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.     

Epidemiology of diarrhoea caused by enterotoxigenic Clostridium perfringens

Enterotoxigenic strains of Clostridium perfringens have recently been implicated in some cases of antibiotic-associated diarrhoea. We present here the results of an epidemiological study of this disease. Five cases of diarrhoea caused by C. perfringens serotype 41 occurred during a 9-week period, and then during a 6-week period there were three cases due to serotype 27 and two due to serotype 24; in all but one case two geriatric wards were involved. In total there were 16 cases in 22 months. All cases were identified by the detection of C. perfringens enterotoxin in the faeces. The mean number of C. perfringens in these cases was 10(8.8) cfu/g of faeces. Of 37 patients who had negative test results for C. perfringens enterotoxin, 18 had positive cultures for C. perfringens, with mean faecal counts of 10(5.3) cfu/g, and nine of these patients had diarrhoea. Thirteen different serotypes were isolated from these 18 patients, including type 41 from seven patients and type 27 from one. Hand carriage of the offending serotype was demonstrated in three of four infected patients, none of four controls and two of 14 ward staff. C. perfringens of serotypes causing disease was isolated from 59% of environmental areas where there was active disease, 27% of areas where there had been disease which had since resolved and 9% of areas where there was no history of disease. The findings imply that cross infection may occur.     

Immunogenicity and cross-reactivity of the 70-Kda iron-regulated protein of Neisseria meningitidis in man and animals

The immune response to different serogroups and serotypes of N. meningitidis has been examined in acute and convalescent sera from patients with meningococcal diseases. The focus of the study was the c. 70-Kda iron-regulated outer-membrane protein (FeRP-70). FeRP-70 was demonstrated on all strains of different serogroups and serotypes examined by sodium dodecylsulphate-polyacrylamide gel electrophoresis or Western blots of outer-membrane proteins (OMPs). Immunoblotting experiments demonstrated the presence of considerable amounts of anti-FeRP-70 IgG antibodies in the acute and convalescent sera of six patients; the antibodies reacted with homologous and heterologous strains. However, sera from two patients who died of severe meningococcal septicaemia had no antibodies against FeRP-70 or any other OMPs demonstrable by immunoblotting. Absorbed rabbit hyperimmune sera reacted with FeRP-70 of their homologous strains, but, unlike human sera, with only a few of the heterologous strains. We believe that FeRP-70 is strongly immunogenic in vivo, cross-reactive amongst different strains, and that man and animals differ considerably in their response to similar meningococcal antigens. The functional attribution of human antibody response against this protein requires further exploration.     

Cellular and molecular mechanisms of antifungal innate immunity at epithelial barriers: The role of C-type lectin receptors

Humans are constantly exposed to fungi, either in the form of commensals at epithelial barriers or as inhaled spores. Innate immune cells play a pivotal role in maintaining commensal relationships and preventing skin, mucosal, or systemic fungal infections due to the expression of pattern recognition receptors that recognize fungal cell wall components and modulate both their activation status and the ensuing adaptive immune response. Commensal fungi also play a critical role in the modulation of homeostasis and disease susceptibility at epithelial barriers. This review will outline cellular and molecular mechanisms of anti-fungal innate immunity focusing on C-type lectin receptors and their relevance in the context of host-fungi interactions at skin and mucosal surfaces in murine experimental models as well as patients susceptible to fungal infections.     

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.     

Relapse-associated worsening in a real-life multiple sclerosis cohort: the role of age and pyramidal phenotype

Background and purpose

The overall disability in patients with relapsing–remitting multiple sclerosis is likely to be partly rather than entirely attributed to relapse.

Materials and methods

The aim was to investigate the determinants of recovery from first relapse and relapse-associated worsening (RAW) in relapsing–remitting multiple sclerosis patients from the Italian MS Registry during a 5-year epoch from the beginning of first-line disease-modifying therapy. To determine recovery, the functional system (FS) score was used to calculate the difference between the score on the date of maximum improvement and the score before the onset of relapse. Incomplete recovery was defined as a combination of partial (1 point in one FS) and poor recovery (2 points in one FS or 1 point in two FSs or any other higher combination). RAW was indicated by a confirmed disability accumulation measured by the Expanded Disability Status Scale score confirmed 6 months after the first relapse.

Results

A total of 767 patients had at least one relapse within 5 years of therapy. Of these patients, 57.8% experienced incomplete recovery. Age (odds ratio [OR] 1.02, 95% confidence interval [CI] 1.01–1.04; p = 0.007) and pyramidal phenotype were associated with incomplete recovery (OR = 2.1, 95% CI 1.41–3.14; p < 0.001). RAW was recorded in 179 (23.3%) patients. Age (OR = 1.02, 95% CI 1.01–1.04; p = 0.029) and pyramidal phenotype (OR = 1.84, 95% CI 1.18–2.88; p = 0.007) were the strongest predictors in the multivariable model.

Conclusions

Age and pyramidal phenotype were the strongest determinants of RAW in early disease epochs.