Fatal pseudomembranous colitis associated with a variant clostridium difficile strain not detected by toxin A immunoassay

The Current Knowledge on Clostridioides difficile Infection in Patients with Inflammatory Bowel Diseases

Clostridioides difficile (C. difficile) represents a major health burden with substantial economic and clinical impact. Patients with inflammatory bowel diseases (IBD) were identified as a risk category for Clostridioides difficile infection (CDI). In addition to traditional risk factors for C. difficile acquisition, IBD-specific risk factors such as immunosuppression, severity and extension of the inflammatory disease were identified. C. difficile virulence factors, represented by both toxins A and B, induce the damage of the intestinal mucosa and vascular changes, and promote the inflammatory host response. Given the potential life-threatening complications, early diagnostic and therapeutic interventions are required. The screening for CDI is recommended in IBD exacerbations, and the diagnostic algorithm consists of clinical evaluation, enzyme immunoassays (EIAs) or nucleic acid amplification tests (NAATs). An increased length of hospitalization, increased colectomy rate and mortality are the consequences of concurrent CDI in IBD patients. Selection of CD strains of higher virulence, antibiotic resistance, and the increasing rate of recurrent infections make the management of CDI in IBD more challenging. An individualized therapeutic approach is recommended to control CDI as well as IBD flare. Novel therapeutic strategies have been developed in recent years in order to manage severe, refractory or recurrent CDI. In this article, we aim to review the current evidence in the field of CDI in patients with underlying IBD, pointing to pathogenic mechanisms, risk factors for infection, diagnostic steps, clinical impact and outcomes, and specific management.

The Relative Role of Toxins A and B in the Virulence of Clotridioides difficile

Most pathogenic strains of C. difficile possess two large molecular weight single unit toxins with four similar functional domains. The toxins disrupt the actin cytoskeleton of intestinal epithelial cells leading to loss of tight junctions, which ultimately manifests as diarrhea in the host. While initial studies of purified toxins in animal models pointed to toxin A (TcdA) as the main virulence factor, animal studies using isogenic mutants demonstrated that toxin B (TcdB) alone was sufficient to cause disease. In addition, the natural occurrence of TcdA−/TcdB+ (TcdA−/B+)mutant strains was shown to be responsible for cases of C. difficile infection (CDI) with symptoms identical to CDI caused by fully toxigenic (A+/B+) strains. Identification of these cases was delayed during the period when clinical laboratories were using immunoassays that only detected TcdA (toxA EIA). Our hospital laboratory at the time performed culture as well as toxA EIA on patient stool samples. A total of 1.6% (23/1436) of all clinical isolates recovered over a 2.5-year period were TcdA−/B+ variants, the majority of which belonged to the restriction endonuclease analysis (REA) group CF and toxinotype VIII. Despite reports of serious disease due to TcdA−/B+ CF strains, these infections were typically mild, often not requiring specific treatment. While TcdB alone may be sufficient to cause disease, clinical evidence suggests that both toxins have a role in disease.

Clostridium Difficile Infection in Inflammatory Bowel Disease Patients

BACKGROUND

The rising incidence of Clostridium difficile infection (CDI) in the general population has been recognized by health care organizations worldwide. The emergence of hypervirulent strains has made CDI more challenging to understand and treat. Inflammatory bowel disease (IBD) patients are at higher risk of infection, including CDI.

OBJECTIVE

A diagnostic approach for recurrent CDI has yet to be validated, particularly for IBD patients. Enzyme immunoassay (EIA) for toxins A and B, as well as glutamate dehydrogenase EIA, are both rapid testing options for the identification of CDI. Without a high index of suspicion, it is challenging to initially differentiate CDI from an IBD flare based on clinical evaluation alone.

METHODS

Here, we provide an up-to-date review on CDI in IBD patients. When caring for an IBD patient with suspected CDI, it is appropriate to empirically treat the presumed infection while awaiting further test results.

RESULTS

Treatment with vancomycin or fidaxomicin, but not oral metronidazole, has been advocated by an expert review from the clinical practice update committee of the American Gastroenterology Association. Recurrent CDI is more common in IBD patients compared to non-IBD patients (32% versus 24%), thus more aggressive treatment is recommended for IBD patients along with early consideration of fecal microbiota transplant.

CONCLUSION

Although the use of infliximab during CDI has been debated, clinical experience exists supporting its use in an IBD flare, even with active CDI when needed.

Clostridium difficile ribotype 017 - characterization, evolution and epidemiology of the dominant strain in Asia

Clostridium difficile ribotype (RT) 017 is an important toxigenic C. difficile RT which, due to a deletion in the repetitive region of the tcdA gene, only produces functional toxin B. Strains belonging to this RT were initially dismissed as nonpathogenic and circulated largely undetected for almost two decades until they rose to prominence following a series of outbreaks in the early 2000s. Despite lacking a functional toxin A, C. difficile RT 017 strains have been shown subsequently to be capable of causing disease as severe as that caused by strains producing both toxins A and B. While C. difficile RT 017 strains can be found in almost every continent today, epidemiological studies suggest that the RT is endemic in Asia and that the global spread of this MLST clade 4 lineage member is a relatively recent event. C. difficile RT 017 transmission appears to be mostly from human to human with only a handful of reports of isolations from animals. An important feature of C. difficile RT 017 strains is their resistance to several antimicrobials and this has been documented as a possible factor driving multiple outbreaks in different parts of the world. This review summarizes what is currently known regarding the emergence and evolution of strains belonging to C. difficile RT 017 as well as features that have allowed it to become an RT of global importance.

Clostridium difficile infection in inflammatory bowel disease: challenges in diagnosis and treatment

The problem of Clostridium difficile infection (CDI) has reached epidemic proportions, particularly in industrialized nations. The pathophysiology, disease course and the potential complications are well appreciated in the general hospitalized patient. However, when CDI occurs in the setting of inflammatory bowel disease (IBD), a number of distinct differences in the diagnosis and clinical management of the infection in this population should be appreciated by gastroenterologists, hospitalists and other care providers. This review highlights the unique aspects of CDI when it occurs in IBD patients with an emphasis on the challenge of distinguishing persistent infection from exacerbation of underlying chronic colitis. An understanding of how CDI may differ in presentation and how management should be altered can prevent serious and life-threatening complications.

Clostridium difficile Toxins A and B: Insights into Pathogenic Properties and Extraintestinal Effects

Clostridium difficile infection (CDI) has significant clinical impact especially on the elderly and/or immunocompromised patients. The pathogenicity of Clostridium difficile is mainly mediated by two exotoxins: toxin A (TcdA) and toxin B (TcdB). These toxins primarily disrupt the cytoskeletal structure and the tight junctions of target cells causing cell rounding and ultimately cell death. Detectable C. difficile toxemia is strongly associated with fulminant disease. However, besides the well-known intestinal damage, recent animal and in vitro studies have suggested a more far-reaching role for these toxins activity including cardiac, renal, and neurologic impairment. The creation of C. difficile strains with mutations in the genes encoding toxin A and B indicate that toxin B plays a major role in overall CDI pathogenesis. Novel insights, such as the role of a regulator protein (TcdE) on toxin production and binding interactions between albumin and C. difficile toxins, have recently been discovered and will be described. Our review focuses on the toxin-mediated pathogenic processes of CDI with an emphasis on recent studies.

Ultrasensitive Detection and Quantification of Toxins for Optimized Diagnosis of Clostridium difficile Infection

Recently developed ultrasensitive and quantitative methods for detection of Clostridium difficile toxins provide new tools for diagnosis and, potentially, for management of C. difficile infection (CDI). Compared to methods that detect toxigenic organism, ultrasensitive toxin detection may allow diagnosis of CDI with increased clinical specificity, without sacrificing clinical sensitivity; measurement of toxin levels may also provide information relevant to disease prognosis. This minireview provides an overview of these new toxin detection technologies and considers what these new tools might add to the field.

Defective mutations within the translocation domain of Clostridium difficile toxin B impair disease pathogenesis

The Clostridium difficile toxin B is one of the main virulence factors and plays an important role in the pathogenesis of C. difficile infection (CDI). We recently revealed crucial residues in the translocation domain of TcdB for the pore formation and toxin translocation. In this study, we investigated the effects of mutating a critical site involved in pore formation, Leu-1106, to residues that differ in size and polarity (Phe, Ala, Cys, Asp). We observed a broad range of effects on TcdB function in vitro consistent with the role of this site in pore formation and translocation. We show that mice challenged systemically with a lethal dose (LD100) of the most defective mutant (L1106K) showed no symptoms of disease highlighting the importance of this residue and the translocation domain in disease pathogenesis. These findings offer insights into the structure function of the toxin translocation pore, and inform novel therapeutic strategies against CDI.

Immune-based treatment and prevention of Clostridium difficile infection

Clostridium difficile (C. difficile) causes over 500,000 infections per year in the US, with an estimated 15,000 deaths and an estimated cost of $1-3 billion. Moreover, a continual rise in the incidence of severe C. difficile infection (CDI) has been observed worldwide. Currently, standard treatment for CDI is the administration of antibiotics. While effective, these treatments do not prevent and may contribute to a disease recurrence rate of 15-35%. Prevention of recurrence is one of the most challenging aspects in the field. A better knowledge of the molecular mechanisms of the disease, the host immune response and identification of key virulence factors of C. difficilenow permits the development of immune-based therapies. Antibodies specific for C. difficile toxins have been shown to effectively treat CDI and prevent disease relapse in animal models and in humans. Vaccination has been recognized as the most cost-effective treatment/prevention for CDI. This review will summarize CDI transmission, epidemiology, major virulent factors and highlights the rational and the development of immune-based approaches against this remerging threat.

Community-acquired Clostridium difficile infection in children: A retrospective study

BACKGROUND

Community acquired-Clostridium difficile infection (CDI) has increased also in children in the last years.

AIMS

To determine the incidence of community-acquired CDI and to understand whether Clostridium difficile could be considered a symptom-triggering pathogen in infants.

METHODS

A five-year retrospective analysis (January 2007-December 2011) of faecal specimens from 124 children hospitalized in the Niguarda Ca' Granda Hospital for prolonged or muco-haemorrhagic diarrhoea was carried out. Stool samples were evaluated for common infective causes of diarrhoea and for Clostridium difficile toxins. Patients with and without CDI were compared for clinical characteristics and known risk factors for infection.

RESULTS

Twenty-two children with CDI were identified in 5 years. An increased incidence of community-acquired CDI was observed, ranging from 0.75 per 1000 hospitalizations in 2007 to 9.8 per 1000 hospitalizations in 2011. Antimicrobial treatment was successful in all 19 children in whom it was administered; 8/22 CDI-positive children were younger than 2 years. No statistically significant differences in clinical presentation were observed between patients with and without CDI, nor in patients with and without risk factors for CDI.

CONCLUSIONS

Our study shows that Clostridium difficile infection is increasing and suggests a possible pathogenic role in the first 2 years of life.

A chimeric protein comprising the glucosyltransferase and cysteine proteinase domains of toxin B and the receptor binding domain of toxin A induces protective immunity against Clostridium difficile infection in mice and hamsters

Clostridium difficile is the major cause of hospital-acquired infectious diarrhea and colitis in developed countries. The pathogenicity of C. difficile is mainly mediated by the release of 2 large potent exotoxins, toxin A (TcdA) and toxin B (TcdB), both of which require neutralization to prevent disease occurrence. We have generated a novel chimeric protein, designated mTcd138, comprised of the glucosyltransferase and cysteine proteinase domains of TcdB and the receptor binding domain of TcdA and expressed it in Bacillus megaterium. To ensure that mTcd138 is atoxic, 2 point mutations were introduced to the glucosyltransferase domain of TcdB, which essentially eliminates toxicity of mTcd138. Parenteral immunizations of mice and hamsters with mTcd138 induced protective antibodies to both toxins and provided protection against infection with the hyper-virulent C. difficile strain UK6.

Identification of toxemia in patients with Clostridium difficile infection

Toxemia can develop in Clostridium difficile-infected animals, and correlates with severe and fulminant disease outcomes. Circumstantial evidence suggests that toxemia may occur in patients with C. difficile infection (CDI), but positive diagnosis is extremely rare. We analyzed the potential for C. difficile toxemia in patients, determined its characteristics, and assessed challenges. C. difficile toxins in serum from patients were tested using an ultrasensitive cell-based assay and further confirmed by Rac1 glucosylation assay. The factors that hinder a diagnosis of toxemia were assessed, including investigation of toxin stability, the level of toxins-specific neutralizing antibodies in sera and its effect on diagnosis limits. CDI patients develop detectable toxemia in some cases (2.3%). Toxins were relatively stable in stored sera. Neutralizing anti-toxin antibodies were present during infection and positively correlated with the diagnosis limits. Thus, the masking effect of toxin-specific neutralizing antibodies is the major obstacle in diagnosing C. difficile toxemia using cell-based bioassays.

The prospect for vaccines to prevent Clostridium difficile infection

Clostridium difficile is a spore-forming anaerobic gram-positive organism that is the leading cause of antibiotic-associated nosocomial infectious diarrhea in the Western world. This article describes the evolving epidemiology of C difficile infection (CDI) in the twenty-first century, evaluates the importance of vaccines against the disease, and defines the roles of both innate and adaptive host immune responses in CDI. The effects of passive immunotherapy and active vaccination against CDI in both humans and animals are also discussed.

Clinical Practice Guidelines for Clostridium difficile Infection in Adults: 2010 Update by the Society for Healthcare Epidemiology of America (SHEA) and the Infectious Diseases Society of America (IDSA)

Since publication of the Society for Healthcare Epidemiology of America position paper onClostridium difficileinfection in 1995, significant changes have occurred in the epidemiology and treatment of this infection.C. difficileremains the most important cause of healthcare-associated diarrhea and is increasingly important as a community pathogen. A more virulent strain ofC. difficilehas been identified and has been responsible for more-severe cases of disease worldwide. Data reporting the decreased effectiveness of metronidazole in the treatment of severe disease have been published. Despite the increasing quantity of data available, areas of controversy still exist. This guideline updates recommendations regarding epidemiology, diagnosis, treatment, and infection control and environmental management.

Clostridium difficile infection: molecular pathogenesis and novel therapeutics

The Gram-positive anaerobic bacterium Clostridium difficile produces toxins A and B, which can cause a spectrum of diseases from pseudomembranous colitis to C. difficile-associated diarrhea. A limited number of C. difficile strains also produce a binary toxin that exhibits ADP ribosyltransferase activity. Here, the structure and the mechanism of action of these toxins as well as their role in disease are reviewed. Nosocomial C. difficile infection is often contracted in hospital when patients treated with antibiotics suffer a disturbance in normal gut microflora. C. difficile spores can persist on dry, inanimate surface for months. Metronidazole and oral vancomycin are clinically used for treatment of C. difficile infection but clinical failure and concern about promotion of resistance are motivating the search for novel non-antibiotic therapeutics. Methods for controlling both toxins and spores, replacing gut microflora by probiotics or fecal transplant, and killing bacteria in the anaerobic gut by photodynamic therapy are discussed.

An optimized, synthetic DNA vaccine encoding the toxin A and toxin B receptor binding domains of Clostridium difficile induces protective antibody responses in vivo

Clostridium difficile-associated disease (CDAD) constitutes a large majority of nosocomial diarrhea cases in industrialized nations and is mediated by the effects of two secreted toxins, toxin A (TcdA) and toxin B (TcdB). Patients who develop strong antitoxin antibody responses can clear C. difficile infection and remain disease free. Key toxin-neutralizing epitopes have been found within the carboxy-terminal receptor binding domains (RBDs) of TcdA and TcdB, which has generated interest in developing the RBD as a viable vaccine target. While numerous platforms have been studied, very little data describes the potential of DNA vaccination against CDAD. Therefore, we created highly optimized plasmids encoding the RBDs from TcdA and TcdB in which any putative N-linked glycosylation sites were altered. Mice and nonhuman primates were immunized intramuscularly, followed by in vivo electroporation, and in these animal models, vaccination induced significant levels of both anti-RBD antibodies (blood and stool) and RBD-specific antibody-secreting cells. Further characterization revealed that sera from immunized mice and nonhuman primates could detect RBD protein from transfected cells, as well as neutralize purified toxins in an in vitro cytotoxicity assay. Mice that were immunized with plasmids or given nonhuman-primate sera were protected from a lethal challenge with purified TcdA and/or TcdB. Moreover, immunized mice were significantly protected when challenged with C. difficile spores from homologous (VPI 10463) and heterologous, epidemic (UK1) strains. These data demonstrate the robust immunogenicity and efficacy of a TcdA/B RBD-based DNA vaccine in preclinical models of acute toxin-associated and intragastric, spore-induced colonic disease.

Variations in virulence and molecular biology among emerging strains of Clostridium difficile

Clostridium difficile is a Gram-positive, spore-forming organism which infects and colonizes the large intestine, produces potent toxins, triggers inflammation, and causes significant systemic complications. Treating C. difficile infection (CDI) has always been difficult, because the disease is both caused and resolved by antibiotic treatment. For three and a half decades, C. difficile has presented a treatment challenge to clinicians, and the situation took a turn for the worse about 10 years ago. An increase in epidemic outbreaks related to CDI was first noticed around 2003, and these outbreaks correlated with a sudden increase in the mortality rate of this illness. Further studies discovered that these changes in CDI epidemiology were associated with the rapid emergence of hypervirulent strains of C. difficile, now collectively referred to as NAP1/BI/027 strains. The discovery of new epidemic strains of C. difficile has provided a unique opportunity for retrospective and prospective studies that have sought to understand how these strains have essentially replaced more historical strains as a major cause of CDI. Moreover, detailed studies on the pathogenesis of NAP1/BI/027 strains are leading to new hypotheses on how this emerging strain causes severe disease and is more commonly associated with epidemics. In this review, we provide an overview of CDI, discuss critical mechanisms of C. difficile virulence, and explain how differences in virulence-associated factors between historical and newly emerging strains might explain the hypervirulence exhibited by this pathogen during the past decade.

Replenishing our defensive microbes

Large-scale characterization of the human microbiota has largely focused on Western adults, yet these populations may be uncharacteristic because of their diets and lifestyles. In particular, the rise of "Western diseases" may in part stem from reduced exposure to, or even loss of, microbes with which humans have coevolved. Here, we review beneficial microbes associated with pathogen resistance, highlighting the emerging role of complex microbial communities in protecting against disease. We discuss ways in which modern lifestyles and practices may deplete physiologically important microbiota, and explore prospects for reintroducing or encouraging the growth of beneficial microbes to promote the restoration of healthy microbial ecosystems.

Protective efficacy induced by recombinant Clostridium difficile toxin fragments

Clostridium difficile is a spore-forming bacterium that can reside in animals and humans. C. difficile infection causes a variety of clinical symptoms, ranging from diarrhea to fulminant colitis. Disease is mediated by TcdA and TcdB, two large enterotoxins released by C. difficile during colonization of the gut. In this study, we evaluated the ability of recombinant toxin fragments to induce neutralizing antibodies in mice. The protective efficacies of the most promising candidates were then evaluated in a hamster model of disease. While limited protection was observed with some combinations, coadministration of a cell binding domain fragment of TcdA (TcdA-B1) and the glucosyltransferase moiety of TcdB (TcdB-GT) induced systemic IgGs which neutralized both toxins and protected vaccinated animals from death following challenge with two strains of C. difficile. Further characterization revealed that despite high concentrations of toxin in the gut lumens of vaccinated animals during the acute phase of the disease, pathological damage was minimized. Assessment of gut contents revealed the presence of TcdA and TcdB antibodies, suggesting that systemic vaccination with this pair of recombinant polypeptides can limit the disease caused by toxin production during C. difficile infection.

A chimeric toxin vaccine protects against primary and recurrent Clostridium difficile infection

The global emergence of Clostridium difficile infection (CDI) has contributed to the recent surge in severe antibiotic-associated diarrhea and colonic inflammation. C. difficile produces two homologous glucosylating exotoxins, TcdA and TcdB, both of which are pathogenic and require neutralization to prevent disease occurrence. However, because of their large size and complex multifunctional domain structures, it has been a challenge to produce native recombinant toxins that may serve as vaccine candidates. Here, we describe a novel chimeric toxin vaccine that retains major neutralizing epitopes from both toxins and confers complete protection against primary and recurrent CDI in mice. Using a nonpathogenic Bacillus megaterium expression system, we generated glucosyltransferase-deficient holotoxins and demonstrated their loss of toxicity. The atoxic holotoxins induced potent antitoxin neutralizing antibodies showing little cross-immunogenicity or protection between TcdA and TcdB. To facilitate simultaneous protection against both toxins, we generated an active clostridial toxin chimera by switching the receptor binding domain of TcdB with that of TcdA. The toxin chimera was fully cytotoxic and showed potent proinflammatory activities. This toxicity was essentially abolished in a glucosyltransferase-deficient toxin chimera, cTxAB. Parenteral immunization of mice or hamsters with cTxAB induced rapid and potent neutralizing antibodies against both toxins. Complete and long-lasting disease protection was conferred by cTxAB vaccinations against both laboratory and hypervirulent C. difficile strains. Finally, prophylactic cTxAB vaccination prevented spore-induced disease relapse, which constitutes one of the most significant clinical issues in CDI. Thus, the rational design of recombinant chimeric toxins provides a novel approach for protecting individuals at high risk of developing CDI.

Nosocomial diarrhea: a review of pathophysiology, etiology, and treatment strategies

Diarrhea is a frequent complication among hospitalized patients. Nosocomial diarrhea is generally diagnosed as increased frequency and decreased consistency of stools developing after 72 hours of hospitalization. The causes of nosocomial diarrhea may be infectious or noninfectious. Noninfectious etiologies occur most commonly, and are often adverse effects of medications or enteral nutrition therapies. Infectious etiologies are most concerning and include Clostridium difficile and norovirus. Patients with nosocomial diarrhea should be placed in isolation with contact precautions in place until the presence of C difficile infection is determined. Irrespective of etiology, diarrhea can cause serious complications in hospitalized patients, including malnutrition, hemodynamic instability, metabolic acidosis, and potentially fatal pseudomembranous colitis. This article reviews nosocomial diarrhea, including its pathophysiology, infectious and noninfectious causes, and treatment strategies based on identified cause.

Adenovirus-based vaccination against Clostridium difficile toxin A allows for rapid humoral immunity and complete protection from toxin A lethal challenge in mice

Clostridium difficile associated diarrhea (CDAD) is a critical public health problem worldwide with over 300,000 cases every year in the United States alone. Clearly, a potent vaccine preventing the morbidity and mortality caused by this detrimental pathogen is urgently required. However, vaccine efforts to combat C. difficile infections have been limited both in scope as well as to efficacy, as such there is not a vaccine approved for use against C. difficile to date. In this study, we have used a highly potent Adenovirus (Ad) based platform to create a vaccine against C. difficile. The Ad-based vaccine was able to generate rapid and robust humoral as well as cellular (T-cell) immune responses in mice that correlated with provision of 100% protection from lethal challenge with C. difficile toxin A. Most relevant to the clinical utility of this vaccine formulation was our result that toxin A specific IgGs were readily detected in plasma of Ad immunized mice as early as 3 days post vaccination. In addition, we found that several major immuno-dominant T cell epitopes were identified in toxin A, suggesting that the role of the cellular arm in protection from C. difficile infections may be more significant than previously appreciated. Therefore, our studies confirm that an Adenovirus based-C. difficile vaccine could be a promising candidate for prophylactic vaccination both for use in high risk patients and in high-risk environments.

Systemic dissemination of Clostridium difficile toxins A and B is associated with severe, fatal disease in animal models

BACKGROUND

Clostridium difficile infection (CDI) can cause a wide range of disease, from mild diarrhea to fulminant systemic disease. The incidence of systemic CDI with fatal consequence has increased rapidly in recent years.

METHODS

Using an ultrasensitive cytotoxicity assay, we measured C. difficile toxin A (TcdA) and C. difficile toxin B (TcdB) in sera and body fluids of piglets and mice exposed to C. difficile to investigate the relationship between the presence of toxins in body fluids and systemic manifestations of CDI.

RESULTS

We found that both TcdA and TcdB disseminate systemically, with toxins present in the sera and body fluids of infected animals, and toxemia is significantly correlated with the development of systemic CDI. The systemic administration of neutralizing antibodies against both toxins blocked the development of systemic disease in mice. We measured cytokine concentrations in the sera of mice and piglets with systemic and nonsystemic CDI and found that proinflammatory mediators were considerably elevated in animals with systemic CDI.

CONCLUSION

Our study demonstrates the existence of a strong correlation between toxemia and the occurrence of systemic disease, supporting the hypothesis that systemic CDI is most likely due to the toxicity of TcdA and TcdB and the induction of proinflammatory cytokines by the toxins.

Clostridium difficile infection: clinical spectrum and approach to management

Clostridium difficile is recognized globally as an important enteric pathogen associated with considerable morbidity and mortality due to the widespread use of antibiotics. The overall incidence of C. difficile-associated diarrhea (CDAD) is increasing due to the emergence of a hypervirulent strain known as NAP1/BI/027. C. difficile acquisition by a host can result in a varied spectrum of clinical conditions inclusive of both colonic and extracolonic manifestations. Repeated occurrence of CDAD, manifested by the sudden re-appearance of diarrhea and other symptoms usually within a week of stopping treatment, makes it a difficult clinical problem. C. difficile infection has also been reported to be involved in exacerbation of inflammatory bowel diseases. The first step in the management of a suspected CDAD case is the withdrawal of the offending agent and changing the antibiotic regimens. Antimicrobial therapy directed against C. difficile viz. metronidazole for mild cases and vancomycin for severe cases is needed. For patients with ileus, oral vancomycin with simultaneous intravenous (IV) metronidazole and intracolonic vancomycin may be given. Depending on the severity of disease, the further line of management may include surgery, IV immunoglobulin treatment or high dose of vancomycin. Adjunctive measures used for CDAD are probiotics and prebiotics, fecotherapy, adsorbents and immunoglobulin therapy. Among the new therapies fidaxomicin has recently been approved by the American Food and Drugs Administration for treatment of CDAD.

Vaccination with parenteral toxoid B protects hamsters against lethal challenge with toxin A-negative, toxin B-positive clostridium difficile but does not prevent colonization

Toxin A has historically been regarded as the primary virulence determinant in Clostridium difficile infection, but naturally occurring toxin A-negative, toxin B-positive (A-/B+) C. difficile strains are known to be virulent. To determine the role of toxin B in these strains, we immunized hamsters with a toxoid prepared from purified toxin B to determine whether they would be protected from lethal challenge with an A-/B+ strain of C. difficile.

Novel one-step method for detection and isolation of active-toxin-producing Clostridium difficile strains directly from stool samples

The alarming emergence of hypervirulent strains of Clostridium difficile with increased toxin production, severity of disease, morbidity, and mortality emphasizes the need for a culture method that permits simultaneous isolation and detection of virulent strains. The C. difficile toxins A and B are critical virulence factors, and strains can either be toxin-producing (virulent) or non-toxin-producing (nonvirulent). Strains that are isolated from human infections generally produce either toxin A or toxin B or both. The methods currently available for culturing C. difficile do not differentiate strains that produce active toxins from strains that do not produce toxins or produce inactive toxins. As a result, the identification and isolation of toxin-producing strains from stool is currently a two-step process. First, the stool is plated on a selective medium, and then suspected colonies are analyzed for toxin production or the presence of the toxin genes. We describe here a novel selective and differential culture method, the Cdifftox plate assay, which combines in a single step the specific isolation of C. difficile strains and the detection of active toxin. This assay was developed based on our recent finding that the A and B toxins of C. difficile cleave chromogenic substrates that have stereochemical characteristics similar to their natural substrate, UDP-glucose. The Cdifftox plate assay is shown here to be extremely accurate (99.8% effective) in detecting toxin-producing strains through the analysis of 528 C. difficile isolates selected from 50 tissue culture cytotoxicity assay-positive clinical stool samples. The Cdifftox plate assay advances and improves the culture approach such that only C. difficile strains will grow on this agar, and virulent strains producing active toxins can be differentiated from nonvirulent strains, which do not produce active toxins. This new method reduces the time and effort required to isolate and confirm toxin-producing C. difficile strains.

Laboratory testing for Clostridium difficile infection: light at the end of the tunnel

Clostridium difficile infection (CDI) is changing as evidenced by increasing virulence, rising incidence, unresponsiveness to metronidazole therapy, and worse outcomes. Thus, it is critical that CDI diagnosis be accurate so ongoing epidemiology, disease prevention, and treatment remain satisfactory. We tested 10 diagnostic assays, including 1 commercial real-time polymerase chain reaction (qPCR) test for the laboratory detection of toxigenic C difficile on 1,000 stool samples. Sensitive culture for toxigenic C difficile using 2 types of media with broth enrichment defined the reference standard. For the study, 1,000 tests were performed on samples from 919 patients. Of the samples, 146 contained evidence for toxigenic C difficile and represented the true-positive results. Only the US Food and Drug Administration-cleared qPCR assay (Becton Dickinson, Franklin Lakes, NJ) and 1 glutamate dehydrogenase test (TechLab, Blacksburg, VA) were not statistically inferior to culture in sensitivity. The common enzyme immunoassay tests all had sensitivity values less than 50%. Clinical laboratory professionals need to seriously consider their diagnostic testing and use the assays that perform best for the detection of CDI.

Clostridium difficile infection in 2010: advances in pathogenesis, diagnosis and management of CDI

Clostridium difficile infection (CDI) publications have advanced in 2010 at a pace paralleling the increased frequency and severity of clinical infection. Both toxins A and B are essential virulence factors, pcr diagnostic testing is rapid, sensitive and specific, and recurrent CDI can be prevented using monoclonal antibodies to toxins A and B.

Impact of Clostridium difficile on inflammatory bowel disease

Clostridium difficile infection (CDI) has been increasing in incidence among those with underlying inflammatory bowel disease (IBD) and is associated with substantial morbidity, the need for surgery and even mortality. The similar clinical presentation between CDI and a flare of underlying IBD makes prompt diagnosis essential to prevent deterioration which would accompany an escalation of immunosuppression in the absence of appropriate antibiotic therapy. Classical risk factors (antibiotic or healthcare exposure) or clinical findings (pseudomembranes) may not be found in many IBD patients with CDI and should not be considered essential for entertaining the diagnosis. Enzyme immunoassays detecting both toxins A and B remain the most widely used test for diagnosis and have acceptable sensitivity, but may require testing of multiple samples in select situations. Both vancomycin and metronidazole appear to be effective and treatment with oral vancomycin is preferred in those with severe disease, including those who require hospitalization. Appropriate infection control measures are essential to restrict patient-to-patient spread within healthcare environments and to prevent recurrences. Several novel therapies are currently under study, including new antibiotic agents and monoclonal antibodies targeted against the toxins. There is a need to broaden these studies to the IBD population. There is also the need to prospectively examine whether CDI has long-term disease-modifying consequences in those with underlying IBD.

The enterotoxicity of Clostridium difficile toxins

The major virulence factors of Clostridium difficile infection (CDI) are two large exotoxins A (TcdA) and B (TcdB). However, our understanding of the specific roles of these toxins in CDI is still evolving. It is now accepted that both toxins are enterotoxic and proinflammatory in the human intestine. Both purified TcdA and TcdB are capable of inducing the pathophysiology of CDI, although most studies have focused on TcdA. C. difficile toxins exert a wide array of biological activities by acting directly on intestinal epithelial cells. Alternatively, the toxins may target immune cells and neurons once the intestinal epithelial barrier is disrupted. The toxins may also act indirectly by stimulating cells to produce chemokines, proinflammatory cytokines, neuropeptides and other neuroimmune signals. This review considers the mechanisms of TcdA- and TcdB-induced enterotoxicity, and recent developments in this field.

Piglet models of acute or chronic Clostridium difficile illness

We examined the piglet model of Clostridium difficile illness (CDI) in humans, because swine are naturally susceptible to C. difficile. The piglet is a reproducible model of acute or chronic CDI with characteristic pseudomembranous colitis. Germ-free piglets were consistently and extensively colonized after oral challenge with the human strain 027/BI/NAP1, establishing an infectious dose-age relationship. This allowed a demarcation between acute fatal and chronic models. The clinical manifestations of disease inclusive of gastrointestinal and systemic symptoms and characteristic mucosal lesions of the large bowel (including pseudomembranous colitis) are described. Additionally, we demonstrate the presence of toxins in feces, body fluids, and serum and a significant elevation in interleukin 8 levels in animals with severe disease. We conclude that piglets infected with C. difficile mimic many of the key characteristics observed in humans with CDI and are suitable animals in which to investigate the role played by virulence attributes, drug efficacy, and vaccine candidates.

Clostridium difficile and the disease it causes

Clostridium difficile is a spore-forming, toxin-producing, anaerobic bacterium abundant in soils and water. Frequent and early colonization of the human intestinal flora is common and often asymptomatic. Antimicrobials given commonly disrupt the intestinal microflora and through proliferation in colon and production of toxin A and B it precipitates C. difficile infection (CDI). The enterocytic detachment and bowel inflammation provoke C. difficile-associated diarrhoea (CDAD) sometimes developing into severe pseudomembranous colitis (PMC) and paralytic ileus. Infection is acquired from an endogenous source or from spores in the environment, most easily facilitated during hospital stay. In the elderly, comorbidity, hospitalization and antimicrobial treatment present as major risk factors and the slow recolonization of the normal flora likely responsible for single or multiple recurrences of CDI (25-50%) post therapy. The key procedure for diagnosis is toxin detection from stool specimens and sometimes in combination with culture to increase sensitivity. In mild cases stopping the offending antimicrobial will lead to resolution (25%) but standard therapy still consist of either oral metronidazole or vancomycin. Alternative agents are presently being developed and fidaxomicin, as well as nitrothiazolide are promising. Furthermore, host factors like low antitoxin A levels in serum relates to increased risk of recurrence and small numbers of patients have received immunoglobulin with good results. An immunogenic toxoid vaccine has been developed and human colostrum rich in specific secretory Ig A also support the future use of immunotherapy. Today we experience a tenfold increase of CDI incidence in the western world and both epidemics and therapeutic failure of metronidazole is contributing to morbidity and mortality. The current epidemic of the C. difficile strain NAP1/027 emerging in 2002 in Canada and the USA has now spread to most parts of Europe and virulence factors like high toxin production and sporulation challenge the therapeutic situation and cause great concern among infection control workers. Excessive use of modern fluoroquinolones is thought to play an important role in facilitating this epidemic since NAP1/027 was shown to have acquired moxifloxacin resistance compared to historical strains of the same genotype. Both the current epidemic like this and other local outbreaks from resistant or virulent strains warrant culture to be routinely performed enabling susceptibility testing and typing of the pathogen. Genotyping is most commonly done today by pulse-field gel electrophoresis (PFGE) or PCR ribotyping but multilocus variable-number tandem-repeat analysis (MLVA) seems promising. Epidemiological surveillance using all these tools will help us to better understand the global spread of C. difficile.

Clostridium difficile and inflammatory bowel disease

The past decade has seen an alarming increase in the burden of disease associated with Clostridium difficile. Several studies have now demonstrated an increasing incidence of C difficile infection in patients with inflammatory bowel disease (IBD) with a more severe course of disease compared with the non-IBD population. This article summarizes the available literature on the impact of C difficile infection on IBD and discusses the various diagnostic testing and treatment options available. Also reviewed are clinical situations specific to patients with IBD that are important for the treating physician to recognize.

Clostridium difficile and inflammatory bowel disease

The past decade has seen an alarming increase in the burden of disease associated with Clostridium difficile. Several studies have now demonstrated an increasing incidence of C difficile infection in patients with inflammatory bowel disease (IBD) with a more severe course of disease compared with the non-IBD population. This article summarizes the available literature on the impact of C difficile infection on IBD and discusses the various diagnostic testing and treatment options available. Also reviewed are clinical situations specific to patients with IBD that are important for the treating physician to recognize.

Diagnostic value of repeated enzyme immunoassays in Clostridium difficile infection

OBJECTIVES

There has been a significant increase in the prevalence, severity, and mortality of Clostridium difficile infection (CDI), with an estimated three million new cases per year in the United States. Yet diagnosing CDI remains problematic. The most commonly used test is stool enzyme immunoassay (EIA) detecting toxin A and/or B, but there are no clear guidelines specifying the optimal number of tests to be ordered in the diagnostic workup, although multiple tests are frequently ordered. Thus, we designed a study with the primary objective of evaluating the diagnostic utility of repeat second and third tests of stool EIA detecting both toxins A and B (EIA (A&B)) in cases with negative initial samples, and sought to describe the physicians' patterns of ordering this test in the workup of suspected CDI.

METHODS

A retrospective study was carried out using a database of all stool EIA (A&B) tests ordered for a presumptive diagnosis of CDI. All patients were adults admitted to a major teaching hospital over a three-and-a-half-year period (tests completed within 5 days of ordering the first test were grouped into a single episode, and only the first three samples per episode were analyzed). Age, gender, and results of stool EIA were tabulated. In addition, physicians' ordering patterns and proportion of positive stools relative to the number of tests ordered were also analyzed. A single positive EIA result was interpreted as evidence for the clinical presence of CDI.

RESULTS

A total of 3,712 patients contributed to 5,865 separate diarrhea episodes (total stool EIA (A&B)=9,178), and 1,165 (19.9%) of these episodes were positive for CDI. Of the positive patients, 73.2% were over the age of 65 years and 54.2% of them were females. The most frequent ordering pattern for presumptive CDI was a single stool test (60.1%), followed by two more tests (23.2%). Three tests were still ordered in 16.6% of the cases. Of the 1,165 positive cases, 1,046 (89.8%) were diagnosed in the very first test, 95 (8.2%) in the second, and only 24 (2.0%) in the third test. In 1,934 instances, a second test was ordered after an initial negative result, of which 95 (4.91%) became positive. In 793 episodes, a third test was ordered after two negative samples, of which only 24 (3.03%) became positive.

CONCLUSIONS

This study highlights the low diagnostic yield of repeat stool EIA (A&B) testing. Findings strongly support the utility of limiting the workup of suspected CDI to a single stool test with only one repeat test in cases of high clinical suspicion, and avoiding the routine ordering of multiple stool samples. As Clostridium difficile is becoming an endemic health-care problem resulting in major financial burdens for the US health-care system, clear guidelines specifying the optimal number of stool EIA (A&B) tests to be ordered in the diagnostic workup of suspected CDI must be established to assist physicians in the practice of evidence-based medicine.

Algorithm combining toxin immunoassay and stool culture for diagnosis of Clostridium difficile infection

Enzyme immunoassays (EIA) to detect glutamate dehydrogenase or toxins A (TcdA) and B (TcdB), a cytotoxicity assay, and bacteriologic culture have disadvantages when applied individually to diagnosis of Clostridium difficile infections. Stool specimens (n = 1,596) were subjected to toxin detection via an enzyme-linked fluorescent immunoassay (ELFA; Vidas CDAB assay) and bacteriologic culture for toxigenic C. difficile in a three-step algorithm with additional toxigenic culture. Isolates (n = 163) from ELFA-negative stool specimens were examined via ELFA for toxin production. We amplified tcdA and tcdB from C. difficile isolates and tcdB from stool specimens that were ELFA positive or equivocal and culture negative, and we compared the results to those obtained with the three-step algorithm. More than 26% of stool specimens (419/1,596) were culture positive, yielding 248 isolates (59.2%) with both toxin genes (tcdA- and tcdB-positive isolates), 88 isolates (21.0%) with either tcdA or tcdB, and 83 (19.8%) that had no toxin genes (tcdA- and tcdB-negative isolates). Among 49 (culture-negative/ELFA-positive or -equivocal) stool specimens, 53.1% (26/49) represented tcdB-positive isolates. Therefore, the total number of PCR-positive cases was 362, and 27.1% (98/362) of these were detected through toxigenic culture. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were 63.3%, 96.7%, 90.5%, and 92.4% (ELFA alone); 92.8%, 93.3%, 80.2%, and 97.8% (culture); and 70.7%, 91.4%, 95.5%, and 100% (three-step algorithm ELFA and bacterial culture with toxigenic culture), respectively, with culture and PCR for tcdA and tcdB as the standards. Thus, sensitivity and specificity were highest using culture and ELFA, respectively, but we recommend the three-step algorithm comprising EIA to detect both toxins and toxigenic culture for C. difficile as a practical method for achieving better PPV and NPV.

Clostridium difficile infection caused by the epidemic BI/NAP1/027 strain

Rates and severity of Clostridium difficile infection (CDI) in hospitals in North America and Europe have increased since 2000 and correlate with dissemination of an epidemic strain characterized by higher than usual toxin A and B production, the presence of a third toxin, binary toxin, and high-level resistance to fluoroquinolone antibiotics. The strain, which is restriction endonuclease analysis group BI, pulse-field gel electrophoresis type NAP1, and polymerase chain reaction ribotype 027, is designated BI/NAP1/027. How this strain has become so widely distributed geographically and produces such severe CDI is the subject of active investigation. The deletion at position 117 of the tcdC gene, a repressor of toxin A and B production, is one possible contributor to increased levels of the toxins. The role of binary toxin is unknown. Recent isolates of BI/NAP1/027 were found to be resistant to fluoroquinolones, which is likely to contribute to the dissemination of this strain. Other virulence factors such as increased sporulation and surface layer protein adherence are also under investigation. Infections caused by this organism are particularly frequent among elderly hospitalized patients, in whom the attributable 30-day mortality is greater than 5%. Major risk factors for BI/NAP1/027 infection include advanced age, hospitalization, and exposure to specific antimicrobials, especially fluoroquinolones and cephalosporins. When CDI is severe, vancomycin treatment is more effective than metronidazole; for mild disease either agent can be used. Control of hospital outbreaks caused by BI/NAP1/027 is difficult but possible through a combination of barrier precautions, environmental cleaning, and antimicrobial stewardship.

Antibody-enhanced, Fc gamma receptor-mediated endocytosis of Clostridium difficile toxin A

Toxin A (TcdA) and toxin B (TcdB) are major virulence factors of Clostridium difficile. These two toxins intoxicate cultured cells by similar mechanisms, and TcdB generally is more potent than TcdA in cultured cells. The exact reason for this difference is unclear. Here, we report that the cellular effects of TcdA can be substantially enhanced via an opsonizing antibody through Fc gamma receptor I (FcgammaRI)-mediated endocytosis. A TcdA-specific monoclonal antibody, A1H3, was found to significantly enhance the cytotoxicity of TcdA to macrophages and monocytes. The A1H3-dependent enhancement of glucosyltransferase activity, cytoskeleton disruption, and tumor necrosis factor alpha production induced by TcdA was further demonstrated using RAW 264.7 cells. Subsequent experiments indicated that the interaction of FcgammaRI with A1H3 underlays the antibody-dependent enhancement of the cellular effects of TcdA. While blocking FcgammaRII and FcgammaRIII with anti-CD16/32 antibodies did not affect the TcdA-mediated glucosylation of Rac1 in RAW 264.7 cells, presaturation of FcgammaRI with anti-CD64 antibodies in THP1 cells significantly reduced this activity. Incubation of a TcdA-A1H3 immune complex with recombinant mouse CD64 completely abrogated the A1H3-mediated enhancement of the glucosyltransferase activity of TcdA in RAW 264.7 cells. Moreover, expression of FcgammaRI in CHO cells strikingly enhanced the sensitivity of these cells to TcdA complexed with A1H3. We showed that the presence of A1H3 facilitated cell surface recruitment of TcdA, contributing to the antibody-dependent, FcgammaRI-mediated enhancement of TcdA activity. Finally, studies using chlorpromazine and endosomal acidification inhibitors revealed an important role of the endocytic pathway in the A1H3-dependent enhancement of TcdA activity.

Toxin B is essential for virulence of Clostridium difficile

Clostridium difficile is the leading cause of infectious diarrhea in hospitals worldwide, because of its virulence, spore-forming ability and persistence1,2. C. difficile-associated diseases (CDAD) are induced by antibiotic treatment or disruption of the normal gastrointestinal flora3,4. Recently, morbidity and mortality resulting from CDAD have increased significantly due to changes in the virulence of the causative strains and antibiotic usage patterns1,2,5,6. Since 2002, epidemic toxinotype III NAP1/027 strains1,2, which produce high levels of the major virulence factors, toxin A and toxin B, have emerged. These toxins have 63% amino acid sequence similarity7 and are members of the large clostridial glucosylating toxin family, which are monoglucosyltransferases that are proinflammatory, cytotoxic and enterotoxic in the human colon8–10. Inside host cells, both toxins catalyze the transfer of glucose onto the Rho family of GTPases, leading to cell death8, 11. However, the role of these toxins in the context of a C. difficile infection is unknown. Here we describe the construction of isogenic tcdA and tcdB mutants of a virulent C. difficile strain and their use in the hamster disease model to show that toxin B is a key virulence determinant. Previous studies showed that purified toxin A alone can induce most of the pathology observed following infection of hamsters with C. difficile8,9, 12 and that toxin B is not toxic in animals unless it is co-administered with toxin A, suggesting that the toxins act synergistically12. Our work provides evidence that toxin B, not toxin A, is essential for virulence, which represents a major paradigm shift. Furthermore, it is clear that the importance of these toxins in the context of infection cannot be predicted exclusively from studies using purified toxins, reinforcing the importance of using the natural infection process to dissect the role of toxins in disease.

The management of Clostridium difficile infection

INTRODUCTION/BACKGROUND

Clostridium difficile is the commonest cause of nosocomial diarrhoea. The epidemiology and clinical phenotype of the disease has dramatically changed with the global emergence of a virulent strain of C. difficile.

SOURCE

This review was compiled using data from individual studies and review articles identified from PubMed. The retrieved articles were also examined for additional references.

AREAS OF AGREEMENT

Appropriate and timely infection control measures are required to control C. difficile infection (CDI) in the hospital environment, and either oral metronidazole or vancomycin remains the mainstay of treatment depending on the severity of infection.

AREAS OF CONTROVERSY

The optimal method for diagnosing CDI remains unclear, as does the best therapeutic strategy for the management of multiple relapses. GROWING POINTS/AREAS TIMELY FOR DEVELOPING RESEARCH: Studies of new antimicrobial agents with activity against C. difficile are required to improve the management of multiply relapsing disease. The use of novel therapeutic approaches that do not require antimicrobials requires urgent research, including the use of immunological or vaccine-based regimen, bacteriotherapy or C. difficile-specific bacteriophages.

A mouse model of Clostridium difficile-associated disease

BACKGROUND & AIMS

Infection with Clostridium difficile causes nosocomial antibiotic-associated diarrhea and colitis. Hamsters historically have been used to investigate disease pathogenesis and treatment, but are not ideal models because of the lack of hamster-specific reagents and genetically modified animals, and because they develop fulminant disease. The aim of this study was to establish a mouse model of antibiotic-induced C. difficile-associated disease (CDAD) that more closely resembles human disease.

METHODS

C57BL/6 mice were exposed to a mixture of antibiotics (kanamycin, gentamicin, colistin, metronidazole, and vancomycin) for 3 days. Two days later, they were given injections of clindamycin and then challenged 1 day later with different doses of C. difficile.

RESULTS

Mice that were exposed to antibiotics and then challenged with C. difficile developed diarrhea and lost weight. Disease severity varied from fulminant to minimal in accordance with the challenge dose. Typical histologic features of CDAD were evident. Oral vancomycin prevented CDAD in all mice, but 68% died from colitis after treatment was discontinued. All animals that survived an initial episode of CDAD showed no evidence of diarrhea or colitis after subsequent rechallenge with C. difficile. Different strains of C. difficile tested in the model showed different levels of virulence in mice.

CONCLUSIONS

We have developed a mouse model of CDAD that closely represents the human disease. In light of the recent substantial increases in CDAD incidence and severity, this model will be valuable in testing new treatments, examining disease pathogenesis, and elucidating mechanisms of protective immunity.

Clostridium difficile and inflammatory bowel disease

Clostridium difficile colitis has doubled in North America over the past 5 years and recent reports have demonstrated an increase in incidence and severity of these infections in patients with inflammatory bowel disease (IBD; Crohn's disease, ulcerative colitis). Studies from single institutions as well as trends identified in nationwide inpatient databases have shown that IBD patients with concomitant C. difficile infection experience increased morbidity and mortality. Results from our center have shown that over half of C. difficile-infected IBD patients will require hospitalization and the colectomy rate may approach 20%. Because C. difficile colitis will both mimic and precipitate an IBD flare, it is essential that clinicians be vigilant to identify and address this infectious complication, as empiric treatment with corticosteroids without appropriate antibiotics may precipitate deterioration. The majority of IBD patients appear to contract C. difficile as outpatients, and a prior history of colitis appears to be the most significant risk factor for acquiring this infection. In addition to C. difficile colitis, IBD patients are now known to be at risk for C. difficile enteritis as well as infections in reconstructed ileoanal pouches. An additional challenge facing C. difficile infections in IBD patients is the decreased efficacy of metronidazole, and the need for oral vancomycin in patients requiring hospitalization. In this review we summarize the present knowledge regarding C. difficile infection in the setting of IBD, including unique clinical scenarios facing IBD patients, diagnostic algorithms, and treatment approaches.