Markers of intestinal inflammation, not bacterial burden, correlate with clinical outcomes in Clostridium difficile infection

The Inflammasome and Type-2 Immunity in Clostridium difficile Infection

Clostridium difficile (reclassified as " Clostridioides ") is the leading cause of hospital-acquired infections in the United States, and is associated with high-patient mortality and high rates of recurrence. Inflammasome priming and activation by the bacterial toxins, TcdA , TcdB , and C. difficile transferase (CDT), initiates a potent immune response that is characterized by interleukin- (IL) 8, IL-1β, and neutrophil recruitment, and is required for pathogen killing. However, it is becoming clearer that a strong inflammatory response during C. difficile infection can result in host tissue damage, and is associated with worse patient outcome. Recent work has begun to show that a type-2 immune response, most often associated with helminth infections, allergy, and asthma, may be protective during C. difficile infection. While the mechanisms through how this response protect are still unclear, there is evidence that it is mediated through eosinophil activity. This chapter will review the immune response to C. difficile, how the inflammasome signaling during infection can deleterious to the host, as well as the current understanding of a protective type-2 immunity. Understanding the host immune response may help to provide insight into novel approaches to prognosis markers, as well as how treat patient C. difficile infection without, or in addition to, antibiotics.

In vitro and in vivo anti-clostridial activity of newly isolated Pediococcus acidilactici SPM138 against Clostridium difficile

Clostridium difficile infection (CDI) has become a growing health concern, as evident from the increase in the mortality rate among elderly or hospitalized patients. Treatment of CDI is usually based on antibiotics (metronidazole and vancomycin), but it has some limitations, including cost and antibiotic resistance. Probiotics could offer an effective remedy to prevent CDI and could be an auxiliary agent in treatment CDI. Here, the anti-clostridial activity of a newly isolated probiotic strain, Pediococcus acidilactici SPM138 (SPM138) was evaluated. The cultivation of C. difficile (CD) with SPM138, inhibited the growth of CD and significantly reduced CD toxins level. The result of MTT assay showed that, incubation with 25% CD culture supernatant decreased the survival rate of HT-29 cells to less than 20%. However, the survival rate of these cells increased to 98% in the presence of the 25% CD + SPM138 supernatant. The mRNA expression of IL-6, IL-8 and PTGS2 in HT-29 cells decreased by more than 60% upon incubation with CD + SPM138 co-cultures as compared to the levels observed after treatment with CD supernatant only. The concentration of IL-8 also decreased by more than 60% upon treatment with CD + SPM138 co-culture supernatant. In a C. difficile PCR ribotype 027-infected mouse model, the concentration of CD toxin in stool samples of SPM138-fed mice was only 37% of that reported in C. difficile 027-infected group. These findings show that P. acidilactici SPM138 may be a promising probiotic in CDI.

Type 3 Immunity during Clostridioides difficile Infection: Too Much of a Good Thing?

Clostridioides (formerly known as Clostridium) difficile is the leading cause of hospital-acquired gastrointestinal infections in the United States and one of three urgent health care threats identified by the Centers for Disease Control and Prevention. C. difficile disease is mediated by the production of toxins that disrupt the epithelial barrier and cause a robust host inflammatory response. Studies in humans as well as animal models of disease have shown that the type of immune response generated against the infection dictates the outcome of disease, often irrespective of bacterial burden. Much of the focus on immunity during C. difficile infection (CDI) has been on type 3 immunity because of the established role for this arm of the immune system in other gastrointestinal inflammatory conditions such as inflammatory bowel disease (IBD). For example, interleukin-22 (IL-22) production by group 3 innate lymphoid cells (ILC3s) protects against pathobionts translocating across the epithelium during CDI. On the other hand, interleukin-17 (IL-17) production by Th17 cells increases CDI-associated mortality. Additionally, neutropenia has been associated with increased susceptibility to CDI in humans, but increased neutrophilia in mouse models correlates with host pathology. Taking the data together, these findings suggest dual roles for type 3 immune responses during infection. Here, we review the complex role of type 3 immunity during CDI and delineate what is known about innate and adaptive cellular immunity as well as the downstream effector cytokines known to be important during this infection.

The xenobiotic sensing pregnane X receptor regulates tissue damage and inflammation triggered by C difficile toxins

Clostridioides difficile (formerly Clostridium difficile; C difficile), the leading cause of nosocomial antibiotic‐associated colitis and diarrhea in the industrialized world, triggers colonic disease through the release two toxins, toxin A (TcdA) and toxin B (TcdB), glucosyltransferases that modulate monomeric G‐protein function and alter cytoskeletal function. The initial degree of the host immune response to C difficile and its pathogenic toxins is a common indicator of disease severity and infection recurrence. Thus, targeting the intestinal inflammatory response during infection could significantly decrease disease morbidity and mortality. In the current study, we sought to interrogate the influence of the pregnane X receptor (PXR), a modulator of xenobiotic and detoxification responses, which can sense and respond to microbial metabolites and modulates inflammatory activity, during exposure to TcdA and TcdB. Following intrarectal exposure to TcdA/B, PXR‐deficient mice (Nr1i2^−/−) exhibited reduced survival, an effect that was associated with increased levels of innate immune cell influx. This exacerbated response was associated with a twofold increase in the expression of Tlr4. Furthermore, while broad‐spectrum antibiotic treatment (to deplete the intestinal microbiota) did not alter the responses in Nr1i2^−/− mice, blocking TLR4 signaling significantly reduced TcdA/B‐induced disease severity and immune responses in these mice. Lastly, to assess the therapeutic potential of targeting the PXR, we activated the PXR with pregnenolone 16α‐carbonitrile (PCN) in wild‐type mice, which greatly reduced the severity of TcdA/B‐induced damage and intestinal inflammation. Taken together, these data suggest that the PXR plays a role in the host's response to TcdA/B and may provide a novel target to dampen the inflammatory tissue damage in C difficile infections.

Recurrent community-acquired Clostridium(Clostridioides)difficile infection in Serbianchildren

Information on recurrent Clostridium difficile infections (rCDI) in children is rare and limited, especially community acquired (CA-CDI).This study was designed to identify risk factors for rCA-CDI in Serbian pediatric population. The study group included 71 children (aged from 1 to 14 years) with a first episode of CDI. Data were collected from 56 (78.87%) children with only one episode of CA-CDI and from 15 (21.13%) children with rCA-CDI were mutually compared. The following parameters were found to be statistically significantly more frequent in the children with rCA-CDI group (p < 0.05); leukemia as underlying disease, treatment with immunosuppressive and-or cytostatic drugs, and treatment with antibiotics. Similarly, previously visits to outpatient facilities, daycare hospitals and hospitals were also associated with rCDI. Analysis of clinical symptoms and laboratory parameters, revealed a statistically significant association of the severity of the first episode of CDI (determined by an increase in body temperature, higher maximum WBC and higher CRP) with development of a rCDI. Ribotype (RT) 027 was more common in children with rCA-CDI (66.7%, p = 0.006). During the seven-year research period, we found a rate of rCA-CDI rate in children of 21.13%. Our study identified several parameters statistically significantly more frequently in children with rCA-CDI. The obtained results will serve as a basis for future larger studies, but new prospective, studies are necessary to build a prediction model of rCDI in children that can be used to guide the treatment to prevent rCDI.

Clinical Practice Guidelines for Clostridium difficile Infection in Adults and Children: 2017 Update by the Infectious Diseases Society of America (IDSA) and Society for Healthcare Epidemiology of America (SHEA)

A panel of experts was convened by the Infectious Diseases Society of America (IDSA) and Society for Healthcare Epidemiology of America (SHEA) to update the 2010 clinical practice guideline on Clostridium difficile infection (CDI) in adults. The update, which has incorporated recommendations for children (following the adult recommendations for epidemiology, diagnosis, and treatment), includes significant changes in the management of this infection and reflects the evolving controversy over best methods for diagnosis. Clostridium difficile remains the most important cause of healthcare-associated diarrhea and has become the most commonly identified cause of healthcare-associated infection in adults in the United States. Moreover, C. difficile has established itself as an important community pathogen. Although the prevalence of the epidemic and virulent ribotype 027 strain has declined markedly along with overall CDI rates in parts of Europe, it remains one of the most commonly identified strains in the United States where it causes a sizable minority of CDIs, especially healthcare-associated CDIs. This guideline updates recommendations regarding epidemiology, diagnosis, treatment, infection prevention, and environmental management.

Characterization of the Immune Response during Infection Caused by Clostridioides difficile

The high risk of complications and death following Clostridioides difficile infection (CDI) requires identifying patients with severe disease and treating them accordingly. We characterized the immune response of CDI patients in relation to infection severity. Concentrations of 28 cytokines and chemokines were measured in serum samples, obtained from 54 CDI patients within a median timeframe of 24–48 h after laboratory confirmation of C. difficile infection. Demographic and clinical data were retrospectively collected from medical records. Disease severity score was determined by “Score indices for Clostridioides difficile infection severity”. Of 54 patients (mean age, 76.6 years, 61.1% female), 38 (70.4%) had mild disease and 16 (29.6%) had moderate disease. Seven cytokines were associated with a more severe CDI: granulocyte-macrophage colony-stimulating factor (p = 0.0106), interleukin (IL)-1β (p = 0.004), IL-8 (p = 0.0098), IL-12p70 (p = 0.0118), interferon-α (p = 0.0282), IL-15 (p = 0.0015), and IL-2 (p = 0.0031). Additionally, there was an increased T-helper 1 response in more severe cases of CDI. Cytokines may serve as biomarkers for early prediction of CDI severity. Better and earlier assessment of illness severity will contribute to the adjustment of medical treatment, including monitoring and follow-up.

IL-33 drives group 2 innate lymphoid cell-mediated protection during Clostridium difficile infection

Clostridium difficile (C. difficile) incidence has tripled over the past 15 years and is attributed to the emergence of hypervirulent strains. While it is clear that C. difficile toxins cause damaging colonic inflammation, the immune mechanisms protecting from tissue damage require further investigation. Through a transcriptome analysis, we identify IL-33 as an immune target upregulated in response to hypervirulent C. difficile. We demonstrate that IL-33 prevents C. difficile-associated mortality and epithelial disruption independently of bacterial burden or toxin expression. IL-33 drives colonic group 2 innate lymphoid cell (ILC2) activation during infection and IL-33 activated ILC2s are sufficient to prevent disease. Furthermore, intestinal IL-33 expression is regulated by the microbiota as fecal microbiota transplantation (FMT) rescues antibiotic-associated depletion of IL-33. Lastly, dysregulated IL-33 signaling via the decoy receptor, sST2, predicts C. difficile-associated mortality in human patients. Thus, IL-33 signaling to ILC2s is an important mechanism of defense from C. difficile colitis.

Here, Frisbee et al. show that hypervirulent Clostridium difficile induces IL-33 expression in the gut and IL-33 reduces mortality and morbidity via group 2 innate lymphoid cells. Furthermore, serum levels of the soluble IL-33 decoy receptor, sST2, are associated with enhanced disease severity in human C. difficile patients.

A possible association between statin use and improved Clostridioides difficile infection mortality in veterans

Clostridioides difficile infection (CDI) is the most common cause of nosocomial diarrhea and places a significant burden on patients and the health care system. Statins could lead to improvements in CDI clinical response due their pleiotropic effects, including immunomodulatory and lipid-lowering effects; however, few studies have assessed this association. The primary objective of this study was to compare CDI health outcomes in statin users and non-users in a national cohort of patients. This was a retrospective cohort study of all adult CDI patients receiving care from the Veterans Health Administration from 2002 to 2014. Patients were divided into two groups based on statin exposure 90 days prior to and during their first CDI encounter. CDI health outcomes, including mortality and CDI recurrence, were compared using a propensity-score matched cohort of statin users and non-users and multivariable logistic regression. A total of 26,149 patients met study inclusion criteria, of which 173 statins-users and 173 non-users were propensity score matched. Thirty-day mortality was significantly lower among statins users with CDI (12.7%) compared to non-users (20.2%) (aOR 0.34; 95% CI 0.16-0.72). Sixty-day CDI recurrence was non-significantly lower among statin-users (9.0%) compared to non-users (16.6%) (aOR 0.68; 95% CI 0.29-1.59). In this nationally-representative study of veterans with CDI, statin use was associated with lower 30-day mortality compared to non-use. Statin use was not associated with 60-day CDI recurrence.

Multilocus Variable-Number Tandem-Repeat Analysis of Clostridioides difficile Clusters in Ribotype 027 Isolates and Lack of Association with Clinical Outcomes

The epidemiology of Clostridioides difficile infection (CDI) has drastically changed since the emergence of the epidemic strain BI/NAP1/027, also known as ribotype 027 (R027). However, the relationship between the infecting C. difficile strain and clinical outcomes is still debated. We hypothesized that certain subpopulations of R027 isolates could be associated with unfavorable outcomes. We applied high-resolution multilocus variable-number tandem-repeat analysis (MLVA) to characterize C. difficile R027 isolates collected from confirmed CDI patients recruited across 10 Canadian hospitals from 2005 to 2008. PCR ribotyping was performed first to select R027 isolates that were then analyzed by MLVA (n = 450). Complicated CDI (cCDI) was defined by the occurrence of any of admission to an intensive care unit, colonic perforation, toxic megacolon, colectomy, and if CDI was the cause or contributed to death within 30 days after enrollment. Three major MLVA clusters were identified, MC-1, MC-3, and MC-10. MC-1 and MC-3 were exclusive to Quebec centers, while MC-10 was found only in Ontario. Fewer cases infected with MC-1 developed cCDI (4%) than those infected with MC-3 and MC-10 (15% and 16%, respectively), but a statistically significant difference was not reached. Our data did not identify a clear association between subpopulations of R027 and different clinical outcomes; however, the data confirmed the utility of MLVA's higher discrimination potential to better characterize CDI populations in an epidemiological analysis. For a patient with CDI, the progression toward an unfavorable outcome is a complex process that probably includes several interrelated strain and host characteristics.

Innate Immune Response and Outcome of Clostridium difficile Infection Are Dependent on Fecal Bacterial Composition in the Aged Host

Background

Clostridium difficile infection (CDI) is a serious threat for an aging population. Using an aged mouse model, we evaluated the effect of age and the roles of innate immunity and intestinal microbiota.

Methods

Aged (18 months) and young (8 weeks) mice were infected with C difficile, and disease severity, immune response, and intestinal microbiome were compared. The same experiment was repeated with intestinal microbiota exchange between aged and young mice before infection.

Results

Higher mortality was observed in aged mice with weaker neutrophilic mobilization in blood and intestinal tissue and depressed proinflammatory cytokines in early infection. Microbiota exchange improved survival and early immune response in aged mice. Microbiome analysis revealed that aged mice have significant deficiencies in Bacteroidetes phylum and, specifically, Bacteroides, Alistipes, and rc4-4 genera, which were replenished by cage switching.

Conclusions

Microbiota-dependent alteration in innate immune response early on during infection may explain poor outcome in aged host with CDI.

Epithelium-specific MyD88 signaling, but not DCs or macrophages, control acute intestinal infection with Clostridium difficile

Infection with Clostridium difficile is one of the major causes of health care acquired diarrhea and colitis. Signaling though MyD88 downstream of TLRs is critical for initiating the early protective host response in mouse models of C. difficile infection (CDI). In the intestine, MyD88 is expressed in various tissues and cell types, such as the intestinal epithelium and mononuclear phagocytes (MNP), including DC or macrophages. Using a genetic gain-of-function system, we demonstrate here that restricting functional MyD88 signaling to the intestinal epithelium, but also to MNPs is sufficient to protect mice during acute CDI by upregulation of the intestinal barrier function and recruitment of neutrophils. Nevertheless, we also show that mice depleted for CD11c-expressing MNPs in the intestine display no major defects in mounting an effective inflammatory response, indicating that the absence of these cells is irrelevant for inducing host protection during acute infection. Together, our results highlight the importance of epithelial-specific MyD88 signaling and demonstrate that although functional MyD88 signaling in DC and macrophages alone is sufficient to correct the phenotype of MyD88-deficiency, these cells do not seem to be essential for host protection in MyD88-sufficient animals during acute infection with C. difficile.

Neutralization of macrophage migration inhibitory factor improves host survival after Clostridium difficile infection

Clostridium difficile is an important cause of nosocomial diarrhea in the western world. Toxins (A, B, and binary toxins) generated by C. difficile bacteria damage intestinal epithelial cells. Hallmarks of host response to C. difficile infection (CDI) include upregulation of inflammatory mediators and tissue infiltration by immune cells. Macrophage migration inhibitory factor (MIF) is an inflammatory cytokine that is known to enhance the host immune response to infectious pathogens. Additionally, MIF can adversely impact host survival to numerous infections. The role of MIF in the pathogenesis of CDI remains poorly understood. Here, we show that patients with CDI had significantly higher circulating MIF compared to patients who had diarrhea but tested negative for C. difficile (non-CDI controls). Similarly, in a mouse model, C. difficile challenge significantly increased levels of plasma and tissue MIF. Antibody-mediated depletion of MIF decreased C. difficile-induced inflammatory responses, clinical disease, and mortality. Together, these results uncover a potential role for MIF in exacerbating CDI and suggest that use of anti-MIF antibodies may represent a therapeutic strategy to curb host inflammatory responses and improve disease outcomes in CDI.

Fecal Host Transcriptomics for Non-Invasive Human Mucosal Immune Profiling: Proof of Concept in Clostridium Difficile Infection

Background:

Host factors play an important role in pathogenesis and disease outcome in Clostridium difficile infection (CDI), and characterization of these responses could uncover potential host biomarkers to complement existing microbe-based diagnostics.

Methods:

We extracted RNA from fecal samples of patients with CDI and profiled human mRNA using amplicon-based next-generation sequencing (NGS). We compared the fecal host mRNA transcript expression profiles of patients with CDI to controls with non-CDI diarrhea.

Results:

We found that the ratio of human actin gamma 1 (ACTG1) to 16S ribosomal RNA (rRNA) was highly correlated with NGS quality as measured by percentage of reads on target. Patients with CDI could be differentiated from those with non-CDI diarrhea based on their fecal mRNA expression profiles using principal component analysis. Among the most differentially expressed genes were ones related to immune response (IL23A, IL34) and actin-cytoskeleton function (TNNT1, MYL4, SMTN, MYBPC3, all adjusted P-values < 1 x 10^-3).

Conclusions:

In this proof-of-concept study, we used host fecal transcriptomics for non-invasive profiling of the mucosal immune response in CDI. We identified differentially expressed genes with biological plausibility based on animal and cell culture models. This demonstrates the potential of fecal transcriptomics to uncover host-based biomarkers for enteric infections.

A low-cost paper-based synthetic biology platform for analyzing gut microbiota and host biomarkers

There is a need for large-scale, longitudinal studies to determine the mechanisms by which the gut microbiome and its interactions with the host affect human health and disease. Current methods for profiling the microbiome typically utilize next-generation sequencing applications that are expensive, slow, and complex. Here, we present a synthetic biology platform for affordable, on-demand, and simple analysis of microbiome samples using RNA toehold switch sensors in paper-based, cell-free reactions. We demonstrate species-specific detection of mRNAs from 10 different bacteria that affect human health and four clinically relevant host biomarkers. We develop a method to quantify mRNA using our toehold sensors and validate our platform on clinical stool samples by comparison to RT-qPCR. We further highlight the potential clinical utility of the platform by showing that it can be used to rapidly and inexpensively detect toxin mRNA in the diagnosis of Clostridium difficile infections.

Currently, gut microbiome profiling largely relies on next-generation sequencing, which is slow and expensive. Here, the authors develop a low-cost, paper-based synthetic biology platform that allows species-specific quantification of bacterial mRNAs and clinically relevant host biomarkers.

Prolonged Mechanical Ventilation Assistance Interacts Synergistically with Carbapenem for Clostridium difficile Infection in Critically Ill Patients

Objectives: Interactions between mechanical ventilation (MV) and carbapenem interventions were investigated for the risk of Clostridium difficile infection (CDI) in critically ill patients undergoing concurrent carbapenem therapy. Methods: Taiwan’s National Intensive Care Unit Database (NICUD) was used in this analytical, observational, and retrospective study. We analyzed 267,871 intubated patients in subgroups based on the duration of MV support: 7–14 days (n = 97,525), 15–21 days (n = 52,068), 22–28 days (n = 35,264), and 29–60 days (n = 70,021). The primary outcome was CDI. Results: Age (>75 years old), prolonged MV assistance (>21 days), carbapenem therapy (>15 days), and high comorbidity scores were identified as independent risk factors for developing CDI. CDI risk increased with longer MV support. The highest rate of CDI was in the MV 29–60 days subgroup (adjusted hazard ratio (AHR) = 2.85; 95% confidence interval (CI) = 1.46–5.58; p < 0.02). Moreover, higher CDI rates correlated with the interaction between MV and carbapenem interventions; these CDI risks were increased in the MV 15–21 days (AHR = 2.58; 95% CI = 1.12–5.91) and MV 29–60 days (AHR = 4.63; 95% CI = 1.14–10.03) subgroups than in the non-MV and non-carbapenem subgroups. Conclusions: Both MV support and carbapenem interventions significantly increase the risk that critically ill patients will develop CDI. Moreover, prolonged MV support and carbapenem therapy synergistically induce CDI. These findings provide new insights into the role of MV support in the development of CDI.

Systemic Inflammatory Responses in Ulcerative Colitis Patients and Clostridium difficile Infection

BACKGROUND/AIMS

Finding differences in systemic inflammatory response in ulcerative colitis (UC), UC with Clostridium difficile infection (CDI), and CDI could lead to a better ability to differentiate between UC with symptomatic CDI and UC with C. difficile colonization, and could identify specific inflammatory pathways for UC or CDI, which could be therapeutic targets.

METHODS

We prospectively collected sera from symptomatic UC patients whose stools were tested for toxigenic C. difficile, and from CDI patients who did not have UC (CDI-noUC). The UC patients with positive tests (UC-CDI) were further categorized into responders to CDI treatment (UC-CDI-R) and non-responders (UC-CDI-NR). We compared serum inflammatory mediators among groups using unadjusted and adjusted multivariable statistics.

RESULTS

We included 117 UC [27 UC-CDI, 90 UC without CDI (UC-noCDI)] and 16 CDI-noUC patients. Principal component analysis (PCA) did not reveal significant differences either between UC-CDI and UC-noCDI groups, or between UC-CDI-R and UC-CDI-NR groups. In contrast, the PCA showed significant separation between the UC and CDI-noUC groups (P = 0.002). In these two groups, hepatocyte growth factor (HGF) and chemokine (C-C motif) ligand 2 (CCL2) levels were significantly lower and IL-23 levels were higher in UC patients in multivariable analyses. The model to distinguish UC from CDI including IL-23, HGF, CCL2, age, gender, and HGB had an AuROC of 0.93.

CONCLUSION

Inflammatory profiles could not distinguish UC-CDI from UC-noCDI, and UC-CDI-R from UC-CDI-NR. However, the UC and CDI-noUC groups were significantly different. Future work should examine whether therapeutic agents inhibiting IL-23 or stimulating HGF can treat UC.

Nucleic Acid Amplification Test Quantitation as Predictor of Toxin Presence in Clostridium difficile Infection

Multistep algorithmic testing in which a sensitive nucleic acid amplification test (NAAT) is followed by a specific toxin A and toxin B enzyme immunoassay (EIA) is among the most accurate methods for Clostridium difficile infection (CDI) diagnosis. The obvious shortcoming of this approach is that multiple tests must be performed to establish a CDI diagnosis, which may delay treatment. Therefore, we sought to determine whether a preliminary diagnosis could be made on the basis of the quantitative results of the first test in algorithmic testing, which provide a measure of organism burden. To do so, we retrospectively analyzed two large collections of samples (n = 2,669 and n = 1,718) that were submitted to the laboratories of two Dutch hospitals for CDI testing. Both hospitals apply a two-step testing algorithm in which a NAAT is followed by a toxin A/B EIA. Of all samples, 208 and 113 samples, respectively, tested positive by NAAT. Among these NAAT-positive samples, significantly lower mean quantification cycle (C_q ) values were found for patients whose stool eventually tested positive for toxin, compared with patients who tested negative for toxin (mean C_q values of 24.4 versus 30.4 and 26.8 versus 32.2; P < 0.001 for both cohorts). Receiver operating characteristic curve analysis was performed to investigate the ability of C_q values to predict toxin status and yielded areas under the curve of 0.826 and 0.854. Using the optimal C_q cutoff values, prediction of the eventual toxin A/B EIA results was accurate for 78.9% and 80.5% of samples, respectively. In conclusion, C_q values can serve as predictors of toxin status but, due to the suboptimal correlation between the two tests, additional toxin testing is still needed.

Cysteine Protease-Mediated Autocleavage of Clostridium difficile Toxins Regulates Their Proinflammatory Activity

BACKGROUND & AIMS

Clostridium difficile toxin A (TcdA) and C difficile toxin toxin B (TcdB), the major virulence factors of the bacterium, cause intestinal tissue damage and inflammation. Although the 2 toxins are homologous and share a similar domain structure, TcdA is generally more inflammatory whereas TcdB is more cytotoxic. The functional domain of the toxins that govern the proinflammatory activities of the 2 toxins is unknown.

METHODS

Here, we investigated toxin domain functions that regulate the proinflammatory activity of C difficile toxins. By using a mouse ilea loop model, human tissues, and immune cells, we examined the inflammatory responses to a series of chimeric toxins or toxin mutants deficient in specific domain functions.

RESULTS

Blocking autoprocessing of TcdB by mutagenesis or chemical inhibition, while reducing cytotoxicity of the toxin, significantly enhanced its proinflammatory activities in the animal model. Furthermore, a noncleavable mutant TcdB was significantly more potent than the wild-type toxin in the induction of proinflammatory cytokines in human colonic tissues and immune cells.

CONCLUSIONS

In this study, we identified a novel mechanism of regulating the biological activities of C difficile toxins in that cysteine protease-mediated autoprocessing regulates toxins' proinflammatory activities. Our findings provide new insight into the pathogenesis of C difficile infection and the design of therapeutics against the disease.

Faecalibacterium prausnitzii and a Prebiotic Protect Intestinal Health in a Mouse Model of Antibiotic and Clostridium difficile Exposure

BACKGROUND

Clostridium difficile (CD) infection (CDI) increases patient morbidity, mortality and healthcare costs. Antibiotic treatment induces gut dysbiosis and is both a major risk factor for CD colonization and treatment of CDI. Probiotics have been trialed to support commensal gut microbiota and reduce CDI. This study investigated commensal microbe Faecalibacterium prausnitzii (FP) and a prebiotic, both known to yield butyrate and be anti-inflammatory and immunomodulatory, on CD colonization and gut integrity in mice.

METHODS

Mice were randomly grouped and supplemented daily with FP, prebiotic, FP + prebiotic, FP/prebiotic supernatant, or saline throughout the entire study. Following treatment with clindamycin for 3 days, mice were exposed to CD. Feces were collected at baseline, the day after antibiotic, and 1, 3, and 5 days after CD exposure and cultured for bacterial overgrowth and CD colonization. On days 1 and 5 after CD exposure, mice were randomly euthanized, and proximal colon was dissected for histological analysis and preparation of RNA for analysis of proinflammatory and anti-inflammatory cytokines.

RESULTS

Although all mice exhibited bacterial overgrowth and CD colonization, bacterial burden resolved quicker in the FP + prebiotic group. This was associated with induction and resolution of innate immune responses, anion exchanger, and tight junction protein preservation in proximal colon. CD toxin virulence potential was questionable as expression of CD toxin B receptor was depleted in the FP + prebiotic group.

CONCLUSION

Supplementation with anti-inflammatory butyrate-supporting commensal bacteria and prebiotic may support innate immune responses and minimize bacterial burden and negative effects during antibiotic and CD exposure.

Diagnostic Guidance for C. difficile Infections

Diagnosis of Clostridium difficile infection (CDI) can be challenging. First of all, there has been debate on which of the two reference assays, cell cytotoxicity neutralization assay (CCNA) or toxigenic culture (TC) should be considered the gold standard for CDI detection. Although the CCNA suffers most from suboptimal storage conditions and subsequent toxin degradation, TC is reported to falsely increase CDI detection rates as it cannot differentiate CDI patients from patients asymptomatically colonised by toxigenic C. difficile. Several rapid assays are available for CDI detection and fall into three broad categories: (1) enzyme immunoassays for glutamate dehydrogenase, (2) enzyme immunoassays for toxins A/B and (3) nucleic acid amplification tests detecting toxin genes. All three categories have their own limitations, being suboptimal specificity and/or sensitivity or the inability to discern colonised patients from CDI patients. In light of these limitations, multi-step algorithmic testing has now been advocated by international guidelines in order to optimize diagnostic accuracy. Despite these recommendations, testing methods between hospitals vary widely, which impacts CDI incidence rates. CDI incidence rates are also influenced by sample selection criteria, as several studies have shown that if not all unformed stool samples are tested for CDI, many cases may be missed due to an absence of clinical suspicion. Since methods for diagnosing CDI remain imperfect, there has been a growing interest in alternative testing strategies like faecal biomarkers, immune modulating interleukins, cytokines and imaging methods. At the moment, these alternative methods might play an adjunctive role, but they are not suitable to replace conventional CDI testing strategies.

The role of toxins in Clostridium difficile infection

Clostridium difficile is a bacterial pathogen that is the leading cause of nosocomial antibiotic-associated diarrhea and pseudomembranous colitis worldwide. The incidence, severity, mortality and healthcare costs associated with C. difficile infection (CDI) are rising, making C. difficile a major threat to public health. Traditional treatments for CDI involve use of antibiotics such as metronidazole and vancomycin, but disease recurrence occurs in about 30% of patients, highlighting the need for new therapies. The pathogenesis of C. difficile is primarily mediated by the actions of two large clostridial glucosylating toxins, toxin A (TcdA) and toxin B (TcdB). Some strains produce a third toxin, the binary toxin C. difficile transferase, which can also contribute to C. difficile virulence and disease. These toxins act on the colonic epithelium and immune cells and induce a complex cascade of cellular events that result in fluid secretion, inflammation and tissue damage, which are the hallmark features of the disease. In this review, we summarize our current understanding of the structure and mechanism of action of the C. difficile toxins and their role in disease.

Cytokines Are Markers of the Clostridium difficile-Induced Inflammatory Response and Predict Disease Severity

The host immune response affects pathogen virulence in Clostridium difficile infection (CDI). Thus, cytokine responses to CDI likely are associated with disease initiation and progression. Understanding the molecular drivers of inflammation and biochemical markers of disease severity is important for developing novel therapies and predicting disease prognosis. In this study, we investigated cytokine production in patients with CDI and evaluated the potential of cytokines to serve as biomarkers for CDI and predictors of disease severity. The systemic cytokine profiles of 36 CDI patients (20 with severe disease) and 8 healthy donors and the toxin-induced cytokine profiles of peripheral blood mononuclear cells (PBMC) were determined. Further, we evaluated glucosyltransferase (GT) activity in regulation of toxin-induced cytokine expression. We found upregulation of the majority of measured cytokines (11/20, 55%) in CDI patients. Interleukin-1β (IL-1β), IL-6, IL-8, IL-17A, and IL-16 were the most upregulated. High serum levels of IL-2 and IL-15 were associated with a poor prognosis in CDI patients, whereas high levels of IL-5 and gamma interferon (IFN-γ) were associated with less severe disease. Both TcdA and TcdB were potent inducers of cytokine responses, as demonstrated by stimulation of a greater number and amount of cytokines. In addition to confirming prior reports on the role of IL-8, IL-1β, and IL-6 in CDI, our data suggest that IL-16 and IL-17A, as well as the IL-1β/Th17 axis, play a key role in driving inflammatory responses in CDI. A functional GT domain of C. difficile toxins was required for the induction of a majority of cytokines investigated.

Invasive listeriosis in a patient with several episodes of antibiotic associated colitis presumably due to Clostridium difficile

A 62-year-old man developed a blood stream infection and meningitis due to Listeria monocytogenes, 20 days after an episode of pseudo-membranous colitis. The patient, hospitalized for the first time for transurethral prostatectomy, was readmitted 20 days later with watery diarrhea. Pseudo-membranous colitis was diagnosed and treated successfully, without testing for Clostridium difficile infection (CDI). After 15 more days, the patient developed again diarrhea, fever and confusion. Hospitalized again, blood and cerebrospinal fluid cultures resulted positive for L. monocytogenes. The patient was treated successfully and a diagnosis of recurrent CDI was confirmed following culture and nucleic acid amplification assays both positive for C. difficile. This is the first report of an invasive listeriosis after CDI underlines the importance of taking greater awareness in complicated blood stream infections that may arise after CDI.

Recurrent Clostridium difficile Infection in Children: Patient Risk Factors and Markers of Intestinal Inflammation

BACKGROUND

The management of Clostridium difficile infection (CDI) in children is complicated by recurrence rates of 20%-30%. The identification of risk factors associated with recurrent disease might allow early recognition of those children at highest risk.

METHODS

Pediatric patients with CDI were identified through clinical laboratory records at 2 tertiary-care children's hospitals from March 2013 through May 2014. Subjects were enrolled and followed for 60 days to assess for recurrent CDI (rCDI). Blood samples were obtained at enrollment to evaluate host interleukin (IL)-8 polymorphisms and anti-toxin A antibody levels; stool samples were obtained for inflammatory markers (lactoferrin, calprotectin, IL-8) and C. difficile ribotype 027 strain status. Thirty days post enrollment, another serum sample was obtained to compare antibody responses.

RESULTS

Of the 28 pediatric patients enrolled, 27 completed follow-up and 8 (30%) experienced rCDI. At enrollment, children with malignancy had significantly lower stool calprotectin, lactoferrin and IL-8 than those without malignancy. There was a trend toward increased stool inflammatory markers in those who later developed rCDI. The IL-8 A/A genotype was not associated with recurrent disease. No patients were found to have ribotype 027 or an antibody increase to toxin A.

CONCLUSIONS

The rate of rCDI in our pediatric cohort was 30%. Children with rCDI had a trend toward higher fecal inflammatory markers with the initial infection, and these values were lower in children with malignancy. Fecal lactoferrin, calprotectin and IL-8 should be further studied to determine their value in predicting the risk of rCDI in children.

Fecal Calprotectin Level Reflects the Severity of Clostridium difficile Infection

Clostridium difficile is a significant nosocomial and community-acquired pathogen, and is the leading cause of antibiotic-induced diarrhea associated with high morbidity and mortality. Given that the treatment outcome depends on the severity of C. difficile infection (CDI), we aimed to establish an efficient method of assessing severity, and focused on the stool biomarker fecal calprotectin (FC). FC directly reflects the intestinal inflammation status of a patient, and can aid in interpreting the current guidelines, which requires the integration of indirect laboratory parameters. The distinction of 80 patients with CDI versus 71 healthy controls and 30 severe infection cases versus 50 mild cases was possible using FC as a marker. The area under the receiver operating characteristic curves were 0.821 and 0.746 with a sensitivity of 75% and 70% and specificity of 79% and 80%, for severe versus mild cases, respectively. We suggest FC as a predictive marker for assessing CDI severity, which is expected to improve the clinical management of CDI.

Host response to Clostridium difficile infection: Diagnostics and detection

Clostridium difficile infection (CDI) is a significant healthcare concern worldwide, and C. difficile is recognised as the most frequent aetiological agent of infectious healthcare-associated diarrhoea in hospitalised adult patients. The clinical manifestation of CDI varies from self-limited diarrhoea to life-threatening colitis. Such a broad disease spectrum can be explained by the impact of host factors. Currently, a complex CDI aetiology is widely accepted, acknowledging the interaction between bacteria and the host. C. difficile strains producing clostridial toxins A and B are considered toxigenic and can cause disease; those not producing the toxins are non-pathogenic. A person colonised with a toxigenic strain will not necessarily develop CDI. It is imperative to recognise patients with active disease from those only colonised with this pathogen and to implement appropriate treatment. This can be achieved by diagnostics that rely on host factors specific to CDI. This review will focus on major aspects of CDI pathogenesis and molecular mechanisms, describing host factors in disease progression and assessment of the host response in order to facilitate the development of CDI-specific diagnostics.

The microbiota and immune response during Clostridium difficile infection

Clostridium difficile is a gram-positive, spore forming anaerobe that infects the gut when the normal microbiota has been disrupted. C. difficile infection (CDI) is the most common cause of hospital acquired infection in the United States, and the leading cause of death due to gastroenteritis. Patients suffering from CDI have varying symptoms which range from mild diarrhea to pseudomembranous colitis and death. The involvement of the immune response to influence disease severity is just beginning to be investigated. There is evidence that the immune response can facilitate either protective or pathogenic phenotypes, suggesting it plays a multifaceted role during CDI. In addition to the immune response, the microbiota is pivotal in dictating the pathogenesis to CDI. A healthy microbiota effectively inhibits infection by restricting the ability of C. difficile to expand in the colon. Thus, understanding which immune mediators and components of the microbiota play beneficial roles during CDI will be important to future therapeutic developments. This review outlines how the microbiota can modulate specific immune mediators, such as IL-23 and others, to influence disease outcome.

Immune responses induced by Clostridium difficile

The spectrum of Clostridium difficile infections is highly variable, ranging from asymptomatic carriage to fatal colitis depending on the strain virulence and on the host, its gut microbiota and its immune response. After disruption of the gut microbiota, C. difficile pathogenesis can be divided into three steps: 1) contamination by spores and their germination; 2) multiplication of vegetative cells and intestinal colonization using colonization factors; 3) production of the toxins TcdA and TcdB, and for some strains, the binary toxin, which are responsible for the clinical signs. Three lines of defense counteract C. difficile. The first line is the epithelial barrier, which is breached by the toxins. Then, a rapid innate immune response follows, which forms the second line of defense. It provides very quick defense reactions against C. difficile but is non-specific and does not confer memory. C. difficile and its virulence factors, the toxins and colonization factors, induce a highly pro-inflammatory response, which can be either beneficial or harmful, but triggers the adaptive immunity as the third line of defense required to control the infectious process. Adaptive immunity provides a highly specific immune response against C. difficile with memory and long lasting immunity. The innate and adaptive immune responses against the toxins and surface components are analyzed as well as their role in disease susceptibility, severity and recurrences.

Understanding the mechanisms of faecal microbiota transplantation

This Review summarizes mechanistic investigations in faecal microbiota transplantation (FMT), which has increasingly been adapted into clinical practice as treatment for Clostridium difficile infection (CDI) that cannot be eliminated with antibiotics alone. Administration of healthy donor faecal microbiota in this clinical situation results in its engraftment and restoration of normal gut microbial community structure and functionality. In this Review, we consider several main mechanisms for FMT effectiveness in treatment of CDI, including direct competition of C. difficile with commensal microbiota delivered by FMT, restoration of secondary bile acid metabolism in the colon and repair of the gut barrier by stimulation of the mucosal immune system. Some of these mechanistic insights suggest possibilities for developing novel, next-generation CDI therapeutics. FMT might also have potential applications for non-CDI indications. The gut can become a reservoir of other potential antibiotic-resistant pathogens under pressure of antibiotic treatments, and restoration of normal microbial community structure by FMT might be a promising approach to protect against infections with these pathogens as well. Finally, FMT could be considered for multiple chronic diseases that are associated with some form of dysbiosis. However, considerable research is needed to optimize the FMT protocols for such applications before their therapeutic promise can be evaluated.

Clostridium difficile colitis: pathogenesis and host defence

Clostridium difficile is a major cause of intestinal infection and diarrhoea in individuals following antibiotic treatment. Recent studies have begun to elucidate the mechanisms that induce spore formation and germination and have determined the roles of C. difficile toxins in disease pathogenesis. Exciting progress has also been made in defining the role of the microbiome, specific commensal bacterial species and host immunity in defence against infection with C. difficile. This Review will summarize the recent discoveries and developments in our understanding of C. difficile infection and pathogenesis.

Microbiota-Regulated IL-25 Increases Eosinophil Number to Provide Protection during Clostridium difficile Infection

Clostridium difficile infection (CDI) is the most common cause of hospital-acquired infection in the United States. Host susceptibility and the severity of infection are influenced by disruption of the microbiota and the immune response. However, how the microbiota regulate immune responses to mediate CDI outcome remains unclear. Here, we have investigated the role of the microbiota-linked cytokine IL-25 during infection. Intestinal IL-25 was suppressed during CDI in humans and mice. Restoration of IL-25 reduced CDI-associated mortality and tissue pathology even though equivalent levels of C. difficile bacteria and toxin remained in the gut. IL-25 protection was mediated by gut eosinophils, as demonstrated by an increase in intestinal eosinophils and a loss of IL-25 protection upon eosinophil depletion. These findings support a mechanism whereby the induction of IL-25-mediated eosinophilia can reduce host mortality during active CDI. This work may provide targets for future development of microbial or immune-based therapies.

Active and Secretory IgA-Coated Bacterial Fractions Elucidate Dysbiosis in Clostridium difficile Infection

C. difficile is a major enteric pathogen with worldwide distribution. Its expansion is associated with broad-spectrum antibiotics which disturb the normal gut microbiome. In this study, the DNA sequencing of highly active bacteria and bacteria opsonized by intestinal secretory immunoglobulin A (SIgA) separated from the whole bacterial community by FACS elucidated how the gut dysbiosis promotes C. difficile infection (CDI). Bacterial groups with inhibitory effects on C. difficile growth, such as Lactobacillales, were mostly inactive in the CDI patients. C. difficile was typical for the bacterial fraction opsonized by SIgA in patients with CDI, while Fusobacterium was characteristic for the SIgA-opsonized fraction of the controls. The study demonstrates that sequencing of specific bacterial fractions provides additional information about dysbiotic processes in the gut. The detected patterns have been confirmed with the whole patient cohort independently of the taxonomic differences detected in the nonfractionated microbiomes.

The onset of Clostridium difficile infection (CDI) has been associated with treatment with wide-spectrum antibiotics. Antibiotic treatment alters the activity of gut commensals and may result in modified patterns of immune responses to pathogens. To study these mechanisms during CDI, we separated bacteria with high cellular RNA content (the active bacteria) and their inactive counterparts by fluorescence-activated cell sorting (FACS) of the fecal bacterial suspension. The gut dysbiosis due to the antibiotic treatment may result in modification of immune recognition of intestinal bacteria. The immune recognition patterns were assessed by FACS of bacterial fractions either coated or not with intestinal secretory immunoglobulin A (SIgA). We described the taxonomic distributions of these four bacterial fractions (active versus inactive and SIgA coated versus non-SIgA coated) by massive 16S rRNA gene amplicon sequencing and quantified the proportion of C. difficile toxin genes in the samples. The overall gut microbiome composition was more robustly influenced by antibiotics than by the C. difficile toxins. Bayesian networks revealed that the C. difficile cluster was preferentially SIgA coated during CDI. In contrast, in the CDI-negative group Fusobacterium was the characteristic genus of the SIgA-opsonized fraction. Lactobacillales and Clostridium cluster IV were mostly inactive in CDI-positive patients. In conclusion, although the proportion of C. difficile in the gut is very low, it is able to initiate infection during the gut dysbiosis caused by environmental stress (antibiotic treatment) as a consequence of decreased activity of the protective bacteria.

IMPORTANCEC. difficile is a major enteric pathogen with worldwide distribution. Its expansion is associated with broad-spectrum antibiotics which disturb the normal gut microbiome. In this study, the DNA sequencing of highly active bacteria and bacteria opsonized by intestinal secretory immunoglobulin A (SIgA) separated from the whole bacterial community by FACS elucidated how the gut dysbiosis promotes C. difficile infection (CDI). Bacterial groups with inhibitory effects on C. difficile growth, such as Lactobacillales, were mostly inactive in the CDI patients. C. difficile was typical for the bacterial fraction opsonized by SIgA in patients with CDI, while Fusobacterium was characteristic for the SIgA-opsonized fraction of the controls. The study demonstrates that sequencing of specific bacterial fractions provides additional information about dysbiotic processes in the gut. The detected patterns have been confirmed with the whole patient cohort independently of the taxonomic differences detected in the nonfractionated microbiomes.

Elevated fecal calprotectin associates with adverse outcomes from Clostridium difficile infection in older adults

BACKGROUND

Clostridium difficile infection (CDI) causes a mild to moderate colitis in most patients, but some, especially older adults, develop severe, adverse outcomes. Biomarkers predicting outcomes are needed to optimize treatments. This study tested whether fecal calprotectin associated with a composite primary outcome of complicated CDI (intensive care unit admission, colectomy, or death due to CDI within 30 days of diagnosis) and/or 8-week recurrence.

METHODS

Stool was collected in Cary-Blair media at the time of diagnosis from inpatients of age >60 years that tested positive for C. difficile (enzyme immunoassay [EIA] for toxin A/B or polymerase chain reaction for the tcdB gene). Fecal calprotectin was measured and normalized to solid stool weight. Analysis was performed using logistic regression. Variables were selected for the final model using likelihood ratio tests.

RESULTS

Fifty patients were included with a mean age 72.8 (± 7.5), and 13 (26%) developed the primary outcome. Clinical variables such as age, gender, and comorbid disease did not associate with complicated CDI/recurrence, nor did traditional biomarkers such as serum albumin or white blood cell count. A high normalized fecal calprotectin (>2000 μg/g) associated with the primary outcome in the final model after adjustment for gender and detectable fecal toxin(s) by EIA (OR 24.9, 95% CI 2.4-257.9, p = 0.007) with a specificity of 91.9%.

CONCLUSION

This study provides evidence that fecal calprotectin level associates with complications from CDI in older adults. Further studies are required to validate these findings in larger cohorts and incorporate them into clinical prediction algorithms.

Impact on toxin production and cell morphology in Clostridium difficile by ridinilazole (SMT19969), a novel treatment for C. difficile infection

OBJECTIVES

Ridinilazole (SMT19969) is a narrow-spectrum, non-absorbable antimicrobial with activity against Clostridium difficile undergoing clinical trials. The purpose of this study was to assess the pharmacological activity of ridinilazole and assess the effects on cell morphology.

METHODS

Antibiotic killing curves were performed using the epidemic C. difficile ribotype 027 strain, R20291, using supra-MIC (4× and 40×) and sub-MIC (0.125×, 0.25× and 0.5×) concentrations of ridinilazole. Following exposure, C. difficile cells were collected for cfu counts, toxin A and B production, and morphological changes using scanning electron and fluorescence microscopy. Human intestinal cells (Caco-2) were co-incubated with ridinilazole-treated C. difficile growth medium to determine the effects on host inflammatory response (IL-8).

RESULTS

Treatment at supra-MIC concentrations (4× and 40× MIC) of ridinilazole resulted in a significant reduction in vegetative cells over 72 h (4 log difference, P < 0.01) compared with controls without inducing spore formation. These results correlated with a 75% decrease in toxin A production (P < 0.05) and a 96% decrease in toxin B production (P < 0.05). At sub-MIC levels (0.5× MIC), toxin A production was reduced by 91% (P < 0.01) and toxin B production was reduced by 100% (P < 0.001), which resulted in a 74% reduction in IL-8 release compared with controls (P < 0.05). Sub-MIC (0.5×)-treated cells formed filamentous structures ∼10-fold longer than control cells. Following fluorescence labelling, the cell septum was not forming in sub-MIC-treated cells, yet the DNA was dividing.

CONCLUSIONS

Ridinilazole had robust killing effects on C. difficile that significantly reduced toxin production and attenuated the inflammatory response. Ridinilazole also elicited significant cell division effects suggesting a potential mechanism of action.

Droplet digital PCR quantifies host inflammatory transcripts in feces reliably and reproducibly

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Direct measurement of gut epithelial immunology is difficult.

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Fecal host transcript can measured using conservative transcript isolation and droplet digital PCR.

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A new method to non-invasively elucidate gut immunology is described.

The gut is the most extensive, interactive, and complex interface between the human host and the environment and therefore a critical site of immunological activity. Non-invasive methods to assess the host response in this organ are currently lacking. Feces are the available analyte which have been in proximity to the gut tissue.

We applied a method of concentrating host transcripts from fecal specimens using a existing bead-based affinity separation method for nucleic acids and quantified transcripts using droplet digital PCR (ddPCR) to determine the copy numbers of a variety of key transcripts in the gut immune system. ddPCR compartmentalizes the reaction in a small aqueous droplet suspended in oil, and counts droplets as either fluorescent or non-fluorescent. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) was used to normalize transcript concentration.

This method was applied to 799 fecal samples from rural Malawian children, and over 20,000 transcript concentrations were quantified. Host mRNA was detected in >99% samples, a threshold for target detection was established at an average expression of 0.02 copies target/GAPDH, above which correlation coefficient between duplicate measurements is >0.95. Quantities of transcript detected using ddPCR were greater than standard qPCR. Fecal sample preservation at the time of collection did not require immediate freezing or the addition of buffers or enzymes. Measurements of transcripts encoding immunoactive proteins correlated with a measure of gut inflammation in the study children, thereby substantiating their relevance. This method allows investigators to interrogate gene expression in the gut.

Pathogenic effects of glucosyltransferase from Clostridium difficile toxins

The glucosyltransferase domain ofClostridium difficiletoxins modifies guanine nucleotide-binding proteins of Rho family. It is the major virulent domain of the holotoxins. Various pathogenic effects ofC. difficiletoxins in response to Rho glucosylation have been investigated including cytoskeleton damage, cell death and inflammation. The most recent studies have revealed some significant characteristics of the holotoxins that are independent of glucosylating activity. These findings arouse discussion about the role of glucosyltransferase activity in toxin pathogenesis and open up new insights for toxin mechanism study. In this review, we summarize the pathogenic effects of glucosyltransferase domain of the toxins in the past years.

Neutrophil-mediated inflammation in the pathogenesis of Clostridium difficile infections

Clostridium difficile is the most important cause of nosocomial infectious diarrhea in the western world. C. difficile infections are a major healthcare burden with approximately 500,000 new cases every year and an estimated annual cost of nearly $1 billion in the U.S. Furthermore, the infections are no longer restricted to health care facilities, and recent studies indicate spread of C. difficile infection to the community as well. The clinical spectrum of C. difficile infection ranges from asymptomatic colonization to severe diarrhea, fulminant colitis and death. This spectrum results from a complex interplay between bacterial virulence factors, the colonic microbiome and the host inflammatory response. The overall vigor of host inflammatory response is believed to be an important determinant of C. difficile disease severity, and a more robust immune response is associated with worse outcomes. Neutrophils are the primary cells that respond to C. difficile invasion and neutrophilic inflammation is the hallmark of C. difficile-associated disease. In this review, we will focus on the role of neutrophils (infiltration to infected tissue, pathogen clearance and resolution of inflammation) in the immuno-pathogenesis of C. difficile-associated disease (CDAD).

Clostridium difficile infection: epidemiology, diagnosis and understanding transmission

Clostridium difficile infection (CDI) continues to affect patients in hospitals and communities worldwide. The spectrum of clinical disease ranges from mild diarrhoea to toxic megacolon, colonic perforation and death. However, this bacterium might also be carried asymptomatically in the gut, potentially leading to 'silent' onward transmission. Modern technologies, such as whole-genome sequencing and multi-locus variable-number tandem-repeat analysis, are helping to track C. difficile transmission across health-care facilities, countries and continents, offering the potential to illuminate previously under-recognized sources of infection. These typing strategies have also demonstrated heterogeneity in terms of CDI incidence and strain types reflecting different stages of epidemic spread. However, comparison of CDI epidemiology, particularly between countries, is challenging due to wide-ranging approaches to sampling and testing. Diagnostic strategies for C. difficile are complicated both by the wide range of bacterial targets and tests available and the need to differentiate between toxin-producing and non-toxigenic strains. Multistep diagnostic algorithms have been recommended to improve sensitivity and specificity. In this Review, we describe the latest advances in the understanding of C. difficile epidemiology, transmission and diagnosis, and discuss the effect of these developments on the clinical management of CDI.

Host Immune Response to Clostridium difficile Infection in Inflammatory Bowel Disease Patients

BACKGROUND

Clostridium difficile infection (CDI) affects patients with inflammatory bowel disease (IBD). The aim of this study was to compare humoral response to C. difficile toxins in IBD patients and control outpatients.

METHODS

We prospectively followed adult IBD patients and control subjects with serum and stool samples obtained at enrollment and during periods of CDI and tested by PCR. Semiquantitative serum levels of IgM, IgG, and IgA to C. difficile toxins A and B were measured.

RESULTS

Overall, 119 stool and 117 serum samples were obtained from 150 subjects. Different levels of IgA to toxin A (P = 0.0016) and toxin B (P = 0.0468) were noted between different IBD groups. Toxin A IgA levels were higher in the Crohn's disease group (P = 0.0321) and ileal pouch anal anastomosis (IPAA) group (P = 0.001) compared with the ulcerative colitis (UC) group, and toxin B IgA levels were higher in the IPAA group compared with the UC group (P = 0.0309). There were lower levels of toxin A IgA in IBD patients compared with those in subjects without new CDI (P = 0.0488) and higher levels in IBD patients with compared with those in subjects without CDI history before enrollment (P = 0.016). There were nonsignificant lower toxin A IgG levels in IBD patients compared with those in subjects without prior CDI (P = 0.095) and higher levels in control subjects with a history of CDI compared with IBD patients with prior CDI (P = 0.049).

CONCLUSIONS

Patients with UC have lower IgA levels to C. difficile toxins compared with those with Crohn's disease and those after IPAA. Patients with IBD with prior CDI failed to demonstrate any increase in antitoxin IgG. Our findings suggest that IBD patients may benefit from immunization strategies targeting C. difficile toxins.

Comparison of pediatric and adult antibiotic-associated diarrhea and Clostridium difficile infections

Antibiotic-associated diarrhea (AAD) and Clostridum difficile infections (CDI) have been well studied for adult cases, but not as well in the pediatric population. Whether the disease process or response to treatments differs between pediatric and adult patients is an important clinical concern when following global guidelines based largely on adult patients. A systematic review of the literature using databases PubMed (June 3, 1978-2015) was conducted to compare AAD and CDI in pediatric and adult populations and determine significant differences and similarities that might impact clinical decisions. In general, pediatric AAD and CDI have a more rapid onset of symptoms, a shorter duration of disease and fewer CDI complications (required surgeries and extended hospitalizations) than in adults. Children experience more community-associated CDI and are associated with smaller outbreaks than adult cases of CDI. The ribotype NAP1/027/BI is more common in adults than children. Children and adults share some similar risk factors, but adults have more complex risk factor profiles associated with more co-morbidities, types of disruptive factors and a wider range of exposures to C. difficile in the healthcare environment. The treatment of pediatric and adult AAD is similar (discontinuing or switching the inciting antibiotic), but other treatment strategies for AAD have not been established. Pediatric CDI responds better to metronidazole, while adult CDI responds better to vancomycin. Recurrent CDI is not commonly reported for children. Prevention for both pediatric and adult AAD and CDI relies upon integrated infection control programs, antibiotic stewardship and may include the use of adjunctive probiotics. Clinical presentation of pediatric AAD and CDI are different than adult AAD and CDI symptoms. These differences should be taken into account when rating severity of disease and prescribing antibiotics.