Clostridium difficile toxins: mechanism of action and role in disease

Insoluble polysaccharides produced in plant cell cultures protect from Clostridioides difficile colitis

Clostridioides difficile infection (CDI) poses a significant health threat due to high recurrence rates. Antimicrobial agents are commonly used to manage CDI-related diarrhoea; however, by aggravating intestinal dysbiosis, antibiotics enable C. difficile spores germination and production of toxins, the main virulence factors. Therefore, the binding of exotoxins using adsorbents represents an attractive alternative medication for the prevention and treatment of relapses. In this study, we provided evidence that the natural insoluble polysaccharides, named ABR119, extracted by plant cell cultures, effectively trap C. difficile toxins. In our experiments, ABR119 exhibited no cytotoxicity in vitro and was safely administered in vivo. In the animal model of C. difficile-associated colitis, ABR119 (50 mg/kg body weight) significantly reduced the colonic myeloperoxidase activity and severity of inflammation, preventing body weight loss. These effects were not evident when we treated animals with wheat bran polysaccharides. We did not detect bacterial killing effects of ABR119 against C. difficile nor against bacterial species of the normal gut microbiota. Moreover, ABR119 did not interfere in vitro with the antimicrobial activities of most clinically used antibiotics. In summary, ABR119 holds promise for treating and preventing C. difficile colitis by trapping the bacterial toxins, warranting further studies to assess the ABR119 potential in human infections caused by C. difficile.

The small acid-soluble proteins of Clostridioides difficile regulate sporulation in a SpoIVB2-dependent manner

Clostridioides difficile is a pathogen whose transmission relies on the formation of dormant endospores. Spores are highly resilient forms of bacteria that resist environmental and chemical insults. In recent work, we found that C. difficile SspA and SspB, two small acid-soluble proteins (SASPs), protect spores from UV damage and, interestingly, are necessary for the formation of mature spores. Here, we build upon this finding and show that C. difficile sspA and sspB are required for the formation of the spore cortex layer. Moreover, using an EMS mutagenesis selection strategy, we identified mutations that suppressed the defect in sporulation of C. difficile SASP mutants. Many of these strains contained mutations in CDR20291_0714 (spoIVB2) revealing a connection between the SpoIVB2 protease and the SASPs in the sporulation pathway. This work builds upon the hypothesis that the small acid-soluble proteins can regulate gene expression.

Elucidating human gut microbiota interactions that robustly inhibit diverse Clostridioides difficile strains across different nutrient landscapes

The human gut pathogen Clostridioides difficile displays substantial inter-strain genetic variability and confronts a changeable nutrient landscape in the gut. We examined how human gut microbiota inter-species interactions influence the growth and toxin production of various C. difficile strains across different nutrient environments. Negative interactions influencing C. difficile growth are prevalent in an environment containing a single highly accessible resource and sparse in an environment containing C. difficile-preferred carbohydrates. C. difficile toxin production displays significant community-context dependent variation and does not trend with growth-mediated inter-species interactions. C. difficile strains exhibit differences in interactions with Clostridium scindens and the ability to compete for proline. Further, C. difficile shows substantial differences in transcriptional profiles in co-culture with C. scindens or Clostridium hiranonis. C. difficile exhibits massive alterations in metabolism and other cellular processes in co-culture with C. hiranonis, reflecting their similar metabolic niches. C. hiranonis uniquely inhibits the growth and toxin production of diverse C. difficile strains across different nutrient environments and robustly ameliorates disease severity in mice. In sum, understanding the impact of C. difficile strain variability and nutrient environments on inter-species interactions could help improve the effectiveness of anti-C. difficile strategies.

Clostridioides difficile exploits xanthine and uric acid as nutrients by utilizing a selenium-dependent catabolic pathway

Selenium is a trace element that plays critical roles in redox biology; it is typically incorporated into "selenoproteins" as the 21st amino acid selenocysteine. Additionally, selenium exists as a labile non-selenocysteine cofactor in a small subset of selenoproteins known as selenium-dependent molybdenum hydroxylases (SDMHs). In purinolytic clostridia, SDMHs are implicated in the degradation of hypoxanthine, xanthine, and uric acid for carbon and nitrogen. While SDMHs have been biochemically analyzed, the genes responsible for the insertion and maturation of the selenium cofactor lack characterization. In this study, we utilized the nosocomial pathogen Clostridioides difficile as a genetic model to begin characterizing this poorly understood selenium utilization pathway and its role in the catabolism of host-derived purines. We first observed that C. difficile could utilize hypoxanthine, xanthine, or uric acid to overcome a growth defect in a minimal medium devoid of glycine and threonine. However, strains lacking selenophosphate synthetase (selD mutants) still grew poorly in the presence of xanthine and uric acid, suggesting a selenium-dependent purinolytic process. Previous computational studies have identified yqeB and yqeC as potential candidates for cofactor maturation, so we subsequently deleted each gene using CRISPR-Cas9 technology. We surprisingly found that the growth of the ΔyqeB mutant in response to each purine was similar to the behavior of the selD mutants, while the ΔyqeC mutant exhibited no obvious phenotype. Our results suggest an important role for YqeB in selenium-dependent purine catabolism and also showcase C. difficile as an appropriate model organism to study the biological use of selenium.IMPORTANCEThe apparent modification of bacterial molybdenum hydroxylases with a catalytically essential selenium cofactor is the least understood mechanism of selenium incorporation. Selenium-dependent molybdenum hydroxylases play an important role in scavenging carbon and nitrogen from purines for purinolytic clostridia. Here, we used Clostridioides difficile as a genetic platform to begin dissecting the selenium cofactor trait and found genetic evidence for a selenium-dependent purinolytic pathway. The absence of selD or yqeB-a predicted genetic marker for the selenium cofactor trait-resulted in impaired growth on xanthine and uric acid, known substrates for selenium-dependent molybdenum hydroxylases. Our findings provide a genetic foundation for future research of this pathway and suggest a novel metabolic strategy for C. difficile to scavenge host-derived purines from the gut.

Molecular Characterization and Potential Host-switching of Swine Farm associated Clostridioides difficile ST11

OBJECTIVE

To conduct molecular prevalence and genetic polymorphism analysis of 24 Swine Farm associated C. difficile ST11 strains, in addition to other representative sequenced ST strains.

METHODS

The collected C. difficile strains underwent whole genome sequencing and bioinformatic analysis using the illumina NovaSeq platform, SPAdes, Prokka, MOB-suite, and FastTree. Virulence and antibiotic resistance genes were identified through NCBI Pathogen Database. Cytotoxicity tests were conducted on HT-29 cells and Vero cells to verify the function of toxin A and toxin B.

RESULTS

The most prevalent resistance genes in ST11 were found to be against β-lactamases, aminoglycosides, and tetracycline. A C. difficile isolate (strain 27) with tcdA deletion and high antibiotic resistance genes was far apart from other swine farm associated ST11 isolates in the phylogenetic branch. The remarkable genetic similarity between animal and human C. difficile strains suggests potential transmission of ST11 strains between animals and humans. The plasmid replicon sequences repUS43 were identified in all ST11 strains except one variant (strain 27), and 91.67% (22/24) of these were assessed by MOB-typer as having mobilizable plasmids.

CONCLUSION

Swine farm associated C. difficile ST11 carried fewer virulence genes than ST11 strains collected from NCBI database. It is critical to monitor the evolution of C. difficile strains to understand their changing characteristics, host-switching, and develop effective control and prevention strategies.

Mucoadhesive Mesalamine Prodrug Nanoassemblies to Target Intestinal Macrophages for the Treatment of Inflammatory Bowel Disease

While mesalamine, a 5-aminosalicylic acid (5-ASA), is pivotal in the management of inflammatory bowel disease (IBD) through both step-up and top-down approaches in clinical settings, its widespread utilization is limited by low bioavailability at the desired site of action due to rapid and extensive absorption in the upper gastrointestinal (GI) tract. Addressing mesalamine's pharmacokinetic challenges, here, we introduce nanoassemblies composed exclusively of a mesalamine prodrug that pairs 5-ASA with a mucoadhesive and cathepsin B-cleavable peptide. In an IBD model, orally administered nanoassemblies demonstrate enhanced accumulation and sustained retention in the GI tract due to their mucoadhesive properties and the epithelial enhanced permeability and retention (eEPR) effect. This retention enables the efficient uptake by intestinal pro-inflammatory macrophages expressing high cathepsin B, triggering a burst release of the 5-ASA. This cascade fosters the polarization toward an M2 macrophage phenotype, diminishes inflammatory responses, and simultaneously facilitates the delivery of active agents to adjacent epithelial cells. Therefore, the nanoassemblies show outstanding therapeutic efficacy in inhibiting local inflammation and contribute to suppressing systemic inflammation by restoring damaged intestinal barriers. Collectively, this study highlights the promising role of the prodrug nanoassemblies in enhancing targeted drug delivery, potentially broadening the use of mesalamine in managing IBD.

The small acid-soluble proteins of Clostridioides difficile regulate sporulation in a SpoIVB2-dependent manner

Clostridioides difficile is a pathogen whose transmission relies on the formation of dormant endospores. Spores are highly resilient forms of bacteria that resist environmental and chemical insults. In recent work, we found that C. difficile SspA and SspB, two small acid-soluble proteins (SASPs), protect spores from UV damage and, interestingly, are necessary for the formation of mature spores. Here, we build upon this finding and show that C. difficile sspA and sspB are required for the formation of the spore cortex layer. Moreover, using an EMS mutagenesis selection strategy, we identified mutations that suppressed the defect in sporulation of C. difficile SASP mutants. Many of these strains contained mutations in CDR20291_0714 (spoIVB2) revealing a connection between the SpoIVB2 protease and the SASPs in the sporulation pathway. This work builds upon the hypothesis that the small acid-soluble proteins can regulate gene expression.

Identification of a hemorrhagic determinant in Clostridioides difficile TcdA and Paeniclostridium sordellii TcsH

Paeniclostridium sordellii hemorrhagic toxin (TcsH) and Clostridioides difficile toxin A (TcdA) are two major members of the large clostridial toxin (LCT) family. These two toxins share ~87% similarity and are known to cause severe hemorrhagic pathology in animals. Yet, the pathogenesis of their hemorrhagic toxicity has been mysterious for decades. Here, we examined the liver injury after systemic exposure to different LCTs and found that only TcsH and TcdA induce overt hepatic hemorrhage. By investigating the chimeric and truncated toxins, we demonstrated that the enzymatic domain of TcsH alone is not sufficient to determine its potent hepatic hemorrhagic toxicity in mice. Likewise, the combined repetitive oligopeptide (CROP) domain of TcsH/TcdA alone also failed to explain their strong hemorrhagic activity in mice. Lastly, we showed that disrupting the first two short repeats of CROPs in TcsH and TcdA impaired hemorrhagic toxicity without causing overt changes in cytotoxicity and lethality. These findings lead to a deeper understanding of toxin-induced hemorrhage and the pathogenesis of LCTs and could be insightful in developing therapeutic avenues against clostridial infections.

IMPORTANCE

Paeniclostridium sordellii and Clostridioides difficile infections often cause hemorrhage in the affected tissues and organs, which is mainly attributed to their hemorrhagic toxins, TcsH and TcdA. In this study, we demonstrate that TcsH and TcdA, but not other related toxins. including Clostridioides difficile toxin B and TcsL, induce severe hepatic hemorrhage in mice. We further determine that a small region in TcsH and TcdA is critical for the hemorrhagic toxicity but not cytotoxicity or lethality of these toxins. Based on these results, we propose that the hemorrhagic toxicity of TcsH and TcdA is due to an uncharacterized mechanism, such as the presence of an unknown receptor, and future studies to identify the interactive host factors are warranted.

Clostridioides difficile toxin B subverts germinal center and antibody recall responses by stimulating a drug-treatable CXCR4-dependent mechanism

Recurrent Clostridioides difficile infection (CDI) results in significant morbidity and mortality. We previously established that CDI in mice does not protect against reinfection and is associated with poor pathogen-specific B cell memory (Bmem), recapitulating our observations with human Bmem. Here, we demonstrate that the secreted toxin TcdB2 is responsible for subversion of Bmem responses. TcdB2 from an endemic C. difficile strain delayed immunoglobulin G (IgG) class switch following vaccination, attenuated IgG recall to a vaccine booster, and prevented germinal center formation. The mechanism of TcdB2 action included increased B cell CXCR4 expression and responsiveness to its ligand CXCL12, accounting for altered cell migration and a failure of germinal center-dependent Bmem. These results were reproduced in a C. difficile infection model, and a US Food and Drug Administration (FDA)-approved CXCR4-blocking drug rescued germinal center formation. We therefore provide mechanistic insights into C. difficile-associated pathogenesis and illuminate a target for clinical intervention to limit recurrent disease.

C. difficile biomarkers, pathogenicity and detection

BACKGROUND

Clostridioides difficile infection (CDI) is the main etiologic agent of antibiotic-associated diarrhea. CDI contributes to gut inflammation and can lead to disruption of the intestinal epithelial barrier. Recently, the rate of CDI cases has been increased. Thus, early diagnosis of C. difficile is critical for controlling the infection and guiding efficacious therapy.

APPROACH

A search strategy was set up using the terms C. difficile biomarkers and diagnosis. The found references were classified into two general categories; conventional and advanced methods.

RESULTS

The pathogenicity and biomarkers of C. difficile, and the collection manners for CDI-suspected specimens were briefly explained. Then, the conventional CDI diagnostic methods were subtly compared in terms of duration, level of difficulty, sensitivity, advantages, and disadvantages. Thereafter, an extensive review of the various newly proposed techniques available for CDI detection was conducted including nucleic acid isothermal amplification-based methods, biosensors, and gene/single-molecule microarrays. Also, the detection mechanisms, pros and cons of these methods were highlighted and compared with each other. In addition, approximately complete information on FDA-approved platforms for CDI diagnosis was collected.

CONCLUSION

To overcome the deficiencies of conventional methods, the potential of advanced methods for C. difficile diagnosis, their direction, perspective, and challenges ahead were discussed.

CSPG4-dependent cytotoxicity for C. difficile TcdB is influenced by extracellular calcium and chondroitin sulfate

TcdB is an intracellular bacterial toxin indispensable to Clostridioides difficile infections. The ability to use chondroitin sulfate proteoglycan 4 (CSPG4) as a primary cell surface receptor is evolutionarily conserved by the two major variants of TcdB. As CSPG4 does not typically undergo receptor-mediated endocytosis, we sought to identify environmental factors that stabilize interactions between TcdB and CSPG4 to promote cell binding and entry into the cytosol. Using a series of TcdB receptor-binding mutants and cell lines with various receptor expression profiles, we discovered that extracellular Ca2+ promotes receptor-specific interactions with TcdB. Specifically, TcdB exhibits preferential binding to CSPG4 in the presence of Ca2+, with the absence of Ca2+ resulting in CSPG4-independent cell surface interactions. Furthermore, Ca2+ did not enhance TcdB binding to chondroitin sulfate (CS), the sole glycosaminoglycan of CSPG4. Instead, CS was found to impact the rate of cell entry by TcdB. Collectively, results from this study indicate that Ca2+ enhances cell binding by TcdB and CS interactions contribute to subsequent steps in cell entry.

IMPORTANCE

Clostridioides difficile is a leading cause of antibiotic-associated gastrointestinal illness, and many disease pathologies are caused by the toxin TcdB. TcdB engages multiple cell surface receptors, with receptor tropisms differing among the variants of the toxin. Chondroitin sulfate proteoglycan 4 (CSPG4) is a critical receptor for multiple forms of TcdB, and insights into TcdB-CSPG4 interactions are applicable to many disease-causing strains of C. difficile. CSPG4 is modified by chondroitin sulfate (CS) and contains laminin-G repeats stabilized by Ca2+, yet the relative contributions of CS and Ca2+ to TcdB cytotoxicity have not been determined. This study demonstrates distinct roles in TcdB cell binding and cell entry for Ca2+ and CS, respectively. These effects are specific to CSPG4 and contribute to the activities of a prominent isoform of TcdB that utilizes this receptor. These findings advance an understanding of factors contributing to TcdB's mechanism of action and contribution to C. difficile disease.

Elucidating human gut microbiota interactions that robustly inhibit diverse Clostridioides difficile strains across different nutrient landscapes

The human gut pathogen Clostridioides difficile displays extreme genetic variability and confronts a changeable nutrient landscape in the gut. We mapped gut microbiota inter-species interactions impacting the growth and toxin production of diverse C. difficile strains in different nutrient environments. Although negative interactions impacting C. difficile are prevalent in environments promoting resource competition, they are sparse in an environment containing C. difficile-preferred carbohydrates. C. difficile strains display differences in interactions with Clostridium scindens and the ability to compete for proline. C. difficile toxin production displays substantial community-context dependent variation and does not trend with growth-mediated inter-species interactions. C. difficile shows substantial differences in transcriptional profiles in the presence of the closely related species C. hiranonis or C. scindens. In co-culture with C. hiranonis, C. difficile exhibits massive alterations in metabolism and other cellular processes, consistent with their high metabolic overlap. Further, Clostridium hiranonis inhibits the growth and toxin production of diverse C. difficile strains across different nutrient environments and ameliorates the disease severity of a C. difficile challenge in a murine model. In sum, strain-level variability and nutrient environments are major variables shaping gut microbiota interactions with C. difficile.

Antibiotics-associated pseudomembranous colitis: a disproportionality analysis of the US food and drug administration adverse event reporting system (FAERS) database

BACKGROUND

Evaluating antibiotics most commonly associated with pseudomembranous colitis (PMC) based on the real-world data is of great significance.

RESEARCH DESIGN AND METHODS

We used the data from FAERS to evaluate the potential association between antibiotics and PMC by disproportionality analyzes.

RESULTS

Eighty-one antibiotics which met the three algorithms simultaneously were enrolled. There were 1683 reports of PMC associated with the enrolled antibiotics. In the top 24 antibiotics, cefoxitin, streptomycin, fosfomycin, and micafungin had a high risk of PMC, but there were few reports in the literature.

CONCLUSIONS

This study was of great significance for healthcare professionals to realize the potential PMC risks of antibiotics.

Enhancing bezlotoxumab binding to C. difficile toxin B2: insights from computational simulations and mutational analyses for antibody design

Clostridioides difficile infection (CDI) is a significant concern caused by widespread antibiotic use, resulting in diarrhea and inflammation from the gram-positive anaerobic bacterium C. difficile. Although bezlotoxumab (Bez), a monoclonal antibody (mAb), was developed to address CDI recurrences, the recurrence rate remains high, partly due to reduced neutralization efficiency against toxin B2. In this study, we aimed to enhance the binding of Bez to C. difficile toxin B2 by combining computational simulations and mutational analyses. We identified specific mutations in Bez, including S28R, S31W/K, Y32R, S56W and G103D/S in the heavy chain (Hc), and S32F/H/R/W/Y in the light chain (Lc), which significantly improved binding to toxin B2 and formed critical protein-protein interactions. Through molecular dynamics simulations, several single mutations, such as HcS28R, LcS32H, LcS32R, LcS32W and LcS32Y, exhibited superior binding affinities to toxin B2 compared to Bez wild-type (WT), primarily attributed to Coulombic interactions. Combining the HcS28R mutation with four different mutations at residue LcS32 led to even greater binding affinities in double mutants (MTs), particularly HcS28R/LcS32H, HcS28R/LcS32R and HcS28R/LcS32Y, reinforcing protein-protein binding. Analysis of per-residue decomposition free energy highlighted key residues contributing significantly to enhanced binding interactions, emphasizing the role of electrostatic interactions. These findings offer insights into rational Bez MT design for improved toxin B2 binding, providing a foundation for developing more effective antibodies to neutralize toxin B2 and combat-related infections.Communicated by Ramaswamy H. Sarma.

Isofagomine Inhibits Multiple TcdB Variants and Protects Mice from Clostridioides difficile-Induced Mortality

Clostridioides difficile causes life-threatening diarrhea and is one of the leading causes of nosocomial infections. During infection, C. difficile releases two gut-damaging toxins, TcdA and TcdB, which are the primary determinants of disease pathogenesis and are important therapeutic targets. Once in the cytosol of mammalian cells, TcdA and TcdB use UDP-glucose to glucosylate host Rho GTPases, which leads to cytoskeletal changes that result in a loss of intestinal integrity. Isofagomine inhibits TcdA and TcdB as a mimic of the glucocation transition state of the glucosyltransferase reaction. However, sequence variants of TcdA and TcdB across the clades of infective C. difficile continue to be identified, and therefore, evaluation of isofagomine inhibition against multiple toxin variants is required. Here, we show that isofagomine inhibits the glucosyltransferase domain of multiple TcdB variants and protects TcdB-induced cell rounding of the most common full-length toxin variants. Furthermore, we demonstrate that isofagomine protects against C. difficile-induced mortality in two murine models of C. difficile infection. Isofagomine treatment of mouse C. difficile infection also permitted the recovery of the gastrointestinal microbiota, an important barrier to preventing recurring C. difficile infection. The broad specificity of isofagomine supports its potential as a prophylactic to protect against C. difficile-induced morbidity and mortality.

Immunogenicity and safety in rabbits of a Clostridioides difficile vaccine combining novel toxoids and a novel adjuvant

Clostridioides difficile infection (CDI) is a serious healthcare-associated disease, causing symptoms such as diarrhea and pseudomembranous colitis. The major virulence factors responsible for the disease symptoms are two secreted cytotoxic proteins, TcdA and TcdB. A parenteral vaccine based on formaldehyde-inactivated TcdA and TcdB supplemented with alum adjuvant, has previously been investigated in humans but resulted in an insufficient immune response. In search for an improved response, we investigated a novel toxin inactivation method and a novel, potent adjuvant. Inactivation of toxins by metal-catalyzed oxidation (MCO) was previously shown to preserve neutralizing epitopes and to annihilate reversion to toxicity. The immunogenicity and safety of TcdA and TcdB inactivated by MCO and combined with a novel carbohydrate fatty acid monosulphate ester-based (CMS) adjuvant were investigated in rabbits. Two or three intramuscular immunizations generated high serum IgG and neutralizing antibody titers against both toxins. The CMS adjuvant increased antibody responses to both toxins while an alum adjuvant control was effective only against TcdA. Systemic safety was evaluated by monitoring body weight, body temperature, and analysis of red and white blood cell counts shortly after immunization. Local safety was assessed by histopathologic examination of the injection site at the end of the study. Body weight gain was constant in all groups. Body temperature increased up to 1 ˚C one day after the first immunization but less after the second or third immunization. White blood cell counts, and percentage of neutrophils increased one day after immunization with CMS-adjuvanted vaccines, but not with alum. Histopathology of the injection sites 42 days after the last injection did not reveal any abnormal tissue reactions. From this study, we conclude that TcdA and TcdB inactivated by MCO and combined with CMS adjuvant demonstrated promising immunogenicity and safety in rabbits and could be a candidate for a vaccine against CDI.

Rapid discrimination between clinical Clostridioides difficile infection and colonization by quantitative detection of TcdB toxin using a real-time cell analysis system

Objectives

It is important to accurately discriminate between clinical Clostridioides difficile infection (CDI) and colonization (CDC) for effective antimicrobial treatment.

Methods

In this study, 37 stool samples were collected from 17 CDC and 20 CDI cases, and each sample were tested in parallel through the real-time cell analysis (RTCA) system, real-time PCR assay (PCR), and enzyme-linked immunosorbent assay (ELISA).

Results

RTCA-measured functional and toxical C. difficile toxin B (TcdB) concentrations in the CDI group (302.58 ± 119.15 ng/mL) were significantly higher than those in the CDC group (18.15 ± 11.81 ng/mL) (p = 0.0008). Conversely, ELISA results revealed no significant disparities in TcdB concentrations between the CDC (26.21 ± 3.57 ng/mL) and the CDI group (17.07 ± 3.10 ng/mL) (p = 0.064). PCR results indicated no significant differences in tcdB gene copies between the CDC (774.54 ± 357.89 copies/μL) and the CDI group (4,667.69 ± 3,069.87 copies/μL) (p = 0.407). Additionally, the functional and toxical TcdB concentrations secreted from C. difficile isolates were measured by the RTCA. The results from the CDC (490.00 ± 133.29 ng/mL) and the CDI group (439.82 ± 114.66 ng/mL) showed no significant difference (p = 0.448). Notably, RTCA-measured functional and toxical TcdB concentration was significantly decreased when mixed with pooled CDC samples supernatant (p = 0.030).

Conclusion

This study explored the novel application of the RTCA assay in effectively discerning clinical CDI from CDC cases.

Localized pseudomembranous gastritis associated with hepatic cirrhosis and portal hypertensive gastropathy: a case report

Pseudomembranes in the large and small intestines are common in hospitalized patients that are immunosuppressed or on certain oral antibiotics. Pseudomembranous enterocolitis, histologically characterized by volcanic-like eruption of inflammatory cellular exudate from the mucosal surface, is mainly attributed to Clostridium difficile toxins and often presents with symptomatic diarrhea. Rarely, there are case reports of similar pseudomembranous lesions limited to the stomach in the absence of intestinal involvement. In this paper, we present a case of localized pseudomembranous gastritis in a 76-year-old patient with personal history limited to prior gastrointestinal bleed, liver cirrhosis, alcohol dependence, diabetes mellitus, and hypertension who was referred to the emergency department from his primary care physician's office due to low hemoglobin.

Probiotics for Prevention and Treatment of Clostridium difficile Infection

Probiotics have been claimed as a valuable tool to restore the balance in the intestinal microbiota following a dysbiosis caused by, among other factors, antibiotic therapy. This perturbed environment could favor the overgrowth of Clostridium difficile, and in fact, the occurrence of C. difficile-associated infections (CDI) is increasing in recent years. In spite of the high number of probiotics able to in vitro inhibit the growth and/or toxicity of this pathogen, its application for treatment or prevention of CDI is still scarce since there are not enough well-defined clinical studies supporting efficacy. Only a few strains, such as Lactobacillus rhamnosus GG and Saccharomyces boulardii, have been studied in more extent. The increasing knowledge about the probiotic mechanisms of action against C. difficile, some of them reviewed here, makes promising the application of these live biotherapeutic agents against CDI. Nevertheless, more effort must be paid to standardize the clinical studies conducted to evaluate probiotic products, in combination with antibiotics, in order to select the best candidate for C. difficile infections.

An Updated View on the Cellular Uptake and Mode-of-Action of Clostridioides difficile Toxins

Research on the human gut pathogen Clostridioides (C.) difficile and its toxins continues to attract much attention as a consequence of the threat to human health posed by hypervirulent strains. Toxin A (TcdA) and Toxin B (TcdB) are the two major virulence determinants of C. difficile. Both are single-chain proteins with a similar multidomain architecture. Certain hypervirulent C. difficile strains also produce a third toxin, namely binary toxin CDT (C. difficile transferase). C. difficile toxins are the causative agents of C. difficile-associated diseases (CDADs), such as antibiotics-associated diarrhea and pseudomembranous colitis. For that reason, considerable efforts have been expended to unravel their molecular mode-of-action and the cellular mechanisms responsible for their uptake. Many of these studies have been conducted in European laboratories. Here, we provide an update on our previous review (Papatheodorou et al. Adv Exp Med Biol, 2018) on important advances in C. difficile toxins research.

Immunization Strategies Against Clostridioides difficile

Clostridioides difficile (C. difficile) infection (CDI) is an important healthcare but also a community-associated disease. CDI is considered a public health threat and an economic burden. A major problem is the high rate of recurrences. Besides classical antibiotic treatments, new therapeutic strategies are needed to prevent infection, to treat patients, and to prevent recurrences. If fecal transplantation has been recommended to treat recurrences, another key approach is to elicit immunity against C. difficile and its virulence factors. Here, after a summary concerning the virulence factors, the host immune response against C. difficile, and its role in the outcome of disease, we review the different approaches of passive immunotherapies and vaccines developed against CDI. Passive immunization strategies are designed in function of the target antigen, the antibody-based product, and its administration route. Similarly, for active immunization strategies, vaccine antigens can target toxins or surface proteins, and immunization can be performed by parenteral or mucosal routes. For passive immunization and vaccination as well, we first present immunization assays performed in animal models and second in humans and associated clinical trials. The different studies are presented according to the mode of administration either parenteral or mucosal and the target antigens and either toxins or colonization factors.

Characterization of community-acquired Clostridioides difficile strains in Israel, 2020-2022

Background

The prevalence of community-acquired Clostridioides difficile infection (CA-CDI) has been rising, due to changes in antibiotics prescribing practices, emergence of hypervirulent strains and improved diagnostics. This study explored CA-CDI epidemiology by examining strain diversity and virulence factors of CA-CDI isolates collected across several geographical regions in Israel.

Methods

Stool samples of 126 CA-CDI patients were subjected to PCR and an immunoassay to identify toxin genes and proteins, respectively. Toxin loci PaLoc and PaCdt were detected by whole-genome sequencing (WGS). Biofilm production was assessed by crystal violet-based assay. Minimum inhibitory concentration was determined using the Etest technique or agar dilution. WGS and multi-locus sequence typing (MLST) were used to classify strains and investigate genetic diversity.

Results

Sequence types (ST) 2 (17, 13.5%), ST42 (13, 10.3%), ST104 (10, 8%) and ST11 (9, 7.1%) were the most common. All (117, 92.8%) but ST11 belonged to Clade 1. No associations were found between ST and gender, geographic area or antibiotic susceptibility. Although all strains harbored toxins genes, 34 (27%) produced toxin A only, and 54 (42.9%) strains produced toxin B only; 38 (30.2%) produced both toxins. Most isolates were biofilm-producers (118, 93.6%), primarily weak producers (83/118, 70.3%). ST was significantly associated with both biofilm and toxin production.

Conclusion

C. difficile isolates in Israel community exhibit high ST diversity, with no dominant strain. Other factors may influence the clinical outcomes of CDI such as toxin production, antibiotic resistance and biofilm production. Further studies are needed to better understand the dynamics and influence of these factors on CA-CDI.

A phase 3 study evaluating the lot consistency, immunogenicity, safety, and tolerability of a Clostridioides difficile vaccine in healthy adults 65 to 85 years of age

BACKGROUND

A toxoid-based Clostridioides difficile vaccine is currently in development. Here, we report lot-to-lot consistency, immunogenicity, safety, and tolerability of 3 C difficile vaccine doses in healthy older adults.

METHODS

This phase 3, placebo-controlled study randomized (1:1:1:1) healthy adults 65 to 85 years of age to 1 of 3 C difficile vaccine lots or placebo. Participants received C difficile vaccine (200 μg total toxoid) or placebo (Months 0, 1, 6). The primary immunogenicity objective was lot-to-lot consistency (2-sided 95 % CIs within 0.5 and 2 for comparisons of geometric mean concentration [GMC] ratios) for toxins A- and B-specific neutralizing antibody levels 1 month after Dose 3. Safety outcomes included local reactions and systemic events ≤7 days after vaccination, adverse events (AEs), and serious AEs (SAEs).

RESULTS

Of 1317 enrolled participants, 1218 completed the study. C difficile vaccine immunogenicity was consistent across lots, with neutralizing antibody responses 1 month after Dose 3 for both toxin A (GMC [95 % CI]: lot 1, 878.8 [786.3, 982.2]; lot 2, 873.0 [779.2, 978.1]; lot 3, 872.9 [782.6, 973.5]) and toxin B (lot 1, 5823.9 [5041.0, 6728.4]; lot 2, 5462.8 [4733.4, 6304.7]; lot 3, 5426.0 [4724.4, 6231.8]). Two-sided 95 % CIs for GMC ratios were within 0.5 and 2 for toxins A and B, indicating lot-to-lot consistency was achieved. C difficile vaccine was well tolerated, with similar rates of local reactions and systemic events among vaccine lots. AE and SAE rates were similar across C difficile vaccine (36.5 % and 4.5 %, respectively) and placebo (35.3 % and 6 %).

CONCLUSIONS

Three doses (Months 0,1,6) of toxoid-based C difficile vaccine induced robust neutralizing antibody responses and were well tolerated in healthy participants 65 to 85 years of age. Lot-to-lot consistency was excellent, indicating the manufacturing process for this C difficile vaccine formulation was well controlled.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT03579459.

Clostridioides difficile PCR ribotypes 001 and 084 can trigger autophagy process in human intestinal Caco-2 cells

Autophagy is a homeostatic process that can promote cell survival or death. However, the exact role of autophagy in Clostridioides difficile infection (CDI) is still not precisely elucidated. Here, we investigate the role of distinct C. difficile ribotypes (RTs) in autophagy induction using Caco-2 cells. The expression analysis of autophagy-associated genes and related miRNAs were examined following treatment of Caco-2 cells with C. difficile after 4 and 8 h using RT-qPCR. Toxin production was assessed using enzyme-linked immunosorbent assay (ELISA). Immunofluorescence analysis was performed to detect MAP1LC3B/LC3B, followed by an autophagic flux analysis. C. difficile significantly reduced the viability of Caco-2 cells in comparison with untreated cells. Elevated levels of LC3-II and SQSTM1/p62 by C. difficile RT001 and RT084 in the presence of E64d/leupeptin confirmed the induction of autophagy activity. Similarly, the immunofluorescence analysis demonstrated that C. difficile RT001 and RT084 significantly increased the amount of LC3-positive structures in Caco-2 cells. The induction of autophagy was further demonstrated by increased levels of LC3B, ULK1, ATG12, PIK3C3/VPS34, BECN1 (beclin 1), ATG5, and ATG16L1 transcripts and reduced levels of AKT and MTOR gene expression. The expression levels of MIR21 and MIR30B, microRNAs that suppress autophagy, were differentially affected by C. difficile. In conclusion, the present work revealed that C. difficile bacteria can induce autophagy through both toxin-dependent and -independent mechanisms. Also, our results suggest the potential role of other C. difficile virulence factors in autophagy modulation using intestinal cells in vitro.

Linked mutations within the pathogenicity locus of Clostridioides difficile increase virulence

BACKGROUND

The clinical manifestations of Clostridioides difficile infections range from diarrhoea to pseudomembranous colitis (PMC) and death. We evaluated the association between gene content in C. difficile clinical isolates and disease severity.

METHODS

Fifty-three C. difficile isolates were subjected to Sanger sequencing, clinical data were used to analyse the association of gene content with disease severity, and 83 non-duplicate isolates were collected to confirm the results. Virulence was further examined by functional in vitro and in vivo experiments.

RESULTS

Among the 53 C. difficile isolates, ribotypes 017 (n = 9, 17.0%) and 012 (n = 8, 15.1%) were predominant. Fifteen strains exhibited a correlation between mutations of pathogenicity locus genes (tcdB, tcdC, tcdR, and tcdE) and were named linked-mutation strains. Ribotypes are not associated with clinical PMC and Linked-mutation strains. The proportion of patients with PMC was higher in the group infected with linked-mutation strains than in the non-linked-mutation group (57.14% vs. 0%, p < 0.001). The linked-mutation rate of C. difficile was higher in patients with PMC than in patients without PMC (89.47% vs. 7.8%, p < 0.0001). Linked-mutation strains showed greater cytotoxicity in vitro and caused more severe tissue damage in a mouse model.

CONCLUSIONS

Linked-mutation strains are associated with high virulence and PMC development. This result will help monitor the clinical prognosis of C. difficile infection and provide key insights for developing therapeutic targets and monoclonal antibodies.

Clostridium innocuum, an emerging pathogen that induces lipid raft-mediated cytotoxicity

Clostridium innocuum is an emerging spore-forming anaerobe that is often observed in Clostridioides difficile-associated inflammatory bowel disease (IBD) exacerbations. Unlike C. difficile, C. innocuum neither produces toxins nor possesses toxin-encoding genetic loci, but is commonly found in both intestinal and extra-intestinal infections. Membrane lipid rafts are composed of dynamic assemblies of cholesterol and sphingolipids, allowing bacteria to gain access to cells. However, the direct interaction between C. innocuum and lipid rafts that confers bacteria the ability to disrupt the intestinal barrier and induce pathogenesis remains unclear. In this study, we investigated the associations among nucleotide-binding oligomerization domain containing 2 (NOD2), lipid rafts, and cytotoxicity in C. innocuum-infected gut epithelial cells. Our results revealed that lipid rafts were involved in C. innocuum-induced NOD2 expression and nuclear factor (NF)-κB activation, triggering an inflammatory response. Reducing cholesterol by simvastatin significantly dampened C. innocuum-induced cell death, indicating that the C. innocuum-induced pathogenicity of cells was lipid raft-dependent. These results demonstrate that NOD2 mobilization into membrane rafts in response to C. innocuum-induced cytotoxicity results in aggravated pathogenicity.

Pathogenicity and virulence of Clostridioides difficile

Clostridioides difficile is the most common cause of nosocomial antibiotic-associated diarrhea, and is responsible for a spectrum of diseases characterized by high levels of recurrence, morbidity, and mortality. Treatment is complex, since antibiotics constitute both the main treatment and the major risk factor for infection. Worryingly, resistance to multiple antibiotics is becoming increasingly widespread, leading to the classification of this pathogen as an urgent threat to global health. As a consummate opportunist, C. difficile is well equipped for promoting disease, owing to its arsenal of virulence factors: transmission of this anaerobe is highly efficient due to the formation of robust endospores, and an array of adhesins promote gut colonization. C. difficile produces multiple toxins acting upon gut epithelia, resulting in manifestations typical of diarrheal disease, and severe inflammation in a subset of patients. This review focuses on such virulence factors, as well as the importance of antimicrobial resistance and genome plasticity in enabling pathogenesis and persistence of this important pathogen.

Inflammatory bowel disease and Clostridium difficile infection: clinical presentation, diagnosis, and management

As a frequent complication of inflammatory bowel disease (IBD), Clostridium difficile infection (CDI) was confirmed to not only aggravate the symptoms of IBD but also result in unexpected outcomes, including death. With the increasing prevalence rate of IBD and the updating of CDI diagnosis, the incidence of CDI in IBD patients is also seen rising. Although a detection method consisting of glutamate dehydrogenase immunoassay or nucleic acid amplification test and then toxin A/B enzyme immunoassay was recommended and widely adopted, the diagnosis of CDI in IBD is still a challenge because of the overlap between the symptoms of CDI in IBD and CDI itself. Vancomycin and fidaxomicin are the first-line therapy for CDI in IBD; however, the treatment has different effects due to the complexity of IBD patients' conditions and the choice of different treatment schemes. Although the use of fecal microbial transplantation is now in the ascendant for IBD management, the prospects are still uncertain and the prevention and treatment of the recurrence of CDI in IBD remain a clinical challenge. In this paper, the epidemiology, pathophysiology, clinical manifestation, prevention, and therapy of CDI in IBD were summarized and presented.

Engineered Secretory Immunoglobulin A provides insights on antibody-based effector mechanisms targeting Clostridiodes difficile

Secretory (S) Immunoglobin (Ig) A is the predominant mucosal antibody, which mediates host interactions with commensal and pathogenic microbes, including Clostridioides difficile. SIgA adopts a polymeric IgA structure that is bound by secretory component (SC). Despite significance, how SIgA supports diverse effector mechanisms is poorly characterized and SIgA-based therapies nonexistent. We engineered chimeric (c) SIgAs, in which we replaced SC domain D2 with a single domain antibody or a monomeric fluorescent protein, allowing us to investigate and enhance SIgA effector mechanisms. cSIgAs exhibited increased neutralization potency against C. difficile toxins, promoted bacterial clumping and cell rupture, and decreased cytotoxicity. cSIgA also allowed us to visualize and/or quantify C. difficile morphological changes and clumping events. Results reveal mechanisms by which SIgA combats C. difficile infection, demonstrate that cSIgA design can modulate these mechanisms, and demonstrate cSIgA's adaptability to modifications that might target a broad range of antigens and effector mechanisms.

A Colonic Organoid Model Challenged with the Large Toxins of Clostridioides difficile TcdA and TcdB Exhibit Deregulated Tight Junction Proteins

BACKGROUND

Clostridioides difficile toxins TcdA and TcdB are responsible for diarrhea and colitis. Lack of functional studies in organoid models of the gut prompted us to elucidate the toxin's effects on epithelial barrier function and the molecular mechanisms for diarrhea and inflammation.

METHODS

Human adult colon organoids were cultured on membrane inserts. Tight junction (TJ) proteins and actin cytoskeleton were analyzed for expression via Western blotting and via confocal laser-scanning microscopy for subcellular localization.

RESULTS

Polarized intestinal organoid monolayers were established from stem cell-containing colon organoids to apply toxins from the apical side and to perform functional measurements in the organoid model. The toxins caused a reduction in transepithelial electrical resistance in human colonic organoid monolayers with sublethal concentrations. Concomitantly, we detected increased paracellular permeability fluorescein and FITC-dextran-4000. Human colonic organoid monolayers exposed to the toxins exhibited redistribution of barrier-forming TJ proteins claudin-1, -4 and tricellulin, whereas channel-forming claudin-2 expression was increased. Perijunctional F-actin cytoskeleton organization was affected.

CONCLUSIONS

Adult stem cell-derived human colonic organoid monolayers were applicable as a colon infection model for electrophysiological measurements. The TJ changes noted can explain the epithelial barrier dysfunction and diarrhea in patients, as well as increased entry of luminal antigens triggering inflammation.

Dual RNA-seq identifies genes and pathways modulated during Clostridioides difficile colonization

IMPORTANCE

The initial interactions between the colonic epithelium and the bacterium are likely critical in the establishment of Clostridioides difficile infection, one of the major causes of hospital-acquired diarrhea worldwide. Molecular interactions between C. difficile and human gut cells have not been well defined mainly due to the technical challenges of studying cellular host-pathogen interactions with this anaerobe. Here we have examined transcriptional changes occurring in the pathogen and host cells during the initial 24 hours of infection. Our data indicate several changes in metabolic pathways and virulence-associated factors during the initial bacterium-host cell contact and early stages of infection. We describe canonical pathways enriched based on the expression profiles of a dual RNA sequencing in the host and bacterium, and functions of bacterial factors that are modulated during infection. This study thus provides fresh insight into the early C. difficile infection process.

Protective Effects of Alginate and Chitosan Oligosaccharides against Clostridioides difficile Bacteria and Toxin

Clostridioides difficile infection is expected to become the most common healthcare-associated infection worldwide. C. difficile-induced pathogenicity is significantly attributed to its enterotoxin, TcdA, which primarily targets Rho-GTPases involved in regulating cytoskeletal and tight junction (TJ) dynamics, thus leading to cytoskeleton breakdown and ultimately increased intestinal permeability. This study investigated whether two non-digestible oligosaccharides (NDOs), alginate (AOS) and chitosan (COS) oligosaccharides, possess antipathogenic and barrier-protective properties against C. difficile bacteria and TcdA toxin, respectively. Both NDOs significantly reduced C. difficile growth, while cell cytotoxicity assays demonstrated that neither COS nor AOS significantly attenuated the TcdA-induced cell death 24 h post-exposure. The challenge of Caco-2 monolayers with increasing TcdA concentrations increased paracellular permeability, as measured by TEER and LY flux assays. In this experimental setup, COS completely abolished, and AOS mitigated, the deleterious effects of TcdA on the monolayer's integrity. These events were not accompanied by alterations in ZO-1 and occludin protein levels; however, immunofluorescence microscopy revealed that both AOS and COS prevented the TcdA-induced occludin mislocalization. Finally, both NDOs accelerated TJ reassembly upon a calcium-switch assay. Overall, this study established the antipathogenic and barrier-protective capacity of AOS and COS against C. difficile and its toxin, TcdA, while revealing their ability to promote TJ reassembly in Caco-2 cells.

Isofagomine inhibits multiple TcdB variants and protects mice from Clostridioides difficile induced mortality

Clostridioides difficile causes life-threatening diarrhea and is the leading cause of healthcare associated bacterial infections in the United States. During infection, C. difficile releases the gut-damaging toxins, TcdA and TcdB, the primary determinants of disease pathogenesis and are therefore therapeutic targets. TcdA and TcdB contain a glycosyltransferase domain that uses UDP-glucose to glycosylate host Rho GTPases, causing cytoskeletal changes that result in a loss of intestinal integrity. Isofagomine inhibits TcdA and TcdB as a mimic of the oxocarbenium ion transition state of the glycosyltransferase reaction. However, sequence variants of TcdA and TcdB across the clades of infective C. difficile continue to be identified and therefore, evaluation of isofagomine inhibition against multiple toxin variants are required. Here we show that Isofagomine inhibits the glycosyltransferase activity of multiple TcdB variants and also protects TcdB toxin-induced cell rounding of the most common full-length toxin variants. Further, isofagomine protects against C. difficile induced mortality in two murine models of C. difficile infection. Isofagomine treatment of mouse C. difficile infection permitted recovery of the gastrointestinal microbiota, an important barrier to prevent recurring C. difficile infection. The broad specificity of isofagomine supports its potential as a prophylactic to protect against C. difficile induced morbidity and mortality.

Modulation of colonic immunometabolic responses during Clostridioides difficile infection ameliorates disease severity and inflammation

Clostridioides difficile infection (CDI) is the leading cause of antibiotic-associated diarrhea, and its clinical symptoms can span from asymptomatic colonization to pseudomembranous colitis and even death. The current standard of care for CDI is antibiotic treatment to achieve bacterial clearance; however, 15 to 35% of patients experience recurrence after initial response to antibiotics. We have conducted a comprehensive, global colonic transcriptomics analysis of a 10-day study in mice to provide new insights on the local host response during CDI and identify novel host metabolic mechanisms with therapeutic potential. The analysis indicates major alterations of colonic gene expression kinetics at the acute infection stage, that are restored during the recovery phase. At the metabolic level, we observe a biphasic response pattern characterized by upregulated glycolytic metabolism during the peak of inflammation, while mitochondrial metabolism predominates during the recovery/healing stage. Inhibition of glycolysis via 2-Deoxy-D-glucose (2-DG) administration during CDI decreases disease severity, protects from mortality, and ameliorates colitis in vivo. Additionally, 2-DG also protects intestinal epithelial cells from C. difficile toxin damage, preventing loss of barrier integrity and secretion of proinflammatory mediators. These data postulate the pharmacological targeting of host immunometabolic pathways as novel treatment modalities for CDI.

Biofilm Formation of Clostridioides difficile, Toxin Production and Alternatives to Conventional Antibiotics in the Treatment of CDI

Clostridioides difficile is considered a nosocomial pathogen that flares up in patients exposed to antibiotic treatment. However, four out of ten patients diagnosed with C. difficile infection (CDI) acquired the infection from non-hospitalized individuals, many of whom have not been treated with antibiotics. Treatment of recurrent CDI (rCDI) with antibiotics, especially vancomycin (VAN) and metronidazole (MNZ), increases the risk of experiencing a relapse by as much as 70%. Fidaxomicin, on the other hand, proved more effective than VAN and MNZ by preventing the initial transcription of RNA toxin genes. Alternative forms of treatment include quorum quenching (QQ) that blocks toxin synthesis, binding of small anion molecules such as tolevamer to toxins, monoclonal antibodies, such as bezlotoxumab and actoxumab, bacteriophage therapy, probiotics, and fecal microbial transplants (FMTs). This review summarizes factors that affect the colonization of C. difficile and the pathogenicity of toxins TcdA and TcdB. The different approaches experimented with in the destruction of C. difficile and treatment of CDI are evaluated.

Butyrate Protects against Clostridium difficile Infection by Regulating Bile Acid Metabolism

Clostridium difficile infection (CDI) is caused by a prevalent nosocomial enteric pathogen, leading to high morbidity and mortality. CDI recurrence after antibiotic treatment is high; therefore, it is necessary to develop novel therapeutics against this enteric pathogen. Butyrate is used to treat many diseases because it provides energy, has anti-inflammatory properties, and maintains intestinal barrier function. An anti-CDI effect for butyrate has been reported; however, the specific mechanism remains elusive. This study aimed to explore the potential role and mechanism of butyrate in the treatment of CDI. Using a CDI mouse model, we found that butyrate significantly inhibited CDI development by regulating bile acid metabolism. Dysregulation of fecal bile acid was significantly higher, and levels of short-chain fatty acids were significantly lower in patients with CDI than those in controls. In CDI mice, butyrate exhibited a protective role by enhancing barrier protection, exerting anti-inflammatory effects, and regulating bile acid metabolism. Butyrate treatment also regulated the production of bile salt hydrolase (BSH) flora and activated farnesoid X receptor (FXR), and its therapeutic effects were reduced in CDI mice treated with BSH or FXR inhibitors. Thus, butyrate treatment may serve as a novel therapeutic approach for patients with CDI. IMPORTANCE Here, we show that levels of fecal short-chain fatty acids (SCFAs), particularly butyrate, are reduced, and normal colon structure is damaged in patients with CDI compared with those in healthy individuals. Bile acid (BA) metabolic disorder in patients with CDI is characterized by increased primary BA levels and decreased secondary BAs. In mice, butyrate alters BA metabolism in CDI and may play a vital role in CDI treatment by promoting secondary BA metabolism. Lastly, butyrate-mediated therapeutic effects in CDI require FXR. Our findings demonstrate that butyrate treatment significantly decreases the severity of CDI-induced colitis in mice and affects BA metabolism and FXR activation, which provides a potential alternative treatment for CDI.

Clostridioides difficile infection in thoroughbred horses in Japan from 2010 to 2021

We encountered 34 Clostridioides difficile (C. difficile) infection (CDI) cases among Thoroughbred horses in Japan from 2010 to 2021. Among them, 79.4% (27/34) either died or were euthanised. The risk factors associated with CDI and mortality among Japanese Thoroughbred horses remain unclear. We used genetic methods to examine C. difficile strains and their relationships with prognosis. Twenty-two (64.7%) cases were hospitalised at the onset of colitis. Outcomes were balanced for hospitalisation rates at the onset of colitis. The mortality rates of cases treated with metronidazole (65.0%) were significantly lower than untreated cases (100%). The predominant genotype of C. difficile isolate was polymerase chain reaction ribotype (RT) 078, isolated from 12 cases (35.3%), followed by RT014 (six cases, 17.6%). Binary toxin (C. difficile transferase [CDT])-positive strains, including all RT078 strains, were isolated from 16 horses. Mortality rates in RT078 strain (75.0%) or CDT-positive strain (83.3%) cases were comparable to that in cases of other types. Sufficient infection control is needed to prevent CDI in Thoroughbred horses. A timely and prompt CDI diagnosis leading to metronidazole treatment would improve CDI outcomes.

Gaining New Insights into Fundamental Biological Pathways by Bacterial Toxin-Based Genetic Screens

Genetic screen technology has been applied to study the mechanism of action of bacterial toxins-a special class of virulence factors that contribute to the pathogenesis caused by bacterial infections. These screens aim to identify host factors that directly or indirectly facilitate toxin intoxication. Additionally, specific properties of certain toxins, such as membrane interaction, retrograde trafficking, and carbohydrate binding, provide robust probes to comprehensively investigate the lipid biosynthesis, membrane vesicle transport, and glycosylation pathways, respectively. This review specifically focuses on recent representative toxin-based genetic screens that have identified new players involved in and provided new insights into fundamental biological pathways, such as glycosphingolipid biosynthesis, protein glycosylation, and membrane vesicle trafficking pathways. Functionally characterizing these newly identified factors not only expands our current understanding of toxin biology but also enables a deeper comprehension of fundamental biological questions. Consequently, it stimulates the development of new therapeutic approaches targeting both bacterial infectious diseases and genetic disorders with defects in these factors and pathways.

Double-Blind, Placebo-Controlled Study of Bezlotoxumab in Children Receiving Antibacterial Treatment for Clostridioides difficile Infection (MODIFY III)

BACKGROUND

Therapies to prevent recurrence of Clostridioides difficile infection (CDI) in pediatric patients are needed. Bezlotoxumab is a fully human monoclonal antibody approved for prevention of recurrent CDI in adults. We assessed the pharmacokinetics, safety, tolerability, and efficacy of bezlotoxumab in pediatric patients.

METHODS

MODIFY III was a multicenter, double-blind, placebo-controlled study of bezlotoxumab in children (1 to <18 years) receiving antibacterial treatment for CDI. Participants were randomized 3:1 to receive a single infusion of bezlotoxumab (10 mg/kg) or placebo and were stratified by age at randomization (cohort 1: 12 to <18 years, cohort 2: 1 to <12 years). The primary objective was to characterize bezlotoxumab pharmacokinetics to support dose selection for pediatric patients; the primary endpoint was the area under the bezlotoxumab serum concentration-time curve (AUC0-inf). Safety, tolerability, and efficacy were monitored for 12 weeks post-infusion.

RESULTS

A total of 148 participants were randomized and 143 were treated: 107 with bezlotoxumab and 36 with placebo (cohort 1 n = 60, cohort 2 n = 83; median age 9.0 years); 52.4% of participants were male and 80.4% were white. Geometric mean ratios (90% CI) for bezlotoxumab AUC0-inf were 1.06 (0.95, 1.18) and 0.82 (0.75, 0.89) h * μg/mL for cohorts 1 and 2, respectively. Bezlotoxumab 10 mg/kg was generally well-tolerated with an adverse event profile similar to placebo, including no treatment discontinuations due to adverse events. CDI recurrence was low and comparable for bezlotoxumab (11.2%) and placebo (14.7%).

CONCLUSIONS

The results of this study support the bezlotoxumab dose of 10 mg/kg for pediatric patients.

TRIAL REGISTRATION

NCT03182907 at ClinicalTrials.gov.

Assessing the Feasibility of Employing a Combination of a Bacteriophage-Derived Endolysin and Spore Germinants to Treat Relapsing Clostridioides difficile Infection

Clostridioides difficile is a Gram-positive, anaerobic, spore-forming bacillus and is a major cause of healthcare-associated infections. Whereas the vegetative form of the pathogen is susceptible to treatment with antibiotics, its ability to persist in the gut as antibiotic-resistant spores means that reinfection can occur in cases were the individual fails to re-establish a protective microflora. Bacteriophages and their lysins are currently being explored as treatment options due to their specificity, which minimizes the disruption to the other members of the gut microflora that are protective. The feasibility of employing recombinant endolysins to target the vegetative form of C. difficile has been demonstrated in animal models. In this study, we cloned and expressed the enzyme active domain of LysCD6356 and confirmed its ability to lyse the vegetative forms of a diverse range of clinical isolates of C. difficile, which included members of the hypervirulent 027 ribotype. Lytic activity was adversely affected by calcium, which is naturally found in the gut and is released from the spore upon germination. Our results suggests that a strategy in which the triggering of spore germination is separated in time from the application of the lysin could be developed as a strategy to reduce the risk of relapsing C. difficile infections.

Host Immunity and Immunization Strategies for Clostridioides difficile Infection

Clostridioides difficile infection (CDI) represents a significant challenge to public health. C. difficile-associated mortality and morbidity have led the U.S. CDC to designate it as an urgent threat. Moreover, recurrence or relapses can occur in up to a third of CDI patients, due in part to antibiotics being the primary treatment for CDI and the major cause of the disease. In this review, we summarize the current knowledge of innate immune responses, adaptive immune responses, and the link between innate and adaptive immune responses of the host against CDI. The other major determinants of CDI, such as C. difficile toxins, the host microbiota, and related treatments, are also described. Finally, we discuss the known therapeutic approaches and the current status of immunization strategies for CDI, which might help to bridge the knowledge gap in the generation of therapy against CDI.

Overview of current detection methods and microRNA potential in Clostridioides difficile infection screening

Clostridioides difficile (formerly called Clostridium difficile, C. difficile) infection (CDI) is listed as an urgent threat on the 2019 antibiotic resistance threats report in the United States by the Centers for Disease Control and Prevention. Early detection and appropriate disease management appear to be essential. Meanwhile, although the majority of cases are hospital-acquired CDI, community-acquired CDI cases are also on the rise, and this vulnerability is not limited to immunocompromised patients. Gastrointestinal treatments and/or gastrointestinal tract surgeries may be required for patients diagnosed with digestive diseases. Such treatments could suppress or interfere with the patient’s immune system and disrupt gut flora homeostasis, creating a suitable microecosystem for C. difficile overgrowth. Currently, stool-based non-invasive screening is the first-line approach to CDI diagnosis, but the accuracy is varied due to different clinical microbiology detection methods; therefore, improving reliability is clearly required. In this review, we briefly summarised the life cycle and toxicity of C. difficile, and we examined existing diagnostic approaches with an emphasis on novel biomarkers such as microRNAs. These biomarkers can be easily detected through non-invasive liquid biopsy and can yield crucial information about ongoing pathological phenomena, particularly in CDI.

Direct and indirect effects of pathogenic bacteria on the integrity of intestinal barrier

Bacterial translocation is a pathological process involving migration of pathogenic bacteria across the intestinal barrier to enter the systemic circulation and gain access to distant organs. This phenomenon has been linked to a diverse range of diseases including inflammatory bowel disease, pancreatitis, and cancer. The intestinal barrier is an innate structure that maintains intestinal homeostasis. Pathogenic infections and dysbiosis can disrupt the integrity of the intestinal barrier, increasing its permeability, and thereby facilitating pathogen translocation. As translocation represents an essential step in pathogenesis, a clear understanding of how barrier integrity is disrupted and how this disruption facilitates bacterial translocation could identify new routes to effective prophylaxis and therapy. In this comprehensive review, we provide an in-depth analysis of bacterial translocation and intestinal barrier function. We discuss currently understood mechanisms of bacterial-enterocyte interactions, with a focus on tight junctions and endocytosis. We also discuss the emerging concept of bidirectional communication between the intestinal microbiota and other body systems. The intestinal tract has established 'axes' with various organs. Among our regulatory systems, the nervous, immune, and endocrine systems have been shown to play pivotal roles in barrier regulation. A mechanistic understanding of intestinal barrier regulation is crucial for the development of personalized management strategies for patients with bacterial translocation-related disorders. Advancing our knowledge of barrier regulation will pave the way for future research in this field and novel clinical intervention strategies.

Clostridioides difficile Toxin B Induced Senescence: A New Pathologic Player for Colorectal Cancer?

Clostridioides difficile (C. difficile) is responsible for a high percentage of gastrointestinal infections and its pathological activity is due to toxins A and B. C. difficile infection (CDI) is increasing worldwide due to the unstoppable spread of C. difficile in the anthropized environment and the progressive human colonization. The ability of C. difficile toxin B to induce senescent cells and the direct correlation between CDI, irritable bowel syndrome (IBS), and inflammatory bowel diseases (IBD) could cause an accumulation of senescent cells with important functional consequences. Furthermore, these senescent cells characterized by long survival could push pre-neoplastic cells originating in the colon towards the complete neoplastic transformation in colorectal cancer (CRC) by the senescence-associated secretory phenotype (SASP). Pre-neoplastic cells could appear as a result of various pro-carcinogenic events, among which, are infections with bacteria that produce genotoxins that generate cells with high genetic instability. Therefore, subjects who develop IBS and/or IBD after CDI should be monitored, especially if they then have further CDI relapses, waiting for the availability of senolytic and anti-SASP therapies to resolve the pro-carcinogenic risk due to accumulation of senescent cells after CDI followed by IBS and/or IBD.

Mucosal Vaccination Strategies against Clostridioides difficile Infection

Clostridioides difficile infection (CDI) presents a major public health threat by causing frequently recurrent, life-threatening cases of diarrhea and intestinal inflammation. The ability of C. difficile to express antibiotic resistance and to form long-lasting spores makes the pathogen particularly challenging to eradicate from healthcare settings, raising the need for preventative measures to curb the spread of CDI. Since C. difficile utilizes the fecal-oral route of transmission, a mucosal vaccine could be a particularly promising strategy by generating strong IgA and IgG responses that prevent colonization and disease. This mini-review summarizes the progress toward mucosal vaccines against C. difficile toxins, cell-surface components, and spore proteins. By assessing the strengths and weaknesses of particular antigens, as well as methods for delivering these antigens to mucosal sites, we hope to guide future research toward an effective mucosal vaccine against CDI.

In Silico Analysis of Changes in Predicted Metabolic Capabilities of Intestinal Microbiota after Fecal Microbial Transplantation for Treatment of Recurrent Clostridioides difficile Infection

IMPORTANCE

Although highly effective in treating recurrent Clostridioides difficile infection (RCDI), the mechanisms of action of fecal microbial transplantation (FMT) are not fully understood.

AIM

The aim of this study was to explore microbially derived products or pathways that could contribute to the therapeutic efficacy of FMT.

METHODS

Stool shotgun metagenomic sequencing data from 18 FMT-treated RCDI patients at 4 points in time were used for the taxonomic and functional profiling of their gut microbiome. The abundance of the KEGG orthology (KO) groups was subjected to univariate linear mixed models to assess the significance of the observed differences between 0 (pre-FMT), 1, 4, and 12 weeks after FMT.

RESULTS

Of the 59,987 KO groups identified by shotgun metagenomic sequencing, 27 demonstrated a statistically significant change after FMT. These KO groups are involved in many cellular processes, including iron homeostasis, glycerol metabolism, and arginine regulation, all of which have been implicated to play important roles in bacterial growth and virulence in addition to modulating the intestinal microbial composition.

CONCLUSION

Our findings suggest potential changes in key KO groups post-FMT, which may contribute to FMT efficacy beyond the restored microbial composition/diversity and metabolism of bile acids and short-chain fatty acids. Future larger studies that include a fecal metabolomics analysis combined with animal model validation work are required to further elucidate the molecular mechanisms.

A leaky human colon model reveals uncoupled apical/basal cytotoxicity in early Clostridioides difficile toxin exposure

Clostridioides difficile (C. difficile) toxins A (TcdA) and B (TcdB) cause antibiotic-associated colitis in part by disrupting epithelial barrier function. Accurate in vitro models are necessary to detect early toxicity kinetics, investigate disease etiology, and develop preclinical models for new therapies. Properties of cancer cell lines and organoids inherently limit these efforts. We developed adult stem cell-derived monolayers of differentiated human colonic epithelium (hCE) with barrier function, investigated the impact of toxins on apical/basal aspects of monolayers, and evaluated whether a leaky epithelial barrier enhances toxicity. Single-cell RNA-sequencing (scRNAseq) mapped C. difficile-relevant genes to human lineages. Transcriptomics compared hCE to Caco-2, informed timing of in vitro stem cell differentiation, and revealed transcriptional responses to TcdA. Transepithelial electrical resistance (TEER) and fluorescent permeability assays measured cytotoxicity. Contribution of TcdB toxicity was evaluated in a diclofenac-induced leaky gut model. scRNAseq demonstrated broad and variable toxin receptor expression. Absorptive colonocytes in vivo displayed increased toxin receptor, Rho GTPase, and cell junction gene expression. Advanced TcdA toxicity generally decreased cytokine/chemokine and increased tight junction and death receptor genes. Differentiated Caco-2 cells remained immature whereas hCE monolayers were similar to mature colonocytes in vivo. Basal exposure of TcdA/B caused greater toxicity and apoptosis than apical exposure. Apical exposure to toxins was enhanced by diclofenac. Apical/basal toxicities are uncoupled with more rapid onset and increased magnitude postbasal toxin exposure. Leaky junctions enhance toxicity of apical TcdB exposure. hCE monolayers represent a physiologically relevant and sensitive system to evaluate the impact of microbial toxins on gut epithelium.NEW & NOTEWORTHY Novel human colonocyte monolayer cultures, benchmarked by transcriptomics for physiological relevance, detect early cytopathic impacts of Clostridioides difficile toxins TcdA and TcdB. A fluorescent ZO-1 reporter in primary human colonocytes is used to track epithelial barrier disruption in response to TcdA. Basal TcdA/B exposure generally caused more rapid onset and cytotoxicity than apical exposure. Transcriptomics demonstrate changes in tight junction, chemokine, and cytokine receptor gene expression post-TcdA exposure. Diclofenac-induced leaky epithelium enhanced apical exposure toxicity.

Intestinal barrier functions in hematologic and oncologic diseases

The intestinal barrier is a complex structure that not only regulates the influx of luminal contents into the systemic circulation but is also involved in immune, microbial, and metabolic homeostasis. Evidence implicating disruption in intestinal barrier functions in the development of many systemic diseases, ranging from non-alcoholic steatohepatitis to autism, or systemic complications of intestinal disorders has increased rapidly in recent years, raising the possibility of the intestinal barrier as a potential target for therapeutic intervention to alter the course and mitigate the complications associated with these diseases. In addition to the disease process being associated with a breach in the intestinal barrier functions, patients with hematologic and oncologic diseases are particularly at high risks for the development of increased intestinal permeability, due to the frequent use of broad-spectrum antibiotics and chemoradiation. They also face a distinct challenge of being intermittently severely neutropenic due to treatment of the underlying conditions. In this review, we will discuss how hematologic and oncologic diseases are associated with disruption in the intestinal barrier and highlight the complications associated with an increase in the intestinal permeability. We will explore methods to modulate the complication. To provide a background for our discussion, we will first examine the structure and appraise the methods of evaluation of the intestinal barrier.

The Environment, Farm Animals and Foods as Sources of Clostridioides difficile Infection in Humans

The recent discovery of the same Clostridioides difficile ribotypes associated with human infection in a broad range of environments, animals and foods, coupled with an ever-increasing rate of community-acquired infections, suggests this pathogen may be foodborne. The objective of this review was to examine the evidence supporting this hypothesis. A review of the literature found that forty-three different ribotypes, including six hypervirulent strains, have been detected in meat and vegetable food products, all of which carry the genes encoding pathogenesis. Of these, nine ribotypes (002, 003, 012, 014, 027, 029, 070, 078 and 126) have been isolated from patients with confirmed community-associated C. difficile infection (CDI). A meta-analysis of this data suggested there is a higher risk of exposure to all ribotypes when consuming shellfish or pork, with the latter being the main foodborne route for ribotypes 027 and 078, the hypervirulent strains that cause most human illnesses. Managing the risk of foodborne CDI is difficult as there are multiple routes of transmission from the farming and processing environment to humans. Moreover, the endospores are resistant to most physical and chemical treatments. The most effective current strategy is, therefore, to limit the use of broad-spectrum antibiotics while advising potentially vulnerable patients to avoid high-risk foods such as shellfish and pork.