The non-toxigenic Clostridium difficile CD37 protects mice against infection with a BI/NAP1/027 type of C. difficile strain

Flagellin is essential for initial attachment to mucosal surfaces by Clostridioides difficile

IMPORTANCE

Clostridioides difficile is one of the leading causes of hospital-acquired infections worldwide and presents challenges in treatment due to recurrent gastrointestinal disease after treatment with antimicrobials. The mechanisms by which C. difficile colonizes the gut represent a key gap in knowledge, including its association with host cells and mucosa. Our results show the importance of flagellin for specific adhesion to mucosal hydrogels and can help to explain prior observations of adhesive defects in flagellin and pilin mutants.

Clostridioides difficile infection and One Health: An Equine Perspective

Clostridioides (Clostridium) difficile presents a significant health risk to humans and animals. The complexity of the bacterial–host interaction affecting pathogenesis and disease development creates an ongoing challenge for epidemiological studies, control strategies and prevention planning. The recent emergence of human disease caused by strains of C. difficile found in animals adds to mounting evidence that C. difficile infection (CDI) may be a zoonosis. In equine populations, C. difficile is a known cause of diarrhoea and gastrointestinal inflammation, with considerable mortality and morbidity. This has a significant impact on both the well‐being of the animal and, in the case of performance and production animals, it may have an adverse economic impact on relevant industries. While C. difficile is regularly isolated from horses, many questions remain regarding the impact of asymptomatic carriage as well as optimization of diagnosis, testing and treatment. This review provides an overview of our understanding of equine CDI while also identifying knowledge gaps and the need for a holistic One Health approach to a complicated issue.

The adaptive immune response to Clostridioides difficile: A tricky balance between immunoprotection and immunopathogenesis

Clostridioides difficile (C. difficile) is the major cause of hospital-acquired gastrointestinal infections in individuals following antibiotics treatment. The pathogenesis of C. difficile infection (CDI) is mediated mainly by the production of toxins that induce tissue damage and host inflammatory responses. While innate immunity is well characterized in human and animal models of CDI, adaptive immune responses remain poorly understood. In this review, the current understanding of adaptive immunity is summarized and its influence on pathogenesis and disease outcome is discussed. The perspectives on what we believe to be the main pending questions and the focus of future research are also provided. There is no doubt that the innate immune response provides a first line of defense to CDI. But, is the adaptive immune response a friend or a foe? Probably it depends on the course of the disease. Adaptive immunity is essential for pathogen eradication, but may also trigger uncontrolled or pathological inflammation. Most of the understanding of the role of T cells is based on findings from experimental models. While they are a very valuable tool for research studies, more studies in human are needed to translate these findings into human disease. Another main challenge is to unravel the role of the different T cell populations on protection or induction of immunopathogenesis.

Microbiological characteristics of human and animal isolates of Clostridioides difficile in Italy: Results of the Istituto Superiore di Sanità in the years 2006-2016

The increased incidence of Clostridioides difficile infection (CDI) and the emergence of highly virulent types highlight the need of microbiological characterization to gain insight CDI epidemiological changes. This paper, reporting data obtained by the Istituto Superiore di Sanità Central Laboratory Service for C. difficile (ISS-CLSCD) in 2006-2016, provides a first long-term microbiological analysis of human and animal C. difficile strains circulating in Italy. The number of human isolates analyzed by ISS-CLSCD significantly increased over the time (170 in 2006-2011 vs 661 in 2012-2016). Independently from the year of isolation, 42% of the clinical isolates belonged to the PCR-ribotype (RT) 018-lineage (RT 018, RT 607, RT 541, PR07661 and PR14328), with RT 018 and RT 607 grouping the majority of isolates. This lineage was significantly associated to CDIs occurred in the General Medicine Units, Clinic Units or Long-Term Care Facilities, while it was rarely found in pediatric patients. Although the percentage of isolates positive for the binary toxin (CDT) was stable during the study (20%), several CDT-positive RTs emerged in 2012-2016, including RT 027. In total, 32 RTs overlapped between animals and humans and six of these RTs were non-toxigenic. The two lineages prevalent in animals, the RT 078-lineage and the RT 569-lineage (RT 569, RT 049, RT 056 and RT 727), were also found in humans, while the RT 018-lineage was rarely detected in animals, suggesting that it is prevalently associated to human infections. Sixty-two percent of clinical isolates showed a multidrug-resistance (MDR) phenotype, with resistance to rifampicin characterizing successful RTs. A MDR phenotype was also observed in 18% of animal isolates, in particular from dogs, supporting animals as potential reservoirs of resistant C. difficile strains. Interestingly, multiple resistances were observed in both human and animal non-toxigenic isolates suggesting their contribution to antibiotic resistance spread among C. difficile population. All these data indicate that CDI is an issue of growing concern in Italy, highlighting the need for a standardized surveillance in our Country and an interdisciplinary approach to deal successfully with this infection.

A Novel Bacteriophage Lysin-Human Defensin Fusion Protein Is Effective in Treatment of Clostridioides difficile Infection in Mice

Clostridioides difficile is the leading cause of worldwide antibiotics-associated diarrhea. In this study, we report the construction and evaluation of a novel bacteriophage lysin-human defensin fusion protein targeting C. difficile. The fusion protein, designated LHD, is composed of two parts connected by a 3-repeating unit linker "(GGGGS)3": the catalytic domain of a lysin protein from a C. difficile bacteriophage phiC2 (LCD), and the functional domain of a human defensin protein HD5. Lytic assays showed that LHD protein had a potent lytic activity against different types of clinical C. difficile strains, including the epidemic 027, 078, 012, and 087 strains. The minimum inhibitory concentration (MIC) of LHD was 0.78 μg/ml, which was lower than the MIC of the protein LCD (1.56 μg/ml), and the MICs of metronidazole (4 μg/ml) and vancomycin (4 μg/ml). In addition, the LHD protein could lyse C. different strains in different pHs (6.0, 7.0, and 8.0). Evaluation of LHD potency in vivo using mouse model of C. difficile infection (CDI) showed that administration of the LHD protein (twice daily for 7 days) was effective in mitigating the symptoms and reducing the death from CDI. Treatment with LHD also significantly decreased the number of C. difficile spores and the toxin level in feces from the infected mice. Our data suggest that this novel lysin-human defensin fusion protein has a potential on CDI control.

The role of the microbiota in infectious diseases

The human body is colonized by a diverse community of microorganisms collectively referred to as the microbiota. Here, we describe how the human microbiota influences susceptibility to infectious diseases using examples from the respiratory, gastrointestinal and female reproductive tract. We will discuss how interactions between the host, the indigenous microbiota and non-native microorganisms, including bacteria, viruses and fungi, can alter the outcome of infections. This Review Article will highlight the complex mechanisms by which the microbiota mediates colonization resistance, both directly and indirectly, against infectious agents. Strategies for the therapeutic modulation of the microbiota to prevent or treat infectious diseases will be discussed, and we will review potential therapies that directly target the microbiota, including prebiotics, probiotics, synbiotics and faecal microbiota transplantation.

Characterization of the virulence of a non-RT027, non-RT078 and binary toxin-positive Clostridium difficile strain associated with severe diarrhea

The expression of the Clostridium difficile binary toxin CDT is generally observed in the RT027 (ST1) and RT078 (ST11) C. difficile isolates, which are associated with severe C. difficile infection (CDI). However, we recently reported that the non-RT027 and non-RT078 C. difficile strain LC693 (TcdA⁺TcdB⁺ CDT⁺, ST201) caused severe diarrhea in a patient in Xiangya Hospital in China. C.difficile LC693 is a member of Clade 3, and in this study, we identified LC693 as RT871 and compared its virulence and pathogenicity to those of C.difficile R20291 (TcdA⁺TcdB⁺CDT⁺, ST1/RT027), UK6 (TcdA⁺TcdB⁺CDT⁺, ST35/RT027), CD630 (TcdA⁺TcdB⁺CDT⁻, ST54, RT012), and 1379 (TcdA⁺TcdB⁺CDT⁻, ST54/RT012), with strain 1379 being an epidemic C.difficile isolate from the same hospital. LC693 displayed a higher sporulation rate than R20291, CD630 or strain 1379. LC693 was comparable to R20291 with respect to spore germination, motility, and biofilm formation, but showed a faster germination rate, higher motility and a higher biofilm formation capability compared to CD630 and strain 1379. The adherence of spores to human gut epithelial cells was similar for all strains.The total toxin release of LC693 was lower than that of R20291, but higher than that of CD630 and strain 1379. Finally, in a mouse model of CDI, LC693 was capable of causing moderate to severe disease. Our findings demonstrate the pathogenicity of non-RT027 and non-RT078 binary toxin-positive C. difficile strains. Furthermore, our data indicate that LC693 may be more virulent than strain 1379, an epidemic strain from the same hospital, and provide the first phenotypic characterization of a non-RT027 and non-RT078 binary toxin-positive ST201 isolate.

Primary Prevention of Clostridium difficile-Associated Diarrhea: Current Controversies and Future Tools

PURPOSE OF REVIEW

Clostridium difficile infection (CDI) is a major cause of morbidity and mortality in hospitalized patients and rates in most places have not decreased significantly despite broad efforts by both hospitals and public health entities. This review aims to provide readers with a better understanding of the limitations of current prevention strategies. We also review potential future tools that may be available for the primary prevention of CDI in the next decade.

RECENT FINDINGS

Research over the last decade has expanded our appreciation of the role of asymptomatic shedding in the healthcare setting and in the community. This review demonstrates that poor quality data underlies even well-established guidance from national authorities on basic topics such as contact precautions, avoidance of alcohol-based hand hygiene products, CDI testing, supplemental cleaning modalities, and the use of bleach solutions. Additionally, we review research on novel preventative interventions such as identification of asymptomatic carriers, supplemental environmental cleaning technologies, vaccines, and the manipulation of the intestinal microbiome. While there is preliminary data that supports further research in all of these areas, the research is not yet robust enough on which to base local or national policy recommendations, though late-phase human clinical trials of CDI vaccine trials are ongoing. Over the last decade, researchers have begun to reassess the traditional infection prevention model for CDI. Data suggesting a greater role for asymptomatic shedders has increased our understanding of current vertical prevention techniques and is forcing researchers to look more at new processes and technologies to decrease disease incidence.

Type IV Pili Promote Clostridium difficile Adherence and Persistence in a Mouse Model of Infection

Cyclic diguanylate (c-di-GMP) is a second messenger that regulates the transition from motile to sessile lifestyles in numerous bacteria and controls virulence factor production in a variety of pathogens. In Clostridium difficile, c-di-GMP negatively regulates flagellum biosynthesis and swimming motility and promotes the production of type IV pili (TFP), biofilm formation, and surface motility in vitro Flagella have been identified as colonization factors in C. difficile, but the role of TFP in adherence to host cells and in colonization of the mammalian gut is unknown. Here we show that c-di-GMP promotes adherence to epithelial cells in vitro, which can be partly attributed to the loss of flagella. Using TFP-null mutants, we demonstrate that adherence to epithelial cells is partially mediated by TFP and that this TFP-mediated adherence requires c-di-GMP regulation. In a mouse model of colonization, the TFP-null mutants initially colonized the intestine as well as the parental strain but were cleared more quickly. Moreover, compared to the parent strain, C. difficile strains lacking TFP were particularly deficient in association with the cecal mucosa. Together these data indicate that TFP and their positive regulation by c-di-GMP promote attachment of C. difficile to the intestinal epithelium and contribute to persistence of C. difficile in the host intestine.

Advances in the diagnosis and treatment of Clostridium difficile infections

Clostridium difficile is a leading cause of antibiotic-associated diarrhea worldwide. The diagnosis of C. difficile infection (CDI) requires both clinical manifestations and a positive laboratory test for C. difficile and/or its toxins. While antibiotic therapy is the treatment of choice for CDI, there are relatively few classes of effective antibiotics currently available. Therefore, the development of novel antibiotics and/or alternative treatment strategies for CDI has received a great deal of attention in recent years. A number of emerging agents such as cadazolid, surotomycin, ridinilazole, and bezlotoxumab have demonstrated activity against C. difficile; some of these have been approved for limited clinical use and some are in clinical trials. In addition, other approaches such as early and accurate diagnosis of CDI as well as disease prevention are important for clinical management. While the toxigenic culture and the cell cytotoxicity neutralization assay are still recognized as the gold standard for the diagnosis of CDI, new diagnostic approaches such as nucleic acid amplification methods have become available. In this review, we will discuss both current and emerging diagnostic and therapeutic modalities for CDI.

Antibiotic Treatments for Clostridium difficile Infection Are Associated with Distinct Bacterial and Fungal Community Structures

Clostridium difficile infection (CDI) is the most common nosocomial infection in the United States, being associated with high recurrence and persistence rates. Though the relationship between intestinal dysbiosis and CDI is well known, it is unclear whether different forms of dysbiosis may potentially affect the course of CDI. How this is further influenced by C. difficile-directed antibiotics is virtually uninvestigated. In this study, diarrheal stool samples were collected from 20 hospitalized patients, half of whom were confirmed to have CDI. Analyzing tissue ex vivo and in duplicate, CDI and non-CDI fecal samples (n = 176) were either not antibiotic treated or treated with metronidazole, vancomycin, or fidaxomicin, the three most common CDI therapies. The microbial community composition, interactions, and predicted metabolic functions were assessed by 16S rRNA gene and internal transcribed spacer sequencing, bipartite network analysis, and phylogenetic investigation of communities by reconstruction of unobserved states. Our results demonstrate that while all C. difficile-directed antibiotics were associated with similar reductions in alpha diversity, beta diversity significantly differed on the basis of the particular antibiotic, with differentiating relative abundances of bacterial and fungal assemblages. With the exception of fidaxomicin, each antibiotic was associated with the emergence of potentially pathogenic fungal operational taxonomic units, with predicted bacterial functions enriched for xenobiotic metabolism that could perpetuate the dysbiosis driving CDI. Toxin-independent mechanisms of colitis related to the relative abundance of pathogenic bacteria and fungi were also noted. This study suggests that a transkingdom interaction between fungi and bacteria may be important in CDI pathophysiology, including being a factor in the historically high persistence and recurrence rates associated with this disease. IMPORTANCE Using human fecal samples and including sequencing for both bacterial and fungal taxa, this study compared the conventional antibiotics used to treat C. difficile infection (CDI) from the perspective of the microbiome, which is particularly relevant, given the relationship between dysbiotic states and the development of CDI. Sequencing and imputed functional analyses suggest that C. difficile-directed antibiotics are associated with distinct forms of dysbiosis that may be influential in the course of CDI. Further, a role for fungal organisms in the perpetuation of the causal dysbiosis of CDI is discussed, suggesting a previously unappreciated, clinically relevant transkingdom interaction that warrants further study.

A Review of Experimental and Off-Label Therapies for Clostridium difficile Infection

In spite of increased awareness and the efforts taken to optimize Clostridium difficile infection (CDI) management, with the limited number of currently available antibiotics for C. difficile the halt of this increasing epidemic remains out of reach. There are, however, close to 80 alternative treatment methods with controversial anti-clostridial efficacy or in experimental phase today. Indeed, some of these therapies are expected to become acknowledged members of the recommended anti-CDI arsenal within the next few years. None of these alternative treatment methods can respond in itself to all the major challenges of CDI management, which are primary prophylaxis in the susceptible population, clinical cure of severe cases, prevention of recurrences, and forestallment of asymptomatic C. difficile carriage and in-hospital spread. Yet, the greater the variety of treatment choices on hand, the better combination strategies can be developed to reach these goals in the future. The aim of this article is to provide a comprehensive summary of these experimental and currently off-label therapeutic options.

Clostridium difficile ribotypes in humans and animals in Brazil

Clostridium difficile is an emerging enteropathogen responsible for pseudomembranous colitis in humans and diarrhoea in several domestic and wild animal species. Despite its known importance, there are few studies about C. difficile polymerase chain reaction (PCR) ribotypes in Brazil and the actual knowledge is restricted to studies on human isolates. The aim of the study was therefore to compare C. difficile ribotypes isolated from humans and animals in Brazil. Seventy-six C. difficile strains isolated from humans (n = 25), dogs (n = 23), piglets (n = 12), foals (n = 7), calves (n = 7), one cat, and one manned wolf were distributed into 24 different PCR ribotypes. Among toxigenic strains, PCR ribotypes 014/020 and 106 were the most common, accounting for 14 (18.4%) and eight (10.5%) samples, respectively. Fourteen different PCR ribotypes were detected among human isolates, nine of them have also been identified in at least one animal species. PCR ribotype 027 was not detected, whereas 078 were found only in foals. This data suggests a high diversity of PCR ribotypes in humans and animals in Brazil and support the discussion of C. difficile as a zoonotic pathogen.