Detection of capsule in strains of Clostridium difficile of varying virulence and toxigenicity

Clostridioides difficile 630Δerm in silico and in vivo - quantitative growth and extensive polysaccharide secretion

Antibiotic-associated infections with Clostridioides difficile are a severe and often lethal risk for hospitalized patients, and can also affect populations without these classical risk factors. For a rational design of therapeutical concepts, a better knowledge of the metabolism of the pathogen is crucial. Metabolic modeling can provide a simulation of quantitative growth and usage of metabolic pathways, leading to a deeper understanding of the organism. Here, we present an elaborate genome-scale metabolic model of C. difficile 630Δerm. The model iHD992 includes experimentally determined product and substrate uptake rates and is able to simulate the energy metabolism and quantitative growth of C. difficile. Dynamic flux balance analysis was used for time-resolved simulations of the quantitative growth in two different media. The model predicts oxidative Stickland reactions and glucose degradation as main sources of energy, while the resulting reduction potential is mostly used for acetogenesis via the Wood-Ljungdahl pathway. Initial modeling experiments did not reproduce the observed growth behavior before the production of large quantities of a previously unknown polysaccharide was detected. Combined genome analysis and laboratory experiments indicated that the polysaccharide is an acetylated glucose polymer. Time-resolved simulations showed that polysaccharide secretion was coupled to growth even during unstable glucose uptake in minimal medium. This is accomplished by metabolic shifts between active glycolysis and gluconeogenesis which were also observed in laboratory experiments.

A Clostridium difficile Cell Wall Glycopolymer Locus Influences Bacterial Shape, Polysaccharide Production and Virulence

Clostridium difficile is a diarrheagenic pathogen associated with significant mortality and morbidity. While its glucosylating toxins are primary virulence determinants, there is increasing appreciation of important roles for non-toxin factors in C. difficile pathogenesis. Cell wall glycopolymers (CWGs) influence the virulence of various pathogens. Five C. difficile CWGs, including PSII, have been structurally characterized, but their biosynthesis and significance in C. difficile infection is unknown. We explored the contribution of a conserved CWG locus to C. difficile cell-surface integrity and virulence. Attempts at disrupting multiple genes in the locus, including one encoding a predicted CWG exporter mviN, were unsuccessful, suggesting essentiality of the respective gene products. However, antisense RNA-mediated mviN downregulation resulted in slight morphology defects, retarded growth, and decreased surface PSII deposition. Two other genes, lcpA and lcpB, with putative roles in CWG anchoring, could be disrupted by insertional inactivation. lcpA^- and lcpB^- mutants had distinct phenotypes, implying non-redundant roles for the respective proteins. The lcpB^- mutant was defective in surface PSII deposition and shedding, and exhibited a remodeled cell surface characterized by elongated and helical morphology, aberrantly-localized cell septae, and an altered surface-anchored protein profile. Both lcpA^- and lcpB^- strains also displayed heightened virulence in a hamster model of C. difficile disease. We propose that gene products of the C. difficile CWG locus are essential, that they direct the production/assembly of key antigenic surface polysaccharides, and thereby have complex roles in virulence.

Clostridium difficile infection is a leading healthcare-onset bacterial disease, and its management and prevention imposes significant clinical and financial burdens worldwide. While toxins TcdA and TcdB are the primary virulence factors, there is increasing interest in, and appreciation of, non-toxin virulence factors in C. difficile pathogenesis. Cell wall glycopolymers (CWGs) are important virulence determinants in many pathogens, but their role(s) in C. difficile pathogenesis is unclear. We propose a model for C. difficile CWG biosynthesis, and demonstrate that alterations in cell wall assembly profoundly impact bacterial morphology and virulence.

New role for human α-defensin 5 in the fight against hypervirulent Clostridium difficile strains

Clostridium difficile infection (CDI), one of the most common hospital-acquired infections, is increasing in incidence and severity with the emergence and diffusion of hypervirulent strains. CDI is precipitated by antibiotic treatment that destroys the equilibrium of the gut microbiota. Human α-defensin 5 (HD5), the most abundant enteric antimicrobial peptide, is a key regulator of gut microbiota homeostasis, yet it is still unknown if C. difficile, which successfully evades killing by other host microbicidal peptides, is susceptible to HD5. We evaluated, by means of viability assay, fluorescence-activated cell sorter (FACS) analysis, and electron microscopy, the antimicrobial activities of α-defensins 1 and 5 against a panel of C. difficile strains encompassing the most prevalent epidemic and hypervirulent PCR ribotypes in Europe (012, 014/020, 106, 018, 027, and 078). Here we show that (i) concentrations of HD5 within the intestinal physiological range produced massive C. difficile cell killing; (ii) HD5 bactericidal activity was mediated by membrane depolarization and bacterial fragmentation with a pattern of damage peculiar to C. difficile bacilli, compared to commensals like Escherichia coli and Enterococcus faecalis; and (iii) unexpectedly, hypervirulent ribotypes were among the most susceptible to both defensins. These results support the notion that HD5, naturally present at very high concentrations in the mucosa of the small intestine, could indeed control the very early steps of CDI by killing C. difficile bacilli at their germination site. As a consequence, HD5 can be regarded as a good candidate for the containment of hypervirulent C. difficile strains, and it could be exploited in the therapy of CDI and relapsing C. difficile-associated disease.

Detecting the dormant: a review of recent advances in molecular techniques for assessing the viability of bacterial endospores

Due to their contribution to gastrointestinal and pulmonary disease, their ability to produce various deadly exotoxins, and their resistance to extreme temperature, pressure, radiation, and common chemical disinfecting agents, bacterial endospores of the Firmicutes phylum are a major concern for public and environmental health. In addition, the hardy and dormant nature of endospores renders them a particularly significant threat to the integrity of robotic extraterrestrial life-detection investigations. To prevent the contamination of critical surfaces with seemingly ubiquitous bacterial endospores, clean rooms maintained at exceedingly stringent cleanliness levels (i.e., fewer than 100,000 airborne particles per ft(3)) are used for surgical procedures, pharmaceutical processing and packaging, and fabrication and assembly of medical devices and spacecraft components. However, numerous spore-forming bacterial species have been reported to withstand typical clean room bioreduction strategies (e.g., UV lights, maintained humidity, paucity of available nutrients), which highlights the need for rapid and reliable molecular methods for detecting, enumerating, and monitoring the incidence of viable endospores. Robust means of evaluating and tracking spore burden not only provide much needed information pertaining to endospore ecophysiology in different environmental niches but also empower decontamination and bioreduction strategies aimed at sustaining the reliability and integrity of clean room environments. An overview of recent molecular advances in detecting and enumerating viable endospores, as well as the expanding phylogenetic diversity of pathogenic and clean room-associated spore-forming bacteria, ensues.

Manganese binds to Clostridium difficile Fbp68 and is essential for fibronectin binding

Clostridium difficile is an etiological agent of pseudomembranous colitis and antibiotic-associated diarrhea. Adhesion is the crucial first step in bacterial infection. Thus, in addition to toxins, the importance of colonization factors in C. difficile-associated disease is recognized. In this study, we identified Fbp68, one of the colonization factors that bind to fibronectin (Fn), as a manganese-binding protein (K(D) = 52.70 ± 1.97 nM). Furthermore, the conformation of Fbp68 changed dramatically upon manganese binding. Manganese binding can also stabilize the structure of Fbp68 as evidenced by the increased T(m) measured by thermodenatured circular dichroism and differential scanning calorimetry (CD, T(m) = 58-65 °C; differential scanning calorimetry, T(m) = 59-66 °C). In addition, enhanced tolerance to protease K also suggests greatly improved stability of Fbp68 through manganese binding. Fn binding activity was found to be dependent on manganese due to the lack of binding by manganese-free Fbp68 to Fn. The C-terminal 194 amino acid residues of Fbp68 (Fbp68C) were discovered to bind to the N-terminal domain of Fn (Fbp68C-NTD, K(D) = 233 ± 10 nM, obtained from isothermal titration calorimetry). Moreover, adhesion of C. difficile to Caco-2 cells can be partially blocked if cells are pretreated with Fbp68C, and the binding of Fbp68C on Fn siRNA-transfected cells was significantly reduced. These results raise the possibility that Fbp68 plays a key role in C. difficile adherence on host cells to initiate infection.

Morphological and genetic diversity of temperate phages in Clostridium difficile

Eight temperate phages were characterized after mitomycin C induction of six Clostridium difficile isolates corresponding to six distinct PCR ribotypes. The hypervirulent C. difficile strain responsible for a multi-institutional outbreak (NAP1/027 or QCD-32g58) was among these prophage-containing strains. Observation of the crude lysates by transmission electron microscopy (TEM) revealed the presence of three phages with isometric capsids and long contractile tails (Myoviridae family), as well as five phages with long noncontractile tails (Siphoviridae family). TEM analyses also revealed the presence of a significant number of phage tail-like particles in all the lysates. Southern hybridization experiments with restricted prophage DNA showed that C. difficile phages belonging to the family Myoviridae are highly similar and most likely related to previously described prophages phiC2, phiC5, and phiCD119. On the other hand, members of the Siphoviridae phage family are more genetically divergent, suggesting that they originated from distantly related ancestors. Our data thus suggest that there are at least three genetically distinct groups of temperate phages in C. difficile; one group is composed of highly related myophages, and the other two groups are composed of more genetically heterogeneous siphophages. Finally, no gene homologous to genes encoding C. difficile toxins or toxin regulators could be identified in the genomes of these phages using DNA hybridization. Interestingly, each unique phage restriction profile correlated with a specific C. difficile PCR ribotype.

Genome sequence of a proteolytic (Group I) Clostridium botulinum strain Hall A and comparative analysis of the clostridial genomes

Clostridium botulinum is a heterogeneous Gram-positive species that comprises four genetically and physiologically distinct groups of bacteria that share the ability to produce botulinum neurotoxin, the most poisonous toxin known to man, and the causative agent of botulism, a severe disease of humans and animals. We report here the complete genome sequence of a representative of Group I (proteolytic) C. botulinum (strain Hall A, ATCC 3502). The genome consists of a chromosome (3,886,916 bp) and a plasmid (16,344 bp), which carry 3650 and 19 predicted genes, respectively. Consistent with the proteolytic phenotype of this strain, the genome harbors a large number of genes encoding secreted proteases and enzymes involved in uptake and metabolism of amino acids. The genome also reveals a hitherto unknown ability of C. botulinum to degrade chitin. There is a significant lack of recently acquired DNA, indicating a stable genomic content, in strong contrast to the fluid genome of Clostridium difficile, which can form longer-term relationships with its host. Overall, the genome indicates that C. botulinum is adapted to a saprophytic lifestyle both in soil and aquatic environments. This pathogen relies on its toxin to rapidly kill a wide range of prey species, and to gain access to nutrient sources, it releases a large number of extracellular enzymes to soften and destroy rotting or decayed tissues.

Diminished intestinal colonization by Clostridium difficile and immune response in mice after mucosal immunization with surface proteins of Clostridium difficile

Clostridium difficile pathogenesis is mainly due to toxins A and B. However, the first step of pathogenesis is the colonization process. We evaluated C. difficile surface proteins as vaccine antigens to diminish intestinal colonization in a human flora-associated mouse model. First, we used the flagellar cap protein FliD of C. difficile, in order to test several immunization routes: intranasal, rectal, and intragastric. The rectal route, which is the most efficient, was used to vaccine groups of mice with different antigen combinations. After immunizations, the mice were challenged with the toxigenic C. difficile and a significant statistical difference between the control group and the immunized groups was observed in the colonization levels of C. difficile.

The multidrug-resistant human pathogen Clostridium difficile has a highly mobile, mosaic genome

We determined the complete genome sequence of Clostridium difficile strain 630, a virulent and multidrug-resistant strain. Our analysis indicates that a large proportion (11%) of the genome consists of mobile genetic elements, mainly in the form of conjugative transposons. These mobile elements are putatively responsible for the acquisition by C. difficile of an extensive array of genes involved in antimicrobial resistance, virulence, host interaction and the production of surface structures. The metabolic capabilities encoded in the genome show multiple adaptations for survival and growth within the gut environment. The extreme genome variability was confirmed by whole-genome microarray analysis; it may reflect the organism's niche in the gut and should provide information on the evolution of virulence in this organism.

Identification and characterization of a fibronectin-binding protein from Clostridium difficile

A 68 kDa fibronectin-binding protein (Fbp68) from Clostridium difficile displaying significant homology to several established or putative Fbps from other bacteria was identified. The one-copy gene is highly conserved in C. difficile isolates. Fbp68 was expressed in Escherichia coli in fusion with glutathione S-transferase; the fusion protein and the native Fbp68 were purified. Immunoblot analysis and cell fractionation experiments revealed that Fbp68 is present on the surface of the bacteria. Far-immuno dot-blotting demonstrated that Fbp68 was capable of fixing fibronectin. Indirect immunofluorescence and ELISA were employed to demonstrate that C. difficile could bind both soluble and immobilized fibronectin. With competitive adherence inhibition assays it was shown that antibodies raised against Fbp68 partially inhibited attachment of C. difficile to fibronectin and Vero cells. Furthermore, Vero cells could fix purified membrane-immobilized Fbp68. Thus Fbp68 appears to be one of the several adhesins identified to date in C. difficile.

Clostridium difficile genotyping based on slpA variable region in S-layer gene sequence: an alternative to serotyping

Recent investigations of Clostridium difficile cell wall components have revealed the presence of an S-layer encoded by the slpA gene. The aim of this study was to determine whether slpA genotyping can be used as an alternative to serotyping. The variable regions of slpA were amplified by PCR from serogroup reference strains and various clinical isolates chosen randomly. Amplified products were analyzed after restriction enzyme digestion and DNA sequencing. The sequences of the variable region of the SlpA protein were found to be strictly identical within a given serogroup but divergent between serogroups. These preliminary results suggest that PCR-restriction fragment length polymorphism, in conjunction with DNA sequencing of the slpA variable region, could constitute an alternative typing method for determining C. difficile serotypes.

Role of FliC and FliD flagellar proteins of Clostridium difficile in adherence and gut colonization

In vitro and in vivo adhesive properties of flagella and recombinant flagellin FliC and flagellar cap FliD proteins of Clostridium difficile were analyzed. FliC, FliD, and crude flagella adhered in vitro to axenic mouse cecal mucus. Radiolabeled cultured cells bound to a high degree to FliD and weakly to flagella deposited on a membrane. The tissue association in the mouse cecum of a nonflagellated strain was 10-fold lower than that of a flagellated strain belonging to the same serogroup, confirming the role of flagella in adherence.

Characterization of a cell surface protein of Clostridium difficile with adhesive properties

Our laboratory has previously shown that Clostridium difficile adherence to cultured cells is enhanced after heat shock at 60 degrees C and that it is mediated by a proteinaceous surface component. The present study was undertaken to identify the surface molecules of this bacterium that could play a role in its adherence to the intestine. The cwp66 gene, encoding a cell surface-associated protein of C. difficile 79-685, was isolated by immunoscreening of a C. difficile gene library with polyclonal antibodies against C. difficile heated at 60 degrees C. The Cwp66 protein (66 kDa) contains two domains, each carrying three imperfect repeats and one presenting homologies to the autolysin CwlB of Bacillus subtilis. A survey of 36 strains of C. difficile representing 11 serogroups showed that the 3' portion of the cwp66 gene is variable; this was confirmed by sequencing of cwp66 from another strain, C-253. Two recombinant protein fragments corresponding to the two domains of Cwp66 were expressed in fusion with glutathione S-transferase in Escherichia coli and purified by affinity chromatography using gluthatione-Sepharose 4B. Antibodies raised against the two domains recognized Cwp66 in bacterial surface extracts. By immunoelectron microscopy, the C-terminal domain was found to be cell surface exposed. When used as inhibitors in cell binding studies, the antibodies and protein fragments partially inhibited adherence of C. difficile to cultured cells, confirming that Cwp66 is an adhesin, the first to be identified in clostridia.

Molecular characterization of fliD gene encoding flagellar cap and its expression among Clostridium difficile isolates from different serogroups

The fliD gene encoding the flagellar cap protein (FliD) of Clostridium difficile was studied in 46 isolates belonging to serogroups A, B, C, D, F, G, H, I, K, X, and S3, including 30 flagellated strains and 16 nonflagellated strains. In all but three isolates, amplification by PCR and reverse transcription-PCR demonstrated that the fliD gene is present and transcribed in both flagellated and nonflagellated strains. PCR-restriction fragment length polymorphism (RFLP) analysis of amplified fliD gene products revealed interstrain homogeneity, with one of two major patterns (a and b) found in all but one of the strains, which had pattern c. A polyclonal monospecific antiserum raised to the recombinant FliD protein reacted in immunoblots with crude flagellar preparations from 28 of 30 flagellated strains but did not recognize FliD from nonflagellated strains. The fliD genes from five strains representative of the three different RFLP groups were sequenced, and sequencing revealed 100% identity between the strains with the same pattern and 88% identity among strains with different patterns. Our results show that even though FliD is a structure exposed to the outer environment, the flagellar cap protein is very well conserved, and this high degree of conservation suggests that it has a very specific function in attachment to cell or mucus receptors.

GroEL (Hsp60) of Clostridium difficile is involved in cell adherence

Previous results have demonstrated that adherence of Clostridium difficile to tissue culture cells is augmented by various stresses; this study focussed on whether the GroEL heat shock protein is implicated in this process. The 1940 bp groESL operon of C. difficile was isolated by PCR. The 1623 bp groEL gene is highly conserved between various C. difficile isolates as determined by RFLP-PCR and DNA sequencing, and the operon is present in one copy on the bacterial chromosome. The 58 kDa GroEL protein was expressed in Escherichia coli in fusion with glutathione S:-transferase and the fusion protein was purified from IPTG-induced bacterial lysates by affinity chromatography on glutathione-Sepharose. A polyclonal, monospecific antiserum was obtained for GroEL which established by immunoelectron microscopy, indirect immunofluorescence and immunoblot analysis that GroEL is released extracellularly after heat shock and can be surface associated. Cell fractionation experiments suggest that GroEL is predominantly cytoplasmic and membrane bound. GroEL-specific antibodies as well as the purified protein partially inhibited C. difficile cell attachment and expression of the protein was induced by cell contact, suggesting a role for GroEL in cell adherence.

A Clostridium difficile gene encoding flagellin

Six strains of Clostridium difficile examined by electron microscopy were found to carry flagella. The flagella of these strains were extracted and the N-terminal sequences of the flagellin proteins were determined. Four of the strains carried the N-terminal sequence MRVNTNVSAL exhibiting up to 90% identity to numerous flagellins. Using degenerate primers based on the N-terminal sequence and the conserved C-terminal sequence of several flagellins, the gene encoding the flagellum subunit (fliC) was isolated and sequenced from two virulent strains. The two gene sequences exhibited 91% inter-strain identity. The gene consists of 870 nt encoding a protein of 290 amino acids with an estimated molecular mass of 31 kDa, while the extracted flagellin has an apparent molecular mass of 39 kDa on SDS-PAGE. The FliC protein displays a high degree of identity in the N- and C-terminal amino acids whereas the central region is variable. A second ORF is present downstream of fliC displaying homology to glycosyltransferases. The fliC gene was expressed in fusion with glutathione S-transferase, purified and a polyclonal monospecific antiserum was obtained. Flagella of C. difficile do not play a role in adherence, since the antiserum raised against the purified protein did not inhibit adherence to cultured cells. PCR-RFLP analysis of amplified flagellin gene products and Southern analysis revealed inter-strain heterogeneity; this could be useful for epidemiological and phylogenetic studies of this organism.

Clostridium difficile cell attachment is modified by environmental factors

Adherence of Clostridium difficile to Vero cells under anaerobic conditions was increased by a high sodium concentration, calcium-rich medium, an acidic pH, and iron starvation. The level of adhesion of nontoxigenic strains was comparable to that of toxigenic strains. Depending on the bacterial culture conditions, Vero cells could bind to one, two, or three bacterial surface proteins with molecular masses of 70, 50, and 40 kDa.

Ruthenium red and the bacterial glycocalyx

Ruthenium red, a promising cationic reagent for electron microscopy (EM), has long been an important tool in histology. The reagent was initially used by botanists as a semispecific stain for pectic substances, but it has gradually been embraced by investigators in microbiology and the animal sciences as a stain for anionic glycosylated polymeric substances. Luft developed a reliable method and demonstrated that ruthenium red was a useful reagent for visualizing ultrastructural detail. Many investigators, using modifications of Luft's approach, have identified numerous applications for this important reagent. Ruthenium red has been used to show the ultrastructural detail of bacterial glycocalyces. Strong, sharp and consistent observations of this ultrastructural component of the bacterial cell have given a better understanding its fibrous anionic matrix. Any variations in staining owing to artifactual alteration of the fine delicate ultrastructural features have been overcome by incorporation of diamine lysine into ruthenium red methods, thus providing flexible processing times under less than ideal laboratory sampling conditions. Ruthenium red has broad utility in the biological sciences, and in combination with lysine, it is an excellent EM stain for enhanced visualization of bacterial glycocalyx from culture or from clinical specimens.

Paraformaldehyde effect on ruthenium red and lysine preservation and staining of the staphylococcal glycocalyx

The utility of lysine in glutaraldehyde-ruthenium red fixatives for the preservation and/or staining of the fibrous staphylococci glycocalyx was improved by inclusion of paraformaldehyde. Short, 20 min prefixation times for paraformaldehyde-glutaraldehyde fixatives containing lysine, with or without ruthenium red, were compared to an extended overnight fixation. Samples were often lost in fixatives that did not contain paraformaldehyde at extended fixation times hampering the effective use of these fixatives for clinical or environmental applications. Inclusion of paraformaldehyde in the fixation with lysine permitted longer fixation times as well as stabilized the staphylococcal glycocalyx. Thus, the technical usefulness of fixatives employing lysine was significantly improved.

Fibronectin and laminin binding of eighteen Clostridium species

The ability of Clostridium difficile, Clostridium perfringens, Clostridium sporogenes and fifteen other Clostridium species to bind to human serum fibronectin or laminin was tested by using protein-coated latex particles. Three groups of Clostridium species were formed, namely the pseudomembranous colitis-causing species Clostridium difficile, the gas gangrene-causing Clostridium species and other Clostridium species, which are infrequently found in human infections. Significantly more strains of gas gangrene-causing Clostridium species, and strains of Clostridium species other than Clostridium difficile recognized fibronectin or laminin than did Clostridium difficile. Experiments with monoclonal antibodies revealed the specificity of the bacterial binding to fibronectin or laminin.

Cloning of a genetic determinant from Clostridium difficile involved in adherence to tissue culture cells and mucus

Our laboratory has previously shown that Clostridium difficile adherence to Caco-2 cells is greatly enhanced after heat shock at 60 degrees C and that it is mediated by a proteinaceous surface component. The experiments described here show that C. difficile could adhere to several types of tissue culture cells (Vero, HeLa, and KB) after heat shock. The type of culture medium (liquid or solid, with or without blood) had little effect on adhesion. To clone the adhesin gene, polyclonal antibodies against C. difficile heated at 60 degrees C were used to screen a genomic library of C. difficile constructed in lambda ZapII. Ten positive clones were identified in the library, one of which (pCL6) agglutinated several types of erythrocytes in the presence of mannose. In Western blots (immunoblots), this clone expressed in Escherichia coli a 40- and a 27-kDa protein; a 27-kDa protein has been previously identified in the surface extracts of heat-shocked C. difficile as a possible adhesin. The clone adhered to Vero, Caco-2, KB, and HeLa cells; the adherence was blocked by anti-C. difficile antibodies, by a surface extract of C. difficile, and by mucus isolated from axenic mice. Furthermore, the clone could attach ex vivo to intestinal mucus isolated from axenic mice. Preliminary studies on the receptor moieties implicated in C. difficile adhesion revealed that glucose and galactose could partially block adhesion to tissue culture cells, as did di- or trisaccharides containing these sugars, suggesting that the adhesin is a lectin. In addition, N-acetylgalactosamine, a component of mucus, and gelatin partially impeded cell attachment.

Haemagglutination activity of toxigenic and non-toxigenic strains of Clostridium difficile

Cell extract of Clostridium difficile strains was fractionated by ammonium sulfate precipitation and sulfated cellulofine column chromatography to detect haemagglutination (HA) activity. HA activity without cytotoxicity was detected in fractions eluted at 0.79-0.91 M NaCl in sulfated cellulofine column chromatography of the cell extract in both toxigenic strain VPI 10463 and non-toxigenic strain KZ 1678, while toxin A was detected in fractions eluted at 0.27-0.29 M NaCl. Antisera were prepared with HA substance-containing fractions of the chromatography. Antiserum to the HA substance(s) of strain VPI 10463 neutralised the HA activity of the fractions of strains VPI 10463 and KZ 1678 at nearly the same titres. Antiserum to the HA substance(s) of strain KZ 1678 also neutralised the HA activity of both strains at nearly the same titres as above. These findings suggest that haemagglutinin(s) is commonly produced by C. difficile strains irrespective of toxin A-producing ability.

Virulence factors in anaerobic bacteri

Various surface structures can be expressed in Bacteroides fragilis, but little is known about capsular structures in other non-spore-forming anaerobes. Fimbriae have been isolated from Bacteroides fragilis and Porphyromonas gingivalis. The importance of iron-repressible outer membrane proteins as virulence factors in Bacteroides fragilis is under study. The low endotoxic activity of Bacteroides fragilis lipopolysaccharide can be attributed to the chemical composition of this organism's lipid A. A tissue culture system for the demonstration of Bacteroides fragilis enterotoxin has recently been described. The toxins A and B of Clostridium difficile are immunologically distinct. The importance of IgA proteases and other enzymes as virulence factors in anaerobic bacteria remains unclear.