New insights for vaccine development against Clostridium 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.

Subtractive genomic approach toward introduction of novel immunogenic targets against Clostridioides difficile: Thinking out of the box

Clostridioides difficile is one of the major causatives of nosocomial infections worldwide. Antibiotic-associated diarrhea, pseudomembranous colitis, and toxic megacolon are the most common forms of C. difficile infection (CDI). Considering the high antibiotic resistance of C. difficile isolates and the low efficacy of immunization with toxin-related vaccines, we suggested that surface-exposed and secreted proteins could be considered as potential immunogenic targets against CDI. Various immuninformatics databases were used to predict antigenicity, allergenicity, B-cell epitopes, MHC-II binding sites, conserved domains, prevalence and conservation of proteins among the most common sequence types, molecular docking, and immunosimulation of immunogenic targets. Finally, 16 proteins belonging to three functional groups were identified, including proteins involved in the cell wall and peptidoglycan layer (nine proteins), flagellar assembly (five proteins), spore germination (one protein), and a protein with unknown function. Molecular docking results showed that among all the mentioned proteins, WP_009892971.1 (Acd) and WP_009890599.1 (a C40 family peptidase) had the strongest interactions with human Toll-like receptor 2 (TLR-2) and TLR-4. This study proposes a combination of C. difficile toxoid (Tcd) and surface-exposed proteins such as Acd as a promising vaccine formulation for protection against circulating clinical strains of C. difficile.

Learning from Nature: Bacterial Spores as a Target for Current Technologies in Medicine (Review)

The capability of some representatives of Clostridium spp. and Bacillus spp. genera to form spores in extreme external conditions long ago became a subject of medico-biological investigations. Bacterial spores represent dormant cellular forms of gram-positive bacteria possessing a high potential of stability and the capability to endure extreme conditions of their habitat. Owing to these properties, bacterial spores are recognized as the most stable systems on the planet, and spore-forming microorganisms became widely spread in various ecosystems.

Spore-forming bacteria have been attracted increased interest for years due to their epidemiological danger. Bacterial spores may be in the quiescent state for dozens or hundreds of years but after they appear in the favorable conditions of a human or animal organism, they turn into vegetative forms causing an infectious process. The greatest threat among the pathogenic spore-forming bacteria is posed by the causative agents of anthrax (B. anthracis), food toxicoinfection (B. cereus), pseudomembranous colitis (C. difficile), botulism (C. botulinum), gas gangrene (C. perfringens).

For the effective prevention of severe infectious diseases first of all it is necessary to study the molecular structure of bacterial spores and the biochemical mechanisms of sporulation and to develop innovative methods of detection and disinfection of dormant cells. There is another side of the problem: the necessity to investigate exo- and endospores from the standpoint of obtaining similar artificially synthesized models in order to use them in the latest medical technologies for the development of thermostable vaccines, delivery of biologically active substances to the tissues and intracellular structures. In recent years, bacterial spores have become an interesting object for the exploration from the point of view of a new paradigm of unicellular microbiology in order to study microbial heterogeneity by means of the modern analytical tools.

Diagnostic and therapy of severe Clostridioides difficile infections in the ICU

PURPOSE OF REVIEW

The purpose of the review is to provide all the recent data focusing on the diagnostic and treatment of Clostridioides difficile infection in patients admitted in the ICU.

RECENT FINDINGS

In the ICU, diagnosis remains complicated with a large number of alternative diagnosis. The treatment classically relies on vancomycin but fidaxomicin and fecal microbiota transplantation are now potential solutions in selected indications.

SUMMARY

Data on ICU-related CDI remain limited and conflicting. To date, there is no unique and simple way to obtain a diagnosis for CDI, the combination of clinical signs and a two-step testing algorithm remains the recommended gold-standard. Two molecules can be proposed for first line treatment: vancomycin and fidaxomicin. Although metronidazole may still be discussed as a treatment option for mild CDI in low-risk patients, its use for ICU-patients does not seem reasonable. Several reports suggest that fecal microbiota transplantation could be discussed, as it is well tolerated and associated with a high rate of clinical cure. CDI is a dynamic and active area of research with new diagnostic techniques, molecules, and management concepts likely changing our approach to this old disease in the near future.

The Bactericidal Activity and Spore Inhibition Effect of Manuka Honey against Clostridioides Difficile

Clostridioides difficile colitis overgrowth occurs when the normal gut microbiome becomes disrupted, often due to antibiotics. Effective treatment remains elusive, due partly to the persistence of its spores in the gut. Natural substances like manuka honey offer an alternative antimicrobial mechanism of action to conventional antibiotics. We investigated the antibiotic activity of manuka honey against 20 C. difficile isolates. The minimum inhibitory concentrations (MICs) and minimal bactericidal concentrations (MBC) of manuka honeys of methylglyoxal (MGO) grades 30⁺, 100⁺, 250⁺, and 400⁺ were determined based on broth microdilution. Sporicidal activity was assessed in a range of honey concentrations by enumerating total viable cell and spore counts at 0–96 h after organism inoculation. The MICs of C. difficile ranged from 4% to >30% (w/v). MIC₅₀ for the four MGO grades were similar at 10–14%. MBC results for the majority of isolates were distributed bimodally at MBC/MIC ratios ≤4 or MBC >30%. Growth kinetics in honey showed total viable cell counts remaining >10⁵ colony-forming units (CFU)/mL at all time points, whereas spore counts remained within 1-log of baseline (10² CFU/mL) in honey but steadily increased in the drug-free control to >10⁵ CFU/mL by 96 h. Manuka honey demonstrated variable inhibitory and bactericidal activity against C. difficile. MGO grade had no noticeable impact on overall MIC distributions or bactericidal activity. Although manuka honey could inhibit spore proliferation, it did not eradicate spores completely.

Nasal Immunization with the C-Terminal Domain of Bcla3 Induced Specific IgG Production and Attenuated Disease Symptoms in Mice Infected with Clostridioides difficile Spores

Clostridioides difficile is a Gram-positive, spore-forming bacterium that causes a severe intestinal infection. Spores of this pathogen enter in the human body through the oral route, interact with intestinal epithelial cells and persist in the gut. Once germinated, the vegetative cells colonize the intestine and produce toxins that enhance an immune response that perpetuate the disease. Therefore, spores are major players of the infection and ideal targets for new therapies. In this context, spore surface proteins of C. difficile, are potential antigens for the development of vaccines targeting C. difficile spores. Here, we report that the C-terminal domain of the spore surface protein BclA3, BclA3_CTD, was identified as an antigenic epitope, over-produced in Escherichia coli and tested as an immunogen in mice. To increase antigen stability and efficiency, BclA3_CTD was also exposed on the surface of B. subtilis spores, a mucosal vaccine delivery system. In the experimental conditions used in this study, free BclA3_CTD induced antibody production in mice and attenuated some C. difficile infection symptoms after a challenge with the pathogen, while the spore-displayed antigen resulted less effective. Although dose regimen and immunization routes need to be optimized, our results suggest BclA3_CTD as a potentially effective antigen to develop a new vaccination strategy targeting C. difficile spores.

Effect of restricted dissolved oxygen on expression of Clostridium difficile toxin A subunit from E. coli

The repeating unit of the C. difficile Toxin A (rARU, also known as CROPS [combined repetitive oligopeptides]) C-terminal region, was shown to elicit protective immunity against C. difficile and is under consideration as a possible vaccine against this pathogen. However, expression of recombinant rARU in E. coli using the standard vaccine production process was very low. Transcriptome and proteome analyses showed that at restricted dissolved oxygen (DO) the numbers of differentially expressed genes (DEGs) was 2.5-times lower than those expressed at unrestricted oxygen. Additionally, a 7.4-times smaller number of ribosome formation genes (needed for translation) were down-regulated as compared with unrestricted DO. Higher rARU expression at restricted DO was associated with up-regulation of 24 heat shock chaperones involved in protein folding and with the up-regulation of the global regulator RNA chaperone hfq. Cellular stress response leading to down-regulation of transcription, translation, and energy generating pathways at unrestricted DO were associated with lower rARU expression. Investigation of the C. difficile DNA sequence revealed the presence of cell wall binding profiles, which based on structural similarity prediction by BLASTp, can possibly interact with cellular proteins of E. coli such as the transcriptional repressor ulaR, and the ankyrins repeat proteins. At restricted DO, rARU mRNA was 5-fold higher and the protein expression 27-fold higher compared with unrestricted DO. The report shows a strategy for improved production of C. difficile vaccine candidate in E. coli by using restricted DO growth. This strategy could improve the expression of recombinant proteins from anaerobic origin or those with cell wall binding profiles.

Vaccine Production to Protect Animals Against Pathogenic Clostridia

Clostridium is a broad genus of anaerobic, spore-forming, rod-shaped, Gram-positive bacteria that can be found in different environments all around the world. The genus includes human and animal pathogens that produce potent exotoxins that cause rapid and potentially fatal diseases responsible for countless human casualties and billion-dollar annual loss to the agricultural sector. Diseases include botulism, tetanus, enterotoxemia, gas gangrene, necrotic enteritis, pseudomembranous colitis, blackleg, and black disease, which are caused by pathogenic Clostridium. Due to their ability to sporulate, they cannot be eradicated from the environment. As such, immunization with toxoid or bacterin-toxoid vaccines is the only protective method against infection. Toxins recovered from Clostridium cultures are inactivated to form toxoids, which are then formulated into multivalent vaccines. This review discusses the toxins, diseases, and toxoid production processes of the most common pathogenic Clostridium species, including Clostridiumbotulinum, Clostridiumtetani, Clostridiumperfringens, Clostridiumchauvoei, Clostridiumsepticum, Clostridiumnovyi and Clostridiumhemolyticum.

Introduction to the special issue for The anaerobe society of the America's 14th Biennial congress in Las Vegas

In June 2018, the Anaerobe Society of the America's (ASA) held their 14th Biennial Congress in Las Vegas, Nevada. The Congress was attended by over 200 individuals from many different countries. The focus of the meeting was the fast-growing area of anaerobes in human and animal infectious disease, computational tools to understand basic biology and therapeutic development, the role of anaerobes in the microbiome, and clinical trials of novel bacterial-based therapies. To strengthen the community of researchers working on anaerobes, the congress held two training workshops on clinical bacteriology and anaerobes in the microbiome, several networking events, as well as a dinner which honored the lifetime achievement award given to Ellen Jo Baron. The meeting was also attended by the grandfather of anaerobic bacteriology and the founder of (ASA), Sydney Finegold, at the age of 97. In all, there was a broad diversity of research presented that showed new ways that anaerobes play a important role in health and disease.