Binary toxin and death after Clostridium difficile infection

Clostridioides difficile-mucus interactions encompass shifts in gene expression, metabolism, and biofilm formation

In a healthy colon, the stratified mucus layer serves as a crucial innate immune barrier to protect the epithelium from microbes. Mucins are complex glycoproteins that serve as a nutrient source for resident microflora and can be exploited by pathogens. We aimed to understand how the intestinal pathogen, Clostridioides diffiicile, independently uses or manipulates mucus to its benefit, without contributions from members of the microbiota. Using a 2-D primary human intestinal epithelial cell model to generate physiologic mucus, we assessed C. difficile-mucus interactions through growth assays, RNA-Seq, biophysical characterization of mucus, and contextualized metabolic modeling. We found that host-derived mucus promotes C. difficile growth both in vitro and in an infection model. RNA-Seq revealed significant upregulation of genes related to central metabolism in response to mucus, including genes involved in sugar uptake, the Wood-Ljungdahl pathway, and the glycine cleavage system. In addition, we identified differential expression of genes related to sensing and transcriptional control. Analysis of mutants with deletions in highly upregulated genes reflected the complexity of C. difficile-mucus interactions, with potential interplay between sensing and growth. Mucus also stimulated biofilm formation in vitro, which may in turn alter viscoelastic properties of mucus. Context-specific metabolic modeling confirmed differential metabolism and predicted importance of enzymes related to serine and glycine catabolism with mucus. Subsequent growth experiments supported these findings, indicating mucus is an important source of serine. Our results better define responses of C. difficile to human gastrointestinal mucus and highlight a flexibility in metabolism that may influence pathogenesis.

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.

Direct detection and characterization of Clostridium difficile from a novel collection device to improve laboratory workflow

Emergence of Clostridium difficile strains with increased virulence emphasizes the importance of early diagnosis and surveillance of C. difficile infection (CDI). In this study, the new FecalSwab™ collection and transport system was evaluated to improve C. difficile diagnosis. The FecalSwab™ was used for direct C. difficile molecular detection, C. difficile culture/toxigenic culture (TC) and bacterial genomic DNA (bgDNA) extraction. Our results demonstrated that the FecalSwab™ medium could be successfully used as template for Xpert C. difficile binary toxin (BT), regardless of the bacterial load of samples, and for C. difficile culture also after a long storage (30 days) of FecalSwab™ tubes at 4 °C. Furthermore, good-quality bgDNA was extracted from the FecalSwab™ medium for the majority (75%) of the samples analyzed. Typing was performed to fully characterize C. difficile strains isolated during this study and 17 different PCR-ribotypes (RTs) were identified. The results obtained indicate that the FecalSwab™ can be successfully used not only in daily diagnostic routine of C. difficile but also in surveillance and retrospective studies.

2019 update of the WSES guidelines for management of Clostridioides (Clostridium) difficile infection in surgical patients

In the last three decades, Clostridium difficile infection (CDI) has increased in incidence and severity in many countries worldwide. The increase in CDI incidence has been particularly apparent among surgical patients. Therefore, prevention of CDI and optimization of management in the surgical patient are paramount. An international multidisciplinary panel of experts from the World Society of Emergency Surgery (WSES) updated its guidelines for management of CDI in surgical patients according to the most recent available literature. The update includes recent changes introduced in the management of this infection.

Prevalence of binary-toxin genes (cdtA and cdtB) among clinical strains of Clostridium difficile isolated from diarrheal patients in Iran

AIM

In this study we investigated the prevalence of binary toxin genes, cdtA and cdtB, in clinical isolates of C. difficile from hospitalized patients with diarrhea.

BACKGROUND

C. difficile binary toxin (CDT) is an action-specific ADP-ribosyltransferase that is produced by some strains of C. difficile. Co-expression of this toxin with tcdA and tcdB can lead to more severe disease in CDI patients.

METHODS

Totally, 930 patients suspected of having CDI was included in this study. All samples were treated with methanol and cultured on selective C. difficile agar plates. The C. difficile isolates were further identified by PCR. Presence of tcdA, tcdB, cdtA, and cdtB genes among the strains were examined by PCR.

RESULTS

Analysis of the PCR results showed a prevalence of 85.2% (144/169) for toxigenic C. diffidile. Toxin genotyping of the strains for tcdA and tcdB genes revealed the toxin profiles of A+B+, A+B-, A-B+ accounting for 86.1% (124/144), 7.6% (11/144), 6.2% (9/144) among the strains, respectively. Totally, 12.4% (21/169) of the C. difficile strains were binary toxin-positive. cdtA-B+, cdtA+‏B‏+ and cdtA+B- were detected in 43% (9/21), 38% (8/21) and 19% (4/21) of the strains, respectively. Interestingly, 12% (3/25) of nontoxigenic C. difficile strains (tcdA-B-) had either cdtA+‏B‏+ or cdtA-B+ profiles.

CONCLUSION

This is the first report for the prevalence of binary toxin genes in C. difficile strains isolated from Iran. Further studies are required to investigate the exact role of binary toxins in the pathogenesis of C. difficile particularly in patients with chronic diarrhea among Iranian populations.

CRISPR Diversity and Microevolution in Clostridium difficile

Virulent strains of Clostridium difficile have become a global health problem associated with morbidity and mortality. Traditional typing methods do not provide ideal resolution to track outbreak strains, ascertain genetic diversity between isolates, or monitor the phylogeny of this species on a global basis. Here, we investigate the occurrence and diversity of clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-associated genes (cas) in C. difficile to assess the potential of CRISPR-based phylogeny and high-resolution genotyping. A single Type-IB CRISPR-Cas system was identified in 217 analyzed genomes with cas gene clusters present at conserved chromosomal locations, suggesting vertical evolution of the system, assessing a total of 1,865 CRISPR arrays. The CRISPR arrays, markedly enriched (8.5 arrays/genome) compared with other species, occur both at conserved and variable locations across strains, and thus provide a basis for typing based on locus occurrence and spacer polymorphism. Clustering of strains by array composition correlated with sequence type (ST) analysis. Spacer content and polymorphism within conserved CRISPR arrays revealed phylogenetic relationship across clades and within ST. Spacer polymorphisms of conserved arrays were instrumental for differentiating closely related strains, e.g., ST1/RT027/B1 strains and pathogenicity locus encoding ST3/RT001 strains. CRISPR spacers showed sequence similarity to phage sequences, which is consistent with the native role of CRISPR-Cas as adaptive immune systems in bacteria. Overall, CRISPR-Cas sequences constitute a valuable basis for genotyping of C. difficile isolates, provide insights into the micro-evolutionary events that occur between closely related strains, and reflect the evolutionary trajectory of these genomes.

Epidemiology, Diagnosis, and Management of Clostridium difficile Infection in Patients with Inflammatory Bowel Disease

Clostridium difficile infection (CDI) is a major source of morbidity and mortality for the U.S. health care system and frequently complicates the course of inflammatory bowel disease (IBD). Patients with IBD are more likely to be colonized with C. difficile and develop active infection than the general population. They are also more likely to have severe CDI and develop subsequent complications such as IBD flare, colectomy, or death. Even after successful initial treatment and recovery, recurrent CDI is common. Management of CDI in IBD is fraught with diagnostic and therapeutic challenges because the clinical presentations of CDI and IBD flare have considerable overlap. Fecal microbiota transplantation can be successful in curing recurrent CDI when other treatments have failed, but may also trigger IBD flare and this warrants caution. New experimental treatments including vaccines, monoclonal antibodies, and nontoxigenic strains of C. difficile offer promise but are not yet available for clinicians. A better understanding of the complex relationship between the gut microbiota, CDI, and IBD is needed.

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.

Differentiating virulent 027 and non-027 Clostridium difficile strains by molecular methods

OBJECTIVE

Hypervirulent Clostridium difficile clade has been shown to include several lineages of ribotype 027 and also other ribotypes. We present data on additional non-027 strains, identified as presumptive 027 by two commercial molecular C. difficile assays.

METHODS

The tested clinical isolates were selected from the national reference laboratory collection on the basis of toxin gene profile similarities with ribotype 027 and tested with XpertC. difficile/Epi and Amplidiag C. difficile+027 assay.

RESULT

Xpert misclassified five ribotypes (016, 019, 080, 176 and variant of type 046) as presumptive 027 and Amplidiag two ribotypes (016, 176). The misclassified strains were rare, covering 1.6% of reference laboratory strain collection.

CONCLUSION

Our findings confirm the concept that there are closely related outliers to hypervirulent 027 clones that can be misclassified as 027, and that these comprise numerous ribotypes, including previously reported four ribotypes (198, 176, 244, 019), and additional three (016, v046, 080) identified in the present study.

Clostridium difficile binary toxin CDT: mechanism, epidemiology, and potential clinical importance

Binary toxin (CDT) is frequently observed in Clostridium difficile strains associated with increased severity of C. difficile infection (CDI). CDT belongs to the family of binary ADP-ribosylating toxins consisting of two separate toxin components: CDTa, the enzymatic ADP-ribosyltransferase which modifies actin, and CDTb which binds to host cells and translocates CDTa into the cytosol. CDTb is activated by serine proteases and binds to lipolysis stimulated lipoprotein receptor. ADP-ribosylation induces depolymerization of the actin cytoskeleton. Toxin-induced actin depolymerization also produces microtubule-based membrane protrusions which form a network on epithelial cells and increase bacterial adherence. Multiple clinical studies indicate an association between binary toxin genes in C. difficile and increased 30-d CDI mortality independent of PCR ribotype. Further studies including measures of binary toxin in stool, analyses of CDI mortality caused by CDT-producing strains, and examination of the relationship of CDT expression to TcdA and TcdB toxin variants and PCR ribotypes are needed.

Hype or hypervirulence: a reflection on problematic C. difficile strains

Clostridium difficile infections (CDI) have emerged as a major cause of healthcare associated disease, and recent epidemiological evidence also suggests an important role in community-acquired diarrhea. This increase is associated with specific types, especially PCR ribotypes 027 and 078, which are sometimes referred to as “hypervirulent”. Over the past years major advances have been made in our understanding of C. difficile pathogenicity, with the identification and characterization of the major clostridial toxins TcdA and TcdB. However, the relation between the toxins, their regulation, and “hypervirulence” remain unclear. Here I review our current understanding of C. difficile pathogenicity and argue that “hypervirulent” is an inadequate term to describe PCR ribotypes 027 and 078, that the ability of C. difficile to cause problematic infections is a consequence of a multifactorial process that extends beyond toxins, sporulation, and antimicrobial resistance, and that vigilance is in order toward types that are closely related to ribotypes 027 and 078, but are currently not considered problematic.

Rapid detection of Clostridium difficile toxins from stool samples using real-time multiplex PCR

In this study, a total of 650 stool samples were tested to show that our method is capable of detecting four Clostridium difficile genes; tcdA, tcdB, encoding toxin A (TcdA) and toxin B (TcdB), and the binary toxin C. difficile transferase genes (cdtA and/or cdtB) encoding CDT toxin. Besides detecting the targeted C. difficile genes, our method can be used to detect the presence of any inhibitory components in the PCR. This assay, combined with a selective culture medium, such as the chromID™ C. difficile, can be applied directly for screening C. difficile-associated disease. The PCR-based assay developed here is rapid (4 h per 21 stool samples) and accurate in diagnosing C. difficile infection, 100 % assay sensitivity and negative predictive value (NPV) were obtained. However, the assay specificity of 99.1 % and positive predictive value (PPV) of 94.9 % were slightly lower than the optimal value of 100 %. The assay protocol outlined here can be used as a rapid screening tool to assist infection control units and in managing infected patients by reducing the number of patients requiring isolation and extended hospitalization. Rapid detection can prevent unnecessary antibiotic therapy and potentially reduce the spread of infection by emerging hypervirulent C. difficile strains.

Clostridium difficile infection in older adults

Clostridium difficile infection, the most frequent cause of nosocomial diarrhea, disproportionately affects older adults. The two most important risk factors for developing C. difficile infection are antimicrobial exposure and age >65 years old. Risk factors specific to older adults are frequent interactions with healthcare systems and age-related changes in physiology, including immune senescence and changes to the gut microbiome. Metronidazole and oral vancomcyin are the mainstays of conventional treatment for C. difficile infection. Alternative therapies include fidaxomicin, a narrow-spectrum macrocyclic antibiotic, and fectal bacteriotherapy, which offers an excellent therapeutic outcome. Strategies to prevent C. difficile infections include enhanced infection control measures and reducing inappropriate antimicrobial use through stewardship.

Clinical and Microbiologic Characteristics of Clostridium difficile Infection Caused by Binary Toxin Producing Strain in Korea

BACKGROUND

Binary toxin-producing Clostridium difficile infections (CDI) are known to be more severe and to cause higher case fatality rates than those by binary toxin-negative isolates. There has been few data of binary toxin-producing CDI in Korea. Objective of the study is to characterize clinical and microbiological trait of CDI cause by binary-toxin producing isolates in Korea.

MATERIALS AND METHODS

From September 2008 through January 2010, clinical characteristics, medication history and treatment outcome of all the CDI patients were collected prospectively. Toxin characterization, PCR ribotyping and antibiotic susceptibility were performed with the stool isolates of C. difficile.

RESULTS

During the period, CDI caused by 11binary toxin-producing isolates and 105 toxin A & toxin B-positive binary toxin-negative isolates were identified. Comparing the disease severity and clinical findings between two groups, leukocytosis and mucoid stool were more frequently observed in patients with binary toxin-positive isolates (OR: 5.2, 95% CI: 1.1 to 25.4, P = 0.043; OR: 7.6, 95% CI: 1.6 to 35.6, P = 0.010, respectively), but clinical outcome of 2 groups did not show any difference. For the risk factors for acquisition of binary toxin-positive isolates, previous use of glycopeptides was the significant risk factor (OR: 6.2, 95% CI: 1.4 to 28.6, P = 0.019), but use of probiotics worked as an inhibitory factor (OR: 0.1, 95% CI: 0.0 to 0.8; P = 0.026). PCR ribotypes of binary toxinproducing C. difficile showed variable patterns: ribotype 130, 4 isolates; 027, 3 isolates; 267 and 122, 1 each isolate and unidentified C1, 2 isolates. All 11 binary toxin-positive isolates were highly susceptible to clindamycin, moxifloxacin, metronidazole, vancomycin and piperacillin-tazobactam, however, 1 of 11 of the isolates was resistant to rifaximin.

CONCLUSIONS

Binary toxin-producing C. difficile infection was not common in Korea and those isolates showed diverse PCR ribotypes with high susceptibility to antimicrobial agents. Glycopeptide use was a risk factor for CDI by those isolates.

Detection of Clostridium difficile toxins A, B and binary toxin with slow off-rate modified aptamers

Rapid and accurate diagnostic tests for Clostridium difficile infections (CDI) are crucial for management of patients with suspected CDI and for infection control. Enzyme immunoassays for detection of the toxins are routinely used but lack adequate sensitivity. We generated slow off-rate modified aptamers (SOMAmer™ reagents) via in vitro selection (SELEX) that bind toxins A, B and binary toxin with high affinity and specificity. Using SOMAmers alone or in conjunction with antibodies, we have developed toxin assays with a 1 pmol/L (300 pg/mL) limit of detection and a 3 log dynamic range. SOMAmers proved useful as capture or detection agents in equilibrium solution binding radioassays, pull-down capture assays, dot blots, and plate- or membrane-based sandwich assays, thus represent a promising alternative to antibodies in diagnostic applications. SOMAmers detected toxins A, B and binary toxin in culture supernatants from toxigenic C. difficile, including a BI/NAP1 strain and historic strains.

Two cases of fulminant colitis due to binary toxin-positive Clostridium difficile that are not PCR ribotype 027 or type 078

Two cases of fulminant colitis due to Clostridium difficile occurred within ten weeks of each other on the same ward of a hospital in Japan. The patients died 2 and 4 days after the onset of colitis. C. difficile isolates obtained from both patients were toxin A-positive, toxin B-positive and binary toxin-positive. These isolates yielded identical results by both PCR ribotyping and slpA sequence typing. However, the banding patterns and slpA sequences of the isolates differed from those of PCR ribotype 027, as well as those of PCR ribotype 078. The tcdC sequences of the isolate differed from those of C. difficile 027, but a single base-pair deletion at position 117 and an 18 bp deletion, both of which were identical to the sequence of the reference strain of 027, were found. This type may be a new hypervirulent strain, but further studies of the epidemiology and pathogenicity of the strain are needed.

Evaluation of multiplex PCR with enhanced spore germination for detection of Clostridium difficile from stool samples of the hospitalized patients

Clostridium difficile poses as the most common etiologic agent of nosocomial diarrhea. Although there are many diagnostic methods to detect C. difficile directly from stool samples, the nucleic acid-based approach has been largely performed in several laboratories due to its high sensitivity and specificity as well as rapid turnaround time. In this study, a multiplex PCR was newly designed with recent accumulated nucleotide sequences. The PCR testing with various C. difficile ribotypes, other Clostridium spp., and non-Clostridium strains revealed 100% specificity with the ability to detect as low as ~22 genomic copy number per PCR reaction. Different combinations of sample processing were evaluated prior to multiplex PCR for the detection of C. difficile in fecal samples from hospitalized patients. The most optimal condition was the non-selective enrichment at 37°C for 1 h in brain heart infusion broth supplemented with taurocholate, followed by the multiplex PCR. The detection limit after sample processing was shown as being 5 spores per gram of fecal sample. Two hundred and thirty-eight fecal samples collected from the University affiliated hospital were analyzed by the enrichment multiplex PCR procedure. The results suggested that the combination of sample processing with the high-performance detection method would be applicable for routine diagnostic use in clinical setting.

Clostridium difficile: a European perspective. J Infect. 2013;66:115-128. [PMID: 23103666 DOI: 10.1016/j.jinf.2012.10.019]

Clostridium difficile infection is the leading cause of diarrhoea in the industrialised world. First identified in 1935, our knowledge about the clonal population structure, toxins and PCR ribotypes is still increasing. New PCR ribotypes and sequence types are frequently added. In the last decade hypervirulent strains have emerged and been associated with increased severity of disease, high recurrence and significant mortality. Although previously a primarily hospital- or health-care acquired infection, since the 1990's C. difficile infections that are community-acquired have been increasingly reported. Risk factors include hospitalisation, advancing age and prior antibiotic use. The ubiquitous presence of C. difficile in the environment and asymptomatic intestinal colonisation may be important reservoirs for infection and the changing epidemiology of C. difficile infection. Although surveillance in Europe is now a requirement of the European Commission, reporting is not standardised or mandatory. Here we review the current literature, guidelines on diagnosis and treatment and conclude by highlighting a number of areas where further research would increase our understanding.

Clostridium difficile: novel insights on an incessantly challenging disease. Curr Opin Infect Dis. 2012;25:405-411. [PMID: 22614522 DOI: 10.1097/qco.0b013e32835533a2]

PURPOSE OF REVIEW

This review comprises recent insights on epidemiology, risk factors, diagnostic approaches, pathophysiologic mechanisms, novel treatment options and prevention strategies of Clostridium difficile infection (CDI).

RECENT FINDINGS

Incidence of Clostridium difficile continues to rise and hypervirulent subtypes such as polymerase chain reaction (PCR) ribotype 027 and 078 have emerged worldwide. Children and postpartum women are increasingly recognized as being at risk for development of CDI and community-associated infection is no longer rare. PCR technology may replace complicated two-step test algorithms in the future, because it is rapid, sensitive and specific. Pathophysiological studies have provided evidence that either one of the two exotoxins A and B is important in conferring virulence - the role of binary toxin requires further investigation. Proton pump inhibitors are now established as important risk factors for acquiring, complicating CDI, and developing recurrences. Fidaxomycin, monoclonal antibodies and intestinal microbiota transplantation are promising new treatment options, especially regarding prevention of recurrent disease. Future prevention strategies involve vaccination and novel insights on reservoirs for ongoing transmission, including the food chain.

SUMMARY

Important advances in research on CDI include novel diagnostic approaches, better understanding of the underlying pathophysiological mechanisms of disease and the development of new approaches to treatment.

Association of decreased serum protein fractions with Clostridium difficile infection in the acute care setting: a case–control study

Aim: This study examines the association of decreased levels of serum proteins with the occurrence of Clostridium difficile-associated diarrhea (CDAD) in hospitalized patients. Materials & methods: This is a retrospective case–control study using a case cohort (n = 171) that had been described in an earlier study and a cohort of 332 contemporaneous controls. Results: Patients with CDAD had significantly lower serum levels of albumin, total protein and globulins, and decreased albumin/globulin ratio (p < 0.0001 for all parameters). After adjustment for confounders, hypoproteinemia was more closely associated with CDAD than either hypoalbuminemia or albumin/globulin ratio. Hypoproteinemia exhibited an odds ratios of 10.6 (95% CI: 6.62–17.0) after adjustment for race, and 11.0 (95% CI: 6.88–17.1) after adjustment for age. Conclusion: Decreased total serum protein is more closely associated with CDAD than hypoalbuminemia.

Ribotyping of Clostridium difficile strains associated with nosocomial transmission and relapses in a Swedish County

Clostridium difficile is an emerging threat in hospital environments. To analyse possible transmission and to distinguish between relapse and reinfection a collection of C. difficile isolates, sampled from 162 consecutive episodes of C. difficile infection, were PCR ribotyped. Two ribotypes (001 and 012) were prone to cause nosocomial acquisition. Moreover, ribotype 001 had a tendency to cause relapses as almost one in two patients with this ribotype had one or more relapses. By using PCR ribotyping strains inclined to cause relapses and strains associated with hospital transmission might be detected. This enables optimized hygiene measures and may improve the choice of treatment regimen.

Clostridium difficile infection: toxins and non-toxin virulence factors, and their contributions to disease establishment and host response

Clostridium difficile infection is the leading cause of antibiotic- and healthcare-associated diarrhea, and its containment and treatment imposes a significant financial burden, estimated to be over $3 billion in the USA alone. Since the year 2000, CDI epidemics/outbreaks have occurred in North America, Europe and Asia. These outbreaks have been variously associated with, or attributed to, the emergence of Clostridium difficile strains with increased virulence, an increase in resistance to commonly used antimicrobials such as the fluoroquinolones, or host susceptibilities, including the use of gastric acid suppressants, to name a few. Efforts to elucidate C. difficile pathogenic mechanisms have been hampered by a lack of molecular tools, manipulatable animal models, and genetic intractability of clinical C. difficile isolates. However, in the past 5 y, painstaking efforts have resulted in the unraveling of multiple C. difficile virulence-associated pathways and mechanisms. We have recently reviewed the disease, its associated risk factors, transmission and interventions (Viswanathan, Gut Microbes 2010). This article summarizes genetics, non-toxin virulence factors, and host-cell biology associated with C. difficile pathogenesis as of 2011, and highlights those findings/factors that may be of interest as future intervention targets.