Distribution of Clostridium difficile variant toxinotypes and strains with binary toxin genes among clinical isolates in an American hospital

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.

Treatment of MRSA Infection: Where are We?

Staphylococcus aureus is a leading cause of septicemia, endocarditis, pneumonia, skin and soft tissue infections, bone and joint infections, and hospital-acquired infections. In particular, methicillin-resistant Staphylococcus aureus (MRSA) is associated with high morbidity and mortality, and continues to be a major public health problem. The emergence of multidrug-resistant MRSA strains along with the wide consumption of antibiotics has made anti-MRSA treatment a huge challenge. Novel treatment strategies (e.g., novel antimicrobials and new administrations) against MRSA are urgently needed. In the past decade, pharmaceutical companies have invested more in the research and development (R&D) of new antimicrobials and strategies, spurred by favorable policies. All research articles were collected from authentic online databases, including Google Scholar, PubMed, Scopus, and Web of Science, by using different combinations of keywords, including 'anti-MRSA', 'antibiotic', 'antimicrobial', 'clinical trial', 'clinical phase', clinical studies', and 'pipeline'. The information extracted from articles was compared to information provided on the drug manufacturer's website and Clinical Trials.gov (https://clinicaltrials.gov/) to confirm the latest development phase of anti-MRSA agents. The present review focuses on the current development status of new anti-MRSA strategies concerning chemistry, pharmacological target(s), indications, route of administration, efficacy and safety, pharmacokinetics, and pharmacodynamics, and aims to discuss the challenges and opportunities in developing drugs for anti-MRSA infections.

A genomic survey of Clostridioides difficile isolates from hospitalized patients in Melbourne, Australia

IMPORTANCE

There has been a decrease in healthcare-associated Clostridioides difficile infection in Australia, but an increase in the genetic diversity of infecting strains, and an increase in community-associated cases. Here, we studied the genetic relatedness of C. difficile isolated from patients at a major hospital in Melbourne, Australia. Diverse ribotypes were detected, including those associated with community and environmental sources. Some types of isolates were more likely to carry antimicrobial resistance determinants, and many of these were associated with mobile genetic elements. These results correlate with those of other recent investigations, supporting the observed increase in genetic diversity and prevalence of community-associated C. difficile, and consequently the importance of sources of transmission other than symptomatic patients. Thus, they reinforce the importance of surveillance for in both hospital and community settings, including asymptomatic carriage, food, animals, and other environmental sources to identify and circumvent important sources of C. difficile transmission.

Molecular epidemiological analyses of Clostridioides difficile isolates in a university hospital in Japan

Background

We performed molecular epidemiological analyses of Clostridioides difficile isolates in a university hospital in Japan to reveal the risk of C. difficile infection.

Methods

Cultured isolates from 919 stool samples from 869 patients obtained from July 2015 to August 2016 were subjected to toxin gene detection, ribotyping, multilocus sequence typing, antimicrobial susceptibility testing, and quantitative real-time polymerase chain reaction testing for C. difficile toxin gene expression.

Results

Of the 919 stool samples from 869 patients, C. difficile was isolated from 153 samples (16.6%), of which 49 (32%) and 104 (68%) were from patients with and without C. difficile infection, respectively. Analyses showed genetic diversity, with ST8 and ST17 strains of healthcare-associated infections, some of which caused C. difficile infections. There was no significant difference in the transcription levels of C. difficile toxin genes between isolates from patients with and without C. difficile infection.

Conclusions

Major Japanese clonal strains, ST8 and ST17, have been in the hospital environment for a long time and cause healthcare-associated C. difficile infections. The C. difficile toxin genes were transcribed in the isolates from both patients with and without C. difficile infection but were no significant relationship with the development of C. difficile infection.

Clostridioides difficile in food and food products of animal origin in Assam, India

OBJECTIVE

Considering the paucity of information about food-associated Clostridioides difficile from India, a study was undertaken to establish the prevalence of C. difficile in a variety of foods of animal origin, together with molecular strain characterization and antimicrobial resistance.

METHODS

A total of 235 samples comprising raw meat and meat products, fish products, and milk and milk products were screened for C. difficile. Toxin genes and other parts of PaLoc were amplified in isolated strains. The resistance pattern towards commonly used antimicrobial agents was studied by the Epsilometric test.

RESULTS

C. difficile was isolated from 17(7.23%) different food samples of animal origin, including toxigenic (6) and non-toxigenic (11) isolates. In four toxigenic strains, the tcdA gene could not be detected under used conditions (tcdA-tcdB+). However, all strains had binary toxin-associated genes (cdtA and cdtB). The antimicrobial resistance was highest in non-toxigenic C. difficile isolates in food of animal origin.

CONCLUSION

Meat, meat products and dry fish, but not milk and milk products were contaminated with C. difficile. Contamination rates were low with diverse toxin profiles and antibiotic resistance patterns among the C. difficile strains.

Comparison of clinical severity, genotype and toxin gene expression of binary toxin-producing Clostridioides difficile clinical isolates in Japan

The emerging Clostridioides difficile strain BI/NAP1/027 has been reported to be associated with more severe clinical symptoms and higher mortality rates, thought in part due to production of a novel binary toxin alongside conventional A and B toxins. However, recent studies suggest that this may not always be the case. Therefore, the purpose of this report was to investigate the correlation between clinical severity and microbiological characteristics of CDT-producing C. difficile isolates in Japan. Eight Japanese isolates of CDT producing C. difficile were investigated using genotyping, cytotoxic activity assays and toxin gene expression. Correlation with clinical severity was performed retrospectively using the patient record. Three of eight patients were assessed as having severe C. difficile infection (CDI). PCR ribotyping resolved six ribotypes including ribotype 027. No specific genes were identified determining severe compared with non-severe cases. Positive correlation of expression levels of tcdA, tcdB and cdtB were observed although these expression levels were not correlated with cytotoxicity. CDI severity index neither correlated with toxin gene expression level nor cytotoxicity. These data indicate that the possession of the CDT gene and toxin gene expression levels may not relate to C. difficile cytotoxicity or clinical severity.

1HN, 13C, and 15N resonance assignments of the Clostridioides difficile receptor binding domain 2 (CDTb, residues 757-876)

Clostridioides difficile is a bacterial pathogen responsible for the majority of nosocomial infections in the developed world. C. difficile infection (CDI) is difficult to treat in many cases because hypervirulent strains have evolved that contain a third toxin, termed the C. difficile toxin (CDT), in addition to the two enterotoxins TcdA and TcdB. CDT is a binary toxin comprised of an enzymatic, ADP-ribosyltransferase (ART) toxin component, CDTa, and a pore-forming or delivery subunit, CDTb. In the absence of CDTa, CDTb assembles into two distinct di-heptameric states, a symmetric and an asymmetric form with both states having two surface-accessible host cell receptor-binding domains, termed RBD1 and RBD2. RBD1 has a unique amino acid sequence, when aligned to other well-studied binary toxins (i.e., anthrax), and it contains a novel Ca2+-binding site important for CDTb stability. The other receptor binding domain, RBD2, is critically important for CDT toxicity, and a domain such as this is missing altogether in other binary toxins and shows further that CDT is unique when compared to other binary toxins. In this study, the 1H, 13C, and 15N backbone and sidechain resonances of the 120 amino acid RBD2 domain of CDTb (residues 757-876) were assigned sequence-specifically and provide a framework for future NMR-based drug discovery studies directed towards targeting the most virulent strains of CDI.

Outbreaks of Typhlocolitis Caused by Hypervirulent Group ST1 Clostridioides difficile in Highly Immunocompromised Strains of Mice

Clostridioides difficile is an enteric pathogen that can cause significant clinical disease in both humans and animals. However, clinical disease arises most commonly after treatment with broad-spectrum antibiotics. The organism's ability to cause naturally occurring disease in mice is rare, and little is known about its clinical significance in highly immunocompromised mice. We report on 2 outbreaks of diarrhea associated with C. difficile in mice. In outbreak 1, 182 of approximately 2, 400 NOD.Cg-Prkdcscid Il2rgtm1Wjl/SzJ (NSG) and related strains of mice became clinically ill after cessation of a 14-d course of 0.12% amoxicillin feed to control an increase in clinical signs associated with Corynebacterium bovis infection. Most mice had been engrafted with human tumors; the remainder were experimentally naïve. Affected animals exhibited 1 of 3 clinical syndromes: 1) peracute death; 2) severe diarrhea leading to euthanasia or death; or 3) mild to moderate diarrhea followed by recovery. A given cage could contain both affected and unaffected mice. Outbreak 2 involved a small breeding colony (approximately 50 mice) of NOD. CB17-Prkdcscid/NCrCrl (NOD-scid) mice that had not received antibiotics or experimental manipulations. In both outbreaks, C. difficile was isolated, and toxins A and B were detected in intestinal content or feces. Histopathologic lesions highly suggestive of C. difficile enterotoxemia included fibrinonecrotizing and neutrophilic typhlocolitis with characteristic 'volcano' erosions or pseudomembrane formation. Genomic analysis of 4 isolates (3 from outbreak 1 and 1 from outbreak 2) revealed that these isolates were closely related to a pathogenic human isolate, CD 196. To our knowledge, this report is the first to describe naturally occurring outbreaks of C. difficile-associated typhlocolitis with significant morbidity and mortality in highly immunocompromised strains of mice.

A Drosophila Model for Clostridium difficile Toxin CDT Reveals Interactions with Multiple Effector Pathways

Clostridium difficile infections (CDIs) cause severe and occasionally life-threatening diarrhea. Hyper-virulent strains produce CDT, a toxin that ADP-ribosylates actin monomers and inhibits actin polymerization. We created transgenic Drosophila lines expressing the catalytic subunit CDTa to investigate its interaction with host signaling pathways in vivo. When expressed in the midgut, CDTa reduces body weight and fecal output and compromises survival, suggesting severe impairment of digestive functions. At the cellular level, CDTa induces F-actin network collapse, elimination of the intestinal brush border, and disruption of intercellular junctions. We confirm toxin-dependent re-distribution of Rab11 to enterocytes' apical surface and observe suppression of CDTa phenotypes by a Dominant-Negative form of Rab11 or RNAi of the dedicated Rab11GEF Crag (DENND4). We also report that Calmodulin (Cam) is required to mediate CDTa activity. In parallel, chemical inhibition of the Cam/Calcineurin pathway by Cyclosporin A or FK506 also reduces CDTa phenotypes, potentially opening new avenues for treating CDIs.

Structure of the cell-binding component of the Clostridium difficile binary toxin reveals a di-heptamer macromolecular assembly

Targeting Clostridium difficile infection is challenging because treatment options are limited, and high recurrence rates are common. One reason for this is that hypervirulent C. difficile strains often have a binary toxin termed the C. difficile toxin, in addition to the enterotoxins TsdA and TsdB. The C. difficile toxin has an enzymatic component, termed CDTa, and a pore-forming or delivery subunit termed CDTb. CDTb was characterized here using a combination of single-particle cryoelectron microscopy, X-ray crystallography, NMR, and other biophysical methods. In the absence of CDTa, 2 di-heptamer structures for activated CDTb (1.0 MDa) were solved at atomic resolution, including a symmetric (SymCDTb; 3.14 Å) and an asymmetric form (AsymCDTb; 2.84 Å). Roles played by 2 receptor-binding domains of activated CDTb were of particular interest since the receptor-binding domain 1 lacks sequence homology to any other known toxin, and the receptor-binding domain 2 is completely absent in other well-studied heptameric toxins (i.e., anthrax). For AsymCDTb, a Ca2+ binding site was discovered in the first receptor-binding domain that is important for its stability, and the second receptor-binding domain was found to be critical for host cell toxicity and the di-heptamer fold for both forms of activated CDTb. Together, these studies represent a starting point for developing structure-based drug-design strategies to target the most severe strains of C. difficile.

High Prevalence of Genetically Related Clostridium Difficile Strains at a Single Hemato-Oncology Ward Over 10 Years

Aims: Clostridium difficile (C. difficile) infection (CDI) is the main cause of healthcare-associated infectious diarrhea. We used whole-genome sequencing (WGS) to measure the prevalence and genetic variability of C. difficile at a single hemato-oncology ward over a 10 year period. Methods: Between 2008 and 2018, 2077 stool samples were obtained from diarrheal patients hospitalized at the Department of Lymphoma; of these, 618 were positive for toxin A/B. 140 isolates were then subjected to WGS on Ion Torrent PGM sequencer. Results: 36 and 104 isolates were recovered from 36 to 46 patients with single and multiple CDIs, respectively. Of these, 131 strains were toxigenic. Toxin gene profiles tcdA(+);tcdB(+);cdtA/cdtB(+) and tcdA(+);tcdB(+);cdtA/cdtB(-) were identified in 122 and nine strains, respectively. No isolates showed reduced susceptibility to metronidazole and vancomycin. All tested strains were resistant to ciprofloxacin, and 72.9, 42.9, and 72.9% of strains were resistant to erythromycin, clindamycin, or moxifloxacin, respectively. Multi-locus sequence typing (MLST) identified 23 distinct sequence types (STs) and two unidentified strains. Strains ST1 and ST42 represented 31 and 30.1% of all strains tested, respectively. However, while ST1 was detected across nearly all years studied, ST42 was detected only from 2009 to 2011. Conclusion: The high proportion of infected patients in 2008-2011 may be explained by the predominance of more transmissible and virulent C. difficile strains. Although this retrospective study was not designed to define outbreaks of C. difficile, the finding that most isolates exhibited high levels of genetic relatedness suggests nosocomial acquisition.

The safety of treatment options for acute bacterial skin and skin structure infections

INTRODUCTION

Acute bacterial skin and skin-structure infections (ABSSSI) may develop in both in-patients and out-patients, possibly with a severe clinical presentation. Since most phase 3 randomized clinical trials have shown non-inferiority in efficacy across different agents, considerations regarding their different safety profiles inevitably play a crucial role in the everyday choice about which of them should be employed for the treatment of ABSSSI.

AREAS COVERED

In this review, the authors discuss the safety profile of different treatment options for ABSSSI.

EXPERT OPINION

The spread of methicillin-resistant Staphylococcus aureus (MRSA) in the last decades has inevitably influenced the therapeutic approach to ABSSSI. Adequate knowledge of the peculiar toxicity profile of each drug active against MRSA is essential for guiding, monitoring and managing adverse events, in turn reducing any unfavorable impact of toxicity on patients' outcomes. In the next five years, potential toxicity will play a critical role in establishing the best available therapy for each specific patient, together with consideration regarding the possibility of avoiding hospitalization or allowing a switch from intravenous to oral therapy and early discharge.

Enterotoxic Clostridia: Clostridioides difficile Infections

Clostridioides difficile is a Gram-positive, anaerobic, spore forming pathogen of both humans and animals and is the most common identifiable infectious agent of nosocomial antibiotic-associated diarrhea. Infection can occur following the ingestion and germination of spores, often concurrently with a disruption to the gastrointestinal microbiota, with the resulting disease presenting as a spectrum, ranging from mild and self-limiting diarrhea to severe diarrhea that may progress to life-threating syndromes that include toxic megacolon and pseudomembranous colitis. Disease is induced through the activity of the C. difficile toxins TcdA and TcdB, both of which disrupt the Rho family of GTPases in host cells, causing cell rounding and death and leading to fluid loss and diarrhea. These toxins, despite their functional and structural similarity, do not contribute to disease equally. C. difficile infection (CDI) is made more complex by a high level of strain diversity and the emergence of epidemic strains, including ribotype 027-strains which induce more severe disease in patients. With the changing epidemiology of CDI, our understanding of C. difficile disease, diagnosis, and pathogenesis continues to evolve. This article provides an overview of the current diagnostic tests available for CDI, strain typing, the major toxins C. difficile produces and their mode of action, the host immune response to each toxin and during infection, animal models of disease, and the current treatment and prevention strategies for CDI.

Pleiotropic Clostridioides difficile Cyclophilin PpiB Controls Cysteine-Tolerance, Toxin Production, the Central Metabolism and Multiple Stress Responses

The Gram-positive pathogen Clostridioides difficile is the main bacterial agent of nosocomial antibiotic associated diarrhea. Bacterial peptidyl-prolyl-cis/trans-isomerases (PPIases) are well established modulators of virulence that influence the outcome of human pathologies during infections. Here, we present the first interactomic network of the sole cyclophilin-type PPIase of C. difficile (CdPpiB) and show that it has diverse interaction partners including major enzymes of the amino acid-dependent energy (LdhA, EtfAB, Had, Acd) and the glucose-derived (Fba, GapA, Pfo, Pyk, Pyc) central metabolism. Proteins of the general (UspA), oxidative (Rbr1,2,3, Dsr), alkaline (YloU, YphY) and cold shock (CspB) response were found bound to CdPpiB. The transcriptional (Lrp), translational (InfC, RFF) and folding (GroS, DnaK) control proteins were also found attached. For a crucial enzyme of cysteine metabolism, O-acetylserine sulfhydrylase (CysK), the global transcription regulator Lrp and the flagellar subunit FliC, these interactions were independently confirmed using a bacterial two hybrid system. The active site residues F50, F109, and F110 of CdPpiB were shown to be important for the interaction with the residue P87 of Lrp. CysK activity after heat denaturation was restored by interaction with CdPpiB. In accordance, tolerance toward cell wall stress caused by the exposure to amoxicillin was reduced. In the absence of CdPpiB, C. difficile was more susceptible toward L-cysteine. At the same time, the cysteine-mediated suppression of toxin production ceased resulting in higher cytotoxicity. In summary, the cyclophilin-type PPIase of C. difficile (CdPpiB) coordinates major cellular processes via its interaction with major regulators of transcription, translation, protein folding, stress response and the central metabolism.

Prevalence and antimicrobial susceptibility pattern of toxigenic Clostridium difficilestrains isolated in Iran

Background/aim

Clostridium difficile is a frequent cause of nosocomial infections and has become a major public health concern in developed nations. In the present study, the prevalence and antimicrobial susceptibility pattern of toxigenic C. difficile strains isolated in Iran were investigated.

Materials and methods

Between June 2016 and May 2017, 2947 inpatient fecal samples were taken from symptomatic adult hospitalized patients in different units of 32 care facilities in Tehran, Iran. C. difficile strains were identified by microbiological/biochemical methods. Susceptibility to 20 antimicrobials was measured by E-test method. Toxin-specific immunoassays and cytotoxicity assays were used to determine in vitro toxin production.

Results

Out of 2947 fecal samples, 538 (18.25%) C. difficile isolates were obtained among those with suspected CDI. In E-test method, all C. difficile isolates were susceptible to fidaxomicin, vancomycin, amoxicillin/clavulanate, and meropenem and were resistant to penicillin G. The prevalence of multidrug resistant C. difficile was 69.33% (373/538). Among 538 C. difficile, 147 (27.32%), 169 (31.41%), and 222 (41.26%) isolates were TcdA+/TcdB+, TcdA-/TcdB+, and TcdA-/TcdB-, respectively.

Conclusion

The results evidently support the hypothesis of a probable role of toxigenic strains of C. difficile in developing gastrointestinal complaints in patients with diarrhea.

Pharmacologic Approach to Management of Clostridium difficile Infection

Clostridium difficile is a gram-positive, anaerobic, spore-forming bacterium that is the leading cause of nosocomial infections in hospitals in the United States. Critically ill patients are at high risk for C. difficile infection (CDI) and face potentially detrimental effects, including prolonged hospitalization, risk of recurrent disease, complicated surgery, and death. CDI requires a multidisciplinary approach to decrease hospital transmission and improve treatment outcomes. This article briefly reviews the current literature and guideline recommendations for treatment and prevention of CDI, with a focus on antibiotic treatment considerations including dosing, routes of administration, efficacy data, adverse effects, and monitoring parameters.

PrsA2 (CD630_35000) of Clostridioides difficile Is an Active Parvulin-Type PPIase and a Virulence Modulator

Clostridioides difficile is the main cause for nosocomial antibiotic associated diarrhea and has become a major burden for the health care systems of industrial countries. Its main virulence factors, the small GTPase glycosylating toxins TcdA and TcdB, are extensively studied. In contrast, the contribution of other factors to development and progression of C. difficile infection (CDI) are only insufficiently understood. Many bacterial peptidyl-prolyl-cis/trans-isomerases (PPIases) have been described in the context of virulence. Among them are the parvulin-type PrsA-like PPIases of Gram-positive bacteria. On this basis, we identified CD630_35000 as the PrsA2 homolog in C. difficile and conducted its enzymatic and phenotypic characterization in order to assess its involvement during C. difficile infection. For this purpose, wild type CdPrsA2 and mutant variants carrying amino acid exchanges mainly in the PPIase domain were recombinantly produced. Recombinant CdPrsA2 showed PPIase activity toward the substrate peptide Ala-Xaa-Pro-Phe with a preference for positively charged amino acids preceding the proline residue. Mutation of conserved residues in its active site pocket impaired the enzymatic activity. A PrsA2 deficient mutant was generated in the C. difficile 630Δerm background using the ClosTron technology. Inactivation of prsA2 resulted in a reduced germination rate in response to taurocholic acid, and in a slight increase in resistance to the secondary bile acids LCA and DCA. Interestingly, in the absence of PrsA2 colonization of mice by C. difficile 630 was significantly reduced. We concluded that CdPrsA2 is an active PPIase that acts as a virulence modulator by influencing crucial processes like sporulation, germination and bile acid resistance resulting in attenuated mice colonization.

Evaluation of an UltraFast LabChip V280 assay for detection of toxigenic Clostridium difficile

In this study, we compared the performance of an UltraFast LabChip (UL) V280 system for Clostridium difficile detection in stool with that of Xpert C. difficile/Epi and VIDAS CDAB. Among 176 stool specimens, UL V280 detected toxigenic C. difficile in 22 (22/176, 12.5%) with a sensitivity, specificity, positive predictive value, negative predictive value (NPV) of 100.0%, 99.4%, 99.5% and 100.0%, respectively, which were higher than 95.2%, 97.4%, 83.3%, and 99.3% of Xpert C. difficile/Epi (P > 0.05). Notably, the sensitivity and NPV of ULV280 were significantly higher than those of VIDAS CDAB 52.4% (P < 0.001, odds ratio [OR] = 20.0, 95% confidence interval [CI] = 2.26-176.81) and 93.8% (P = 0.002, OR = 10.27, 95% CI = 1.30-81.17). UL V280 turnaround time (35 min) and cost (6.24 Dollars [$]) per specimen were less than those for Xpert C. difficile/Epi (47 min, 59.26 $) and VIDAS CDAB (65 min, 11.70 $). UL V280 possessed an analytical sensitivity limit of 2500 CFU/ml, 95% [CI] = (Ct: 30.76-34.90), and no cross-reactions with other pathogens were found. The study demonstrates that UL V280 based on a microfluidic chip is a rapid, accurate, easy, and cost-effective diagnostic test for toxigenic C. difficile in stool.

High rate of Clostridium difficile among young adults presenting with diarrhea at two hospitals in Kenya

Background:

Clostridium difficile infection (CDI) is the leading cause of antibiotic-associated diarrhea worldwide. As a result, the US Centers for Disease Control and Prevention have designated C. difficile as an urgent threat. Despite the global public health risk posed by CDI, little is known about its epidemiology on the African continent. This article describes the common occurrence of CDI from a cross-section of consecutively seen, randomly enrolled patients presenting with diarrhea at two major hospitals in Kenya.

Methods:

Patients presenting with diarrhea at two major hospitals in Kenya from May to July 2017 were enrolled. After signing the informed consent, stool samples, demographic data, medical history, prior antibiotic use, and HIV status were obtained from the patients. C. difficile was detected and validated by toxigenic culture and PCR.

Results:

The average age of the patients was 35.5 years (range 3–86 years); 59% were male and 41% were female. Out of 105 patient s tools tested, 98 (93.3%) were positive for C. difficile by culture. PCR analysis confirmed C. Difficile-specific genes, tcdA, tcdB, and tcdC, in the strains isolated from the stools. Further, 82.5% of the stools had C. difficile isolates bearing the frame-shift delection associated with hypervirulent strains. Remarkably, 91.9% of the stools that tested positive for C. difficile came from patients under 60 years old, with 64.3% being less than 40 years of age.The majorityof the patients (85%) reported over-the-counter antibiotic use in the last 30 days before the hospital visit.

Conclusions:

Together, the results revealed an unusually high incidence of C. difficile in the stools analyzed, especially among young adults who are thought to be less vulnerable. Comprehensive research is urgently needed to examine the epidemiology, risk factors, pathogenesis, comorbidities, clinical outcomes, antibiotic susceptibility, and genetic makeup of C. difficile strains circulating on the African continent.

Identification and Characterization of Clostridium difficile Sequence Type 37 Genotype by Matrix-Assisted Laser Desorption IonizationTime of Flight Mass Spectrometry

Clostridium difficile multilocus sequence type 37 (ST37), which mainly corresponds to ribotype 017, has been a dominant genotype circulating in China. In this study, we report the use of matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) to analyze and characterize 204 C. difficile clinical isolates, including 49 ST37 and 155 non-ST37 isolates collected in China and other countries. The distributions of two major protein peaks (m/z 3,242 and 3,286) were significantly different between ST37 and non-ST37 prototype strains and clinical isolates. This difference was reproducible when analysis was performed on different colonies in different runs. This finding was repeated and confirmed by both bioMérieux Vitek MS and Bruker Microflex LT systems on isolates recovered from a variety of geographic regions worldwide. The combination of the two peaks was present in 47 of 49 ST37 isolates, resulting in a sensitivity of 95.9%. In contrast, the peak combination was absent in 153 of 155 non-ST37 isolates, resulting in a specificity of 98.7%. Our results suggest that MALDI-TOF MS is a rapid and reliable tool to identify C. difficile genotype ST37. Work is in progress to characterize the two molecules having peaks at m/z 3,242 and 3,286, which appear to be specific to C. difficile genotype ST37.

Detection of antibiotic resistance toxigenic Clostridium difficile in processed retail lettuce

Objectives: Clostridium difficile is the major cause of infectious diarrhoea in humans after antimicrobial treatment. Clostridium difficile has been isolated from food animals and meat. The main purpose of this study was to characterize C. difficile isolated from retail lettuce and determine the antibiotic resistance using five common clinical-selected antibiotics (metronidazole, vancomycin, clindamycin, erythromycin, and cefotaxime).

Materials and Methods: Lettuce samples (grown in California, Arkansas, and Louisiana) were purchased from retail stores.

Results: Toxigenic C. difficile was isolated from 13.8 per cent (41/297) of the lettuce samples. Among the toxigenic isolates, only 82.9 per cent (34/41) produced toxin B, 17.1 per cent (7/41) produced both toxin A and toxin B, and two of the Louisiana C. difficile isolates were identified as ribotype 027. Under the treatment of the five antibiotics, the virulence C. difficile isolates were identified as having antibiotic resistance to metronidazole, vancomycin, and erythromycin.

Conclusion: The present study reports the highest prevalence of toxigenic C. difficile in US retail lettuce. The antibiotic resistance to metronidazole, vancomycin, and erythromycin of the isolated C. difficile from retail lettuces could lead to public health concerns.

Is there a relationship between the presence of the binary toxin genes in Clostridium difficile strains and the severity of C. difficile infection (CDI)?

Some strains of Clostridium difficile produce a binary toxin, in addition to the main C. difficile virulence factors (toxins A and B). There have been conflicting reports regarding the role of binary toxin and its relationship to the severity of C. difficile infection (CDI). Samples, isolates and clinical data were collected as part of a prospective multicentre diagnostic study. Clostridium difficile isolates (n = 1259) were tested by polymerase chain reaction (PCR) assay to detect binary toxin genes cdtA and cdtB. The PCR binary toxin gene results were compared with clinical severity and outcome data, including 30-day all-cause mortality. The 1259 isolates corresponded to 1083 different patients (October 2010 to September 2011). The prevalence of binary toxin positive strains was significantly higher in faecal samples with detectable toxin A/B than in those without toxin but that were positive by cytotoxigenic culture (26.3% vs. 10.3%, p < 0.001). The presence of binary toxin correlated moderately with markers of CDI severity (white cell count, serum albumin concentration and serum creatinine concentration). However, the risk ratio for all-cause mortality was 1.68 for binary toxin positive patients and patients were significantly less likely to survive if they had CDI caused by a binary toxin gene positive strain, even after adjusting for age (p < 0.001). The presence of binary toxin genes does not predict the clinical severity of CDI, but it is significantly associated with the risk of all-cause mortality.

Nonantimicrobial drug targets for Clostridium difficile infections

Clostridium difficile infection (CDI) is a major public health problem worldwide. Treatment has become complicated due to the emergence of strains with increased toxigenicity and sporulation rate, together with rampant antibiotics use that disrupts colonization resistance of the colonic microbiota. As a result, there is a critical need for nonantibiotic treatments. Therapies based on inhibiting the toxins, bacterial structures responsible for colonization, virulence and restoration of the gut microbiota are the most important nonantibiotic targets to combat CDI. This report outlines these targets and how they could become the focus of future therapeutic agents. Inhibiting colonization and virulence factors during CDI will disrupt pathogen persistence and decrease exposure to the inflammatory toxins, allowing the immune system to clear the infection.

Clostridium difficile infection: Evolution, phylogeny and molecular epidemiology

Over the recent decades, Clostridium difficile infection (CDI) has emerged as a global public health threat. Despite growing attention, C. difficile remains a poorly understood pathogen, however, the exquisite sensitivity offered by next generation sequencing (NGS) technology has enabled analysis of the genome of C. difficile, giving us access to massive genomic data on factors such as virulence, evolution, and genetic relatedness within C. difficile groups. NGS has also demonstrated excellence in investigations of outbreaks and disease transmission, in both small and large-scale applications. This review summarizes the molecular epidemiology, evolution, and phylogeny of C. difficile, one of the most important pathogens worldwide in the current antibiotic resistance era.

A Clostridioides difficile bacteriophage genome encodes functional binary toxin-associated genes

Pathogenic clostridia typically produce toxins as virulence factors which cause severe diseases in both humans and animals. Whereas many clostridia like e.g., Clostridium perfringens, Clostridium botulinum or Clostridium tetani were shown to contain toxin-encoding plasmids, only toxin genes located on the chromosome were detected in Clostridioides difficile so far. In this study, we determined, annotated, and analyzed the complete genome of the bacteriophage phiSemix9P1 using single-molecule real-time sequencing technology (SMRT). To our knowledge, this represents the first C. difficile-associated bacteriophage genome that carries a complete functional binary toxin locus in its genome.

Evaluation of Xpert C. difficile, BD MAX Cdiff, IMDx C. difficile for Abbott m2000, and Illumigene C. difficile Assays for Direct Detection of Toxigenic Clostridium difficile in Stool Specimens

BACKGROUND

We evaluated the performance of four commercial nucleic acid amplification tests (NAATs: Xpert C. difficile, BD MAX Cdiff, IMDx C. difficile for Abbott m2000, and Illumigene C. difficile) for direct and rapid detection of Clostridium difficile toxin genes.

METHODS

We compared four NAATs on the same set of 339 stool specimens (303 prospective and 36 retrospective specimens) with toxigenic culture (TC).

RESULTS

Concordance rate among four NAATs was 90.3% (306/339). Based on TC results, the sensitivity and specificity were 90.0% and 92.9% for Xpert; 86.3% and 89.3% for Max; 84.3% and 94.4% for IMDx; and 82.4% and 93.7% for Illumigene, respectively. For 306 concordant cases, there were 11 TC-negative/NAATs co-positive cases and 6 TC-positive/NAATs co-negative cases. Among 33 discordant cases, 18 were only single positive in each NAAT (Xpert, 1; Max, 12; IMDx, 1; Illumigene, 4). Positivity rates of the four NAATs were associated with those of semi-quantitative cultures, which were maximized in grade 3 (>100 colony-forming unit [CFU]) compared with grade 1 (<10 CFU).

CONCLUSIONS

Commercial NAATs may be rapid and reliable methods for direct detection of tcdA and/or tcdB in stool specimens compared with TC. Some differences in the sensitivity of the NAATs may partly depend on the number of toxigenic C. difficile in stool specimens.

Host response to Clostridium difficile infection: Diagnostics and detection

Clostridium difficile infection (CDI) is a significant healthcare concern worldwide, and C. difficile is recognised as the most frequent aetiological agent of infectious healthcare-associated diarrhoea in hospitalised adult patients. The clinical manifestation of CDI varies from self-limited diarrhoea to life-threatening colitis. Such a broad disease spectrum can be explained by the impact of host factors. Currently, a complex CDI aetiology is widely accepted, acknowledging the interaction between bacteria and the host. C. difficile strains producing clostridial toxins A and B are considered toxigenic and can cause disease; those not producing the toxins are non-pathogenic. A person colonised with a toxigenic strain will not necessarily develop CDI. It is imperative to recognise patients with active disease from those only colonised with this pathogen and to implement appropriate treatment. This can be achieved by diagnostics that rely on host factors specific to CDI. This review will focus on major aspects of CDI pathogenesis and molecular mechanisms, describing host factors in disease progression and assessment of the host response in order to facilitate the development of CDI-specific diagnostics.

Accessory Gene Regulator-1 Locus Is Essential for Virulence and Pathogenesis of Clostridium difficile

Clostridium difficile infection (CDI) is responsible for most of the definable cases of antibiotic- and hospital-associated diarrhea worldwide and is a frequent cause of morbidity and mortality in older patients. C. difficile, a multidrug-resistant anaerobic pathogen, causes disease by producing toxins A and B, which are controlled by an accessory gene regulator (Agr) quorum signaling system. Some C. difficile strains encode two Agr loci in their genomes, designated agr1 and agr2 The agr1 locus is present in all of the C. difficile strains sequenced to date, whereas the agr2 locus is present in a few strains. The functional roles of agr1 and agr2 in C. difficile toxin regulation and pathogenesis were unknown until now. Using allelic exchange, we deleted components of both agr loci and examined the mutants for toxin production and virulence. The results showed that the agr1 mutant cannot produce toxins A and B; toxin production can be restored by complementation with wild-type agr1 Furthermore, the agr1 mutant is able to colonize but unable to cause disease in a murine CDI model. These findings have profound implications for CDI treatment because we have uncovered a promising therapeutic target for the development of nonantibiotic drugs to treat this life-threatening emerging pathogen by targeting the toxins directly responsible for disease.

IMPORTANCE

Within the last decade, the number of cases of C. difficile infections has been increasing exponentially in the United States, resulting in about 4.8 billion U.S. dollars in health care costs annually. As a multidrug-resistant, spore-forming, anaerobic pathogen, C. difficile overpopulates the colon after the gut microbiota has been altered by antibiotic therapy. With increasing resistance to antibiotic treatment of C. difficile infections, patients are experiencing higher costs of health care and a lower quality of life as treatment options decrease. During infection, C. difficile produces toxins A and B, which directly cause disease. As a result, the toxins have become promising nonantibiotic treatment targets. Here, we have identified a pathway responsible for activating the production of the toxins. This important finding opens up a unique therapeutic target for the development of a novel nonantibiotic therapy for C. difficile infections.

EGA Protects Mammalian Cells from Clostridium difficile CDT, Clostridium perfringens Iota Toxin and Clostridium botulinum C2 Toxin

The pathogenic bacteria Clostridium difficile, Clostridium perfringens and Clostridium botulinum produce the binary actin ADP-ribosylating toxins CDT, iota and C2, respectively. These toxins are composed of a transport component (B) and a separate enzyme component (A). When both components assemble on the surface of mammalian target cells, the B components mediate the entry of the A components via endosomes into the cytosol. Here, the A components ADP-ribosylate G-actin, resulting in depolymerization of F-actin, cell-rounding and eventually death. In the present study, we demonstrate that 4-bromobenzaldehyde N-(2,6-dimethylphenyl)semicarbazone (EGA), a compound that protects cells from multiple toxins and viruses, also protects different mammalian epithelial cells from all three binary actin ADP-ribosylating toxins. In contrast, EGA did not inhibit the intoxication of cells with Clostridium difficile toxins A and B, indicating a possible different entry route for this toxin. EGA does not affect either the binding of the C2 toxin to the cells surface or the enzyme activity of the A components of CDT, iota and C2, suggesting that this compound interferes with cellular uptake of the toxins. Moreover, for C2 toxin, we demonstrated that EGA inhibits the pH-dependent transport of the A component across cell membranes. EGA is not cytotoxic, and therefore, we propose it as a lead compound for the development of novel pharmacological inhibitors against clostridial binary actin ADP-ribosylating toxins.

Molecular Characterization of Clostridium difficile Isolates from Human Subjects and the Environment

Clostridium difficile is a spore-forming, gram-positive, anaerobic bacillus that can cause C. difficile infection (CDI). However, only a few studies on the prevalence and antibiotic resistance of C. difficile in healthy individuals in China have been reported. We employed a spore enrichment culture to screen for C. difficile in the stool samples of 3699 healthy Chinese individuals who were divided into 4 groups: infants younger than 2 years of age and living at home with their parents; children aged 1 to 8 years of age and attending three different kindergarten schools; community-dwelling healthy adult aged 23-60 years old; and healthcare workers aged 28-80 years old. The C. difficile isolates were analyzed for the presence of toxin genes and typed by PCR ribotyping and multilocus sequence typing (MLST). The minimum inhibitory concentration of 8 antimicrobial agents was determined for all of the isolates using the agar dilution method. The intestinal carriage rate in the healthy children was 13.6% and ranged from 0% to 21% depending on age. The carriage rates in the 1654 community-dwelling healthy adults and 348 healthcare workers were 5.5% and 6.3%, respectively. Among the isolates, 226 were toxigenic (225 tcdA+/tcdB+ and 1 tcdA+/tcdB+ ctdA+/ctdB+). Twenty-four ribotypes were found, with the dominant type accounting for 29.7% of the isolates. The toxigenic isolates were typed into 27 MLST genotypes. All of the strains were susceptible to vancomycin, metronidazole, fidaxomicin, and rifaximin. High resistance to levofloxacin and ciprofloxacin at rates of 39.8% and 98.3%, respectively, were observed. ST37 isolates were more resistant to levofloxacin than the other STs. The PCR ribotypes and sequence types from the healthy populations were similar to those from the adult patients.

Sensitive assays enable detection of serum IgG antibodies against Clostridium difficile toxin A and toxin B in healthy subjects and patients with Clostridium difficile infection

BACKGROUND

Pathogenic Clostridium difficile produces two proinflammatory exotoxins, toxin A and toxin B. Low level of serum antitoxin IgG antibodies is a risk factor for the development of primary and recurrent C. difficile infection (CDI).

RESULTS

We developed and validated two sensitive, titer-based electrochemiluminescence assays for the detection of serum antibody levels against C. difficile toxins A and B. These assays demonstrated excellent precision. The sensitivity of the assays allowed the detection of antitoxin A and antitoxin B IgG antibodies in all tested serum samples during assay validation.

CONCLUSION

The validated titer-based assays enable assessment of antitoxin A and antitoxin B IgG antibodies as potential biomarkers to identify patients with CDI at increased risk for CDI recurrence.

Analysis of TcdB Proteins within the Hypervirulent Clade 2 Reveals an Impact of RhoA Glucosylation on Clostridium difficile Proinflammatory Activities

Clostridium difficile strains within the hypervirulent clade 2 are responsible for nosocomial outbreaks worldwide. The increased pathogenic potential of these strains has been attributed to several factors but is still poorly understood. During a C. difficile outbreak, a strain from this clade was found to induce a variant cytopathic effect (CPE), different from the canonical arborizing CPE. This strain (NAP1V) belongs to the NAP1 genotype but to a ribotype different from the epidemic NAP1/RT027 strain. NAP1V and NAP1 share some properties, including the overproduction of toxins, the binary toxin, and mutations in tcdC. NAP1V is not resistant to fluoroquinolones, however. A comparative analysis of TcdB proteins from NAP1/RT027 and NAP1V strains indicated that both target Rac, Cdc42, Rap, and R-Ras but only the former glucosylates RhoA. Thus, TcdB from hypervirulent clade 2 strains possesses an extended substrate profile, and RhoA is crucial for the type of CPE induced. Sequence comparison and structural modeling revealed that TcdBNAP1 and TcdBNAP1V share the receptor-binding and autoprocessing activities but vary in the glucosyltransferase domain, consistent with the different substrate profile. Whereas the two toxins displayed identical cytotoxic potencies, TcdBNAP1 induced a stronger proinflammatory response than TcdBNAP1V as determined in ex vivo experiments and animal models. Since immune activation at the level of intestinal mucosa is a hallmark of C. difficile-induced infections, we propose that the panel of substrates targeted by TcdB is a determining factor in the pathogenesis of this pathogen and in the differential virulence potential seen among C. difficile strains.

Novel therapeutic strategies for Clostridium difficile infections

INTRODUCTION

In recent years, Clostridium difficile has become the primary cause of antibiotic-associated diarrhea and pseudomembranous colitis, resulting in long and complicated hospital stays that represent a serious burden for patients as well as health care systems. Currently, conservative treatment of C. difficile infection (CDI) relies on the antibiotics vancomycin, metronidazole or fidaxomicin, or in case of multiple recurrences, fecal microbiota transplantation (FMT).

AREAS COVERED

The fast-spreading, epidemic nature of this pathogen urgently necessitates the search for alternative treatment strategies as well as antibiotic targets. Accordingly, in this review, we highlight the recent findings regarding virulence associated traits of C. difficile, evaluate their potential as alternative drug targets, and present current efforts in designing inhibitory compounds, with the aim of pointing out possibilities for future treatment strategies.

EXPERT OPINION

Increased attention on systematic analysis of the virulence mechanisms of C. difficile has already led to the identification of several alternative drug targets. In the future, applying state of the art 'omics' and the development of novel infection models that mimic the human gut, a highly complex ecological niche, will unveil the genomic and metabolic plasticity of this pathogen and will certainly help dealing with future challenges.

An Update on Clostridium difficile Toxinotyping

Toxinotyping is a PCR-restriction fragment length polymorphism (RFLP)-based method for differentiation of Clostridium difficile strains according to the changes in the pathogenicity locus (PaLoc), a region coding for toxins A and B. Toxinotypes are a heterogenous group of strains that are important in the development of molecular diagnostic tests and vaccines and are a good basis for C. difficile phylogenetic studies. Here we describe an overview of the 34 currently known toxinotypes (I to XXXIV) and some changes in nomenclature.

Clostridium difficile-associated intestinal diseases

Clostridium difficile (CD), as one of the normal flora in human and animal intestine, is a Gram-positive anaerobic bacillus. It could cause opportunistic infections, resulting in CD-associated diarrhea, CD-associated colitis and other intestinal diseases. There have ever been massive epidemics of CD infection in both China and other countries, and it has became a global public health problem. The main pathogenic toxins of CD are toxin A, toxin B and newly discovered binary toxins (CDT). For CD infection prevention and treatment, the reasonable use of new antimicrobial drugs, traditional Chinese medicine, probiotics, CD vaccine and other clinical treatments can be adopted.

Multiplex Real-Time PCR Method for Simultaneous Identification and Toxigenic Type Characterization of Clostridium difficile From Stool Samples

Background

The aim of this study was to develop and validate a multiplex real-time PCR assay for simultaneous identification and toxigenic type characterization of Clostridium difficile.

Methods

The multiplex real-time PCR assay targeted and simultaneously detected triose phosphate isomerase (tpi) and binary toxin (cdtA) genes, and toxin A (tcdA) and B (tcdB) genes in the first and sec tubes, respectively. The results of multiplex real-time PCR were compared to those of the BD GeneOhm Cdiff assay, targeting the tcdB gene alone. The toxigenic culture was used as the reference, where toxin genes were detected by multiplex real-time PCR.

Results

A total of 351 stool samples from consecutive patients were included in the study. Fifty-five stool samples (15.6%) were determined to be positive for the presence of C. difficile by using multiplex real-time PCR. Of these, 48 (87.2%) were toxigenic (46 tcdA and tcdB-positive, two positive for only tcdB) and 11 (22.9%) were cdtA-positive. The sensitivity, specificity, negative predictive value (NPV), and positive predictive value (PPV) of the multiplex real-time PCR compared with the toxigenic culture were 95.6%, 98.6%, 91.6%, and 99.3%, respectively. The analytical sensitivity of the multiplex real-time PCR assay was determined to be 103colonyforming unit (CFU)/g spiked stool sample and 0.0625 pg genomic DNA from culture. Analytical specificity determined by using 15 enteric and non-clostridial reference strains was 100%.

Conclusions

The multiplex real-time PCR assay accurately detected C. difficile isolates from diarrheal stool samples and characterized its toxin genes in a single PCR run.

Toxin synthesis by Clostridium difficile is regulated through quorum signaling

Clostridium difficile infection (CDI) is dramatically increasing as a cause of antibiotic- and hospital-associated diarrhea worldwide. C. difficile, a multidrug-resistant pathogen, flourishes in the colon after the gut microbiota has been altered by antibiotic therapy. Consequently, it produces toxins A and B that directly cause disease. Despite the enormous public health problem posed by this pathogen, the molecular mechanisms that regulate production of the toxins, which are directly responsible for disease, remained largely unknown until now. Here, we show that C. difficile toxin synthesis is regulated by an accessory gene regulator quorum-signaling system, which is mediated through a small (<1,000-Da) thiolactone that can be detected directly in stools of CDI patients. These findings provide direct evidence of the mechanism of regulation of C. difficile toxin synthesis and offer exciting new avenues both for rapid detection of C. difficile infection and development of quorum-signaling-based non-antibiotic therapies to combat this life-threatening emerging pathogen.

IMPORTANCE

Clostridium difficile infection (CDI) is the most common definable cause of hospital-acquired and antibiotic-associated diarrhea in the United States, with the total cost of treatment estimated between 1 and 4.8 billion U.S. dollars annually. C. difficile, a Gram-positive, spore-forming anaerobe, flourishes in the colon after the gut microbiota has been altered by antibiotic therapy. As a result, there is an urgent need for non-antibiotic CDI treatments that preserve the colonic microbiota. C. difficile produces toxins A and B, which are directly responsible for disease. Here, we report that C. difficile regulates its toxin synthesis by quorum signaling, in which a novel signaling peptide activates transcription of the disease-causing toxin genes. This finding provides new therapeutic targets to be harnessed for novel nonantibiotic therapy for C. difficile infections.

Prevalence and characterization of enterotoxigenic Bacteroides fragilis and toxigenic Clostridium difficile in a Taipei emergency department

BACKGROUND/PURPOSE

Enterotoxigenic Bacteroides fragilis (ETBF) and toxin-encoding Clostridium difficile (TXCD) are associated with gastroenteritis. Routine anaerobic blood culture for recovery of these anaerobic pathogens is not used for the detection of their toxins, especially for toxin-variant TXCD. The aim of this study was to investigate the prevalence and risk factors of the genotypes of these anaerobes in patients with acute diarrheal illnesses.

METHODS

The data and samples of 513 patients with gastroenteritis were collected in a Taipei emergency department from March 1, 2006 to December 31, 2009. Nonenterotoxigenic B. fragilis (NTBF) and ETBF and the toxin genotypes of TXCD were detected by molecular methods.

RESULTS

The prevalence rates of NTBF, ETBF, and TXCD infections were 33.14%, 1.56%, and 2.34%, respectively. ETBF infections often occurred in the elderly (average age = 67.13 years) and during the cold, dry winters. TXCD infections were widely distributed in age and often occurred in the warm, wet springs and summers. The symptoms of ETBF-infected patients were significantly more severe than those of NTBF-infected patients.

CONCLUSION

This study identified and analyzed the prevalence, risk factors, and clinical presentations of these anaerobic infections. Future epidemiologic and clinical studies are needed to understand the role of ETBF and TXCD in human gastroenteritis.

Investigation of toxin gene diversity and antimicrobial resistance of Clostridium difficile strains

The incidence of Clostridium difficile infection (CDI) has been previously reported in a number of studies. However, data collected from the Chinese population is limited. In the present study, the diversity of the toxin genes, tcdA and tcdB, of 57 Clostridium difficile (C. difficile) isolates from a Chinese population were investigated by polymerase chain reaction (PCR) (38 A⁺B⁺, 14 A^-B⁺ and 5 A^-B^-). Quantitative PCR was used to check the expression of these two genes and it was found that the genes were not expressed by all the strains. The absence of tcdA or tcdB expression in certain strains could be due to the lower expression of tcdD and the higher expression of tcdC, which are positive and negative regulators for these two toxin genes, respectively. In addition, the antimicrobial susceptibilities of 57 isolates were investigated. Therefore, these data would aid in the future prevention of CDI outbreaks and improve the understanding of the infection.

Cyclophilin-facilitated membrane translocation as pharmacological target to prevent intoxication of mammalian cells by binary clostridial actin ADP-ribosylated toxins

Clostridium botulinum C2 toxin, Clostridium perfringens iota toxin and Clostridium difficile CDT belong to the family of binary actin ADP-ribosylating toxins and are composed of a binding/translocation component and a separate enzyme component. The enzyme components ADP-ribosylate G-actin in the cytosol of target cells resulting in depolymerization of F-actin, cell rounding and cell death. The binding/translocation components bind to their cell receptors and form complexes with the respective enzyme components. After receptor-mediated endocytosis, the binding/translocation components form pores in membranes of acidified endosomes and the enzyme components translocate through these pores into the cytosol. This step is facilitated by the host cell chaperone heat shock protein 90 and peptidyl-prolyl cis/trans isomerases including cyclophilin A. Here, we demonstrate that a large isoform of cyclophilin A, the multi-domain enzyme cyclophilin 40 (Cyp40), binds to the enzyme components C2I, Ia and CDTa in vitro. Isothermal titration calorimetry revealed a direct binding to C2I with a calculated affinity of 101 nM and to Ia with an affinity of 1.01 μM. Closer investigation for the prototypic C2I revealed that binding to Cyp40 did not depend on its ADP-ribosyltransferase activity but was stronger for unfolded C2I. The interaction of C2I with Cyp40 was also demonstrated in lysates from C2-treated cells by pull-down. Treatment of cells with a non-immunosuppressive cyclosporine A derivative, which still binds to and inhibits the peptidyl-prolyl cis/trans isomerase activity of cyclophilins, protected cells from intoxication with C2, iota and CDT toxins, offering an attractive approach for development of novel therapeutic strategies against binary actin ADP-ribosylating toxins.

Tailored cyclodextrin pore blocker protects mammalian cells from clostridium difficile binary toxin CDT

Some Clostridium difficile strains produce, in addition to toxins A and B, the binary toxin Clostridium difficile transferase (CDT), which ADP-ribosylates actin and may contribute to the hypervirulence of these strains. The separate binding and translocation component CDTb mediates transport of the enzyme component CDTa into mammalian target cells. CDTb binds to its receptor on the cell surface, CDTa assembles and CDTb/CDTa complexes are internalised. In acidic endosomes, CDTb mediates the delivery of CDTa into the cytosol, most likely by forming a translocation pore in endosomal membranes. We demonstrate that a seven-fold symmetrical positively charged β-cyclodextrin derivative, per-6-S-(3-aminomethyl)benzylthio-β-cyclodextrin, which was developed earlier as a potent inhibitor of the translocation pores of related binary toxins of Bacillus anthracis, Clostridium botulinum and Clostridium perfringens, protects cells from intoxication with CDT. The pore blocker did not interfere with the CDTa-catalyzed ADP-ribosylation of actin or toxin binding to Vero cells but inhibited the pH-dependent membrane translocation of CDTa into the cytosol. In conclusion, the cationic β-cyclodextrin could serve as the lead compound in a development of novel pharmacological strategies against the CDT-producing strains of C. difficile.

Protein expression, characterization, crystallization and preliminary X-ray crystallographic analysis of a Fic protein from Clostridium difficile

Fic domains in proteins are found in abundance in nature from the simplest prokaryotes to animals. Interestingly, Fic domains found in two virulence factors of Gram-negative bacteria have recently been demonstrated to catalyse the transfer of the AMP moiety from ATP to small host GTPases. This post-translational modification has attracted considerable interest and a role for adenylylation in pathology and physiology is emerging. This work was aimed at the structural characterization of a newly identified Fic protein of the Gram-positive bacterium Clostridium difficile. A constitutively active inhibitory helix mutant of C. difficile Fic was overexpressed in Escherichia coli, purified and crystallized by the vapour-diffusion technique. Preliminary X-ray crystallographic analysis shows that the crystals diffract to at least 1.68 Å resolution at a synchrotron X-ray source. The crystals belonged to the orthorhombic space group P2₁2₁2₁, with unit-cell parameters a=45.6, b=80.8, c=144.7 Å, α=β=γ=90°. Two molecules per asymmetric unit corresponds to a Matthews coefficient of 2.37 Å3 Da(-1) and a solvent content of 48%.

Comparison of polymerase chain reaction ribotyping, toxinotyping and nutritional aspects of toxin production of Clostridium difficile strains

Clostridium difficile (C. difficile) is the leading cause of infectious diarrhea in hospitals worldwide. Enterotoxin A (TcdA) and cytotoxin B (TcdB), have been identified as the main virulence factors of C. difficile. In China, data on polymerase chain reaction (PCR) ribotypes and abilities of hospital-derived C. difficile isolates to produce TcdA and TcdB are sparse. In this study, we identified 40 C. difficile isolates from the Taizhou hospital and investigated their PCR ribotypes based on the 16S-23S rRNA gene intergenic spacer region. The ability of different ribotypes to produce TcdA and TcdB was determined by immunochromatography and cytotoxicity assays, respectively. The effects of the nutritional status on the production of these toxins were also investigated.

Vaccines against Clostridium difficile

Clostridium difficile infection (CDI) is recognized as a major cause of nosocomial diseases ranging from antibiotic related diarrhea to fulminant colitis. Emergence during the last 2 decades of C. difficile strains associated with high incidence, severity and lethal outcomes has increased the challenges for CDI treatment. A limited number of drugs have proven to be effective against CDI and concerns about antibiotic resistance as well as recurring disease solicited the search for novel therapeutic strategies. Active vaccination provides the attractive opportunity to prevent CDI, and intense research in recent years led to development of experimental vaccines, 3 of which are currently under clinical evaluation. This review summarizes recent achievements and remaining challenges in the field of C. difficile vaccines, and discusses future perspectives in view of newly-identified candidate antigens.

Bacterial enteric infections in children: etiology, clinical manifestations and antimicrobial therapy

Bacterial enteric infections have a huge impact on human health, particularly among the pediatric population. Despite the explosion of knowledge of the pathogenesis of bacterial enteric infections experienced in the past decade, the number of diarrheal episodes and childhood deaths reported continues to increase in many areas of the world. Specific antimicrobial therapy is indicated for certain confirmed infections, notably shigellosis, enterotoxigenic and enteroinvasive Escherichia coli infections, typhoid fever and cholera. Antimicrobial therapy may have a role in severe and prolonged gastrointestinal illness caused by nontyphoid Salmonella and Campylobacter. However, the use of antimicrobial agents may increase the risk of hemolytic uremic syndrome in children with E. coli O157:H7 infection. Bacterial genome sequencing and better understanding of the pathogenic mechanisms involved in the onset of diarrhea are leading to new preventive interventions, such as enteric vaccines, which may have a significant impact on the magnitude of this human plague.