecal sample of a patient who was clinically suspected of gastrointestinal infection and had a recent history of antibiotic exposure and diarrhea. The strain was identified by 16s rRNA sequencing as Clostridium perfringens. The strain's pathogenesis was analyzed through its complete genome, specifically antimicrobial resistance-related genes. The Clostridium perfringens IRMC2505A genome contains 19 (Alr, Ddl, dxr, EF-G, EF-Tu, folA, Dfr, folP, gyrA, gyrB, Iso-tRNA, kasA, MurA, rho, rpoB, rpoC, S10p, and S12p) antibiotic-susceptible genetic species according to the k-mer-based detection of antimicrobial resistance genes. Genome mapping using CARD and VFDB databases revealed significant (p-value = 1 × 10^-26) genes with aligned reads against antibiotic-resistant genes or virulence factors, including phospholipase C, perfringolysin O, collagenase, hyaluronidase, alpha-clostripain, exo-alpha-sialidase, and sialidase activity. In conclusion, this is the first report on C. perfringens from Saudi Arabia that conducted whole genome sequencing of IRMC2505A and confirmed the strain as an MDR bacterium with several virulence factors. Developing control strategies requires a detailed understanding of the epidemiology of C. perfringens, its virulence factors, and regional antimicrobial resistance patterns.

Epsilon toxin-producing Clostridium perfringens colonize the multiple sclerosis gut microbiome overcoming CNS immune privilege

Multiple sclerosis (MS) is a complex disease of the CNS thought to require an environmental trigger. Gut dysbiosis is common in MS, but specific causative species are unknown. To address this knowledge gap, we used sensitive and quantitative PCR detection to show that people with MS were more likely to harbor and show a greater abundance of epsilon toxin-producing (ETX-producing) strains of C. perfringens within their gut microbiomes compared with individuals who are healthy controls (HCs). Isolates derived from patients with MS produced functional ETX and had a genetic architecture typical of highly conjugative plasmids. In the active immunization model of experimental autoimmune encephalomyelitis (EAE), where pertussis toxin (PTX) is used to overcome CNS immune privilege, ETX can substitute for PTX. In contrast to PTX-induced EAE, where inflammatory demyelination is largely restricted to the spinal cord, ETX-induced EAE caused demyelination in the corpus callosum, thalamus, cerebellum, brainstem, and spinal cord, more akin to the neuroanatomical lesion distribution seen in MS. CNS endothelial cell transcriptional profiles revealed ETX-induced genes that are known to play a role in overcoming CNS immune privilege. Together, these findings suggest that ETX-producing C. perfringens strains are biologically plausible pathogens in MS that trigger inflammatory demyelination in the context of circulating myelin autoreactive lymphocytes.

LncRNA ALDB-898 modulates intestinal epithelial cell damage caused by Clostridium perfringens type C in piglet by regulating ssc-miR-122-5p/OCLN signaling

Diarrhea of piglets caused by Clostridium perfringens type C (C. perfringens type C) infection is a global problem afflicting piglet production. Long noncoding RNA (LncRNA) and microRNA (miRNA) have emerged as critical regulators of this pathological process, but the underlying molecular mechanisms remain unclear. In this study, we first observed the expression changes of ALDBSSCG0000000898 (ALDB-898) and ssc-miR-122-5p in infected ileum tissue of piglets with C. perfringens type C, and then used C. perfringens beta2 toxin (CPB2) to induce intestinal porcine epithelial cells (IPEC-J2) to construct an injury model. Cytometry kit 8 (CCK-8), lactate dehydrogenase (LDH), real-time quantitative polymerase chain reaction (RT-qPCR), Western blot, flow cytometry and fluorescein isothiocyanate-dextran 4 (FITC-Dextran 4) flux assays were performed to study the effect of ALDB-898 and ssc-miR-122-5p in apoptosis, inflammation and intestinal barrier damage and inflammatory in IPEC-J2 cells induced by CPB2. In addition, dual-luciferase reporter gene analysis was performed to confirm the relationship between ssc-miR-122-5p and ALDB-898 or ssc-miR-122-5p and occludin (OCLN), respectively. There were lower expression levels of ALDB-898 and OCLN and higher expression levels of ssc-miR-122-5p in diarrhea piglets caused by Clostridium perfringens type C. ALDB-898 and OCLN were significantly decreased and ssc-miR-122-5p was increased in IPEC-J2 after exposure to the CPB2 in a dose- and time-dependent manner. ALDB-898 overexpression mitigated CPB2-induced cell injury by promoting viability, restraining apoptosis, cytotoxicity, and inflammatory response, as well as weakening the destruction of the intestinal barrier. Further mechanisms disclosed that ALDB-898 functioned as a competing endogenous RNA (ceRNA) via binding to ssc-miR-122-5p, and OCLN was a target of ssc-miR-122-5p. Importantly, the ssc-miR-122-5p mimic led to abolishing the protective function of ALDB-898 on CPB2-induced IPEC-J2 cell damage, and the addition of OCLN reversed the negative impact of ssc-miR-122-5p, thereby restoring the protection of ALDB-898. Our data showed that ALDB-898 could enhance the expression of OCLN through competitive binding ssc-miR-122-5p to suppress CPB2-induced damage. The ALDB-898/ssc-miR-122-5p/OCLN signaling may be a candidate therapeutic pathway for diarrhea of piglets.

Expression, Purification, and Characterization of the Recombinant, Two-Component, Response Regulator ArlR from Fusobacterium nucleatum

Fusobacterium nucleatum is associated with the incidence and development of multiple diseases, such as periodontitis and colorectal cancer (CRC). Until now, studies have proved only a few proteins to be associated with such pathogenic diseases. The two-component system is one of the most prevalent forms of bacterial signal transduction related to intestinal diseases. Here, we report a novel, recombinant, two-component, response regulator protein ArlR from the genome of F. nucleatum strain ATCC 25,586. We optimized the expression and purification conditions of ArlR; in addition, we characterized the interaction of this response regulator protein with the corresponding histidine kinase and DNA sequence. The full-length ArlR was successfully expressed in six E. coli host strains. However, optimum expression conditions of ArlR were present only in E. coli strain BL21 CodonPlus (DE3) RIL that was later induced with isopropyl β-D-1-thiogalactopyranoside (IPTG) for 8 h at 25 °C. The SDS-PAGE analysis revealed the molecular weight of the recombinant protein as 27.3 kDa with approximately 90% purity after gel filtration chromatography. Because ArlR was biologically active after its purification, it accepted the corresponding phosphorylated histidine kinase phosphate group and bound to the analogous DNA sequence. The binding constant between ArlR and the corresponding histidine kinase was about 2.1 μM, whereas the binding constant between ArlR and its operon was 6.4 μM. Altogether, these results illustrate an effective expression and purification method for the novel two-component system protein ArlR.

Expression of α- and ε-toxin genes in Clostridium perfringens type D vaccine strain in contact with the Caco-2 cell line

BACKGROUND

Clostridium perfringens commonly resides in the gastrointestinal tract and can survive in different environmental conditions. This pathogen produces several protein toxins including the potent ε-toxin which is classified as a category B toxin by the Centers for Disease Control and Prevention (CDC). In several studies, the induction of C. perfringens type C or D to produce toxins much more rapidly by close contact of bacteria with Caco-2 cells has been reported.

AIMS

The effect of close contact of enterocyte-like Caco-2 cells with C. perfringens type D (vaccine strain) on the production time of ε- and α-toxins was studied.

METHODS

During C. perfringens type D contact with Caco-2 cells for 5 h, ε- and α-toxins expressions (at 0, 2, and 5 h) were evaluated by a quantitative real-time PCR assay. Non-contacted bacteria with cells were included as the negative control in this research.

RESULTS

Bacterial contact with the Caco-2 cells induces a significant effect on the mean expression of the ε-toxin gene (etx) (P<0.05). Two h after contact, the highest level of gene expression was detected in the experimental group. Bacterial harvesting time, cell treatment, and their interactions did not affect significantly the mean expression of the α-toxin gene (cpa) (P>0.05).

CONCLUSION

According to the findings of the present study, 2 h of bacterial contact with Caco-2 cells could stimulate etx gene expression in the C. perfringens type D vaccine strain.

Navarro M, Li J, Shrestha A, Uzal F, A. McClane B. Pathogenicity and virulence of Clostridium perfringens

Clostridium perfringens is an extremely versatile pathogen of humans and livestock, causing wound infections like gas gangrene (clostridial myonecrosis), enteritis/enterocolitis (including one of the most common human food-borne illnesses), and enterotoxemia (where toxins produced in the intestine are absorbed and damage distant organs such as the brain). The virulence of this Gram-positive, spore-forming, anaerobe is largely attributable to its copious toxin production; the diverse actions and roles in infection of these toxins are now becoming established. Most C. perfringens toxin genes are encoded on conjugative plasmids, including the pCW3-like and the recently discovered pCP13-like plasmid families. Production of C. perfringens toxins is highly regulated via processes involving two-component regulatory systems, quorum sensing and/or sporulation-related alternative sigma factors. Non-toxin factors, such as degradative enzymes like sialidases, are also now being implicated in the pathogenicity of this bacterium. These factors can promote toxin action in vitro and, perhaps in vivo, and also enhance C. perfringens intestinal colonization, e.g. NanI sialidase increases C. perfringens adherence to intestinal tissue and generates nutrients for its growth, at least in vitro. The possible virulence contributions of many other factors, such as adhesins, the capsule and biofilms, largely await future study.

Gossip in the gut: Quorum sensing, a new player in the host-microbiota interactions

Bacteria are known to communicate with each other and regulate their activities in social networks by secreting and sensing signaling molecules called autoinducers, a process known as quorum sensing (QS). This is a growing area of research in which we are expanding our understanding of how bacteria collectively modify their behavior but are also involved in the crosstalk between the host and gut microbiome. This is particularly relevant in the case of pathologies associated with dysbiosis or disorders of the intestinal ecosystem. This review will examine the different QS systems and the evidence for their presence in the intestinal ecosystem. We will also provide clues on the role of QS molecules that may exert, directly or indirectly through their bacterial gossip, an influence on intestinal epithelial barrier function, intestinal inflammation, and intestinal carcinogenesis. This review aims to provide evidence on the role of QS molecules in gut physiology and the potential shared by this new player. Better understanding the impact of intestinal bacterial social networks and ultimately developing new therapeutic strategies to control intestinal disorders remains a challenge that needs to be addressed in the future.

Evidence That VirS Is a Receptor for the Signaling Peptide of the Clostridium perfringens Agr-like Quorum Sensing System

C. perfringens beta toxin (CPB) is essential for the virulence of type C strains, a common cause of fatal necrotizing enteritis and enterotoxemia in humans and domestic animals. Production of CPB, as well as several other C. perfringens toxins, is positively regulated by both the Agr-like QS system and the VirS/R two-component regulatory system. This study presents evidence that the VirS membrane sensor protein is a receptor for the AgrD-derived SP and that the second extracellular loop of VirS is important for SP binding. Understanding interactions between SP and VirS improves knowledge of C. perfringens pathogenicity and may provide insights for designing novel strategies to reduce C. perfringens toxin production during infections.

Since both the Agr (accessory gene regulator)-like quorum sensing (QS) system and VirS/VirR (VirS/R) two-component regulatory system of Clostridium perfringens positively regulate production of several toxins, including C. perfringens beta toxin (CPB), it has been hypothesized the VirS membrane sensor protein is an Agr-like QS signaling peptide (SP) receptor. To begin evaluating whether VirS is an SP receptor, this study sequenced the virS gene in C. perfringens strains CN3685 and CN1795 because it was reported that agrB mutants of both strains increase CPB production in response to the pentapeptide 5R, likely the natural SP, but only the CN3685 agrB mutant responds to 8R, which is 5R plus a 3-amino-acid tail. This sequencing identified differences between the predicted VirS extracellular loop 2 (ECL2) of CN3685 versus that of CN1795. To explore if those ECL2 differences explain strain-related variations in SP sensitivity and support VirS as an SP receptor, virS agrB double-null mutants of each strain were complemented to swap which VirS protein they produce. CPB Western blotting showed that this complementation changed the natural responsiveness of each strain to 8R. A pulldown experiment using biotin-5R demonstrated that VirS can bind SP. To further support VirS:SP binding and to identify a VirS binding site for SP, a 14-mer peptide corresponding to VirS ECL2 was synthesized. This ECL2 peptide inhibited 5R signaling to agrB mutant and wild-type strains. This inhibition was specific, since a single N to D substitution in the ECL2 peptide abrogated these effects. Collectively, these results support VirS as an important SP receptor and may assist development of therapeutics.

Clostridium perfringens type C necrotic enteritis in pigs: diagnosis, pathogenesis, and prevention

Clostridium perfringens type C causes severe and lethal necrotic enteritis (NE) in newborn piglets. NE is diagnosed through a combination of pathology and bacteriologic investigations. The hallmark lesion of NE is deep, segmental mucosal necrosis with marked hemorrhage of the small intestine. C. perfringens can be isolated from intestinal samples in acute cases but it is more challenging to identify pathogenic strains in subacute-to-chronic cases. Toxinotyping or genotyping is required to differentiate C. perfringens type C from commensal type A strains. Recent research has extended our knowledge about the pathogenesis of the disease, although important aspects remain to be determined. The pathogenesis involves rapid overgrowth of C. perfringens type C in the small intestine, inhibition of beta-toxin (CPB) degradation by trypsin inhibitors in the colostrum of sows, and most likely initial damage to the small intestinal epithelial barrier. CPB itself acts primarily on vascular endothelial cells in the mucosa and can also inhibit platelet function. Prevention of the disease is achieved by immunization of pregnant sows with C. perfringens type C toxoid vaccines, combined with proper sanitation on farms. For the implementation of prevention strategies, it is important to differentiate between disease-free and pathogen-free status of a herd. The latter is more challenging to maintain, given that C. perfringens type C can persist for a long time in the environment and in the intestinal tract of adult animals and thus can be distributed via clinically and bacteriologically inapparent carrier animals.

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.

A sandwich duplex immuno PCR for rapid and sensitive identification of Clostridium perfringens alpha and enterotoxin

The prevalence and lethality associated with C. perfringens alpha (CPA) and enterotoxin (CPE) toxaemia necessitate the need for rapid and definitive detection systems to initiate management measures. In the present study, a sandwich duplex immuno-capture PCR (SD-IPCR) was developed by employing IgY antibodies against a bivalent protein r-Cpae derived from CPA and CPE for antigen capture and reporter antibodies against truncated CPA or CPE conjugated to oligomers of distinguishable size for antigen revealing and signal amplification. The avian immunoglobulin's (IgY) were devoid of reactivity with S. aureus protein A (SpA), a commensal that often co-exists with C. perfringens. The assay was specific, had a detection limit (LOD) of 1 pg/ml for both CPA and CPE in PBS and improved the LOD by 10⁴ folds compared to an analogous sandwich ELISA with same set of antibodies. In spiking studies, a ten-fold reduction in LOD was observed in case of intestinal tissue samples (10 pg/ml) however, no change in LOD was observed when SD-IPCR was applied on to faecal, serum or muscle tissue samples. Of the 136 natural samples examined, the SD-IPCR could detect CPA and CPE in 29.4% and 35.3% samples, while the sandwich ELISAs could detect the same in 25.7% and 25% samples respectively owing to the relatively lesser sensitivity. The LOD and specificity of the SD-IPCR demonstrates its applicability as an efficient and rapid platform for direct detection CPA and CPE from diverse samples matrices in clinical microbiological and meat testing laboratories.

Intestinal Microbiota as a Host Defense Mechanism to Infectious Threats

The intestinal microbiota is a complex microbial community, with diverse and stable populations hosted by the gastrointestinal tract since birth. This ecosystem holds multiple anti-infectious, anti-inflammatory, and immune modulating roles decisive for intestinal homeostasis. Among these, colonization resistance refers to the dynamic antagonistic interactions between commensals and pathogenic flora. Hence, gut bacteria compete for the same intestinal niches and substrates, while also releasing antimicrobial substances such as bacteriocines and changing the environmental conditions. Short chain fatty acids (SCFAs) generated in anaerobic conditions prompt epigenetic regulatory mechanisms that favor a tolerogenic immune response. In addition, the commensal flora is involved in the synthesis of bactericidal products, namely secondary biliary acids or antimicrobial peptides (AMPs) such as cathellicidin-LL37, an immunomodulatory, antimicrobial, and wound healing peptide. Gut microbiota is protected through symbiotic relations with the hosting organism and by quorum sensing, a specific cell-to-cell communication system. Any alterations of these relationships favor the uncontrollable multiplication of the resident pathobionts or external entero-pathogens, prompting systemic translocations, inflammatory reactions, or exacerbations of bacterial virulence mechanisms (T6SS, T3SS) and ultimately lead to gastrointestinal or systemic infections. The article describes the metabolic and immunological mechanisms through which the intestinal microbiota is both an ally of the organism against enteric pathogens and an enemy that favors the development of infections.

Metabolic dependent and independent pH-drop shuts down VirSR quorum sensing in Clostridium perfringens

Clostridium perfringens produces various exotoxins and enzymes that cause food poisoning and gas gangrene. The genes involved in virulence are regulated by the agr-like quorum sensing (QS) system, which consists of a QS signal synthesis system and a VirSR two-component regulatory system (VirSR TCS) which is a global regulatory system composed of signal sensor kinase (VirS) and response regulator (VirR). We found that the perfringolysin O gene (pfoA) was transiently expressed during mid-log phase of bacterial growth; its expression was rapidly shut down thereafter, suggesting the existence of a self-quorum quenching (sQQ) system. The sQQ system was induced by the addition of stationary phase culture supernatant (SPCS). Activity of the sQQ system was heat stable, and was present following filtration through the ultrafiltration membrane, suggesting that small molecules acted as sQQ agents. In addition, sQQ was also induced by pure acetic and butyric acids at concentrations equivalent to those in the stationary phase culture, suggesting that organic acids produced by C. perfringens were involved in sQQ. In pH-controlled batch culture, sQQ was greatly diminished; expression level of pfoA extended to late-log growth phase, and was eventually increased by one order of magnitude. Furthermore, hydrochloric acid induced sQQ at the same pH as was used in organic acids. SPCS also suppressed the expression of genes regulated by VirSR TCS. Overall, the expression of virulence factors of C. perfringens was downregulated by the sQQ system, which was mediated by primary acidic metabolites and acidic environments. This suggested the possibility of pH-controlled anti-virulence strategies.

Role of vitamin D on gut microbiota in cystic fibrosis

This review explores the potential for vitamin D to favorably alter the gut microbiota, given emerging evidence of the role of vitamin D in controlling mucosal inflammation in the gut. It will focus on cystic fibrosis (CF) patients, a population with both vitamin D deficiency due to gut malabsorption and an altered gut microbiota composition. Recent evidence shows that vitamin D acts to maintain the integrity of the gut mucosal barrier by enhancement of intercellular junctions that control mucosal permeability and reduction of pro-inflammatory cytokines such as IL-8. In addition, vitamin D receptor-mediated signaling has been shown to inhibit inflammation-induced apoptosis of intestinal epithelial cells. As a result of these effects on the intestinal mucosa, maintenance of sufficient vitamin D status may be essential for the development of a healthy gut microbiota, particularly in conditions defined by chronic mucosal inflammation such as CF. We hypothesize here that high dose vitamin D may be used to favorably manipulate the aberrant mucosa seen in patients with CF. This may result in improved clinical outcomes in association with a low inflammatory environment that allows beneficial bacteria to outcompete opportunistic pathogens. Current evidence is sparse but encouraging, and additional evidence is needed to establish vitamin D as a therapeutic approach for gut microbiota modification.

Effect of Clostridium perfringens β-Toxin on Platelets

Clostridium perfringensβ-toxin (CPB) is the major virulence factor of C.perfringens type C causing a hemorrhagic enteritis in animals and humans. In experimentally infected pigs, endothelial binding of CPB was shown to be associated with early vascular lesions and hemorrhage but without obvious thrombosis of affected vessels, suggesting altered hemostasis in the early phase of the disease. The objective of the present study was to investigate the effect of CPB on platelets, with respect to primary hemostasis. Our results demonstrate that CPB binds to porcine and human platelets and forms oligomers resulting in a time- and dose-dependent cell death. Platelets showed rapid ultrastructural changes, significantly decreased aggregation and could no longer be activated by thrombin. This indicates that CPB affects the physiological function of platelets and counteracts primary hemostasis. Our results add platelets to the list of target cells of CPB and extend the current hypothesis of its role in the pathogenesis of C. perfringens type C enteritis.

The Agr-Like Quorum Sensing System Is Required for Pathogenesis of Necrotic Enteritis Caused by Clostridium perfringens in Poultry

Clostridium perfringens encodes at least two different quorum sensing (QS) systems, the Agr-like and LuxS, and recent studies have highlighted their importance in the regulation of toxin production and virulence. The role of QS in the pathogenesis of necrotic enteritis (NE) in poultry and the regulation of NetB, the key toxin involved, has not yet been investigated. We have generated isogenic agrB-null and complemented strains from parent strain CP1 and demonstrated that the virulence of the agrB-null mutant was strongly attenuated in a chicken NE model system and restored by complementation. The production of NetB, a key NE-associated toxin, was dramatically reduced in the agrB mutant at both the transcriptional and protein levels, though not in a luxS mutant. Transwell assays confirmed that the Agr-like QS system controls NetB production through a diffusible signal. Global gene expression analysis of the agrB mutant identified additional genes modulated by Agr-like QS, including operons related to phospholipid metabolism and adherence, which may also play a role in NE pathogenesis. This study provides the first evidence that the Agr-like QS system is critical for NE pathogenesis and identifies a number of Agr-regulated genes, most notably netB, that are potentially involved in mediating its effects. The Agr-like QS system thus may serve as a target for developing novel interventions to prevent NE in chickens.

Rethinking the role of alpha toxin in Clostridium perfringens-associated enteric diseases: a review on bovine necro-haemorrhagic enteritis

Bovine necro-haemorrhagic enteritis is an economically important disease caused by Clostridium perfringens type A strains. The disease mainly affects calves under intensive rearing conditions and is characterized by sudden death associated with small intestinal haemorrhage, necrosis and mucosal neutrophil infiltration. The common assumption that, when causing intestinal disease, C. perfringens relies upon specific, plasmid-encoded toxins, was recently challenged by the finding that alpha toxin, which is produced by all C. perfringens strains, is essential for necro-haemorrhagic enteritis. In addition to alpha toxin, other C. perfringens toxins and/or enzymes might contribute to the pathogenesis of necro-haemorrhagic enteritis. These additional virulence factors might contribute to breakdown of the protective mucus layer during initial stage of pathogenesis, after which alpha toxin, either or not in synergy with other toxins such as perfringolysin O, can act on the mucosal tissue. Furthermore, alpha toxin alone does not cause intestinal necrosis, indicating that other virulence factors might be needed to cause the extensive tissue necrosis observed in necro-haemorrhagic enteritis. This review summarizes recent research that has increased our understanding of the pathogenesis of bovine necro-haemorrhagic enteritis and provides information that is indispensable for the development of novel control strategies, including vaccines.

Regulation of Toxin Production in Clostridium perfringens

The Gram-positive anaerobic bacterium Clostridium perfringens is widely distributed in nature, especially in soil and the gastrointestinal tracts of humans and animals. C. perfringens causes gas gangrene and food poisoning, and it produces extracellular enzymes and toxins that are thought to act synergistically and contribute to its pathogenesis. A complicated regulatory network of toxin genes has been reported that includes a two-component system for regulatory RNA and cell-cell communication. It is necessary to clarify the global regulatory system of these genes in order to understand and treat the virulence of C. perfringens. We summarize the existing knowledge about the regulatory mechanisms here.

Lack of Vitamin D Receptor Causes Dysbiosis and Changes the Functions of the Murine Intestinal Microbiome

PURPOSE

The microbiome modulates numerous aspects of human physiology and is a crucial factor in the development of various human diseases. Vitamin D deficiency and downregulation of the vitamin D receptor (VDR) are also associated with the pathogenesis of diseases such as inflammatory bowel disease, cancers, obesity, diabetes, and asthma. VDR is a nuclear receptor that regulates the expression of antimicrobial peptides and autophagy regulator ATG16L1. Vitamin D may promote a balanced intestinal microbiome and improve glucose homeostasis in diabetes. However, how VDR regulates microbiome is not well known. In the current study, we hypothesize that VDR status regulates the composition and functions of the intestinal bacterial community.

METHODS

Fecal and cecal stool samples were harvested from Vdr knockout (Vdr(-/-)) and wild-type mice for bacterial DNA and then sequenced with 454 pyrosequencing. The sequences were denoised and clustered into operational taxonomic units, then queried against the National Center for Biotechnology Information database. Metagenomics were analyzed, and the abundances of genes involved in metabolic pathways were compared by reference to the Kyoto Encyclopedia of Genes and Genomes and Clusters of Orthologous Groups databases.

FINDINGS

In the Vdr(-/-) mice, Lactobacillus was depleted in the fecal stool, whereas Clostridium and Bacteroides were enriched. Bacterial taxa along the Sphingobacteria-to-Sphingobacteriaceae lineage were enriched, but no genera reached statistical significance. In the cecal stool, Alistipes and Odoribacter were depleted, and Eggerthella was enriched. Notably, all of the taxa upstream of Eggerthella remained unchanged. A comparison of Vdr(-/-) and wild-type samples revealed 40 (26 enriched, 14 depleted) and 72 (41 enriched, 31 depleted) functional modules that were significantly altered in the cecal and fecal microbiomes, respectively (both, P < 0.05), due to the loss of Vdr. In addition to phylogenetic differences in gut microbiome with different intestinal origins, we identify several important pathways, such as nucleotide-binding oligomerization domain-like receptor, affected by Vdr status, including amino acid, carbohydrate, and fatty acid synthesis and metabolism, detoxification, infections, signal transduction, and cancer and other diseases.

IMPLICATIONS

Our study fills knowledge gaps by having investigated the microbial profile affected by VDR. Insights from our findings can be exploited to develop novel strategies to treat or prevent various diseases by restoring VDR function and healthy microbe-host interactions.

The Myelin and Lymphocyte Protein MAL Is Required for Binding and Activity of Clostridium perfringens ε-Toxin

Clostridium perfringens ε-toxin (ETX) is a potent pore-forming toxin responsible for a central nervous system (CNS) disease in ruminant animals with characteristics of blood-brain barrier (BBB) dysfunction and white matter injury. ETX has been proposed as a potential causative agent for Multiple Sclerosis (MS), a human disease that begins with BBB breakdown and injury to myelin forming cells of the CNS. The receptor for ETX is unknown. Here we show that both binding of ETX to mammalian cells and cytotoxicity requires the tetraspan proteolipid Myelin and Lymphocyte protein (MAL). While native Chinese Hamster Ovary (CHO) cells are resistant to ETX, exogenous expression of MAL in CHO cells confers both ETX binding and susceptibility to ETX-mediated cell death. Cells expressing rat MAL are ~100 times more sensitive to ETX than cells expressing similar levels of human MAL. Insertion of the FLAG sequence into the second extracellular loop of MAL abolishes ETX binding and cytotoxicity. ETX is known to bind specifically and with high affinity to intestinal epithelium, renal tubules, brain endothelial cells and myelin. We identify specific binding of ETX to these structures and additionally show binding to retinal microvasculature and the squamous epithelial cells of the sclera in wild-type mice. In contrast, there is a complete absence of ETX binding to tissues from MAL knockout (MAL-/-) mice. Furthermore, MAL-/- mice exhibit complete resistance to ETX at doses in excess of 1000 times the symptomatic dose for wild-type mice. We conclude that MAL is required for both ETX binding and cytotoxicity.

Characterization of Clostridium perfringens TpeL toxin gene carriage, production, cytotoxic contributions, and trypsin sensitivity

Large clostridial toxins (LCTs) are produced by at least four pathogenic clostridial species, and several LCTs are proven pivotal virulence factors for both human and veterinary diseases. TpeL is a recently identified LCT produced by Clostridium perfringens that has received relatively limited study. In response, the current study surveyed carriage of the tpeL gene among different C. perfringens strains, detecting this toxin gene in some type A, B, and C strains but not in any type D or E strains. This study also determined that all tested strains maximally produce, and extracellularly release, TpeL at the late-log or early-stationary growth stage during in vitro culture, which is different from the maximal late-stationary-phase production reported previously for other LCTs and for TpeL production by C. perfringens strain JIR12688. In addition, the present study found that TpeL levels in culture supernatants can be repressed by either glucose or sucrose. It was also shown that, at natural production levels, TpeL is a significant contributor to the cytotoxic activity of supernatants from cultures of tpeL-positive strain CN3685. Lastly, this study identified TpeL, which presumably is produced in the intestines during diseases caused by TpeL-positive type B and C strains, as a toxin whose cytotoxicity decreases after treatment with trypsin; this finding may have pathophysiologic relevance by suggesting that, like beta toxin, TpeL contributes to type B and C infections in hosts with decreased trypsin levels due to disease, diet, or age.

Structure-function analysis of peptide signaling in the Clostridium perfringens Agr-like quorum sensing system

The accessory growth regulator (Agr)-like quorum sensing (QS) system of Clostridium perfringens controls the production of many toxins, including beta toxin (CPB). We previously showed (J. E. Vidal, M. Ma, J. Saputo, J. Garcia, F. A. Uzal, and B. A. McClane, Mol Microbiol 83:179-194, 2012, http://dx.doi.org/10.1111/j.1365-2958.2011.07925.x) that an 8-amino-acid, AgrD-derived peptide named 8-R upregulates CPB production by this QS system. The current study synthesized a series of small signaling peptides corresponding to sequences within the C. perfringens AgrD polypeptide to investigate the C. perfringens autoinducing peptide (AIP) structure-function relationship. When both linear and cyclic ring forms of these peptides were added to agrB null mutants of type B strain CN1795 or type C strain CN3685, the 5-amino-acid peptides, whether in a linear or ring (thiolactone or lactone) form, induced better signaling (more CPB production) than peptide 8-R for both C. perfringens strains. The 5-mer thiolactone ring peptide induced faster signaling than the 5-mer linear peptide. Strain-related variations in sensing these peptides were detected, with CN3685 sensing the synthetic peptides more strongly than CN1795. Consistent with those synthetic peptide results, Transwell coculture experiments showed that CN3685 exquisitely senses native AIP signals from other isolates (types A, B, C, and D), while CN1795 barely senses even its own AIP. Finally, a C. perfringens AgrD sequence-based peptide with a 6-amino-acid thiolactone ring interfered with CPB production by several C. perfringens strains, suggesting potential therapeutic applications. These results indicate that AIP signaling sensitivity and responsiveness vary among C. perfringens strains and suggest C. perfringens prefers a 5-mer AIP to initiate Agr signaling.

IMPORTANCE

Clostridium perfringens possesses an Agr-like quorum sensing (QS) system that regulates virulence, sporulation, and toxin production. The current study used synthetic peptides to identify the structure-function relationship for the signaling peptide that activates this QS system. We found that a 5-mer peptide induces optimal signaling. Unlike other Agr systems, a linear version of this peptide (in addition to thiolactone and lactone versions) could induce signaling. Two C. perfringens strains were found to vary in sensitivity to these peptides. We also found that a 6-mer peptide can inhibit toxin production by some strains, suggesting therapeutic applications.

Towards an understanding of the role of Clostridium perfringens toxins in human and animal disease

Clostridium perfringens uses its arsenal of >16 toxins to cause histotoxic and intestinal infections in humans and animals. It has been unclear why this bacterium produces so many different toxins, especially since many target the plasma membrane of host cells. However, it is now established that C. perfringens uses chromosomally encoded alpha toxin (a phospholipase C) and perfringolysin O (a pore-forming toxin) during histotoxic infections. In contrast, this bacterium causes intestinal disease by employing toxins encoded by mobile genetic elements, including C. perfringens enterotoxin, necrotic enteritis toxin B-like, epsilon toxin and beta toxin. Like perfringolysin O, the toxins with established roles in intestinal disease form membrane pores. However, the intestinal disease-associated toxins vary in their target specificity, when they are produced (sporulation vs vegetative growth), and in their sensitivity to intestinal proteases. Producing many toxins with diverse characteristics likely imparts virulence flexibility to C. perfringens so it can cause an array of diseases.