Clostridial toxins: sensing a target in a hostile gut environment

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.

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.

Single nucleotide polymorphisms of the tcdC gene and presence of the binary toxin gene predict recurrent episodes of Clostridium difficile infection

OBJECTIVE

To identify Clostridium difficile genotypes, which are associated with recurrent C difficile infection (RCDI).

BACKGROUND

Reliable bacterial genetic factors predicting RCDI are currently lacking.

METHODS

Inpatients and outpatients 18 years or older treated at our institution for C difficile infection (CDI) of any severity were consecutively enrolled. CDI was defined as symptoms of colitis with a positive PCR stool test. Each bacterial isolate was studied for virulence factors: tcdC mutations, including single nucleotide polymorphisms (SNPs) via PCR, the presence of genes for toxins A, B and binary toxin using restriction fragment length polymorphism, and identification of ribotype by PCR. χ tests, t tests, and logistic and linear regression were used to determine which virulence factors predicted RCDI and the need for hospital admission, with corrections made for multiple statistical comparisons.

RESULTS

Seventy-three patients (male: 52%; mean age: 66 ± 15 years) were studied. Binary toxin gene (P = 0.03) was associated with at least 1 episode of RCDI, as was the presence of SNPs C184T (P = 0.006) and A117T (P = 0.003). The presence of the binary toxin gene with either of these tcdC SNPs increased RCDI by 80% (P = 0.0002) but did not predict the need for hospital admission. None of the other virulence factors, including ribotype 027, were predictive of RCDI.

CONCLUSIONS

The presence of the binary toxin gene and tcdC SNPs C184T and A117T strongly predict RCDI. The presence of both tcdC SNPs and the binary toxin gene significantly increased the risk of RCDI, which might warrant longer antibiotic courses to eradicate the infection.

Lactobacillus rhamnosus L34 and Lactobacillus casei L39 suppress Clostridium difficile-induced IL-8 production by colonic epithelial cells

Background

Clostridium difficile is the main cause of hospital-acquired diarrhea and colitis known as C. difficile-associated disease (CDAD).With increased severity and failure of treatment in CDAD, new approaches for prevention and treatment, such as the use of probiotics, are needed. Since the pathogenesis of CDAD involves an inflammatory response with a massive influx of neutrophils recruited by interleukin (IL)-8, this study aimed to investigate the probiotic effects of Lactobacillus spp. on the suppression of IL-8 production in response to C. difficile infection.

Results

We screened Lactobacillus conditioned media from 34 infant fecal isolates for the ability to suppress C. difficile-induced IL-8 production from HT-29 cells. Factors produced by two vancomycin-resistant lactobacilli, L. rhamnosus L34 (LR-L34) and L.casei L39 (LC-L39), suppressed the secretion and transcription of IL-8 without inhibiting C. difficile viability or toxin production. Conditioned media from LR-L34 suppressed the activation of phospho-NF-κB with no effect on phospho-c-Jun. However, LC-L39 conditioned media suppressed the activation of both phospho-NF-κB and phospho-c-Jun. Conditioned media from LR-L34 and LC-L39 also decreased the production of C. difficile-induced GM-CSF in HT-29 cells. Immunomodulatory factors present in the conditioned media of both LR-L34 and LC-L39 are heat-stable up to 100°C and > 100 kDa in size.

Conclusions

Our results suggest that L. rhamnosus L34 and L. casei L39 each produce factors capable of modulating inflammation stimulated by C. difficile. These vancomycin-resistant Lactobacillus strains are potential probiotics for treating or preventing CDAD.

Clostridium difficile antibodies: a patent evaluation (WO2013028810)

INTRODUCTION

Incidence and severity of Clostridium difficile infection (CDI) are increasing worldwide. Toxins A (TcdA) and B (TcdB) and host immune response are the major determinates of CD pathogenesis and represent a new, stimulating therapeutic target to control CDI.

AREAS COVERED

The present patent and literature on the pathogenesis and treatment of CD were critically reviewed. The patent was described and put into clinical context, highlighting possible advantages and barriers to use. It consists of a blend of monoclonal antibodies (mAbs) and antigen-binding portions that neutralize TcdA, targeting the enterocyte-binding domain. It demonstrated good efficacy in in vivo models and seems promising in clinical practice. However, recent evidence reshaped the central role of TcdA.

EXPERT OPINION

Current treatments are inadequate to control CDI and recurrence. Toxin-targeted mAbs are one of the most promising approaches for CDI, including infection by hypervirulent strains. At-risk subjects and those experiencing recurrence are the ideal targets for this second-line treatment; however CDI epidemiology is fast-changing and mAbs may represent a powerful option also for other patients. The re-evaluation of the pathogenic role of TcdA may potentially limit the use of this product; however, the possible administration in combination with other therapeutic agents may optimize its efficacy.

Evaluation of multiplex PCR with enhanced spore germination for detection of Clostridium difficile from stool samples of the hospitalized patients

Clostridium difficile poses as the most common etiologic agent of nosocomial diarrhea. Although there are many diagnostic methods to detect C. difficile directly from stool samples, the nucleic acid-based approach has been largely performed in several laboratories due to its high sensitivity and specificity as well as rapid turnaround time. In this study, a multiplex PCR was newly designed with recent accumulated nucleotide sequences. The PCR testing with various C. difficile ribotypes, other Clostridium spp., and non-Clostridium strains revealed 100% specificity with the ability to detect as low as ~22 genomic copy number per PCR reaction. Different combinations of sample processing were evaluated prior to multiplex PCR for the detection of C. difficile in fecal samples from hospitalized patients. The most optimal condition was the non-selective enrichment at 37°C for 1 h in brain heart infusion broth supplemented with taurocholate, followed by the multiplex PCR. The detection limit after sample processing was shown as being 5 spores per gram of fecal sample. Two hundred and thirty-eight fecal samples collected from the University affiliated hospital were analyzed by the enrichment multiplex PCR procedure. The results suggested that the combination of sample processing with the high-performance detection method would be applicable for routine diagnostic use in clinical setting.