Association of Fidaxomicin with C. difficile Spores: Effects of Persistence on Subsequent Spore Recovery, Outgrowth and Toxin Production

Clostridioides difficile infection: history, epidemiology, risk factors, prevention, clinical manifestations, treatment, and future options

SUMMARYClostridioides difficile infection (CDI) is one of the major issues in nosocomial infections. This bacterium is constantly evolving and poses complex challenges for clinicians, often encountered in real-life scenarios. In the face of CDI, we are increasingly equipped with new therapeutic strategies, such as monoclonal antibodies and live biotherapeutic products, which need to be thoroughly understood to fully harness their benefits. Moreover, interesting options are currently under study for the future, including bacteriophages, vaccines, and antibiotic inhibitors. Surveillance and prevention strategies continue to play a pivotal role in limiting the spread of the infection. In this review, we aim to provide the reader with a comprehensive overview of epidemiological aspects, predisposing factors, clinical manifestations, diagnostic tools, and current and future prophylactic and therapeutic options for C. difficile infection.

Improving Clostridioides difficile Infectious Disease Treatment Response via Adherence to Clinical Practice Guidelines

Clostridioides difficile (C. difficile) is a predominant nosocomial infection, and guidelines for improving diagnosis and treatment were published in 2017. We conducted a single-center, retrospective 10-year cohort study of patients with primary C. difficile infectious disease (CDID) at the largest referral Lithuanian university hospital, aiming to evaluate the clinical and laboratory characteristics of CDID and their association with the outcomes, as well as implication of concordance with current Clinical Practice Guidelines. The study enrolled a total of 370 patients. Cases with non-concordant CDID treatment resulted in more CDID-related Intensive Care Unit (ICU) admissions (7.5 vs. 1.8%) and higher CDID-related mortality (13.0 vs. 1.8%) as well as 30-day all-cause mortality (61.0 vs. 36.1%) and a lower 30-day survival compared with CDID cases with concordant treatment (p < 0.05). Among cases defined by two criteria for severe CDID, only patients with non-concordant metronidazole treatment had refractory CDID (68.8 vs. 0.0%) compared with concordant vancomycin treatment. In the presence of non-concordant metronidazole treatment for severe CDID, only cases defined by two severity criteria had more CDID-related ICU admissions (18.8 vs. 0.0%) and higher CDID-related mortality (25.0 vs. 2.0%, p < 0.05) compared with cases defined by one criterion. Severe comorbidities and the continuation of concomitant antibiotics administered at CDID onset reduced (p < 0.05) the 30-day survival and increased (p = 0.053) 30-day all-cause mortality, with 57.6 vs. 10.7% and 52.0 vs. 25.0%, respectively. Conclusions: CDID treatment non-concordant with the guidelines was associated with various adverse outcomes. In CDID with leukocytes ≥ 15 × 109/L and serum creatinine level > 133 µmol/L (>1.5 mg/dL), enteral vancomycin should be used to avoid refractory response, as metronidazole use was associated with CDID-related ICU admission and CDID-related mortality. Severe comorbidities worsened the outcomes as they were associated with reduced 30-day survival. The continuation of concomitant antibiotic therapy increased 30-day all-cause mortality; thus, it needs to be reasonably justified, deescalated or stopped.

Clinical Efficacy of Fidaxomicin and Oral Metronidazole for Treating Clostridioides difficile Infection and the Associated Recurrence Rate: A Retrospective Cohort Study

Clostridioides difficile infection (CDI) has significant implications for healthcare economics. Although clinical trials have compared fidaxomicin (FDX) and vancomycin, comparisons of FDX and oral metronidazole (MNZ) are limited. Therefore, we compared the therapeutic effects of FDX and oral MNZ. Patients diagnosed with CDI between January 2015 and March 2023 were enrolled. Those treated with oral MNZ or FDX were selected and retrospectively analyzed. The primary outcome was the global cure rate. Secondary outcomes included factors contributing to the CDI global cure rate; the rate of medication change owing to initial treatment failure; and incidence rates of clinical cure, recurrence, and all-cause mortality within 30 days. Of the 264 enrolled patients, 75 and 30 received initial oral MNZ and FDX treatments, respectively. The corresponding CDI global cure rates were 53.3% and 70% (p = 0.12). In multivariate analysis, FDX was not associated with the global cure rate. In the MNZ group, 18.7% of the patients had to change medications owing to initial treatment failure. The FDX group had a higher clinical cure rate and lower recurrence rate than the MNZ group, although not significant. However, caution is necessary owing to necessary treatment changes due to MNZ failure.

The natural product chlorotonil A preserves colonization resistance and prevents relapsing Clostridioides difficile infection

Clostridioides difficile infections (CDIs) remain a healthcare problem due to high rates of relapsing/recurrent CDIs (rCDIs). Breakdown of colonization resistance promoted by broad-spectrum antibiotics and the persistence of spores contribute to rCDI. Here, we demonstrate antimicrobial activity of the natural product class of chlorotonils against C. difficile. In contrast to vancomycin, chlorotonil A (ChA) efficiently inhibits disease and prevents rCDI in mice. Notably, ChA affects the murine and porcine microbiota to a lesser extent than vancomycin, largely preserving microbiota composition and minimally impacting the intestinal metabolome. Correspondingly, ChA treatment does not break colonization resistance against C. difficile and is linked to faster recovery of the microbiota after CDI. Additionally, ChA accumulates in the spore and inhibits outgrowth of C. difficile spores, thus potentially contributing to lower rates of rCDI. We conclude that chlorotonils have unique antimicrobial properties targeting critical steps in the infection cycle of C. difficile.

Emerging Options for the Prevention and Management of Clostridioides difficile Infection

Agents in development for the prevention or treatment of Clostridioides difficile infection can be split into three broad categories: antibiotics, microbiome restoration, and vaccines. Given the extensive list of agents currently in development, this narrative review will focus on agents that have progressed into late-stage clinical trials, defined as having a Phase III clinical trial registered on ClinicalTrials.gov. These agents include one antibiotic (ridinilazole), three live biotherapeutic products (LBPs) (CP101, RBX2660, and SER109), and two toxoid vaccines (PF06425090 and a second toxoid vaccine). As new prevention and treatment strategies enter the market, clinicians and administrators will need knowledge of these products to make rational decisions on how best to adopt them into clinical practice.

Microbiome therapeutics for the treatment of recurrent Clostridioides difficile infection

INTRODUCTION

The gut microbiome is implicated in Clostridioides difficile infection (CDI) and recurrent CDI (rCDI).

AREAS COVERED

This review covers the mechanisms by which microbiome therapeutics treat rCDI, their efficacy and safety, and clinical trial design considerations for future research.

EXPERT OPINION

Altering the chemical environment of the gut and reconstituting colonization resistance is a promising strategy for preventing and treating rCDI. Fecal microbiota transplant (FMT) is safe and effective for the treatment of rCDI. However, limitations of FMT have prompted investigation into alternative microbiome therapeutics. These alternative microbiome therapies require further evaluation, and adaptive trial designs should be strongly considered to more rapidly discern variables including the need for bowel preparation, timing and selection of pre-treatment antibiotics, and dose and duration of microbiome therapeutics. A broad range of adverse events must be prospectively evaluated in these controlled trials, as microbiome therapeutics have the potential for numerous effects. Future studies will lead to a greater understanding of the mechanisms by which microbiome therapies can break the cycle of rCDI, which should ultimately yield a personalized approach to rCDI treatment that restores an individual's specific deficit(s) in colonization resistance to C. difficile.

Clostridioides difficile Spore Formation and Germination: New Insights and Opportunities for Intervention

Spore formation and germination are essential for the bacterial pathogen Clostridioides difficile to transmit infection. Despite the importance of these developmental processes to the infection cycle of C. difficile, the molecular mechanisms underlying how this obligate anaerobe forms infectious spores and how these spores germinate to initiate infection were largely unknown until recently. Work in the last decade has revealed that C. difficile uses a distinct mechanism for sensing and transducing germinant signals relative to previously characterized spore formers. The C. difficile spore assembly pathway also exhibits notable differences relative to Bacillus spp., where spore formation has been more extensively studied. For both these processes, factors that are conserved only in C. difficile or the related Peptostreptococcaceae family are employed, and even highly conserved spore proteins can have differential functions or requirements in C. difficile compared to other spore formers. This review summarizes our current understanding of the mechanisms controlling C. difficile spore formation and germination and describes strategies for inhibiting these processes to prevent C. difficile infection and disease recurrence.

Inhibition of spores to prevent the recurrence of Clostridioides difficile infection - A possibility or an improbability?

Clostridioides difficile is one of the most common nosocomial gastrointestinal pathogens, and recurrence is a problematic issue because approximately 20-30% of patients experience at least one episode of recurrence, even after treatment with a therapeutic drug of choice for C. difficile infection (CDI), such as vancomycin. CDI recurrence has a multifactorial complex mechanism, in which gut microbiota disruption coincident with viable C. difficile spores, is considered the most important factor. The effectiveness of an anti-C. difficile antimicrobial agent against CDI cannot guarantee its inhibitory effect on C. difficile spores and vice versa. However, an antimicrobial agent, such as fidaxomicin, which has a good inhibitory effect on both C. difficile vegetative cells and spores is assumed to not only treat CDI but also prevent its recurrence. Prolonged adherence to the exosporium has been proposed as a possible mechanism of inhibiting spores, and as a result, redesigning anti-C. difficile antimicrobial agents with the ability to adhere to the exosporium may provide another pathway for the development of anti-C. difficile spore agents. For example, vancomycin lacks an inhibitory effect against C. difficile spores, but a vancomycin-loaded spore-targeting iron oxide nanoparticle that selectively binds to C. difficile spores has been developed to successfully delay spore germination. Some new antimicrobial agents in phase II clinical trials, including cadazolid and ridinilazole, have shown exceptional anti-C. difficile and spore-inhibiting effects that can be expected to not only treat CDI but also prevent its recurrence in the future.

Systems biology evaluation of refractory Clostridioides difficile infection including multiple failures of fecal microbiota transplantation

BACKGROUND

Fecal microbiota transplantation (FMT) aims to cure Clostridioides difficile infection (CDI) through reestablishing a healthy microbiome and restoring colonization resistance. Although often effective after one infusion, patients with continued microbiome disruptions may require multiple FMTs. In this N-of-1 study, we use a systems biology approach to evaluate CDI in a patient receiving chronic suppressive antibiotics with four failed FMTs over two years.

METHODS

Seven stool samples were obtained between 2016-18 while the patient underwent five FMTs. Stool samples were cultured for C. difficile and underwent microbial characterization and functional gene analysis using shotgun metagenomics. C. difficile isolates were characterized through ribotyping, whole genome sequencing, metabolic pathway analysis, and minimum inhibitory concentration (MIC) determinations.

RESULTS

Growing ten strains from each sample, the index and first four recurrent cultures were single strain ribotype F078-126, the fifth was a mixed culture of ribotypes F002 and F054, and the final culture was ribotype F002. One single nucleotide polymorphism (SNP) variant was identified in the RNA polymerase (RNAP) β-subunit RpoB in the final isolated F078-126 strain when compared to previous F078-126 isolates. This SNV was associated with metabolic shifts but phenotypic differences in fidaxomicin MIC were not observed. Microbiome differences were observed over time during vancomycin therapy and after failed FMTs.

CONCLUSION

This study highlights the importance of antimicrobial stewardship in patients receiving FMT. Continued antibiotics play a destructive role on a transplanted microbiome and applies selection pressure for resistance to the few antibiotics available to treat CDI.

Impact of Oral Metronidazole, Vancomycin, and Fidaxomicin on Host Shedding and Environmental Contamination with Clostridioides difficile

OBJECTIVES

Shedding of Clostridioides difficile spores from infected individuals contaminates the hospital environment and contributes to infection transmission. We assessed whether antibiotic selection impacts C. difficile shedding and contamination of the hospital environment.

METHODS

In this prospective, unblinded, randomized controlled trial of hospitalized adults with C. difficile infection, subjects were randomized 1:1:1 to receive fidaxomicin, oral vancomycin, or metronidazole. The primary outcome was change in environmental contamination rate while on treatment. Secondary outcomes included stool shedding, total burden of contamination, and molecular relatedness of stool versus environmental C. difficile isolates.

RESULTS

33 patients were enrolled and 31 (94%) completed the study. Fidaxomicin (-0.36 log10 CFU/day, 95% CI -0.52 to -0.19, p<0.01) and vancomycin (-0.17 log10 CFU/day, 95% CI -0.34 to -0.01, p=0.05) were associated with more rapid decline in C. difficile shedding compared to metronidazole (-0.01 log10 CFU/day, 95% CI -0.10 to +0.08). Both vancomycin (6.3%, 95% CI 4.7-8.3%) and fidaxomicin (13.1%, 95% CI 10.7-15.9%) were associated with lower rates of environmental contamination than metronidazole (21.4%, 95% CI 18.0-25.2%). When specifically modeling within-subject change over time, fidaxomicin (aOR 0.83, 95% CI 0.70-0.99, p=0.04) was associated with more rapid decline in environmental contamination than vancomycin or metronidazole. Overall, 207 of 233 (88.8%) of environmental C. difficile isolates matched subject stool isolates by ribotyping, without significant difference by treatment.

CONCLUSIONS

Fidaxomicin, and to a lesser extent vancomycin, reduces C. difficile shedding and contamination of the hospital environment relative to metronidazole. Treatment choice may play a role in reducing healthcare-associated C. difficile transmission.

Visualization of fidaxomicin association with the exosporium layer of Clostridioides difficile spores

BACKGROUND

Fidaxomicin has novel pharmacologic effects on C. difficile spore formation including outgrowth inhibition and persistent spore attachment. However, the mechanism of fidaxomicin attachment on spores has not undergone rigorous microscopic studies.

MATERIALS & METHODS

Fidaxomicin attachment to C. difficile spores of three distinct ribotypes and C. difficile mutant spores with inactivation of exosporium or spore-coat protein-coding genes were visualized using confocal microscopy with a fidaxomicin-bodipy compound (green fluorescence). The pharmacologic effect of the fidaxomicin-bodipy compound was determined. Confocal microscopy experiments included direct effect on C. difficile wild-type and mutant spores, effect of exosporium removal, and direct attachment to a comparator spore forming organism, Bacillus subtilis.

RESULTS

The fidaxomicin-bodipy compound MIC was 1 mg/L compared to 0.06 mg/L for unlabeled fidaxomicin, a 16-fold increase. Using confocal microscopy, the intracellular localization of fidaxomicin into vegetative C. difficile cells was observed consistent with its RNA polymerase mechanism of action and inhibited spore outgrowth. The fidaxomicin-bodipy compound was visualized outside of the core of C. difficile spores with no co-localization with the membrane staining dye FM4-64. Exosporium removal reduced fidaxomicin-bodipy association with C. difficile spores. Reduced fidaxomicin-bodipy was observed in C. difficile mutant spores for the spore surface proteins CdeC and CotE.

CONCLUSION

This study visualized a direct attachment of fidaxomicin to C. difficile spores that was diminished with mutants of specific exosporium and spore coat proteins. These data provide advanced insight regarding the anti-spore properties of fidaxomicin.

Treatment issues in recurrent Clostridioides difficile infections and the possible role of germinants

Clostridioides difficile is the number one cause of hospital-acquired infections in the United States and one of the CDC's urgent-level pathogen threats. The inflammation caused by pathogenic C. difficile results in diarrhea and pseudomembranous colitis. Patients who undergo clinically successful treatment for this disease commonly experience recurrent infections. Current treatment options can eradicate the vegetative cell form of the bacteria but do not impact the spore form, which is impervious to antibiotics and resists conventional environmental cleaning procedures. Antibiotics used in treating C. difficile infections (CDI) often do not eradicate the pathogen and can prevent regeneration of the microbiome, leaving them vulnerable to recurrent CDI and future infections upon subsequent non-CDI-directed antibiotic therapy. Addressing the management of C. difficile spores in the gastrointestinal (GI) tract is important to make further progress in CDI treatment. Currently, no treatment options focus on reducing GI spores throughout CDI antibiotic therapy. This review focuses on colonization of the GI tract, current treatment options and potential treatment directions emphasizing germinant with antibiotic combinations to prevent recurrent disease.

Fidaxomicin for the treatment of Clostridioides difficile in children

Fidaxomicin is an oral narrow-spectrum novel 18-membered macrocyclic antibiotic that was initially approved in 2011 by the US FDA for the treatment of Clostridioides difficile infections (CDI) in adults. In February 2020, the FDA approved fidaxomicin for the treatment of CDI in children age >6 months. In adults, fidaxomicin is as efficacious as vancomycin in treating CDI and reduces the risk of recurrent CDI. An investigator-blinded, randomized, multicenter, multinational clinical trial comparing the efficacy and safety of fidaxomicin with vancomycin in children was recently published confirming similar findings as previously reported in adults. Fidaxomicin is the first FDA-approved treatment for CDI in children and offers a promising option for reducing recurrent CDI in this population.

Curcumin: A natural derivative with antibacterial activity against Clostridium difficile

OBJECTIVES

The rapid emergence of hypervirulent Clostridium difficile (C. difficile) isolates and the paucity of effective anti-clostridial antibiotics call for extensive research to identify new treatment options. This study aimed to test the anti-clostridial activity of bioactive extracts of turmeric, which is a natural herb widely known for its profound medicinal properties.

METHODS

The MICs of turmeric derivatives were determined against 27 C. difficile strains, including hypervirulent (BI/NAP1/027) and clinical toxigenic isolates. Additionally, their ability to inhibit C. difficile toxin production and spore formation was investigated. Furthermore, the safety profiles of turmeric derivatives regarding their effects on human gut microflora - such as Bacteroides, Lactobacillus and Bifidobacterium - were evaluated.

RESULTS

Curcuminoids, the major phytoconstituents of turmeric - including curcumin, demethoxycurcumin and bisdemethoxycurcumin - inhibited growth of C. difficile at concentrations ranging from 4 to 32μg/mL. Additionally, curcuminoids showed no negative effect on major populating species of the human gut. Curcumin was more effective than fidaxomicin in inhibiting C. difficile toxin production, but less so in inhibiting spore formation.

CONCLUSION

The findings suggest that curcumin has potential as an anti-clostridial agent. More work is needed to further investigate the efficacy of curcumin as a stand-alone drug or as a supplement of current drugs of choice, as it has no antagonistic activities but might overcome their drawbacks.

[Antimicrobial profile and clinical evidence of fidaxomicin (Dafclir®), a therapeutic agent for Clostridioides (Clostridium) difficile infection]

Fidaxomicin (Dafclir^® Tablets 200 mg) is a member of a novel class of oral, 18-membered macrocyclic antibiotic agents used for the treatment of patients with Clostridioides (Clostridium) difficile (C. difficile) infection (CDI), approved in Japan in July 2018. Preclinical studies demonstrated that fidaxomicin inhibits RNA synthesis by bacterial DNA-dependent RNA polymerase derived from C. difficile, shows antibacterial activities against C. difficile clinically isolated in Japan, and is bactericidal against C. difficile. Fidaxomicin was less likely to disrupt gut microflora due to its narrow antimicrobial spectrum, showing antibacterial activities against limited gram-positive bacteria including C. difficile, but not against gram-negative bacteria, as determined by minimum inhibitory concentration (MIC) measurement against American Type Culture Collection strains. Fidaxomicin inhibited spore production, subsequent spore recovery/outgrowth after removal of fidaxomicin, outgrowth to vegetative cells, and toxin production under fidaxomicin at lower MIC. Additionally, it had protective effects on lethal CDI in animal models. In clinical studies conducted in Europe, US, and Japan, fidaxomicin 200 mg twice daily for 10 days showed higher clinical cure, higher global cure (cure with no recurrence), and lower recurrence rate compared with oral vancomycin 125 mg four times daily for 10 days. Adverse events observed in the fidaxomicin group were similar to those in the vancomycin group, and no clinically important findings regarding safety and tolerability were reported. In conclusion, in vitro, in vivo and clinical evidence indicate that fidaxomicin is an effective treatment for C. difficile, with limited disruption to gut microflora, for adult patients with CDI in Japan.

Investigating the transient and persistent effects of heat on Clostridium difficile spores

Purpose. Clostridium difficile spores are extremely resilient to high temperatures. Sublethal temperatures are associated with the 'reactivation' of dormant spores, and are utilized to maximize C. difficile spore recovery. Spore eradication is of vital importance to the food industry. The current study seeks to elucidate the transient and persisting effects of heating C. difficile spores at various temperatures.Methods. Spores of five C. difficile strains of different ribotypes (001, 015, 020, 027 and 078) were heated at 50, 60 and 70-80 °C for 60 min in phosphate-buffered saline (PBS) and enumerated at 0, 15, 30, 45 and 60 min. GInaFiT was used to model the kinetics of spore inactivation. In subsequent experiments, spores were transferred to enriched brain heart infusion (BHI) broths after 10 min of 80 °C heat treatment in PBS; samples were enumerated at 90 min and 24 h.Results. The spores of all strains demonstrated log-linear inactivation with tailing when heated for 60 min at 80 °C [(x̄=7.54±0.04 log₁₀ vs 4.72±0.09 log₁₀ colony-forming units (c.f.u.) ml^{- 1}; P<0.001]. At 70 °C, all strains except 078 exhibited substantial decline in recovery over 60 min. Interestingly, 50 °C heat treatment had an inhibitory effect on 078 spore recovery at 0 vs 60 min (7.61±0.06 log₁₀ c.f.u. ml^{- 1} vs 6.13±0.05 log₁₀ c.f.u. ml^{- 1}; P<0.001). Heating at 70/80 °C inhibited the initial germination and outgrowth of both newly produced and aged spores in enriched broths. This inhibition appeared to be transient; after 24 h vegetative counts were higher in heat-treated vs non-heat-treated spores (x̄=7.65±0.04 log₁₀ c.f.u. ml^{- 1} vs 6.79±0.06 log₁₀ c.f.u. ml^{- 1}; P<0.001).Conclusions. The 078 spores were more resistant to the inhibitory effects of higher temperatures. Heat initially inhibits spore germination, but the subsequent outgrowth of vegetative populations accelerates after the initial inhibitory period.

Management of Clostridioides difficile colitis: insights for the gastroenterologist

Clostridioides difficile infection (CDI) is a common cause of diarrhea in both inpatient and outpatient settings. The last few years have seen major changes in the treatment spectrum of CDI, most notably, recommendations against using metronidazole for initial CDI, the addition of fidaxomicin and bezlotoxumab, and emergence of microbial replacement therapies. Several other therapies are undergoing clinical trials. This narrative review focuses on the treatment of CDI with a summary of literature on the newer modalities and the treatment guidelines issued by Infectious Diseases Society of America and European Society of Clinical Microbiology and Infectious Diseases.

Comparison of the 2010 and 2017 Infectious Diseases Society of America guidelines on the diagnosis and treatment of Clostridium difficile infection

PURPOSE OF REVIEW

To highlights the key changes in the updated Infectious Diseases Society of America and Society for Healthcare Epidemiology of America guidelines with respect to the diagnosis and treatment of Clostridium difficile infection (CDI).

RECENT FINDINGS

CDI continues as a major threat to healthcare institutions and as a community-associated infection related primarily to antibiotic exposure. Infectious Diseases Society of America/Society for Healthcare Epidemiology of America produced extensive CDI guidelines in 2010; in 2018, updated guidance has been published. The new guidelines include key changes with respect to the treatment and diagnosis of CDI.

SUMMARY

Updated, evidence guidelines allow optimization of the diagnosis of CDI and the use of therapeutic interventions, in particular to reduce the risk of recurrent infection.

Identification of Clostridium difficile Immunoreactive Spore Proteins of the Epidemic Strain R20291

PURPOSE

Clostridium difficile infections are the leading cause of diarrhea associated with the use of antibiotics. During infection, C. difficile initiates a sporulation cycle leading to the persistence of C. difficile spores in the host and disease dissemination. The development of vaccine and passive immunization therapies against C. difficile has focused on toxins A and B. In this study, an immunoproteome-based approach to identify immunogenic proteins located on the outer layers of C. difficile spores as potential candidates for the development of immunotherapy and/or diagnostic methods against this devastating infection is used.

EXPERIMENTAL DESIGN

To identify potential immunogenic proteins on the surface of C. difficile R20291, spore coat/exosporium extracts are separated by 2D electrophoresis (2-DE) and analyzed for reactivity against C. difficile spore-specific goat sera. Finally, the selected spots are in-gel digested with chymotrypsin, peptides generated are separated by nanoUPLC followed by MS/MS using Quad-TOF-MS, corroborated by Ultimate 3000RS-nano-UHPLC coupled to Q-Exactive-Plus-Orbitrap MS.

RESULTS

The analysis identify five immunoreactive proteins: spore coat proteins CotE, CotA, and CotCB; exosporium protein CdeC; and a cytosolic methyltransferase.

CONCLUSION

This data provides a list of spore surface protein candidates as antigens for vaccine development against C. difficile infections.

Analysis of Clostridium difficile biofilms: imaging and antimicrobial treatment

Background

Clostridium difficile, a spore-forming Gram-positive anaerobic bacillus, is the most common causative agent of healthcare-associated diarrhoea. Formation of biofilms may protect C. difficile against antibiotics, potentially leading to treatment failure. Furthermore, bacterial spores or vegetative cells may linger in biofilms in the gut causing C. difficile infection recurrence.

Objectives

In this study, we evaluated and compared the efficacy of four antibiotics (fidaxomicin, surotomycin, vancomycin and metronidazole) in penetrating C. difficile biofilms and killing vegetative cells.

Methods

C. difficile biofilms grown initially for 48 or 72 h using the colony biofilm model were then treated with antibiotics at a concentration of 25 × MIC for 24 h. Vegetative cells and spores were enumerated. The effect of treatment on biofilm structure was studied by scanning electron microscopy (SEM). The ability of fidaxomicin and surotomycin to penetrate biofilms was studied using fluorescently tagged antibiotics.

Results

Both surotomycin and fidaxomicin were significantly more effective than vancomycin or metronidazole (P < 0.001) at killing vegetative cells in established biofilms. Fidaxomicin was more effective than metronidazole at reducing viable spore counts in biofilms (P < 0.05). Fluorescently labelled surotomycin and fidaxomicin penetrated C. difficile biofilms in < 1 h. After 24 h of treatment, SEM demonstrated that both fidaxomicin and surotomycin disrupted the biofilm structure, while metronidazole had no observable effect.

Conclusions

Fidaxomicin is effective in disrupting C. difficile biofilms, killing vegetative cells and decreasing spore counts.

Impact of Oral Fidaxomicin Administration on the Intestinal Microbiota and Susceptibility to Clostridium difficile Colonization in Mice

Clostridium difficile infection (CDI), a common cause of hospital-acquired infections, typically occurs after disruption of the normal gut microbiome by broad-spectrum antibiotics. Fidaxomicin is a narrow-spectrum antibiotic that demonstrates a reduced impact on the normal gut microbiota and is approved for the treatment of CDI. To further explore the benefits of this property, we used a murine model to examine the effects of fidaxomicin versus vancomycin on gut microbiota and susceptibility to C. difficile colonization while tracking microbiota recovery over time. Mice were exposed to fidaxomicin or vancomycin by oral gavage for 3 days and subsequently challenged with C. difficile spores at predetermined time points up to 21 days postexposure to antibiotics. Fecal samples were subsequently collected for analysis. Twenty-four hours postchallenge, mice were euthanized and the colon contents harvested. The microbiota was characterized using 16S rRNA gene sequencing. All fidaxomicin-exposed mice (except for one at day 8) were resistant to C. difficile colonization. However, 9 of 15 vancomycin-exposed mice were susceptible to C. difficile colonization until day 12. All vancomycin-exposed mice recovered colonization resistance by day 16. Bacterial diversity was similar prior to antibiotic exposure in both arms and decreased substantially after exposure. A shift in taxonomic structure and composition occurred after both exposures; however, the shift was greater in vancomycin-exposed than in fidaxomicin-exposed mice. In summary, compared with vancomycin, fidaxomicin exposure had less impact on microbiota composition, promoted faster microbial recovery, and had less impact on the loss of C. difficile colonization resistance.

Novel FR-900493 Analogues That Inhibit the Outgrowth of Clostridium difficile Spores

The spectrum of antibacterial activity for the nucleoside antibiotic FR-900493 (1) can be extended by chemical modifications. We have generated a small focused library based on the structure of 1 and identified UT-17415 (9), UT-17455 (10), UT-17460 (11), and UT-17465 (12), which exhibit anti-Clostridium difficile growth inhibitory activity. These analogues also inhibit the outgrowth of C. difficile spores at 2× minimum inhibitory concentration. One of these analogues, 11, relative to 1 exhibits over 180-fold and 15-fold greater activity against the enzymes, phospho-MurNAc-pentapeptide translocase (MraY) and polyprenyl phosphate-GlcNAc-1-phosphate transferase (WecA), respectively. The phosphotransferase inhibitor 11 displays antimicrobial activity against several tested bacteria including Bacillus subtilis, Clostridium spp., and Mycobacterium smegmatis, but no growth inhibitory activity is observed against the other Gram-positive and Gram-negative bacteria. The selectivity index (Vero cell cytotoxicity/C. difficileantimicrobial activity) of 11 is approximately 17, and 11 does not induce hemolysis even at a 100 μM concentration.

Investigating the effect of supplementation on Clostridioides (Clostridium) difficile spore recovery in two solid agars

BACKGROUND

A variety of supplemented solid media are used within Clostridium difficile research to optimally recover spores. Our study sought to investigate different media and additives, providing a method of optimised C. difficile spore recovery. Additionally, due to the results observed in the initial experiments, the inhibitory effects of three amino acids (glycine, l-histidine &l-phenylalanine) on C. difficile spore outgrowth were investigated.

METHODS

Spores of five C. difficile strains (PCR ribotypes 001,015,020,027,078) were recovered on two commonly used solid media (BHI & CCEY, or cycloserine-cefoxitin egg yolk) supplemented with various concentrations of germinants (taurocholate, glycine & lysozyme). Agar-incorporation minimum inhibitory concentration (MIC) testing was carried out for glycine and taurocholate on vegetative cells and spores of all five strains. Additionally a BHI broth microassay method was utilised to test the growth of C. difficile in the presence of increasing concentrations (0,1,2,3,4%) of three amino acids (glycine,l-histidine,l-phenyalanine).

RESULTS

CCEY agar alone and BHI supplemented with taurocholate (0.1/1%) provided optimal recovery for C. difficile spores. Glycine was inhibitory to spore recovery at higher concentrations, although these varied between the two media used. In agar-incorporated MIC testing, glycine concentrations higher than 2% (20 g/L) were inhibitory to both C. difficile spore and vegetative cell growth versus the control (mean absorbance = 0.33 ± 0.02 vs 0.12 ± 0.01) (P < 0.001). This indicates a potential mechanism whereby glycine interferes with vegetative cell growth. Further microbroth testing provided evidence of inhibition by two amino acids other than glycine, l-histidine and l-phenylalanine.

CONCLUSIONS

We provide two media for optimal recovery of C. difficile spores (CCEY alone and BHI supplemented with 0.1/1% taurocholate). CCEY is preferred for isolation from faecal samples. For pure cultures, either CCEY or supplemented BHI agar are appropriate. The inhibitory nature of three amino acids (glycine,l-histidine,l-phenylalanine) to C. difficile vegetative cell proliferation is also highlighted.

A Systematic Literature Review of Economic Evaluations of Antibiotic Treatments for Clostridium difficile Infection

BACKGROUND AND OBJECTIVE

Clostridium difficile infection (CDI) is associated with high management costs, particularly in recurrent cases. Fidaxomicin treatment results in lower recurrence rates than vancomycin and metronidazole, but has higher acquisition costs in Europe and the USA. This systematic literature review summarises economic evaluations (EEs) of fidaxomicin, vancomycin and metronidazole for treatment of CDI.

METHODS

Electronic databases (MEDLINE®, Embase, Cochrane Library) and conference proceedings (ISPOR, ECCMID, ICAAC and IDWeek) were searched for publications reporting EEs of fidaxomicin, vancomycin and/or metronidazole in the treatment of CDI. Reference bibliographies of identified manuscripts were also reviewed. Cost-effectiveness was evaluated according to the overall population of patients with CDI, as well as in subgroups with severe CDI or recurrent CDI, or those at higher risk of recurrence or mortality.

RESULTS

Overall, 27 relevant EEs, conducted from the perspective of 12 different countries, were identified. Fidaxomicin was cost-effective versus vancomycin and/or metronidazole in 14 of 24 EEs (58.3%), vancomycin was cost-effective versus fidaxomicin and/or metronidazole in five of 27 EEs (18.5%) and metronidazole was cost-effective versus fidaxomicin and/or vancomycin in two of 13 EEs (15.4%). Fidaxomicin was cost-effective versus vancomycin in most of the EEs evaluating specific patient subgroups. Key cost-effectiveness drivers were cure rate, recurrence rate, time horizon, drug costs and length and cost of hospitalisation.

CONCLUSIONS

In most EEs, fidaxomicin was demonstrated to be cost-effective versus metronidazole and vancomycin in patients with CDI. These results have relevance to clinical practice, given the high budgetary impact of managing CDI and increasing restrictions on healthcare budgets.

OTHER

This analysis was initiated and funded by Astellas Pharma Inc.