Differential effects of varying concentrations of clostridium difficile toxin A on epithelial barrier function and expression of cytokines

BACKGROUND: Presentation after Clostridium difficile infection may depend on the level of epithelial exposure to toxins. We investigated epithelial barrier function and expression of interleukin (IL)-8 and transforming growth factor (TGF)-beta in response to varying concentrations of C. difficile toxin A. METHODS: T84 cells were either preexposed or continuously exposed to C. difficile toxin A (0.01-1000 ng/mL). Barrier function was assessed by measurements of transepithelial electrical resistance. RESULTS: Preexposure to < or =10 ng/mL toxin A led to an increase in the release of TGF-beta 1, but there was no change in the expression of IL-8. In contrast, after preexposure to >10 ng/mL toxin A, there was enhanced expression of IL-8, but release of TGF-beta 1 was similar to that in control monolayers. After preexposure to >10 ng/mL toxin A, there was complete and irreversible loss of electrical resistance. At lower concentrations, loss of resistance across monolayers was followed by recovery, which was enhanced by all 3 recombinant isoforms of TGF-beta. Pretreatment with recombinant isoforms of TGF-beta or coculture with TGF-beta 3-expressing colonic subepithelial myofibroblasts was also protective. CONCLUSIONS: In C. difficile infection, the development and severity of colonic inflammation may depend on the exposure of intestinal epithelial cells to toxins and the expression of proinflammatory (IL-8) and protective (TGF-beta) factors.     

Isotactic 1-butene polymerization promoted by C2-symmetric metallocene catalysts

1-Butene polyinsertion promoted by two typical C₂-symmetric zirconocene catalysts (i.e. rac-ethylenebis(1-indenyl)ZrCl₂ ( 1 ) and rac-dimethylsilylbis(1-indenyl)ZrCl₂) ( 2 ) was investigated under both hydrooligomerization and polymerization conditions and compared with that of propene. It was found that, in spite of a similar regiospecificity for the two monomers, the fraction of “dormant” sites is higher in 1-butene polymerization, as a result of a (much) lower reactivity of a 2,1 last-inserted unit. Accordingly, in the investigated cases, 2,1 units of 1-butene were not incorporated in the growing chains but either isomerized to 4,1 units or remained at the chain end until they underwent chain transfer via β-hydrogen elimination. Experimental evidence is also presented of an epimerization reaction of the growing poly(1-butene) chain with a 1,2 last-inserted unit, leading to a decrease of polymer stereoregularity with decreasing monomer concentration.     

Comparison of different vaccines and induced immune response against Campylobacter jejuni colonization in the infant mouse

The degree of protection conferred by vaccinated dams on infant mice against colonization by Campylobacter jejuni depended on the bacterial strain, preparation, and route of administration of the vaccine. In some instances of homologous protection, serum bactericidal titres correlated well with protection. However, boiled C. jejuni vaccine, which was non-protective, also elicited a strong bactericidal antibody response. Conversely, bactericidal activity could not be demonstrated against strains capable of cross-protection. There was a good correlation between high campylobacter-specific IgG response and bactericidal activity.     

Protection of hamsters against Clostridium difficile ileocaecitis by prior colonisation with non-pathogenic strains

Prior colonisation of clindamycin-treated hamsters with non-toxigenic strains of C. difficile protected them from subsequent colonisation with a toxigenic pathogenic strain. In total, 13 of 18 'protected' hamsters survived for up to 27 days whereas all 27 animals challenged with the toxigenic strain alone died within 48 h. Protection was not evident if a heat-killed suspension was used or if the colonising non-toxigenic strain was first removed with vancomycin. No antitoxic activity could be detected in the faeces of animals colonised with the non-toxigenic strains. Other species of clostridia did not protect against the lethal effects of subsequent exposure to the toxigenic strain. Conversely, non-toxigenic strains would not protect the animals from the lethal effects of a different clostridial pathogen, C. spiroforme. In most cases, even in the protected animals, the toxigenic strain eventually became dominant and caused disease, with translocation across the gut wall occurring early in the disease process. It was also shown that a non-toxigenic strain of C. difficile can adhere to gut mucosa. It is proposed that the protection afforded by the non-toxigenic strains may be due to competition for ecological niches.     

Clostridium difficile--a spectrum of virulence and analysis of putative virulence determinants in the hamster model of antibiotic-associated colitis

Each of nine different toxigenic strains of Clostridium difficile was administered orally to groups of hamsters pre-treated with clindamycin and housed individually in sterile isolator boxes. Faecal pellets and caecal contents from well, diarrhoeic, moribund and freshly dead animals were analysed for C. difficile and toxins A (enterotoxin) and B (cytotoxin), and tissue obtained when animals were killed was examined histologically. Not all strains were equally virulent in this model. Four strains of C. difficile killed all animals within 48 h and are designated as highly virulent for hamsters. These strains were clinical isolates from three cases of disease in man and one case in a hamster. Five strains caused death of some animals but only after 5 and upt to 13 days and are designated as less virulent for hamsters. These strains were isolated from asymptomatic infants (2) and household pets (2), and from the environment (1). The surviving test hamsters were killed after 14 days and, in most cases, were colonised by C. difficile, though levels of toxins A and B in caecal contents were low. None of the cultures used for challenge was capsulate or hydrophobic. There was no correlation between virulence and production of toxins A and B in vitro in tryptic-nitrate broth. With two strains examined, there was a correlation between virulence and toxin A (but not toxin B) production in caecal emulsions derived from clindamycin pre-treated hamsters. Caecal contents from the majority of moribund and freshly dead animals had quantities of toxin A sufficient to cause disease or death if given orogastrically. Toxin B was not produced in a fixed ratio with toxin A. The data support the view that high virulence of C. difficile is determined by efficient disease-inducing colonisation of the gut and the ability to generate, rapidly, high levels of toxin A in vivo.     

Diarrhoea due to enterotoxigenic Clostridium perfringens: clinical features and management of a cluster of ten cases

Clostridium perfringens has recently been shown to be associated with antibiotic-associated diarrhoea. We describe here the clinical features and management of an outbreak of diarrhoea in a Geriatric Unit. Ten cases were due to enterotoxigenic C. perfringens and in these cases there was a highly significant correlation with recent antibiotic administration (P = 0.0001). The importance of early recognition of C. perfringens as a cause of infective diarrhoea in the elderly is stressed.