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

Differences of the Fecal Microflora With Clostridium difficile Therapies

BACKGROUND

During treatment of Clostridium difficile infection (CDI), patterns of pathogen reduction in relationship to changes in components of the normal microbiota are hypothesized to be predictive of response to treatment and subsequent sustained cure.

METHODS

At a single center, subjects enrolled into phase 2 and 3 C. difficile treatment clinical trials (2003-2008) provided fecal samples to assess killing of C. difficile and changes to components of the microbiome. Quantitative bacterial cultures, measurement of C. difficile toxin titers, quantitative polymerase chain reaction of fecal samples for Bacteroidetes, Clostridium clusters XIVa and IV, and C. difficile were performed.

RESULTS

Quantitative bacterial cultures showed a mean log10 C. difficile count (colony-forming units [CFU]) of 6.7 ± 2.0 at study entry; vancomycin treatment consistently reduced C. difficile counts to the limit of detection (2.0 log10 CFU/g), whereas metronidazole was associated with mean C. difficile counts 1.5-2 log10 higher at 10 days of treatment. In patients receiving tolevamer, C. difficile persisted in high counts during treatment; response to treatment was correlated with neutralization of toxin along with persistence of normal microbiota components. However, this was achieved in approximately half of subjects. Both vancomycin and metronidazole further suppressed microbiome components during treatment of CDI. Lactobacilli were observed to be a microbiome component that persisted during treatment of CDI.

CONCLUSIONS

Differences of pathogen clearance and microbiome perturbation during treatment of CDI appear to explain treatment outcomes. The hypothesis that probiotic microbes could help prevent onset of CDI is supported by the observation of persistence of lactobacilli during and after treatment of CDI.

Risk Factors and Outcomes for Bloodstream Infections Secondary to Clostridium difficile Infection

We determined the incidence, risk factors, and outcomes of bloodstream infections (BSI) subsequent to Clostridium difficile infection (CDI). We performed a retrospective study of all patients with definite diagnosis of CDI admitted from January 2014 to December 2014 in two large hospitals in Rome. Two groups of patients were analyzed: those with CDI and subsequent BSI (CDI/BSI(+)) and those with CDI and no evidence of primary BSI (CDI/BSI(-)). Data about clinical features, microbiology, treatments, and mortality were obtained. Overall, 393 cases of CDI were included in the final analysis: 72 developed a primary nosocomial BSI, while 321 had CDI without microbiological and clinical evidence of BSI. Etiologic agents of BSI were Candida species (47.3%), Enterobacteriaceae (19.4%), enterococci (13.9%), and mixed infections (19.4%). In multivariate analysis, ribotype 027 status (odds ratio [OR], 6.5), CDI recurrence (OR, 5.5), severe CDI infection (OR, 8.3), and oral vancomycin at >500 mg/day (OR, 3.1) were recognized as factors independently associated with the development of nosocomial BSI. Thirty-day mortality from CDI diagnosis was higher for patients of the CDI/BSI(+) group than for the controls (38.9 versus 13.1%; P < 0.001). Among patients of the CDI/BSI(+) group, mortality attributable to primary BSI was as high as 57%. Our findings suggest that severe CDI is complicated by the development of nosocomial BSI. Candida species and enteric bacteria appear to be the leading causative pathogens and are associated with poor outcomes.

Metagenomic Approach for Identification of the Pathogens Associated with Diarrhea in Stool Specimens

The potential to rapidly capture the entire microbial community structure and/or gene content makes metagenomic sequencing an attractive tool for pathogen identification and the detection of resistance/virulence genes in clinical settings. Here, we assessed the consistency between PCR from a diagnostic laboratory, quantitative PCR (qPCR) from a research laboratory, 16S rRNA gene sequencing, and metagenomic shotgun sequencing (MSS) for Clostridium difficile identification in diarrhea stool samples. Twenty-two C. difficile-positive diarrhea samples identified by PCR and qPCR and five C. difficile-negative diarrhea controls were studied. C. difficile was detected in 90.9% of C. difficile-positive samples using 16S rRNA gene sequencing, and C. difficile was detected in 86.3% of C. difficile-positive samples using MSS. CFU inferred from qPCR analysis were positively correlated with the relative abundance of C. difficile from 16S rRNA gene sequencing (r(2) = -0.60) and MSS (r(2) = -0.55). C. difficile was codetected with Clostridium perfringens, norovirus, sapovirus, parechovirus, and anellovirus in 3.7% to 27.3% of the samples. A high load of Candida spp. was found in a symptomatic control sample in which no causative agents for diarrhea were identified in routine clinical testing. Beta-lactamase and tetracycline resistance genes were the most prevalent (25.9%) antibiotic resistance genes in these samples. In summary, the proof-of-concept study demonstrated that next-generation sequencing (NGS) in pathogen detection is moderately correlated with laboratory testing and is advantageous in detecting pathogens without a priori knowledge.

Recurrent Clostridium difficile infection: From colonization to cure

Clostridium difficile infection (CDI) is increasingly prevalent, dangerous and challenging to prevent and manage. Despite intense national and international attention the incidence of primary and of recurrent CDI (PCDI and RCDI, respectively) have risen rapidly throughout the past decade. Of major concern is the increase in cases of RCDI resulting in substantial morbidity, morality and economic burden. RCDI management remains challenging as there is no uniformly effective therapy, no firm consensus on optimal treatment, and reliable data regarding RCDI-specific treatment options is scant. Novel therapeutic strategies are critically needed to rapidly, accurately, and effectively identify and treat patients with, or at-risk for, RCDI. In this review we consider the factors implicated in the epidemiology, pathogenesis and clinical presentation of RCDI, evaluate current management options for RCDI and explore novel and emerging therapies.

The Bug Stops Here: Innate Lymphoid Cells in Clostridium difficile Infection

The contribution of the innate immune response to the resolution of Clostridium difficile infection (CDI) remains incompletely defined. In this issue of Cell Host & Microbe, Abt et al. demonstrated that innate lymphoid cells and the effector cytokine IFN-γ are important for recovery from the acute phase of CDI.

Role of obesity and adipose tissue-derived cytokine leptin during Clostridium difficile infection

Obesity is among the most pressing health concerns in the world since it is increasingly common even in the developing world, and is clearly associated with increased risk for chronic debilitating diseases and death. Furthermore, obesity can influence the pathogenesis of infectious diseases by affecting the balance of pathogen clearance and pathological inflammation. The mechanisms that result in enhanced inflammation in obese individuals are poorly understood. Clostridium difficile is a major cause of nosocomial infections worldwide. Recent studies have shown that obesity is associated with increased risk of C. difficile infections. In this review, we will discuss our current knowledge of the role of obesity in determining risk of C. difficile infections, and focus on the role of the adipose tissue-derived cytokine leptin in C. difficile infections.

Inflammasome activation contributes to interleukin-23 production in response to Clostridium difficile

Clostridium difficile is the most common hospital-acquired pathogen, causing antibiotic-associated diarrhea in over 250,000 patients annually in the United States. Disease is primarily mediated by toxins A and B, which induce potent proinflammatory signaling in host cells and can activate an ASC-containing inflammasome. Recent findings suggest that the intensity of the host response to infection correlates with disease severity. Our lab has identified the proinflammatory cytokine interleukin-23 (IL-23) as a pathogenic mediator during C. difficile infection (CDI). The mechanisms by which C. difficile induces IL-23, however, are not well understood, and the role of toxins A and B in this process is unclear. Here, we show that toxins A and B alone are not sufficient for IL-23 production but synergistically increase the amount of IL-23 produced in response to MyD88-dependent danger signals, including pathogen-associated molecular patterns (PAMPs) and host-derived damage associated molecular patterns (DAMPs). Danger signals also enhanced the secretion of IL-1β in response to toxins A and B, and subsequent IL-1 receptor signaling accounted for the majority of the increase in IL-23 that occurred in the presence of the toxins. Inhibition of inflammasome activation in the presence of extracellular K⁺ likewise decreased IL-23 production. Finally, we found that IL-1β was increased in the serum of patients with CDI, suggesting that this systemic response could influence downstream production of pathogenic IL-23. Identification of the synergy of danger signals with toxins A and B via inflammasome signaling represents a novel finding in the mechanistic understanding of C. difficile-induced inflammation.

Clostridium difficile is among the leading causes of death due to health care-associated infection, and factors determining disease severity are not well understood. C. difficile secretes toxins A and B, which cause inflammation and tissue damage, and recent findings suggest that some of this tissue damage may be due to an inappropriate host immune response. We have found that toxins A and B, in combination with both bacterium- and host-derived danger signals, can induce expression of the proinflammatory cytokines IL-1β and IL-23. Our results demonstrate that IL-1β signaling enhances IL-23 production and could lead to increased pathogenic inflammation during CDI.

Phosphatidylcholine and the intestinal mucus layer: in vitro efficacy against Clostridium difficile-associated polymorphonuclear neutrophil activation

BACKGROUND

Phosphatidylcholine (PC), an important component of intestinal mucus, protects against Clostridium difficile toxin-induced intestinal barrier injury in vitro. Polymorphonuclear neutrophil (PMN) activation may contribute to intestinal injury and systemic toxicity in patients with C. difficile-associated disease. We therefore hypothesized that the intestinal barrier function against C. difficile toxin by exogenous PC would ameliorate PMN activation.

METHODS

Intestinal epithelial cell (IEC) monolayers were cocultured with C. difficile toxin A and/or exogenous PC. Naïve PMNs were cocultured with IEC culture supernatants and PMN activation, and chemotactic potential determined.

RESULTS

PC treatment of IEC abrogated the enhanced PMN activation and chemotactic potential following toxin A exposure (P < .001).

CONCLUSIONS

Exogenous PC ameliorated PMN activation from IECs exposed to C. difficile toxin. Administration of exogenous PC may be a useful adjunctive treatment in severely ill or immunocompromised patients with C. difficile-associated disease.

Exogenous phosphatidylcholine supplementation improves intestinal barrier defense against Clostridium difficile toxin

BACKGROUND

The incidence and severity of Clostridium difficile colitis have increased dramatically in the last decade. Disease severity is related to C. difficile virulence factors, including toxins A and B, as well as the patient's immune status. The intestinal mucus is an important component of innate barrier function in the intestine. Phosphatidylcholine (PC) is a key constituent of the intestinal mucus barrier, and exogenous PC administration has had therapeutic efficacy in patients with ulcerative colitis. We studied the protective function of exogenous PC on C. difficile toxin effects on the intestinal barrier in vitro.

METHODS

Mucus-producing (HT29-MTX strain) and non-mucus-producing (HT29 strain) intestinal epithelial monolayers were cocultured with PC and C. difficile toxin A added to the apical media. Basal chamber culture supernatants were subsequently obtained, and tumor necrosis factor and interleukin 6 were quantitated by enzyme-linked immunosorbent assay. In other experiments, HT29 toxin A uptake, intestinal monolayer permeability, necrosis, and actin microfilament disruption were determined.

RESULTS

There was a threefold to fourfold decrease in tumor necrosis factor and interleukin 6 levels and similar decreases in toxin A uptake and permeability changes in intestinal epithelial cells with mucus or PC versus control. Intestinal epithelial cell necrosis was reduced by more than 50% with either mucus or PC versus control. The integrity of HT29 cell cytoskeleton was demonstrated by both the mucus layer of the HT29-MTX strain and by exogenous PC administration by phalloidin staining of actin microfilaments.

CONCLUSION

PC supplementation was effective in improving intestinal barrier defense against C. difficile toxin A challenge. PC administration may be a useful therapeutic adjunct in severe cases of C. difficile colitis or in patients who do not improve with conventional treatment.

The molecular basis of Clostridium difficile disease and host response

PURPOSE OF REVIEW

Clostridium difficile infection (CDI) ranges from asymptomatic colonization to severe colitis and death. The physiologic and molecular mechanisms determining disease outcome are thus far poorly understood. Here, we review recent advances in the relationship between host response to infection and disease outcome. Furthermore, we review recent studies on the relationship between intestinal microbial ecology and pathogenesis of CDI.

RECENT FINDINGS

Severe CDI is characterized by toxin-induced epithelial injury and marked intestinal inflammation. Recent studies demonstrate that systemic markers of inflammation correlate with disease outcome. Peripheral neutrophil count, C-reactive protein, and proinflammatory cytokines are elevated in patients with severe disease as compared with asymptomatic controls. Furthermore, fecal inflammatory biomarkers are better predictors of disease severity and diarrhea persistence than C. difficile abundance. A landmark study reported higher than 80% success rate of fecal microbiota transplantation for treatment of recurrent CDI. The commensal microbes responsible for C. difficile protection, and the molecular basis by which microbial ecology impacts disease outcome, are under active investigation.

SUMMARY

Under conditions of altered microbial ecology, C. difficile incites epithelial injury and marked intestinal inflammation, the primary determinant of disease outcome. Restoration of a diverse intestinal microbial population by fecal microbiota transplantation attenuates disease and prevents recurrence by mechanisms that are yet to be fully elucidated.

Challenges and opportunities in the management of Clostridium difficile infection

Clostridium difficile infection (CDI) is increasing in all regions of the world where sought. There is no gold standard for diagnosis of CDI, with available tests having limitations. Prevention of CDI will be seen with antibiotic stewardship, improved disinfection of hospitals and nursing homes, chemo- and immuno-prophylaxis and next generation probiotics. The important therapeutic agents are oral vancomycin and fidaxomicin with metronidazole being used only in mild cases or when oral therapy cannot be given. Current therapy of CDI for 10 days is associated with high rate of recurrence that may be prevented by prolonging initial therapy. Future treatment strategies will focus on drugs that inhibit C. difficile, reduce toxin activity and inflammation in the gut, and improve colonic flora diversity.

Clostridium difficile recurrence is characterized by pro-inflammatory peripheral blood mononuclear cell (PBMC) phenotype

Clostridium difficile infection (CDI) is a prevalent nosocomial and increasingly community-acquired problem. Little is known about the productive cellular response in patients. We used flow cytometry to define inflammatory (Th1 and Th17) and regulatory [Foxp3(+) T-regulatory (Treg)] cells present in circulating peripheral blood mononuclear cells (PBMC) from CDI patients. We consented 67 inpatients that tested either positive or negative for CDI and 16 healthy controls and compared their PBMC phenotypes. PBMC were collected, isolated, and stained for CD3, CD8 and either IL17 (Th17), IFN-γ (Th1) or Foxp3 (Treg) and analysed using flow cytometry. Twenty thousand events were collected in the lymphocyte gate (gate 1) and T-cell phenotypes were defined. CDI patients who clear the primary initial infection have greater numbers of non-CD3 PBMC. CDI patients who develop recurrence of CDI have a greater percentage of CD3(+)CD8(+), CD3(+)CD4(+)Foxp3 and fewer low granular CD3(-)Foxp3(+) PBMC. These patients have greater numbers of IFN-γ-producing lymphocytes, as well as PBMC phenotypes represented by increased IFN-γ- and IL17-co-expressing CD4(+)CD3(+). This initial pro-inflammatory phenotype decreases with repeated recurrence, demonstrating importance of timing of sample collection and history of symptoms. Patients with a history of recurrence had increased Foxp3(+)CD3(+)CD4(+) and IL17(+)CD3(+)CD4(+) populations. Hence, CDI recurrence is hallmarked by greater numbers of circulating CD3(+) lymphocytes skewed towards a Th1/Th17 inflammatory population as well as possible immune plasticity (Th17/Treg).

The roles of host and pathogen factors and the innate immune response in the pathogenesis of Clostridium difficile infection

Clostridium difficile (C. difficile) is the most common cause of nosocomial antibiotic-associated diarrhea and the etiologic agent of pseudomembranous colitis. The clinical manifestation of C. difficile infection (CDI) is highly variable, from asymptomatic carriage, to mild self-limiting diarrhea, to the more severe pseudomembranous colitis. Furthermore, in extreme cases, colonic inflammation and tissue damage can lead to toxic megacolon, a condition requiring surgical intervention. C. difficile expresses two key virulence factors; the exotoxins, toxin A (TcdA) and toxin B (TcdB), which are glucosyltransferases that target host-cell monomeric GTPases. In addition, some hypervirulent strains produce a third toxin, binary toxin or C. difficile transferase (CDT), which may contribute to the pathogenesis of CDI. More recently, other factors such as surface layer proteins (SLPs) and flagellin have also been linked to the inflammatory responses observed in CDI. Although the adaptive immune response can influence the severity of CDI, the innate immune responses to C. difficile and its toxins play crucial roles in CDI onset, progression, and overall prognosis. Despite this, the innate immune responses in CDI have drawn relatively little attention from clinical researchers. Targeting these responses may prove useful clinically as adjuvant therapies, especially in refractory and/or recurrent CDI. This review will focus on recent advances in our understanding of how C. difficile and its toxins modulate innate immune responses that contribute to CDI pathogenesis.

Host recognition of Clostridium difficile and the innate immune response

Clostridium difficile is a Gram-positive, spore forming bacillus and the most common cause of antibiotic-associated diarrhea in the United States. Clinical outcomes of C. difficile infection (CDI) range from asymptomatic colonization to pseudomembranous colitis, sepsis and death. Disease is primarily mediated by the action of the Rho-glucosylating toxins A and B, which induce potent pro-inflammatory signaling within the host. The role of this inflammatory response during infection is just beginning to be appreciated, with recent data suggesting inflammatory markers correlate closely with disease severity. In addition to the toxins, multiple innate immune signaling pathways have been implicated in establishing an inflammatory response during infection. In intoxication-based models of disease, inflammation typically enhances pathogenesis, while protection from infection seems to require some level of inflammatory response. Thus, the host immune response plays a key role in shaping the course of infection and a balanced inflammatory response which eradicates infection without damaging host tissues is likely required for successful resolution of disease.

Calprotectin and lactoferrin faecal levels in patients with Clostridium difficile infection (CDI): a prospective cohort study

Measurement of both calprotectin and lactoferrin in faeces has successfully been used to discriminate between functional and inflammatory bowel conditions, but evidence is limited for Clostridium difficile infection (CDI). We prospectively recruited a cohort of 164 CDI cases and 52 controls with antibiotic-associated diarrhoea (AAD). Information on disease severity, duration of symptoms, 30-day mortality and 90-day recurrence as markers of complicated CDI were recorded. Specimens were subject to microbiological culture and PCR-ribotyping. Levels of faecal calprotectin (FC) and lactoferrin (FL) were measured by ELISA. Statistical analysis was conducted using percentile categorisation. ROC curve analysis was employed to determine optimal cut-off values. Both markers were highly correlated with each other (r² = 0.74) and elevated in cases compared to controls (p<0.0001; ROC>0.85), although we observed a large amount of variability across both groups. The optimal case-control cut-off point was 148 mg/kg for FC and 8.1 ng/µl for FL. Median values for FL in CDI cases were significantly greater in patients suffering from severe disease compared to non-severe disease (104.6 vs. 40.1 ng/µl, p = 0.02), but were not significant for FC (969.3 vs. 512.7 mg/kg, p = 0.09). Neither marker was associated with 90-day recurrence, prolonged CDI symptoms, positive culture results and colonisation by ribotype 027. Both FC and FL distinguished between CDI cases and AAD controls. Although FL was associated with disease severity in CDI patients, this showed high inter-individual variability and was an isolated finding. Thus, FC and FL are unlikely to be useful as biomarkers of complicated CDI disease.

Serum mannose-binding lectin concentration, but not genotype, is associated with Clostridium difficile infection recurrence: a prospective cohort study

Low mannose-binding lectin concentration, but not genotype, was associated with disease recurrence in a large prospective cohort of patients with Clostridium difficile infection.

Background. Mannose-binding lectin (MBL) plays a key role in the activation of the lectin-complement pathway of innate immunity, and its deficiency has been linked with several acute infections. However, its role in predisposing to, or modulating disease severity in, Clostridium difficile infection (CDI) has not been investigated.

Methods. We prospectively recruited 308 CDI case patients and 145 control patients with antibiotic-associated diarrhea (AAD). CDI outcome measures were disease severity, duration of symptoms, 30-day mortality, and 90-day recurrence. Serum concentrations of MBL were determined using a commercial enzyme-linked immunosorbent assay transferred to an electrochemiluminescence–based platform. MBL2 polymorphisms were typed using a combination of pyrosequencing and TaqMan genotyping assays.

Results. The frequency of the MBL2 genetic variants was similar to that reported in other white populations. MBL serum concentrations in CDI and AAD subjects were determined by MBL2 exonic variants B, C, and D and the haplotypes (LYPB, LYQC, and HYPD). There was no difference in either MBL concentrations or genotypes between cases and controls. MBL concentration, but not genotype, was a determinant of CDI recurrence (odds ratios, 3.18 [95% confidence interval {CI}, 1.40–7.24] and 2.61 [95% CI, 1.35–5.04] at the <50 ng/mL and <100 ng/mL cutoff points, respectively; P < .001). However, neither MBL concentration nor MBL2 genotype was linked with the other CDI outcomes.

Conclusions. Serum MBL concentration did not differentiate between CDI cases and AAD controls, but among CDI cases, MBL concentration, but not genotype, was associated with CDI recurrence, indicating that MBL acts as a modulator of disease, rather than a predisposing factor.

Corticosteroid use is associated with a reduced incidence of Clostridium difficile-associated diarrhea: a retrospective cohort study

The impact of corticosteroid use on the incidence of Clostridium difficile-associated diarrhea (CDAD) was examined retrospectively in 532 patients receiving antibiotic treatment for respiratory infections. As determined by logistic regression, corticosteroids were associated with a decreased incidence of CDAD (Odds Ratio 0.12, 95% Confidence Interval 0.006-0.95).

Reinforcement of the intestinal mucus layer protects against Clostridium difficile intestinal injury in vitro

BACKGROUND

Clostridium difficile infection is increasing in incidence and severity. Attributable factors include virulence factors, including C difficile toxins A and B, as well as host immunologic status. The mucus component of the intestinal barrier is impaired by malnutrition, shock insults, and alterations in the gut microbiome. Exogenous phosphatidylcholine (PC) administration results in reinforcement of the mucus layer and is of therapeutic benefit in chronic ulcerative colitis. We therefore studied the role of exogenous PC combined with secretory immunoglobulin A (IgA) in intestinal barrier function against C difficile infection in vitro.

STUDY DESIGN

Dimeric IgA was placed in the basal chambers of mucus-producing (HT29-methotrexate) and non-mucus-producing (HT29) strains of intestinal epithelial monolayers and allowed to undergo transcytosis and, in additional experiments, exogenous colostral IgA (30 ng/mL) was added to the apical media. After subsequent coculture with PC and C difficile toxin A in the apical chamber, tumor necrosis factor-α, interleukin-6, toxin A uptake, intestinal epithelial cell monolayer permeability, and necrosis were determined.

RESULTS

A significant decrease of 4- to 5-fold in tumor necrosis factor-α and interleukin-6 levels and equally significant decreases in toxin A uptake and permeability changes in the intestinal cell monolayers with mucus or PC and transcytosed or colostral IgA vs control are shown. All groups analyzed also displayed a 2- to 3-fold reduction in necrosis.

CONCLUSIONS

Mucus or "exogenous" mucus in the form of PC has a synergistic role with secretory IgA in barrier defense against C difficile toxin A. Exogenous PC administration can be a therapeutic adjunct in patients with severe or recalcitrant C difficile infection.

The systemic inflammatory response to Clostridium difficile infection

Background

The systemic inflammatory response to Clostridium difficile infection (CDI) is incompletely defined, particularly for patients with severe disease.

Methods

Analysis of 315 blood samples from 78 inpatients with CDI (cases), 100 inpatients with diarrhea without CDI (inpatient controls), and 137 asymptomatic outpatient controls without CDI was performed. Serum or plasma was obtained from subjects at the time of CDI testing or shortly thereafter. Severe cases had intensive care unit admission, colectomy, or death due to CDI within 30 days after diagnosis. Thirty different circulating inflammatory mediators were quantified using an antibody-linked bead array. Principal component analysis (PCA), multivariate analysis of variance (MANOVA), and logistic regression were used for analysis.

Results

Based on MANOVA, cases had a significantly different inflammatory profile from outpatient controls but not from inpatient controls. In logistic regression, only chemokine (C-C motif) ligand 5 (CCL5) levels were associated with cases vs. inpatient controls. Several mediators were associated with cases vs. outpatient controls, especially hepatocyte growth factor, CCL5, and epithelial growth factor (inversely associated). Eight cases were severe and associated with elevations in IL-8, IL-6, and eotaxin.

Conclusions

A broad systemic inflammatory response occurs during CDI and severe cases appear to differ from non-severe infections.

Recent insights into Clostridium difficile pathogenesis

PURPOSE OF REVIEW

Clostridium difficile infection (CDI) is the leading cause of antibiotic-associated diarrhea and pseudomembranous colitis in the healthcare setting. An emerging consensus suggests that CDI is caused by pathogenic toxin production, gut microbial dysbiosis and altered host inflammatory responses. The aim of this review is to summarize and highlight recent advances focused on CDI pathogenic mechanisms.

RECENT FINDINGS

Potential paradigm shifts relating to the mechanisms of toxin action and inhibition have recently been reported, with new insights into spore germination and surface protein function also gaining traction. Multiomic analysis of microbiome dysbiosis has identified important CDI-associated microbial community shifts that may form the basis of future targeted bacteriotherapy, and functional metabolite biomarkers that require further characterization. Classical innate and adaptive immunity against CDI is rapidly being delineated, with novel innate S-nitrosylation signals also being identified.

SUMMARY

Studies in patients and animal disease models are shedding new light on the critical roles of the microbiota, metabolome and host responses in primary and recurrent CDI. An improved understanding of the CDI disease pathogenesis will provide the basis for developing new therapies for treating disease and preventing recurrence.

Clostridium difficile infection: management strategies for a difficult disease

Clostridium difficile was first described as a cause of diarrhea in 1978 and in the last three decades has reached an epidemic state with increasing incidence and severity in both healthcare and community settings. There also has been a rise in severe outcomes from C. difficile infection (CDI). There have been tremendous advancements in the field of CDI with the identification of newer risk factors, recognition of CDI in populations previously thought not at risk and development of better diagnostic modalities. Several treatment options are available for CDI apart from metronidazole and vancomycin, and include new drugs such as fidaxomicin and other options such as fecal microbiota transplantation. This review discusses the epidemiology, risk factors and outcomes from CDI, and focuses primarily on existing and evolving treatment modalities.

Ribotype 027 Clostridium difficile infections with measurable stool toxin have increased lactoferrin and are associated with a higher mortality

We evaluated clinical and diagnostic indicators of severe C. difficile infection (CDI) and their association with poor clinical outcome. A total of 210 patients positive according to PCR (toxin B: tcdB) were included, with patients having a median age of 62 years and a Charlson co-morbidity index (CI) score of 5. Ninety-one percent (n = 191) were positive by toxigenic culture and 61 % (n = 129) had stool toxin. Toxin-positive patients had significantly higher fecal lactoferrin (mean 316 μg/g versus 106 μg/g stool; p < 0.0001). Forty percent of patients (n = 85) were infected with ribotype 027 and significantly more of these patients had measurable stool toxin (79 % vs. 50 %; p < 0.0001). The mean fecal lactoferrin was significantly higher for toxin-positive 027 CDI compared with the 027 toxin-negative group (317 vs 60 μg/g; p = 0.0014). Ribotype 027 CDI with stool toxin showed a higher all-cause, 100-day mortality compared with non-027 with stool toxin (36 % vs 18 %; p = 0.017). Logistic regression univariate analysis for odds ratio (OR) and p values revealed that age (OR = 1.1), intensive care unit treatment (OR = 2.7), CI (OR = 1.2), 027 CDI (OR = 2.1), white blood cell count (OR = 1.0), albumin level (OR = 0.1), and stool toxin-positive 027 CDI (OR = 2.5) were significantly associated with 100-day mortality (p < 0.05). In conclusion, CDI PCR-positive patients with 027 infection and stool toxin have increased lactoferrin and are at an increased risk of death.

Intestinal inflammatory biomarkers and outcome in pediatric Clostridium difficile infections

OBJECTIVES

To identify specific fecal biomarkers for symptomatic Clostridium difficile infection and predictors of poor outcomes.

STUDY DESIGN

We enrolled 65 children with positive C difficile testing (cases) and 37 symptomatic controls. We also analyzed stool samples from colonized and non-colonized asymptomatic children. We performed enzyme immunoassays to determine fecal interleukin (IL)-8, lactoferrin, and phosphorylated-p38 protein concentrations, and quantitative polymerase chain reaction to determine IL-8 and chemokine ligand (CXCL)-5 RNA relative transcript abundances, and C difficile bacterial burden.

RESULTS

Of 68 asymptomatic controls, 16 were colonized with C difficile. Phosphorylated-p38 was specific for C difficile infection but lacked sensitivity. Fecal cytokines were elevated in samples from symptomatic children, whether cases or controls. In children with C difficile infection, fecal CXCL-5 and IL-8 messenger RNA abundances at diagnosis correlated with persistent diarrhea after 5 days of C difficile infection therapy and with treatment with vancomycin. When children with concomitant viral gastroenteritis were excluded, these correlations persisted. Time-to-diarrhea resolution was significantly longer in patients with elevated fecal cytokines at diagnosis. A logistic regression model identified high CXCL-5 messenger RNA abundance as the only predictor of persistent diarrhea. Conversely, fecal C difficile bacterial burden was not different in symptomatic and asymptomatic children and did not correlate with any clinical outcome measure.

CONCLUSIONS

Fecal inflammatory cytokines may be useful in distinguishing C difficile colonization from disease and identifying children with C difficile infection likely to have prolonged diarrhea.

Viral co-infections are common and are associated with higher bacterial burden in children with clostridium difficile infection

Clostridium difficile infections in children are increasing. In this cohort study, we enrolled 62 children with diarrhea and C difficile. We performed polymerase chain reaction assays to detect viral agents of gastroenteritis and quantify C difficile burden. Fifteen (24%) children diagnosed as having C difficile infection had a concomitant viral co-infection. These patients tended to be younger and had a higher C difficile bacterial burden than children with no viral co-infections (median difference = 565,957 cfu/mL; P = 0.011), but were clinically indistinguishable. The contribution of viral co-infection to C difficile disease in children warrants future investigation.

The P2Y6 receptor mediates Clostridium difficile toxin-induced CXCL8/IL-8 production and intestinal epithelial barrier dysfunction

C. difficile is a Gram-positive spore-forming anaerobic bacterium that is the leading cause of nosocomial diarrhea in the developed world. The pathogenesis of C. difficile infections (CDI) is driven by toxin A (TcdA) and toxin B (TcdB), secreted factors that trigger the release of inflammatory mediators and contribute to disruption of the intestinal epithelial barrier. Neutrophils play a key role in the inflammatory response and the induction of pseudomembranous colitis in CDI. TcdA and TcdB alter cytoskeletal signaling and trigger the release of CXCL8/IL-8, a potent neutrophil chemoattractant, from intestinal epithelial cells; however, little is known about the surface receptor(s) that mediate these events. In the current study, we sought to assess whether toxin-induced CXCL8/IL-8 release and barrier dysfunction are driven by the activation of the P2Y₆ receptor following the release of UDP, a danger signal, from intoxicated Caco-2 cells. Caco-2 cells express a functional P2Y₆ receptor and release measurable amounts of UDP upon exposure to TcdA/B. Toxin-induced CXCL8/IL-8 production and release were attenuated in the presence of a selective P2Y₆ inhibitor (MRS2578). This was associated with inhibition of TcdA/B-induced activation of NFκB. Blockade of the P2Y₆ receptor also attenuated toxin-induced barrier dysfunction in polarized Caco-2 cells. Lastly, pretreating mice with the P2Y₆ receptor antagonists (MSR2578) attenuated TcdA/B-induced inflammation and intestinal permeability in an intrarectal toxin exposure model. Taken together these data outline a novel role for the P2Y₆ receptor in the induction of CXCL8/IL-8 production and barrier dysfunction in response to C. difficile toxin exposure and may provide a new therapeutic target for the treatment of CDI.

Clostridium difficile infection after adult autologous stem cell transplantation: a multicenter study of epidemiology and risk factors

We sought to describe the epidemiology of Clostridium difficile infection (CDI) among adult recipients of autologous hematopoietic stem cell transplantation (auto-HSCT) within the first year after HSCT in centers with variable epidemiology of hypertoxigenic strains. A multicenter, retrospective nested case-control study was conducted among 873 auto-HSCT recipients at Johns Hopkins Hospital (JHH) and Hôpital Maisonneuve-Rosemont (HMR) between January 2003 and December 2008. Despite center differences in the prevalence of NAP-1 strains during the study period (21% to 43% at JHH versus 80% to 84% in HMR), the 1-year incidence of CDI was similar in the 2 hospitals (6.2% at JHH versus 5.7% at HMR). The median time to infection was 11 days (interquartile range, 1 to 27 days). In case-control analyses, grade ≥2 mucositis (odds ratio [OR], 3.00; P = .02) and receipt of a fourth-generation cephalosporin (OR, 2.76; P = .04) were identified as predictors for CDI. Mucositis was the strongest predictor of risk for CDI in multivariate analysis (adjusted OR, 2.77; P = .03). CDI is a common and early complication of auto-HSCT. Treatment-related gastrointestinal mucosal damage, along with the potentially modifiable risk of antimicrobial exposure, influence the risk for CDI early after auto-HSCT.

In vivo physiological and transcriptional profiling reveals host responses to Clostridium difficile toxin A and toxin B

Toxin A (TcdA) and toxin B (TcdB) of Clostridium difficile cause gross pathological changes (e.g., inflammation, secretion, and diarrhea) in the infected host, yet the molecular and cellular pathways leading to observed host responses are poorly understood. To address this gap, we evaluated the effects of single doses of TcdA and/or TcdB injected into the ceca of mice, and several endpoints were analyzed, including tissue pathology, neutrophil infiltration, epithelial-layer gene expression, chemokine levels, and blood cell counts, 2, 6, and 16 h after injection. In addition to confirming TcdA's gross pathological effects, we found that both TcdA and TcdB resulted in neutrophil infiltration. Bioinformatics analyses identified altered expression of genes associated with the metabolism of lipids, fatty acids, and detoxification; small GTPase activity; and immune function and inflammation. Further analysis revealed transient expression of several chemokines (e.g., Cxcl1 and Cxcl2). Antibody neutralization of CXCL1 and CXCL2 did not affect TcdA-induced local pathology or neutrophil infiltration, but it did decrease the peripheral blood neutrophil count. Additionally, low serum levels of CXCL1 and CXCL2 corresponded with greater survival. Although TcdA induced more pronounced transcriptional changes than TcdB and the upregulated chemokine expression was unique to TcdA, the overall transcriptional responses to TcdA and TcdB were strongly correlated, supporting differences primarily in timing and potency rather than differences in the type of intracellular host response. In addition, the transcriptional data revealed novel toxin effects (e.g., altered expression of GTPase-associated and metabolic genes) underlying observed physiological responses to C. difficile toxins.