The pathogenicity of Clostridium difficile

Current and Ongoing Developments in Targeting Clostridioides difficile Infection and Recurrence

Clostridioides difficile is a Gram-positive, spore-forming anaerobic bacterial pathogen that causes severe gastrointestinal infection in humans. This review provides background information on C. difficile infection and the pathogenesis and toxigenicity of C. difficile. The risk factors, causes, and the problem of recurrence of disease and current therapeutic treatments are also discussed. Recent therapeutic developments are reviewed including small molecules that inhibit toxin formation, disrupt the cell membrane, inhibit the sporulation process, and activate the host immune system in cells. Other treatments discussed include faecal microbiota treatment, antibody-based immunotherapies, probiotics, vaccines, and violet-blue light disinfection.

A monoclonal antibody collection for C. difficile typing ?

Clostridioides difficile is the leading cause of antibiotic-associated diarrhea and pseudomembranous colitis in adults. Various C. difficile strains circulate currently, associated with different outcomes and antibiotic resistance profiles. However, most studies still focus on the reference strain 630 that does not circulate anymore, partly due to the lack of immunological tools to study current clinically important C. difficile PCR ribotypes. The goal of this study was to generate monoclonal antibodies recognizing various epidemic ribotypes of C. difficile. To do so, we immunized mice expressing human variable antibody genes with the Low Molecular Weight (LMW) subunit of the surface layer protein SlpA from various C. difficile strains. Monoclonal antibodies purified from hybridomas bound LMW with high-affinity and whole bacteria from current C. difficile ribotypes with different cross-specificities. This first collection of anti-C. difficile mAbs represent valuable tools for basic and clinical research.

Anti-S-layer monoclonal antibodies impact Clostridioides difficile physiology

Clostridioides difficile (C. difficile), a gram-positive anaerobic and spore-forming bacterium, is the leading cause of nosocomial antibiotic-associated diarrhea in adults which is characterized by high levels of recurrence and mortality. Surface (S)-layer Protein A (SlpA), the most abundantly expressed protein on the bacterial surface, plays a crucial role in the early stages of infection although the nature of its involvement in C. difficile physiology is yet to be fully understood. Anti-S-layer antibodies have been identified in the sera of convalescent patients and have been correlated with improved outcomes of C. difficile infection (CDI). However, the precise mechanisms by which anti-S-layer antibodies confer protection to the host remain unknown. In this study, we report the first monoclonal antibodies (mAbs) targeting the S-layer of reference strain 630. Characterization of these mAbs unraveled important roles for the S-layer protein in growth, toxin secretion, and biofilm formation by C. difficile, with differential and even opposite effects of various anti-SlpA mAbs on these functions. Moreover, one anti-SlpA mAb impaired C. difficile growth and conferred sensitivity to lysozyme-induced lysis. The results of this study show that anti-S-layer antibody responses can be beneficial or harmful for the course of CDI and provide important insights for the development of adequate S-layer-targeting therapeutics.

Clostridioides difficile infection leading to fulminant colitis with toxic megacolon

Clostridioidesdifficile infection (CDI) is the culprit of millions of nosocomial infections in the United States. Programs that successfully decrease its incidence, therefore, render cost savings for the healthcare system. Toxic megacolon and perforation are two of the most significant complications with increased mortality rates. We report a 23-year-old nursing home resident hospitalized for fever, cough, and green sputum. After 3 days of antibiotic therapy, he developed abdominal distension, diarrhea, and vomiting and underwent a total colectomy. The colon was dilated to a maximum of 11 cm with markedly edematous mucosa and yellow pseudomembranes. Qualitative PCR of the stool detected Clostridioides difficile toxin B gene. While there is no consensus for the required interval between antibiotic treatment and CDI, this presentation 3 days after starting the antibiotic therapy is earlier than most proposed ranges.

A Rare Case of Pseudomembrane-Associated Ulcerative Colitis

Ulcerative colitis (UC) is a chronic, life-long inflammatory bowel disease that normally presents with bloody diarrhea, fever, abdominal pain, and leukocytosis. Diagnosis is usually based on clinical presentation, endoscopy with biopsy, and exclusion of alternative diagnoses. In very rare cases, pseudomembranes may be found on colonoscopy in patients with an early UC flare. Historically, the objective finding of pseudomembranes has been exclusively used to diagnose a Clostridioides difficile infection (CDI); however, diagnostic testing must be correctly utilized to confirm whether a CDI is truly the cause of the presence of pseudomembranes, and not an alternative etiology, such as UC. In this case, we discuss a 43-year-old female who presented to the hospital with worsening chronic bloody diarrhea after being seen in the outpatient clinic for a questionable CDI. She underwent endoscopic evaluation revealing pseudomembranous colitis; however, C. difficile testing showed one positive gastrointestinal (GI) pathogen panel and multiple negative antigens and toxin enzyme immunoassays (EIA). With a clinical suspicion of early UC, the patient was treated with mesalamine enemas and improved clinically before discharge. Several months later, she underwent endoscopic evaluation with biopsy, which showed findings consistent with a diagnosis of UC.

Epigallocatechin-3-Gallate Improves Intestinal Gut Microbiota Homeostasis and Ameliorates Clostridioides difficile Infection

Clostridioides difficile infection is closely related to the intestinal flora disorders induced by antibiotics, and changes in the intestinal flora may cause the occurrence and development of Clostridioides difficile infection. Epigallocatechin-3-gallate (EGCG) is one of the major bioactive ingredients of green tea and has been suggested to alleviate the growth of C. difficile in vitro. EGCG can ameliorate several diseases, such as obesity, by regulating the gut microbiota. However, whether EGCG can attenuate C. difficile infection by improving the gut microbiota is unknown. After establishing a mouse model of C. difficile infection, mice were administered EGCG (25 or 50 mg/kg/day) or PBS intragastrically for 2 weeks to assess the benefits of EGCG. Colonic pathology, inflammation, the intestinal barrier, gut microbiota composition, metabolomics, and the transcriptome were evaluated in the different groups. Compared with those of the mice in the CDI group, EGCG improved survival rates after infection, improved inflammatory markers, and restored the damage to the intestinal barrier. Furthermore, EGCG could improve the intestinal microbial community caused by C. difficile infection, such as by reducing the relative abundance of Enterococcaceae and Enterobacteriaceae. Moreover, EGCG can increase short-chain fatty acids, improve amino acid metabolism, and downregulate pathways related to intestinal inflammation. EGCG alters the microbiota and alleviates C. difficile infection, which provides new insights into potential therapies.

Application of recombinant antibodies for treatment of Clostridioides difficile infection: Current status and future perspective

Clostridioides difficile (C. difficile), known as the major cause of antibiotic-associated diarrhea, is regarded as one of the most common healthcare-associated bacterial infections worldwide. Due to the emergence of hypervirulent strains, development of new therapeutic methods for C. difficile infection (CDI) has become crucially important. In this context, antibodies have been introduced as valuable tools in the research and clinical environments, as far as the effectiveness of antibody therapy for CDI was reported in several clinical investigations. Hence, production of high-performance antibodies for treatment of CDI would be precious. Traditional approaches of antibody generation are based on hybridoma technology. Today, application of in vitro technologies for generating recombinant antibodies, like phage display, is considered as an appropriate alternative to hybridoma technology. These techniques can circumvent the limitations of the immune system and they can be exploited for production of antibodies against different types of biomolecules in particular active toxins. Additionally, DNA encoding antibodies is directly accessible in in vitro technologies, which enables the application of antibody engineering in order to increase their sensitivity and specificity. Here, we review the application of antibodies for CDI treatment with an emphasis on recombinant fragment antibodies. Also, this review highlights the current and future prospects of the aforementioned approaches for antibody-mediated therapy of CDI.

Frontiers in antibiotic alternatives for Clostridioides difficile infection

Clostridioides difficile (C. difficile) is a gram-positive, anaerobic spore-forming bacterium and a major cause of antibiotic-associated diarrhea. Humans are naturally resistant to C. difficile infection (CDI) owing to the protection provided by healthy gut microbiota. When the gut microbiota is disturbed, C. difficile can colonize, produce toxins, and manifest clinical symptoms, ranging from asymptomatic diarrhea and colitis to death. Despite the steady-if not rising-prevalence of CDI, it will certainly become more problematic in a world of antibiotic overuse and the post-antibiotic era. C. difficile is naturally resistant to most of the currently used antibiotics as it uses multiple resistance mechanisms. Therefore, current CDI treatment regimens are extremely limited to only a few antibiotics, which include vancomycin, fidaxomicin, and metronidazole. Therefore, one of the main challenges experienced by the scientific community is the development of alternative approaches to control and treat CDI. In this Frontier article, we collectively summarize recent advances in alternative treatment approaches for CDI. Over the past few years, several studies have reported on natural product-derived compounds, drug repurposing, high-throughput library screening, phage therapy, and fecal microbiota transplantation. We also include an update on vaccine development, pre- and pro-biotics for CDI, and toxin antidote approaches. These measures tackle CDI at every stage of disease pathology via multiple mechanisms. We also discuss the gaps and concerns in these developments. The next epidemic of CDI is not a matter of if but a matter of when. Therefore, being well-equipped with a collection of alternative therapeutics is necessary and should be prioritized.

Cytomegalovirus-associated pseudomembranous colitis in a kidney transplant recipient

Pseudomembranous colitis (PMC) is classically associated with Clostridium difficile infection. We report a rare case of cytomegalovirus (CMV)-associated PMC in a 52-year-old female patient who had undergone kidney transplantation more than 20 years ago and was on low dose prednisolone and ciclosporin. She presented with an acute history of fever, lethargy, vomiting and diarrhoea on admission. Computed tomography of the abdomen showed extensive colitis, and colonoscopy revealed extensive pseudomembrane formation. Multiple tests for Clostridium difficile and other common microbiological causes of colitis were negative. CMV DNAemia and colonic biopsies confirmed the diagnosis of CMV colitis. The patient responded to prompt CMV treatment, as demonstrated by clinical, endoscopic, and histological response. While CMV is a common pathogen in the solid organ transplant population that is familiar to most transplant physicians, it may present atypically as PMC. Here, we review the literature on CMV-associated PMC and its relevance to solid organ transplant recipients. To our knowledge, this is the first reported case of CMV-associated PMC in a kidney transplant recipient.

Clostridioides difficile Infection in Chronic Kidney Disease-An Overview for Clinicians

Increased incidence of Clostridioides difficile infection (CDI), occurrence of severe and complicated CDI, and more frequent occurrence of drug-resistant, recurrent or non-hospital CDI has become a worldwide clinical problem. CDI is more common in patients with chronic kidney disease (CKD) than in the general population. CDI seems to be associated with frequent hospitalization, frequently used antibiotic therapy, dysbiosis, and abnormalities of the immune system observed in CKD patients. Dysbiosis is a common disorder found in CKD patients. It may be related to insufficient fiber content in the diet, reduced amount of consumed fluids and often reduced physical activity, constipation, impaired gastrointestinal motility, multidrug pharmacotherapy, and uremic milieu in CKD stage 5. In patients with CKD the clinical manifestations of CDI are similar to the general population; however, more frequent recurrence of CDI and higher prevalence of severe CDI are reported. Moreover, the increase in CDI related mortality is observed more in CKD patients than in the general population. The aim of this review paper is to summarize the current knowledge concerning the epidemiology, pathogenesis, clinical picture, and prevention and treatment in CKD patients.

From Nursery to Nursing Home: Emerging Concepts in Clostridioides difficile Pathogenesis

Clostridioides difficile is a Gram-positive, spore-forming, anaerobic bacterium that infects the human gastrointestinal tract, causing a wide range of disorders that vary in severity from mild diarrhea to toxic megacolon and/or death. Over the past decade, incidence, severity, and costs associated with C. difficile infection (CDI) have increased dramatically in both the pediatric and adult populations. The factors driving this rapidly evolving epidemiology remain largely unknown but are likely due in part to previously unappreciated host, microbiota, and environmental factors. In this review, we will cover the risks and challenges of CDI in adult and pediatric populations and examine asymptomatic colonization in infants. We will also discuss the emerging role of diet, pharmaceutical drugs, and pathogen-microbiota interactions in C. difficile pathogenesis, as well as the impact of host-microbiota interactions in the manifestation of C. difficile-associated disease. Finally, we highlight new areas of research and novel strategies that may shed light on this complex infection and provide insights into the future of microbiota-based therapeutics for CDI.

Early Surgical Intervention for Fulminant Pseudomembranous Colitis

The objective of this study of a retrospective case series was to determine factors associated with survival after surgical intervention in pseudomembranous colitis (PMC). The study was conducted at a tertiary care medical center and comprised 36 patients who underwent colectomy for fulminant PMC from 1995 to 2006. Patients including 21 females ranged from 40 to 89 years of age (mean, 70 years). Comorbidities included diabetes (39%), cardiovascular disease (77%), chronic obstructive pulmonary disease (47%), and intake of immunosuppressive medications (45%). Seventy-two per cent received antibiotics in the previous 2 months. Only patients with a confirmation of PMC on pathology specimens were included in the study. All patients underwent colectomy. Patients were stratified into two groups: survivors and nonsurvivors. Various clinical factors/parameters used in the management of patients with PMC were studied in these two groups. Survival was correlated with mean white blood cell count (23,000 survivors versus 40,000 nonsurvivors, P < 0.01); multisystem organ failure (16 per cent survivors versus 47 per cent nonsurvivors, P < 0.05); and preoperative pressors (16 per cent survivors versus 47 per cent nonsurvivors, P < 0.05). Overall mortality for the study period was 47 per cent. Mortality rate analysis revealed a lower rate for the more recent years (32 per cent for 2000 to 2006 versus 65 per cent for 1995 to 1999, P < 0.05). In the more recent years, the time elapsing before colectomy was also lower (1.4 days versus 2.5 days, nonsignificant), and patients had less preoperative hemodynamic instability (70 per cent versus 31 per cent, P < 0.03). In one institution, survival after surgery for PMC was found to be associated with a mean white blood cell count (<37,000), nondependence on preoperative vasopressors, and surgical intervention before the onset of hemodynamic instability.

Immunogenicity and Protection from Receptor-Binding Domains of Toxins as Potential Vaccine Candidates for Clostridium difficile

The receptor-binding domains (RBDs) located in toxin A and toxin B of Clostridium difficile are known to be nontoxic and immunogenic. We need to develop a new type vaccine based on RBDs. In this study, we expressed and purified recombinant proteins (named RBD-TcdA and RBD-TcdB) as vaccine candidates containing the RBDs of toxin A and toxin B, respectively, from the C. difficile reference strain VPI10463. The immunogenicity and protection of the vaccine candidates RBD-TcdA, RBD-TcdB, and RBD-TcdA/B was evaluated by ELISA and survival assays. The data indicated that mice immunized with all vaccine candidates displayed potent levels of RBD-specific serum IgG. Following intramuscular immunization of mice with RBD-TcdA and/or RBD-TcdB, these vaccine candidates triggered immune responses that protected mice compared to mice immunized with aluminum hydroxide alone. Taken together, the results of this study reveal that recombinant proteins containing RBDs of C. difficile toxins can be used for vaccine development. Additionally, we found that an RBD-TcdA/B vaccine can elicit a stronger humoral immune response and provide better immunoprotection than the univalent vaccines. This RBD vaccine candidate conferred significant protection against disease symptoms and death caused by toxins from a wild-type C. difficile strain.

Distribution of Clostridium Difficile Ribotypes in Macedonian Patients and their Antimicrobial Susceptibility

BACKGROUND:

Clostridium difficile is a major nosocomial pathogen. In Europe, this bacterium is mostly characterised by PCR ribotyping. Most of the Clostridium difficile infections (CDI) are treated with vancomycin or metronidazole, although prolonged antibiotic use is considered as one of the main risk factors for CDI.

AIM:

This study aimed to detect the presence of various C. difficile ribotypes in hospitalised patients and to investigate their toxigenicity and antibiotic susceptibility.

MATERIAL AND METHODS:

All stool samples obtained from each patient were inoculated on Columbia blood agar and cycloserine cefoxitine fructose agar (CCFA) for isolation of C. difficile. Glutamate dehydrogenase and toxins A and B were investigated by immunochromatographic tests. Final confirmation of the isolates was performed by Vitek 2 and MALDI-TOF. A total of 21 isolates were collected for further investigation. PCR ribotyping was performed as described by Janezic and Rupnik. PCR ribotype profiles were analysed using software (Bionumerics, Applied Maths). Antibiotic susceptibility was determined by E-tests for metronidazole, vancomycin, tetracycline, clindamycin, erythromycin, imipenem, ciprofloxacin and moxifloxacin.

RESULTS:

About 48% of C. difficile isolates belonged to ribotype 001/072. So, this ribotype was the most common ribotype in this study. The remaining 52% of C. difficile isolates consisted of 10 different ribotypes: 017, SLO 160, SLO 187, SLO 120, 255/258, 014/020, 046, 002, 070 and 027. Furthermore, 20 (95.2 %) out of 21 isolates of C. difficile were toxigenic. Toxins A and B were detected simultaneously in 90.5 % of C. difficile isolates. Two isolates from the ribotype 017 were toxin B positive only. Treatments with any of the following antimicrobials: clindamycin, erythromycin, ciprofloxacin and moxifloxacin (as well as many other antibiotics), could be a risk factor for CDI due to the high resistance of the strains in this study. About 90% of the strains from the most common ribotype 001/072 have MICs for clindamycin and erythromycin > 256 µg/ml.

CONCLUSION:

All strains isolated are highly resistant to ciprofloxacin. All strains were susceptible to vancomycin (median MIC was 0.63 µg/ml) and metronidazole (median MIC was 0.084 µg/ml), so these two antimicrobials remain optimal treatment option for CDI.

Clinical and Pathological Features of Ulcerative Colitis in Patients with and without Clostridium Difficile Infection; An Observational Study

BACKGROUND

A dramatic rise in the rate of clostridium difficile infection (CDI) in patients with inflammatory bowel disease (IBD) has been reported in recent years.

METHODS

In this observational case control study, 65 patients were included and were divided into two groups of IBD + CDI as case group and IBD without CDI as control group.

RESULTS

35 patients who had positive test for clostridium difficile were assigned to the case group. The control group consisted of 30 patients with negative test for clostridium difficile. Pancolitis was seen in the cases more statistically significant than the controls and proctitis was seen more among the controls than the cases (p = 0.001). The cases were on immunosuppressive (p = 0.001) and antibiotic (p = 0.02) therapy more than the controls. Colonoscopic findings revealed more severe and extensive inflammation among the cases versus milder inflammation among the controls, but these differences were not statistically significant (p = 0.2). Colectomy was seen in 10% of controls and none of the cases and this difference was statistically significant (p value = 0.05). More fecal calprotectin were seen among the cases than the controls and this difference was statistically significant (p < 0.05)

CONCLUSION

This study showed more clostridium difficile infection among the patients on antibiotic or immunosuppressive therapy. Pathological investigation revealed more severe and extensive inflammation among the cases than the controls. Cases had clinically more severe signs and symptoms with higher mayo scores than the controls. ESR (Erythrocyte sedimentation rate) and fecal calprotectin were higher in patients with positive clostridium difficile infection and serum albumin was lower in such patients.

Effect of natural products on the production and activity of Clostridium difficile toxins in vitro

Clostridium difficile infection is a toxin-mediated disease of the colon. C. difficile virulence is primarily attributed to the production of toxin A and toxin B; thus this study was aimed to investigate the effect of a range of natural products on the production and activity of C. difficile toxins in vitro. Twenty-two natural products were investigated against four C. difficile strains. The activity of products against toxins was determined using Vero and HT-29 cells cytotoxicity and neutral red uptake assays. The indirect effect of products on toxin-mediated cytotoxicity was determined using the same cell lines. The effect of seven products on toxin production by C. difficile was determined using ELISA. Zingerone (0.3 mg/ml) protected both cell lines from C. difficile cytopathic effects, confirmed by the neutral red uptake assay (P < 0.05). Three Leptospermum honeys (4% w/v), fresh onion bulb extract (12.5% v/v) and trans-cinnamaldehyde (0.005% v/v) all reduced toxin production and activity significantly (P ≤ 0.023). Garlic clove powder (4.7 mg/ml) only reduced toxin activity (P ≤ 0.047). Overall, several natural products had activity against C. difficile toxins in vitro encouraging further investigation against C. difficile toxins in vivo.

Bacteriophages are more virulent to bacteria with human cells than they are in bacterial culture; insights from HT-29 cells

Bacteriophage therapeutic development will clearly benefit from understanding the fundamental dynamics of in vivo phage-bacteria interactions. Such information can inform animal and human trials, and much can be ascertained from human cell-line work. We have developed a human cell-based system using Clostridium difficile, a pernicious hospital pathogen with limited treatment options, and the phage phiCDHS1 that effectively kills this bacterium in liquid culture. The human colon tumorigenic cell line HT-29 was used because it simulates the colon environment where C. difficile infection occurs. Studies on the dynamics of phage-bacteria interactions revealed novel facets of phage biology, showing that phage can reduce C. difficile numbers more effectively in the presence of HT-29 cells than in vitro. Both planktonic and adhered Clostridial cell numbers were successfully reduced. We hypothesise and demonstrate that this observation is due to strong phage adsorption to the HT-29 cells, which likely promotes phage-bacteria interactions. The data also showed that the phage phiCDHS1 was not toxic to HT-29 cells, and phage-mediated bacterial lysis did not cause toxin release and cytotoxic effects. The use of human cell lines to understand phage-bacterial dynamics offers valuable insights into phage biology in vivo, and can provide informative data for human trials.

Sensitizing Clostridium difficile Spores with Germinants on Skin and Environmental Surfaces Represents a New Strategy for Reducing Spores via Ambient Mechanisms

Background

Clostridium difficile is a leading cause of healthcare-associated infections worldwide. Prevention of C. difficile transmission is challenging because spores are not killed by alcohol-based hand sanitizers or many commonly used disinfectants. One strategy to control spores is to induce germination, thereby rendering the spores more susceptible to benign disinfection measures and ambient stressors.

Methods/Results

C. difficile spores germinated on skin after a single application of cholic acid-class bile salts and co-germinants; for 4 C. difficile strains, recovery of viable spores from skin was reduced by ~0.3 log₁₀CFU to 2 log₁₀CFU after 2 hours and ~1 log₁₀CFU to > 2.5 log₁₀CFU after 24 hours. The addition of taurocholic acid to 70% and 30% ethanol significantly enhanced reduction of viable spores on skin and on surfaces. Desiccation, and to a lesser extent the presence of oxygen, were identified as the stressors responsible for reductions of germinated spores on skin and surfaces. Additionally, germinated spores became susceptible to killing by pH 1.5 hydrochloric acid, suggesting that germinated spores that remain viable on skin and surfaces might be killed by gastric acid after ingestion. Antibiotic-treated mice did not become colonized after exposure to germinated spores, whereas 100% of mice became colonized after exposure to the same quantity of dormant spores.

Conclusions

Germination could provide a new approach to reduce C. difficile spores on skin and in the environment and to render surviving spores less capable of causing infection. Our findings suggest that it may be feasible to develop alcohol-based hand sanitizers containing germinants that reduce spores on hands.

Clostridium difficile infection: Updates in management

Clostridium difficile was first identified in 1978 as a diarrhea-causing bacterium in humans. In the last three decades, C. difficile infection (CDI) has reached an epidemic state, both in health care and community settings worldwide. There has been substantial progress in the field of CDI, including identification of novel risk factors, presence of CDI in individuals not considered at risk previously, and treatment options including new drugs, monoclonal antibodies, and fecal microbiota transplantation. This review discusses epidemiology, novel and traditional risk factors, and updates in management for CDI.

Wall Teichoic Acids Are Involved in the Medium-Induced Loss of Function of the Autolysin CD11 against Clostridium difficile

Bacterial lysins are potent antibacterial enzymes with potential applications in the treatment of bacterial infections. Some lysins lose activity in the growth media of target bacteria, and the underlying mechanism remains unclear. Here we use CD11, an autolysin of Clostridium difficile, as a model lysin to demonstrate that the inability of this enzyme to kill C. difficile in growth medium is not associated with inhibition of the enzyme activity by medium, or the modification of the cell wall peptidoglycan. Rather, wall teichoic acids (WTAs) appear to prevent the enzyme from binding to the cells and cleaving the cell wall peptidoglycan. By partially blocking the biosynthetic pathway of WTAs with tunicamycin, cell binding improved and the lytic efficacy of CD11 was significantly enhanced. This is the first report of the mechanism of lysin inactivation in growth medium, and provides insights into understanding the behavior of lysins in complex environments, including the gastrointestinal tract.

A Quantitative Analysis of FDA Adverse Event Reports with Oral Bisphosphonates and Clostridium difficile

BACKGROUND

Studies have shown associations between Clostridium difficile infection (CDI) and non-antimicrobial medications including proton pump inhibitors, osteoporosis medications, and antidepressants.

OBJECTIVES

Our primary objective was to evaluate oral bisphosphonates and reported CDI adverse drug reactions in the United States using the Food and Drug Administration Adverse Event Reporting System data (FAERS).

METHODS

We performed a disproportionality analysis evaluating the proportion of reports with bisphosphonates and CDI compared with other adverse drug reactions in the database. A relatively increased number of reports for a given adverse drug reaction (ADR) is termed a "signal." Four major measures of association are used to describe reports: reporting odds ratio, proportional reporting ratio, information component, and empirical Bayes geometric mean. Drugs with statistically significant safety signals were stratified by age (18-40, 41-65, and 65+ years) and gender.

RESULTS

Alendronate had 0.4% (103/23,603) reports with CDI. There were 0.4% (16/3672) and 0.2% (17/7945) of reports for risedronate and ibandronate, respectively. Alendronate (Fosamax) was the only drug with a significant signal using all four calculation methods. For reports with gender available, alendronate CDI ADRs were more common for women (0.45% [93/20,586]) versus men (0.25% [4/1568]), and a signal was detected with all four methods. For reports with age available, there were limited alendronate reports for those 18-39 years of age, and CDI reports were present in 0.50% (27/5350) of cases of 40-64 years and 0.49% (42/8525) of cases aged 65 or older.

CONCLUSION

Alendronate was associated with a high number of CDI ADRs relative to other drugs in FAERS. This signal was strongest for women and those 40 years or older. This interesting finding should be interpreted with caution, and further research is warranted.

Recombinant Mucin-Type Fusion Proteins with a Galα1,3Gal Substitution as Clostridium difficile Toxin A Inhibitors

The capability of a recombinant mucin-like fusion protein, P-selectin glycoprotein ligand-1/mouse IgG2b (PSGL-1/mIgG2b), carrying Galα1,3Galβ1,4GlcNAc determinants to bind and inhibit Clostridium difficile toxin A (TcdA) was investigated. The fusion protein, produced by a glyco-engineered stable CHO-K1 cell line and designated C-PGC2, was purified by affinity and gel filtration chromatography from large-scale cultures. Liquid chromatography-mass spectrometry was used to characterize O-glycans released by reductive β-elimination, and new diagnostic ions to distinguish Galα1,3Gal- from Galα1,4Gal-terminated O-glycans were identified. The C-PGC2 cell line, which was 20-fold more sensitive to TcdA than the wild-type CHO-K1, is proposed as a novel cell-based model for TcdA cytotoxicity and neutralization assays. The C-PGC2-produced fusion protein could competitively inhibit TcdA binding to rabbit erythrocytes, making it a high-efficiency inhibitor of the hemagglutination property of TcdA. The fusion protein also exhibited a moderate capability for neutralization of TcdA cytotoxicity in both C-PGC2 and CHO-K1 cells, the former with and the latter without cell surface Galα1,3Galβ1,4GlcNAc sequences. Future studies in animal models of C. difficile infection will reveal its TcdA-inhibitory effect and therapeutic potential in C. difficile-associated diseases.

A Prospective, Case Control Study Evaluating the Association between Clostridium Difficile Toxins in the Colon of Neonatal Swine and Gross and Microscopic Lesions

Clostridium difficile infection in swine has most often been described in suckling pigs, where it has been associated with mesocolonic edema and typhlocolitis. This prospective study was designed to assess the correlation between the presence of C. difficile toxins (TCd) in the colon contents of neonatal pigs and a number of parameters, including gross evidence of diarrhea, mesocoloninc edema, typhlitis, and colitis. C. difficile was isolated from 51% (66/129) of large intestines and TCd was detected in the colon contents of 50% (65/129) of the piglets. Fifty-eight percent (38/65) of TCd-positive piglets had normal to pelleted colon and rectal contents, whereas 75% (48/64) of TCd-negative pigs had gross evidence of diarrhea. Clostridium difficile toxin-positive animals were significantly more likely to have normal to pelleted feces. Edema of the mesocolon was observed in 38/65 (59%) of TCd-positive piglets. Because a high number of TCd-positive piglets (41%) lacked edema of the mesocolon and a high number of TCd-negative pigs had mesocolonic edema (51%), a statistically significant association between TCd and mesocolonic edema was not identified. Seventy-five percent (49/65) of TCd-positive piglets had colitis and 47/65 (72%) had typhlitis. The association between TCd and both colitis and typhlitis was statistically significant. Apparently healthy piglets were obtained from 5 separate sites. Because TCd was detected in the colon contents of 23/29 (79%) apparently healthy piglets obtained from 5 separate sites, and 70% of TCd-positive control pigs had colitis, C. difficile may represent an important subclinical issue in neonatal swine.

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.

A Cumulative Spore Killing Approach: Synergistic Sporicidal Activity of Dilute Peracetic Acid and Ethanol at Low pH Against Clostridium difficile and Bacillus subtilis Spores

The synergistic combination of dilute peracetic acid and ethanol at low pH provides a novel approach for development of a rapid and effective method for reducing C. difficile spores on skin.

Background. Alcohol-based hand sanitizers are the primary method of hand hygiene in healthcare settings, but they lack activity against bacterial spores produced by pathogens such as Clostridium difficile and Bacillus anthracis. We previously demonstrated that acidification of ethanol induced rapid sporicidal activity, resulting in ethanol formulations with pH 1.5–2 that were as effective as soap and water washing in reducing levels of C difficile spores on hands. We hypothesized that the addition of dilute peracetic acid (PAA) to acidified ethanol would enhance sporicidal activity while allowing elevation of the pH to a level likely to be well tolerated on skin (ie, >3).

Methods. We tested the efficacy of acidified ethanol solutions alone or in combination with PAA against C difficile and Bacillus subtilis spores in vitro and against nontoxigenic C difficile spores on hands of volunteers.

Results. Acidification of ethanol induced rapid sporicidal activity against C difficile and to a lesser extent B subtilis. The addition of dilute PAA to acidified ethanol resulted in synergistic enhancement of sporicidal activity in a dose-dependent fashion in vitro. On hands, the addition of 1200–2000 ppm PAA enhanced the effectiveness of acidified ethanol formulations, resulting in formulations with pH >3 that were as effective as soap and water washing.

Conclusions. Acidification and the addition of dilute PAA induced rapid sporicidal activity in ethanol. Our findings suggest that it may be feasible to develop effective sporicidal ethanol formulations that are safe and tolerable on skin.

TS, Setlow P, Donskey CJ. Unlocking the Sporicidal Potential of Ethanol: Induced Sporicidal Activity of Ethanol against Clostridium difficile and Bacillus Spores under Altered Physical and Chemical Conditions

Background

Due to their efficacy and convenience, alcohol-based hand sanitizers have been widely adopted as the primary method of hand hygiene in healthcare settings. However, alcohols lack activity against bacterial spores produced by pathogens such as Clostridium difficile and Bacillus anthracis. We hypothesized that sporicidal activity could be induced in alcohols through alteration of physical or chemical conditions that have been shown to degrade or allow penetration of spore coats.

Principal Findings

Acidification, alkalinization, and heating of ethanol induced rapid sporicidal activity against C. difficile, and to a lesser extent Bacillus thuringiensis and Bacillus subtilis. The sporicidal activity of acidified ethanol was enhanced by increasing ionic strength and mild elevations in temperature. On skin, sporicidal ethanol formulations were as effective as soap and water hand washing in reducing levels of C. difficile spores.

Conclusions

These findings demonstrate that novel ethanol-based sporicidal hand hygiene formulations can be developed through alteration of physical and chemical conditions.

Occurrence of Clostridium difficile in two types of wastewater treatment plants

Wastewater is a potential environmental source of Clostridium difficile, although a direct link with community-acquired C. difficile infection (CA-CDI) in humans has not yet been established. The present study was performed to determine the occurrence of C. difficile in two types of wastewater treatment plants (WWTPs) in Isfahan, Iran. A total of 95 samples were taken from a conventional activated sludge treatment plant and a waste stabilization ponds system, and analyzed for the presence of C. difficile. C. difficile was found in 13.6% (3/22) of digested sludge samples. However, no C. difficile was detected in inlet and outlet samples or in raw sludge of activated sludge. C. difficile was also detected in 5% (2/40) of the samples from waste stabilization ponds. Polymerase chain reaction (PCR) analysis showed that all strains of C. difficile detected were toxigenic (tcdB gene positive). This study shows that C. difficile was present in WWTPs, which might constitute a potential source of community-acquired C. difficile infection.

Co-infection as a confounder for the role of Clostridium difficile infection in children with diarrhoea: a summary of the literature

Although Clostridium difficile is a major cause of antibiotic-associated diarrhoea in adults, the incidence and severity of C. difficile infection (CDI) in children is unclear. One complicating factor in assessing the role of CDI in children is the possibility of co-infection with other gastrointestinal pathogens. In this review, we summarise the literature concerning C. difficile co-infections in young children, in an attempt to discuss the rate of co-infections and their potential role in the severity of CDI clinical presentation. We identified 31 studies where co-infections were analysed, comprising 1,718 patients with positive C. difficile tests. The pooled percentage of reported co-infections was 20.7% (range 0-100%). Viral co-infections were most commonly reported (46%), with bacteria and parasites accounting for 14.9% and 0.01% of cases, respectively. However, the panel of co-infections tested for varied considerably among studies and 38% of stated co-infections did not have a pathogen reported. Substantial variation in how and when tests for gastrointestinal co-infections are carried out, small sample sizes and a lack of clear CDI case definitions preclude meaningful conclusions on the true rate of co-infections in this patient population. This review suggests that co-infections may be common in children with diarrhoea who tested positive for C. difficile. Given a lack of CDI case definitions, especially in young children under the age of 5 years, a broad panel of pathogens should be tested for to exclude other microbiological causes. However, the summarised poor quality of the available literature on this subject highlights a need for further studies.

Induced sporicidal activity of chlorhexidine against Clostridium difficile spores under altered physical and chemical conditions

Background

Chlorhexidine is a broad-spectrum antimicrobial commonly used to disinfect the skin of patients to reduce the risk of healthcare-associated infections. Because chlorhexidine is not sporicidal, it is not anticipated that it would have an impact on skin contamination with Clostridium difficile, the most important cause of healthcare-associated diarrhea. However, although chlorhexidine is not sporicidal as it is used in healthcare settings, it has been reported to kill spores of Bacillus species under altered physical and chemical conditions that disrupt the spore’s protective barriers (e.g., heat, ultrasonication, alcohol, or elevated pH). Here, we tested the hypothesis that similarly altered physical and chemical conditions result in enhanced sporicidal activity of chlorhexidine against C. difficile spores.

Principal Findings

C. difficile spores became susceptible to heat killing at 80°C within 15 minutes in the presence of chlorhexidine, as opposed to spores suspended in water which remained viable. The extent to which the spores were reduced was directly proportional to the concentration of chlorhexidine in solution, with no viable spores recovered after 15 minutes of incubation in 0.04%–0.0004% w/v chlorhexidine solutions at 80°C. Reduction of spores exposed to 4% w/v chlorhexidine solutions at moderate temperatures (37°C and 55°C) was enhanced by the presence of 70% ethanol. However, complete elimination of spores was not achieved until 3 hours of incubation at 55°C. Elevating the pH to ≥9.5 significantly enhanced the killing of spores in either aqueous or alcoholic chlorhexidine solutions.

Conclusions

Physical and chemical conditions that alter the protective barriers of C. difficile spores convey sporicidal activity to chlorhexidine. Further studies are necessary to identify additional agents that may allow chlorhexidine to reach its target within the spore.

Utility of Clostridium difficile toxin B for inducing anti-tumor immunity

Clostridium difficile toxin B (TcdB) is a key virulence factor of bacterium and induces intestinal inflammatory disease. Because of its potent cytotoxic and proinflammatory activities, we investigated the utility of TcdB in developing anti-tumor immunity. TcdB induced cell death in mouse colorectal cancer CT26 cells, and the intoxicated cells stimulated the activation of mouse bone marrow-derived dendritic cells and subsequent T cell activation in vitro. Immunization of BALB/c mice with toxin-treated CT26 cells elicited potent anti-tumor immunity that protected mice from a lethal challenge of the same tumor cells and rejected pre-injected tumors. The anti-tumor immunity generated was cell-mediated, long-term, and tumor-specific. Further experiments demonstrated that the intact cell bodies were important for the immunogenicity since lysing the toxin-treated tumor cells reduced their ability to induce antitumor immunity. Finally, we showed that TcdB is able to induce potent anti-tumor immunity in B16-F10 melanoma model. Taken together, these data demonstrate the utility of C. difficile toxin B for developing anti-tumor immunity.

Is the interleukin 8 promoter polymorphism rs4073/-251T >A associated with Clostridium difficile infection?

The interleukin 8 gene single-nucleotide polymorphism rs4073/-251T >A predisposes to Clostridium difficile infection (CDI), but this association has not been independently validated. In this study, we were unable to replicate this association in either a white cohort or by meta-analysis, suggesting that rs4073/-251T >A is unlikely to constitute a major risk factor for CDI.

Lipoprotein CD0873 is a novel adhesin of Clostridium difficile

Clostridium difficile is a cause of antibiotic-associated diarrhea and colitis, a healthcare-associated intestinal disease. Colonization of the gut is a critical step in the course of infection. The C. difficile lipoprotein CD0873 was identified as a putative adhesin through a bioinformatics approach. Surface exposure of CD0873 was confirmed and a CD0873 mutant was generated. The CD0873 mutant showed a significant reduction in adherence to Caco-2 cells and wild-type bacteria preincubated with anti-CD0873 antibodies showed significantly decreased adherence to Caco-2 cells. In addition, we demonstrated that purified recombinant CD0873 protein alone associates with Caco-2 cells. This is the first definitive identification of a C. difficile adhesin, which now allows work to devise improved measures for preventing and treating disease.

Detecting the dormant: a review of recent advances in molecular techniques for assessing the viability of bacterial endospores

Due to their contribution to gastrointestinal and pulmonary disease, their ability to produce various deadly exotoxins, and their resistance to extreme temperature, pressure, radiation, and common chemical disinfecting agents, bacterial endospores of the Firmicutes phylum are a major concern for public and environmental health. In addition, the hardy and dormant nature of endospores renders them a particularly significant threat to the integrity of robotic extraterrestrial life-detection investigations. To prevent the contamination of critical surfaces with seemingly ubiquitous bacterial endospores, clean rooms maintained at exceedingly stringent cleanliness levels (i.e., fewer than 100,000 airborne particles per ft(3)) are used for surgical procedures, pharmaceutical processing and packaging, and fabrication and assembly of medical devices and spacecraft components. However, numerous spore-forming bacterial species have been reported to withstand typical clean room bioreduction strategies (e.g., UV lights, maintained humidity, paucity of available nutrients), which highlights the need for rapid and reliable molecular methods for detecting, enumerating, and monitoring the incidence of viable endospores. Robust means of evaluating and tracking spore burden not only provide much needed information pertaining to endospore ecophysiology in different environmental niches but also empower decontamination and bioreduction strategies aimed at sustaining the reliability and integrity of clean room environments. An overview of recent molecular advances in detecting and enumerating viable endospores, as well as the expanding phylogenetic diversity of pathogenic and clean room-associated spore-forming bacteria, ensues.

Novel strategies for enhanced removal of persistent Bacillus anthracis surrogates and Clostridium difficile spores from skin

Background

Removing spores of Clostridium difficile and Bacillus anthracis from skin is challenging because they are resistant to commonly used antimicrobials and soap and water washing provides only modest efficacy. We hypothesized that hygiene interventions incorporating a sporicidal electrochemically generated hypochlorous acid solution (Vashe^®) would reduce the burden of spores on skin.

Methods

Hands of volunteers were inoculated with non-toxigenic C. difficile spores or B. anthracis spore surrogates to assess the effectiveness of Vashe solution for reducing spores on skin. Reduction in spores was compared for Vashe hygiene interventions versus soap and water (control). To determine the effectiveness of Vashe solution for removal of C. difficile spores from the skin of patients with C. difficile infection (CDI), reductions in levels of spores on skin were compared for soap and water versus Vashe bed baths.

Results

Spore removal from hands was enhanced with Vashe soak (>2.5 log₁₀ reduction) versus soap and water wash or soak (~2.0 log₁₀ reduction; P<0.05) and Vashe wipes versus alcohol wipes (P<0.01). A combined approach of soap and water wash followed by soaking in Vashe removed >3.5 log₁₀ spores from hands (P<0.01 compared to washing or soaking alone). Bed baths using soap and water (N =26 patients) did not reduce the percentage of positive skin cultures for CDI patients (64% before versus 57% after bathing; P =0.5), whereas bathing with Vashe solution (N =21 patients) significantly reduced skin contamination (54% before versus 8% after bathing; P =0.0001). Vashe was well-tolerated with no evidence of adverse effects on skin.

Conclusions

Vashe was safe and effective for reducing the burden of B. anthracis surrogates and C. difficile spores on hands. Bed baths with Vashe were effective for reducing C. difficile on skin. These findings suggest a novel strategy to reduce the burden of spores on skin.

Expanding the repertoire of gene tools for precise manipulation of the Clostridium difficile genome: allelic exchange using pyrE alleles

Sophisticated genetic tools to modify essential biological processes at the molecular level are pivotal in elucidating the molecular pathogenesis of Clostridium difficile, a major cause of healthcare associated disease. Here we have developed an efficient procedure for making precise alterations to the C. difficile genome by pyrE-based allelic exchange. The robustness and reliability of the method was demonstrated through the creation of in-frame deletions in three genes (spo0A, cwp84, and mtlD) in the non-epidemic strain 630Δerm and two genes (spo0A and cwp84) in the epidemic PCR Ribotype 027 strain, R20291. The system is reliant on the initial creation of a pyrE deletion mutant, using Allele Coupled Exchange (ACE), that is auxotrophic for uracil and resistant to fluoroorotic acid (FOA). This enables the subsequent modification of target genes by allelic exchange using a heterologous pyrE allele from Clostridium sporogenes as a counter-/negative-selection marker in the presence of FOA. Following modification of the target gene, the strain created is rapidly returned to uracil prototrophy using ACE, allowing mutant phenotypes to be characterised in a PyrE proficient background. Crucially, wild-type copies of the inactivated gene may be introduced into the genome using ACE concomitant with correction of the pyrE allele. This allows complementation studies to be undertaken at an appropriate gene dosage, as opposed to the use of multicopy autonomous plasmids. The rapidity of the ‘correction’ method (5–7 days) makes pyrE⁻ strains attractive hosts for mutagenesis studies.

Activate to eradicate: inhibition of Clostridium difficile spore outgrowth by the synergistic effects of osmotic activation and nisin

BACKGROUND

Germination is the irreversible loss of spore-specific properties prior to outgrowth. Because germinating spores become more susceptible to killing by stressors, induction of germination has been proposed as a spore control strategy. However, this strategy is limited by superdormant spores that remain unaffected by germinants. Harsh chemicals and heat activation are effective for stimulating germination of superdormant spores but are impractical for use in a hospital setting, where Clostridium difficile spores present a challenge. Here, we tested whether osmotic activation solutes will provide a mild alternative for stimulation of superdormant C. difficile spores in the presence of germinants as previously demonstrated in several species of Bacillus. In addition, we tested the hypothesis that the limitations of superdormancy can be circumvented with a combined approach using nisin, a FDA-approved safe bacteriocin, to inhibit outgrowth of germinated spores and osmotic activation solutes to enhance outgrowth inhibition by stimulating superdormant spores.

PRINCIPAL FINDINGS

Exposure to germination solution triggered ~1 log(10) colony forming units (CFU) of spores to germinate, and heat activation increased the spores that germinated to >2.5 log(10)CFU. Germinating spores, in contrast to dormant spores, became susceptible to inhibition by nisin. The presence of osmotic activation solutes did not stimulate germination of superdormant C. difficile spores exposed to germination solution. But, in the absence of germination solution, osmotic activation solutes enhanced nisin inhibition of superdormant spores to >3.5 log(10)CFU. The synergistic effects of osmotic activation solutes and nisin were associated with loss of membrane integrity.

CONCLUSIONS

These findings suggest that the synergistic effects of osmotic activation and nisin bypass the limitations of germination as a spore control strategy, and might be a novel method to safely and effectively reduce the burden of C.difficile spores on skin and environmental surfaces.

Role of apoptosis in disease

Since the initial description of apoptosis, a number of different forms of cell death have been described. In this review we will focus on classic caspase-dependent apoptosis and its variations that contribute to diseases. Over fifty years of research have clarified molecular mechanisms involved in apoptotic signaling as well and shown that alterations of these pathways lead to human diseases. Indeed both reduced and increased apoptosis can result in pathology. More recently these findings have led to the development of therapeutic approaches based on regulation of apoptosis, some of which are in clinical trials or have entered medical practice.

Toxigenic Clostridium difficile PCR ribotypes from wastewater treatment plants in southern Switzerland

The occurrence of Clostridium difficile in nine wastewater treatment plants in the Ticino Canton (southern Switzerland) was investigated. The samples were collected from raw sewage influents and from treated effluents. Forty-seven out of 55 characterized C. difficile strains belonged to 13 different reference PCR ribotypes (009, 010, 014, 015, 039, 052, 053, 066, 070, 078, 101, 106, and 117), whereas 8 strains did not match any of those available in our libraries. The most frequently isolated ribotype (40%) was 078, isolated from six wastewater treatment plants, whereas ribotype 066, a toxigenic emerging ribotype isolated from patients admitted to hospitals in Europe and Switzerland, was isolated from the outgoing effluent of one plant. The majority of the isolates (85%) were toxigenic. Forty-nine percent of them produced toxin A, toxin B, and the binary toxin (toxigenic profile A(+) B(+) CDT(+)), whereas 51% showed the profile A(+) B(+) CDT(-). Interestingly, eight ribotypes (010, 014, 015, 039, 066, 078, 101, and 106) were among the riboprofiles isolated from symptomatic patients admitted to the hospitals of the Ticino Canton in 2010. Despite the limitation of sampling, this study highlights that toxigenic ribotypes of C. difficile involved in human infections may occur in both incoming and outgoing biological wastewater treatment plants. Such a finding raises concern about the possible contamination of water bodies that receive wastewater treatment plant effluents and about the safe reuse of treated wastewater.

Identifying patients at risk of severe Clostridium difficile-associated disease

Clostridium difficile infection is responsible for a wide spectrum of clinical presentations, ranging from mild diarrhoea to fatal toxic colitis. This article reviews factors which may identify individuals who are at high risk of severe C. difficile-associated disease, and aims to help clinicians predict patients at risk of severe disease.

Retracted: Apoptosis of CT26 colorectal cancer cells induced by Clostridium difficile toxin A stimulates potent anti-tumor immunity

Clostridium difficile toxin A (TcdA) is one of the main pathogenic factors released by C. difficile. Due to its potent cytotoxic and proinflammatory activities, we investigated the anti-tumor activity of TcdA. CT26 colorectal cancer cells were challenged with recombinant TcdA, and it was found that TcdA could induce apoptosis of CT26 cells. Calreticulin (CRT) exposure to the cell surface during TcdA-induced apoptosis suggested that this apoptosis may correlate with immunogenicity. Moreover, TcdA-treated apoptotic CT26 cells were highly immunogenic since they could stimulate DC activation, T-cell activation, and anti-tumor activity. Furthermore, the anti-tumor immune response generated was specific and long-term. In summary, these studies demonstrate that C. difficile toxin A can induce apoptotic death of CT26 colorectal cancer cells and stimulate potent anti-tumor immunity.

Spores of Clostridium difficile clinical isolates display a diverse germination response to bile salts

Clostridium difficile spores play a pivotal role in the transmission of infectious diarrhoea, but in order to cause disease spores must complete germination and return to vegetative cell growth. While the mechanisms of spore germination are well understood in Bacillus, knowledge of C. difficile germination remains limited. Previous studies have shown that bile salts and amino acids play an important role in regulating the germination response of C. difficile spores. Taurocholate, in combination with glycine, can stimulate germination, whereas chenodeoxycholate has been shown to inhibit spore germination in a C. difficile clinical isolate. Our recent studies of C. difficile sporulation characteristics have since pointed to substantial diversity among different clinical isolates. Consequently, in this study we investigated how the germination characteristics of different C. difficile isolates vary in response to bile salts. By analysing 29 isolates, including 16 belonging to the BI/NAP1/027 type, we show that considerable diversity exists in both the rate and extent of C. difficile germination in response to rich medium containing both taurocholate and glycine. Strikingly, we also show that although a potent inhibitor of germination for some isolates, chenodeoxycholate does not inhibit the germination, or outgrowth, of all C. difficile strains. Finally, we provide evidence that components of rich media may induce the germination of C. difficile spores, even in the absence of taurocholate. Taken together, these data suggest that the mechanisms of C. difficile spore germination in response to bile salts are complex and require further study. Furthermore, we stress the importance of studying multiple isolates in the future when analysing the nutrients or chemicals that either stimulate or inhibit C. difficile spore germination.

Clostridium difficile infection in HIV-seropositive individuals and transplant recipients

Immunocompromise is a commonly cited risk factor for Clostridium difficile infection (CDI). We reviewed the experimental and epidemiological literature on CDI in three immunocompromised groups, HIV-seropositive individuals, haematopoietic stem cell or bone marrow transplant recipients and solid organ transplant recipients. All three groups have varying degrees of impairment of humoral immunity, a major factor influencing the outcome of CDI. Soluble HIV proteins such as nef and immunosuppressive agents such as cyclosporin, azathioprine and mycophenalate mofetil modify signalling from the key cellular pathways triggered by C. difficile toxin A, although there is a paucity of data on how these factors may interact with pathways activated by toxin B. Despite this, there has been little direct investigation into the effect of immunosuppression on the pathogenesis of CDI. Epidemiological studies consistently show increased rates of CDI in these populations, which are higher in those with greater degrees of immunocompromise such as individuals with advanced AIDS not receiving combination antiretroviral therapy or allogeneic haematopoietic stem cell transplant recipients. Less consistently data suggests immunocompromise in each group also impacts rates of severe, recurrent or complicated CDI. However all these conditions are characterised by high levels of antibiotic use and prolonged hospital stay, both powerful drivers of CDI risk.

Reconsidering the sporulation characteristics of hypervirulent Clostridium difficile BI/NAP1/027

Clostridium difficile is the leading cause of antibiotic-associated diarrhoea and a major burden to healthcare services worldwide. In recent years, C. difficile strains belonging to the BI/NAP1/027 type have become highly represented among clinical isolates. These so-called 'hypervirulent' strains are associated with outbreaks of increased disease severity, higher relapse rates and an expanded repertoire of antibiotic resistance. Spores, formed during sporulation, play a pivotal role in disease transmission and it has been suggested that BI/NAP1/027 strains are more prolific in terms of sporulation in vitro than 'non-epidemic' C. difficile types. Work in our laboratory has since provided credible evidence to the contrary suggesting that the strain-to-strain variation in C. difficile sporulation characteristics is not type-associated. However, the BI/NAP1/027 type is still widely stated to have an increased rate of sporulation. In this study, we analysed the sporulation rates of 53 C. difficile strains, the largest sample size used to-date in such a study, including 28 BI/NAP1/027 isolates. Our data confirm that significant variation exists in the rate at which different C. difficile strains form spores. However, we clearly show that the sporulation rate of the BI/NAP1/027 type was no higher than that of non-BI/NAP1/027 strains. In addition, we observed substantial variation in sporulation characteristics within the BI/NAP1/027 type. This work highlights the danger of assuming that all strains of one type behave similarly without studying adequate sample sizes. Furthermore, we stress the need for more rigorous experimental procedures in order to quantify C. difficile sporulation more accurately in the future.

Sporulation studies in Clostridium difficile

Clostridium difficile is a leading cause of healthcare-associated diarrhoea. In recent years, certain C. difficile types have become highly represented among clinical isolates and are associated with outbreaks of increased disease severity, higher relapse rates and an expanded repertoire of antibiotic resistance. Endospores, produced during sporulation, play a pivotal role in infection and disease transmission and it has been suggested in the literature that these so-called 'hypervirulent' C. difficile types are more prolific in terms of sporulation in vitro. However, work in our laboratory has provided evidence to the contrary suggesting that although there is significant strain-to-strain variation in C. difficile sporulation characteristics this variation does not appear to be type-associated. On analysis of the literature, it is apparent that the methods used to quantify sporulation in previous studies have varied greatly and sample sizes have remained small. The conflicting data in the literature may, therefore, not necessarily be generally representative of C. difficile sporulation. Instead, these inconsistencies may reflect differences in the experimental design of each study. In this review, the need for further investigations of C. difficile sporulation rates is highlighted. Specifically, the advantages and disadvantages of the different experimental approaches previously used are discussed and a standard set of principles for measuring C. difficile sporulation in the future is proposed.