Drivers of Clostridioides difficile hypervirulent ribotype 027 spore germination, vegetative cell growth and toxin production in vitro

Cyclic diguanylate differentially regulates the expression of virulence factors and pathogenesis-related phenotypes in Clostridioides difficile

Clostridioides difficile infection (CDI) caused by toxigenic C. difficile is the leading cause of antimicrobial and healthcare-associated diarrhea. The pathogenicity of C. difficile relies on the synergistic effect of multiple virulence factors, including spores, flagella, type IV pili (T4P), toxins, and biofilm. Spores enable survival and transmission of C. difficile, while adhesion factors such as flagella and T4P allow C. difficile to colonize and persist in the host intestine. Subsequently, C. difficile produces the toxins TcdA and TcdB, causing pseudomembranous colitis and other C. difficile-associated diseases; adhesion factors bind to the extracellular matrix to form biofilm, allowing C. difficile to evade drug and immune system attack and cause recurrent infection. Cyclic diguanylate (c-di-GMP) is a near-ubiquitous second messenger that extensively regulates morphology, the expression of virulence factors, and multiple physiological processes in C. difficile. In this review, we summarize current knowledge of how c-di-GMP differentially regulates the expression of virulence factors and pathogenesis-related phenotypes in C. difficile. We highlight that C. difficile spore formation and expression of toxin and flagella genes are inhibited at high intracellular levels of c-di-GMP, while T4P biosynthesis, cell aggregation, and biofilm formation are induced. Recent studies have enhanced our understanding of the c-di-GMP signaling networks in C. difficile and provided insights for the development of c-di-GMP-dependent strategies against CDI.

Exploring the Toxin-Mediated Mechanisms in Clostridioides difficile Infection

Clostridioides difficile infection (CDI) is the leading cause of nosocomial antibiotic-associated diarrhea, and colitis, with increasing incidence and healthcare costs. Its pathogenesis is primarily driven by toxins produced by the bacterium C. difficile, Toxin A (TcdA) and Toxin B (TcdB). Certain strains produce an additional toxin, the C. difficile transferase (CDT), which further enhances the virulence and pathogenicity of C. difficile. These toxins disrupt colonic epithelial barrier integrity, and induce inflammation and cellular damage, leading to CDI symptoms. Significant progress has been made in the past decade in elucidating the molecular mechanisms of TcdA, TcdB, and CDT, which provide insights into the management of CDI and the future development of novel treatment strategies based on anti-toxin therapies. While antibiotics are common treatments, high recurrence rates necessitate alternative therapies. Bezlotoxumab, targeting TcdB, is the only available anti-toxin, yet limitations persist, prompting ongoing research. This review highlights the current knowledge of the structure and mechanism of action of C. difficile toxins and their role in disease. By comprehensively describing the toxin-mediated mechanisms, this review provides insights for the future development of novel treatment strategies and the management of CDI.

The effect of cold storage and cooking on the viability of Clostridioides difficile spores in consumer foods

The increased detection of clinical cases of Clostridioides difficile coupled with the persistence of clostridial spores at various stages along the food chain suggest that this pathogen may be foodborne. This study examined C. difficile (ribotypes 078 and 126) spore viability in chicken breast, beef steak, spinach leaves and cottage cheese during refrigerated (4 °C) and frozen (-20 °C) storage with and without a subsequent sous vide mild cooking (60 °C, 1 h). Spore inactivation at 80 °C in phosphate buffer solution, beef and chicken were also investigated to provide D_80°C values and determine if PBS was a suitable model system for real food matrices. There was no decrease in spore concentration after chilled or frozen storage and/or sous vide cooking at 60 °C. Non-log-linear thermal inactivation was observed for both C. difficile ribotypes at 80 °C in phosphate buffer solution (PBS), beef and chicken. The predicted PBS D_80°C values of 5.72±[2.90, 8.55] min and 7.50±[6.61, 8.39] min for RT078 and RT126, respectively, were in agreement with the food matrices D_80°C values of 5.65 min (95% CI range from 4.29 to 8.89 min) for RT078 and 7.35 min (95% CI range from 6.81 to 7.01 min) for RT126. It was concluded that C. difficile spores survive chilled and frozen storage and mild cooking at 60 °C but may be inactivated at 80 °C. Moreover thermal inactivation in PBS was representative of that observed in real food matrices (beef and chicken).

Host and microbial-derived metabolites for Clostridioides difficile infection: Contributions, mechanisms and potential applications

Clostridioides difficile infection (CDI), which mostly occurs in hospitalized patients, is the most common and costly health care-associated disease. However, the biology of C. difficile remains incompletely understood. Current therapeutics are still challenged by the frequent recurrence of CDI. Advances in metabolomics facilitate our understanding of the etiology of CDI, which is not merely an alteration in the structure of the gut microbial community but also a dysbiosis metabolic setting promoting the germination, expansion and virulence of C. difficile. Therefore, we summarized the gut microbial and metabolic profiles for CDI under different conditions, such as those of postantibiotic treatment and postfecal microbiota transplantation. The current understanding of the role of host and gut microbial-derived metabolites as well as other nutrients in preventing or alleviating the disease symptoms of CDI will also be provided in this review. We hope that a specific nutrient-centric dietary strategy or the administration of certain nutrients to the colon could serve as an alternate line of investigation for the prophylaxis and mitigation of CDI in the future. Nevertheless, rigorously designed basic studies and randomized controlled trials need to be conducted to assess the functional mechanisms and effects of such therapeutics.

Akkermansia muciniphila Ameliorates Clostridioides difficile Infection in Mice by Modulating the Intestinal Microbiome and Metabolites

Clostridioides difficile is a common cause of nosocomial infection. Antibiotic-induced dysbiosis in the intestinal microbiota is a core cause of C. difficile infection (CDI). Akkermansia muciniphila plays an active role in maintaining gastrointestinal balance and might offer the protective effects on CDI as probiotics. Here, we investigated the effects and mechanisms of A. muciniphila on CDI. C57BL/6 mice (n = 29) were administered A. muciniphila Muc T (3 × 109 CFUs, 0.2 mL) or phosphate-buffered saline (PBS) by oral gavage for 2 weeks. Mice were pretreated with an antibiotic cocktail and subsequently challenged with the C. difficile strain VPI 10463. A. muciniphila treatment prevented weight loss in mice and reduced the histological injury of the colon. And it also alleviated inflammation and improved the barrier function of the intestine. The administration effects of A. muciniphila may be associated with an increase in short-chain fatty acid production and the maintenance of bile acids' steady-state. Our results provide evidence that administration of A. muciniphila to CDI mice, with an imbalance in the microbial community structure, lead to a decrease in abundance of members of the Enterobacteriaceae and Enterococcaceae. In short, A. muciniphila shows a potential anti-CDI role by modulating gut microbiota and the metabolome.

Clostridioides difficile spore germination: initiation to DPA release

Germination by Clostridioides difficile spores is an essential step in pathogenesis. Spores are metabolically dormant forms of bacteria that resist severe conditions. Work over the last 10 years has elucidated that C. difficile spores germinate thorough a novel pathway. This review summarizes our understanding of C. difficile spore germination and the factors involved in germinant recognition, cortex degradation and DPA release.

Negative interactions determine Clostridioides difficile growth in synthetic human gut communities

Understanding the principles of colonization resistance of the gut microbiome to the pathogen Clostridioides difficile will enable the design of defined bacterial therapeutics. We investigate the ecological principles of community resistance to C. difficile using a synthetic human gut microbiome. Using a dynamic computational model, we demonstrate that C. difficile receives the largest number and magnitude of incoming negative interactions. Our results show that C. difficile is in a unique class of species that display a strong negative dependence between growth and species richness. We identify molecular mechanisms of inhibition including acidification of the environment and competition over resources. We demonstrate that Clostridium hiranonis strongly inhibits C. difficile partially via resource competition. Increasing the initial density of C. difficile can increase its abundance in the assembled community, but community context determines the maximum achievable C. difficile abundance. Our work suggests that the C. difficile inhibitory potential of defined bacterial therapeutics can be optimized by designing communities featuring a combination of mechanisms including species richness, environment acidification, and resource competition.