Binary toxin producing Clostridium difficile strains

Clostridium difficile produces three toxins, TcdA, TcdB and CDT. TcdA and TcdB are single-stranded molecules acting as glucosyltransferases specific for small GTPases. CDT is an actin specific ADP-ribosylating binary toxin characteristically composed of two independent components, enzymatic CDTa (48 kDa) and binding CDTb (99 kDa). The cdtA and cdtB genes were sequenced in two CDT-positive strains of C. difficile (CD 196 and 8864) and at least two CDT-negative strains with truncated form of binary toxin genes are known (VPI 10463 and C. difficile genome strain 630). The prevalence of binary toxin producing strains is estimated to be from 1.6% to 5.5%, although a much higher proportion has been reported in some studies. The role of the binary toxin as an additional virulence factor is discussed.     

Analysis of prevalence, risk factors and molecular epidemiology of Clostridium difficile infection in Kuwait over a 3-year period

We conducted a prospective study to evaluate the prevalence and epidemiology of CDI in Kuwait government hospitals over a 3-year period, January 2003 to December 2005, to determine the ribotypes responsible for CDI and to estimate the prevalence of ribotype 027. We also conducted a case-control study to identify the risk factors in our patient population. A total of 697 stool samples from patients with suspected CDI were obtained and sent to Anaerobe Reference Laboratory, Faculty of Medicine, Kuwait University for Clostridium difficile toxin detection, culture and PCR ribotyping. During the period, 73 (10.5%) out of 697 patients met the case definition of CDI. Of these, 56 (76.7%) were hospital-acquired and 17 (23.3%) were from outpatient clinics. Thus, the prevalence of hospital-acquired CDI amongst patients with diarrhoea was 8% over the study period; the prevalence in 2003, 2004 and 2005 was 9.7%, 7.8% and 7.2%, respectively. Our data showed that 42.9% of the CDI patients were above 60 years, of which >79% were aged 71 years and above. Patients with CDI were more likely than the controls to have been exposed to immunosuppressive drugs and feeding via nasogastric tube. The most common ribotypes isolated during this study were 002, 001, 126 and 140 and they represent 55.1% of all isolates. PCR ribotype 027 was not isolated.     

p-Cresol formation by cell-free extracts of Clostridium difficile

Cell-free extracts of Clostridium difficile were shown to form p-cresol by decarboxylation of p-hydroxyphenylacetic acid. This activity required both high and low molecular weight fractions. The active component of the low molecular weight fraction had properties of an amino acid and could be replaced by serine, threonine or the corresponding alpha keto acids. Pyruvate was shown to function catalytically. Since the high molecular weight fraction was O₂-sensitive and since dithionite was as effective as pyruvate with some high molecular weight fractions, the alpha keto acids probably serve as low potential reducing agents in this system. Because of instability, the p-cresolforming enzyme could not be purified.     

Sporulation studies in Clostridium difficile

Clostridium difficile is a leading cause of healthcare-associated diarrhoea. In recent years, certain C. difficile types have become highly represented among clinical isolates and are associated with outbreaks of increased disease severity, higher relapse rates and an expanded repertoire of antibiotic resistance. Endospores, produced during sporulation, play a pivotal role in infection and disease transmission and it has been suggested in the literature that these so-called ‘hypervirulent’ C. difficile types are more prolific in terms of sporulation in vitro. However, work in our laboratory has provided evidence to the contrary suggesting that although there is significant strain-to-strain variation in C. difficile sporulation characteristics this variation does not appear to be type-associated. On analysis of the literature, it is apparent that the methods used to quantify sporulation in previous studies have varied greatly and sample sizes have remained small. The conflicting data in the literature may, therefore, not necessarily be generally representative of C. difficile sporulation. Instead, these inconsistencies may reflect differences in the experimental design of each study. In this review, the need for further investigations of C. difficile sporulation rates is highlighted. Specifically, the advantages and disadvantages of the different experimental approaches previously used are discussed and a standard set of principles for measuring C. difficile sporulation in the future is proposed.     

Efficient expression and purification of methyltransferase in acetyl-coenzyme a synthesis pathway of the human pathogen Clostridium difficile

The Wood-Ljungdahl pathway is responsible for acetyl-CoA biosynthesis and used as a major mean of generating energy for growth in some anaerobic microbes. Series of genes, from the anaerobic human pathogen Clostridium difficile, have been identified that show striking similarity to the genes involved in this pathway including methyltetrahydrofolate- and corrinoid-dependent methyltransferase. This methyltransferase plays a central role in this pathway that transfers the methyl group from methyltetrahydrofolate to a cob(I)amide center in the corrinoid iron-sulfur protein. In this study, we developed two efficient expression and purification methods for methyltransferase from C. difficile for the first time with two expression vectors MBPHT-mCherry2 and pETDuet-1, respectively. Using the latter vector, more than 50mg MeTr was produced per liter Luria-Bertani broth media. The recombinant methyltransferase was well characterized by SDS-PAGE, gel filtration chromatography, enzyme assay and far-UV circular dichroism (CD). Furthermore, a highly effective approach was established for determining the methyl transfer activity of the methyltetrahydrofolate- and cobalamin-dependent methyltransferase using exogenous cobalamin as a substrate by stopped-flow method. These results will provide a solid basis for further study of the methyltransferase and the Wood-Ljungdahl pathway.     

Molecular cloning, overexpression in Escherichia coli, and purification of 6x his-tagged C-terminal domain of Clostridium difficile toxins A and B

Genomic DNA from ribotype-01 and -17 Clostridium difficile strains was used for amplification of the sequences encoding the carboxy-terminal domain of toxins A (TcdA) and B (TcdB). The deduced C-terminal TcdB ribotype-01 and -17 domains share 99.5% amino acid sequence identity while TcdA ribotype-17 comprises a 607 amino acid deletion compared to TcdA-01. When compared to previously sequenced C. difficile toxins, 99.3% amino acid identity was found between TcdA-01 and TcdA from strain VPI10643 and 98.8% identity between TcdA-17 and TcdA from strain F-1470. The obtained sequences were fused in 3' to a sequence encoding a hexahistidine tag and cloned into an Escherichia coli expression vector. The recombinant proteins were expressed in E. coli and purified using single-step metal-chelate chromatography. The recombinant carboxy-terminal domain of TcdA-01 was purified from the soluble E. coli lysate fraction whereas TcdA-17 and TcdB-17 carboxy-terminal domains were purified from inclusion bodies. At least 40 mg of each protein was purified per liter of bacterial culture. The recombinant toxin domains were detected specifically by Western blot and ELISA with antibodies against native C. difficile toxins. This study demonstrated that the carboxy-terminal domains of TcdA and TcdB can be produced using an E. coli expression system and easily purified. These recombinant, stable, and non-toxic proteins provide a convenient source for use in the diagnosis of C. difficile infections, instead of native toxins, as controls and calibrators in immunoassay kits and to obtain specific monoclonal antibodies.     

Adaptation of Clostridium difficile toxin A for use as a protein translocation system

A cellular delivery system is a useful biotechnology tool, with many possible applications. Two derivatives of Clostridium difficile toxin A (TcdA) have been constructed (GFP-TcdA and Luc-TcdA), by fusing reporter genes to functional domains of TcdA, and evaluated for their ability to translocate their cargo into mammalian cells. The cysteine protease and receptor binding domains of TcdA have been examined and found to be functional when expressed in the chimeric construct. Whereas GFP failed to internalize in the context of the TcdA fusion, significant cellular luciferase activity was detected in vero cell lysates after treatment with Luc-TcdA. Treatment with bafilomycin A1, which inhibits endosomal acidification, traps the luciferase activity within endosomes. To further understand these results, clarified lysates were subjected to molecular weight sieving, demonstrating that active luciferase was released from Luc-TcdA after translocation and internal processing.     

The diverse sporulation characteristics of Clostridium difficile clinical isolates are not associated with type

Clostridium difficile causes diarrhoeal diseases ranging from asymptomatic carriage to a fulminant, relapsing, and potentially fatal colitis. Endospore production plays a vital role in transmission of infection, and in order to cause disease these spores must then germinate and return to vegetative cell growth. Type BI/NAP1/027 strains of C. difficile have recently become highly represented among clinical isolates and are associated with increased disease severity. It has also been suggested that these 'epidemic' types generally sporulate more prolifically than 'non-epidemic' strains, although the few existing reports are inconclusive and encompass only a small number of isolates. In order to better understand any differences in sporulation rates between epidemic and non-epidemic C. difficile types, we analysed these characteristics using 14 C. difficile clinical isolates of a variety of types. Sporulation rates varied greatly between individual BI/NAP1/027 isolates, but this variation did not appear to be type-associated. Furthermore, a number of BI/NAP1/027 spores appeared to form colonies with a lower frequency than specific non-BI/NAP1/027 strains. The data suggest that (i) careful experimental design is required in order to accurately quantify sporulation; and (ii) current evidence cannot link differences in sporulation rates with the disease severity of the BI/NAP1/027 type.     

Cellular stability of Rho-GTPases glucosylated by Clostridium difficile toxin B

Mono-glucosylation of Rho, Rac, and Cdc42 by Clostridium difficile toxin B (TcdB) induces changes of actin dynamics and apoptosis. When fibroblasts were treated with TcdB, an apparent decrease of the cellular Rac1 level was observed when applying anti-Rac1(Mab 102). This decrease was not based on degradation as inhibition of the proteasome by lactacystin did not stabilise cellular Rac1 levels. The application of anti-Rac1 (Mab 23A8) showed that the cellular Rac1 level slightly increased in TcdB-treated fibroblasts; thus, the apparent loss of cellular Rac1 was not due to degradation but due to impaired recognition of glucosylated Rac1 by anti-Rac1 (Mab 102). In contrast, recognition of RhoA by anti-RhoA (Mab 26C4) and Cdc42 by anti-Cdc42 (Mab 44) was not altered by glucosylation; a transient decrease of cellular RhoA and Cdc42 in TcdB-treated fibroblasts was indeed due to proteasomal degradation, as inhibition of the proteasome by lactacystin stabilised both cellular RhoA and Cdc42 levels. The finding that the apparent decrease of Rac1 reflects Rac1 glucosylation offers a valuable tool to determine Rac1 glucosylation.     

Polymorphisms in grapevine DNA detected by the RAPD PCR technique

A sensitivie, reproducible technique is described for detecting polymorphisms between the nuclear DNA of grapevine isolates using the RAPD PCR technique. Unique fingerprints of a number of cultivars were readily distinguished by using either single primers or mixtures of two primers. The method will be used to provide a databank of fingerprints for the rapid identification of grapevine cultivars, and to develop phylogenetic relationships. It will also be extended and modified in an attempt to detect polymorphisms between DNAs of clonal selections of individual cultivars.     

Isolation and characterization of a strictly anaerobic,cellulolytic spore former: Clostridium chartatabidum sp. nov.

Cellulolytic, strictly anaerobic spore-forming bacteria were isolated from chloroform treated rumen contents. They were different from previously described cellulolytic rumen clostridia in several characteristics. They formed subterminal rod-shaped spores approximately 0.7 m by 3.5 m. In broth cultures the growth rate was maximal at 39°C and after log growth extensive autolysis occurred. Fermentation products consisted of acetate, butyrate, hydrogen and ethanol. The GC content was 31%.     

Structural determinants of Clostridium difficile toxin A glucosyltransferase activity

The principle virulence factors in Clostridium difficile pathogenesis are TcdA and TcdB, homologous glucosyltransferases capable of inactivating small GTPases within the host cell. We present crystal structures of the TcdA glucosyltransferase domain in the presence and absence of the co-substrate UDP-glucose. Although the enzymatic core is similar to that of TcdB, the proposed GTPase-binding surface differs significantly. We show that TcdA is comparable with TcdB in its modification of Rho family substrates and that, unlike TcdB, TcdA is also capable of modifying Rap family GTPases both in vitro and in cells. The glucosyltransferase activities of both toxins are reduced in the context of the holotoxin but can be restored with autoproteolytic activation and glucosyltransferase domain release. These studies highlight the importance of cellular activation in determining the array of substrates available to the toxins once delivered into the cell.     

Clostridium difficile Hfq can replace Escherichia coli Hfq for most of its function

A gene for the Hfq protein is present in the majority of sequenced bacterial genomes. Its characteristic hexameric ring-like core structure is formed by the highly conserved N-terminal regions. In contrast, the C-terminal forms an extension, which varies in length, lacks homology, and is predicted to be unstructured. In Gram-negative bacteria, Hfq facilitates the pairing of sRNAs with their mRNA target and thus affects gene expression, either positively or negatively, and modulates sRNA degradation. In Gram-positive bacteria, its role is still poorly characterized. Numerous sRNAs have been detected in many Gram-positive bacteria, but it is not yet known whether these sRNAs act in association with Hfq. Compared with all other Hfqs, the C. difficile Hfq exhibits an unusual C-terminal sequence with 75% asparagine and glutamine residues, while the N-terminal core part is more conserved. To gain insight into the functionality of the C. difficile Hfq (Cd-Hfq) protein in processes regulated by sRNAs, we have tested the ability of Cd-Hfq to fulfill the functions of the E. coli Hfq (Ec-Hfq) by examining various functions associated with Hfq in both positive and negative controls of gene expression. We found that Cd-Hfq substitutes for most but not all of the tested functions of the Ec-Hfq protein. We also investigated the role of the C-terminal part of the Hfq proteins. We found that the C-terminal part of both Ec-Hfq and Cd-Hfq is not essential but contributes to some functions of both the E. coli and C. difficile chaperons.     

Influence of Culture Parameters on Biological Hydrogen Production by Clostridium saccharoperbutylacetonicum ATCC 27021

Summary Various medium components (carbon and nitrogen sources, iron, inoculum size) and environmental factors (initial pH and the agitation speed) were evaluated for their effects on the rate and the yield of hydrogen production by Clostridium saccharoperbutylacetonicum. Among the carbon sources assessed, cells grown on disaccharides (lactose, sucrose and maltose) produced on the average more than twice (2.81 mol-H2/mol sugar) as much hydrogen as monosaccharides (1.29 mol-H2/mol sugar), but there was no correlation between the carbon source and the production rate. The highest yield (2.83 mol/mol) was obtained in lactose and sucrose but the highest production rate (1.75 mmol/h) in sucrose. Using glucose as carbon source, yeast extract was the best nitrogen source. A parallel increase between the production rate and the yield was obtained by increasing glucose concentration up to 40 g/l (1.76 mol-H2/mol, 3.39 mmol/h), total nitrogen as yeast extract up to 0.1% (1.41 mol/mol, 1.91 mmol/h) and agitation up to 100 rev/min (1.66 mol-H2/mol, 1.86 mmol/h). On the other hand, higher production rates were favoured in preference to the yield at a neutral initial pH 7 (2.27 mmol/h), 1000 mg iron/l or more (1.99 mmol/h), and a larger inoculum size, 10%, (2.36 mmol/h) whereas an initial alkaline pH of 8.5 (1.72 mol/mol), a lower iron concentration of 25 mg/l (1.74 mol/mol) and smaller inoculum size, 1%, (1.85 mol/mol) promoted higher yield over production rate.     

Characterization of Clostridium sp. RKD producing botulinum-like neurotoxin

A Gram positive, motile, rod-shaped, strictly anaerobic bacterium isolated from intestine of decaying fish was identified as Clostridium sp. RKD and produced a botulinum type B-like neurotoxin as suggested by mouse bioassay and protection with anti botulinum antibodies. The neurotoxicity was functionally characterized by the phrenic nerve hemi-diaphragm assay. Phylogenetic analysis based on 16S rDNA sequence, placed it at a different position from the reported strains of Clostridium botulinum. The strain exhibited differences from both Clostridium botulinum and Clostridium tetani with respect to morphological, biochemical and chemotaxonomic characteristics. Botulinum group specific and serotype specific primers amplified the DNA fragments of 260 and 727 bp, respectively, indicating presence of botulinum type 'B' toxin gene. Sequence of nearly 700 bp amplified using primers specific for botulinum neurotoxin type B gene, did not show any significant match in the database when subjected to BLAST search.     

Reset of a critically disturbed microbial ecosystem: faecal transplant in recurrent Clostridium difficile infection

Recurrent Clostridium difficile infection (CDI) can be effectively treated by infusion of a healthy donor faeces suspension. However, it is unclear what factors determine treatment efficacy. By using a phylogenetic microarray platform, we assessed composition, diversity and dynamics of faecal microbiota before, after and during follow-up of the transplantation from a healthy donor to different patients, to elucidate the mechanism of action of faecal infusion. Global composition and network analysis of the microbiota was performed in faecal samples from nine patients with recurrent CDI. Analyses were performed before and after duodenal donor faeces infusion, and during a follow-up of 10 weeks. The microbiota data were compared with that of the healthy donors. All patients successfully recovered. Their intestinal microbiota changed from a low-diversity diseased state, dominated by Proteobacteria and Bacilli, to a more diverse ecosystem resembling that of healthy donors, dominated by Bacteroidetes and Clostridium groups, including butyrate-producing bacteria. We identified specific multi-species networks and signature microbial groups that were either depleted or restored as a result of the treatment. The changes persisted over time. Comprehensive and deep analyses of the microbiota of patients before and after treatment exposed a therapeutic reset from a diseased state towards a healthy profile. The identification of microbial groups that constitute a niche for C. difficile overgrowth, as well as those driving the reinstallation of a healthy intestinal microbiota, could contribute to the development of biomarkers predicting recurrence and treatment outcome, identifying an optimal microbiota composition that could lead to targeted treatment strategies.     

Changes in the cell wall of Clostridium species following passage in animals

Morphological changes in clostridial isolates after animal passage with other flora in mixed infections were studied by utilizing a subcutaneous abscess model in mice. We used 26 isolates of 7 clostridial species, and one isolate each of Bacteroides fragilis and Klebsiella pneumoniae. Abscesses were induced by all 7 Clostridium perfringens and 3 Clostridium butyricum isolates and by some of the other isolates. A thick granular wall prior to animal inoculation was shown only in C. perfringens, C. butyricum, and C. difficile. This structure was observed in other clostridia only following their animal passage alone or when co-inoculated with K. pneumoniae or B. fragilis.     

Peptide antibiotic and actin-binding protein as mixed-type inhibitors of Clostridium difficile CDT toxin activities

CDT from Clostridium difficile is an ADP-ribosyltransferase that causes rapid actin disaggregation and cell death. For efficient catalysis, CDT required specific divalent cations and binding by NAD which can be substituted by ATP but not ADP. Increasing isolation of CDT-producing strains prompted our search for antagonists like the anti-C. difficile agents bacitracin and vancomycin which were effective CDT inhibitors. Other CDT transferase and glycohydrolase inhibitors with consistently low IC50 values were heterocyclic peptide antibiotics containing modified amino acids such as polymyxin B and beta-lactam cephalosporins. The strongest inhibitors were actin-binding proteins which possess extensive interfaces with G-actin, adjoining the CDT-ADP-ribose+ acceptor site and nucleotide cleft. Analysis of the extent and mode of inhibition and actin interaction sites provided fresh evidences on the designation of actin interface domains with actin-binding proteins. Our results uphold ADP-ribosylation as an innate physiologic process in cellular cytoskeletal reorganization regulated by endogenous metabolites.