Clostridium difficile is the commonest cause of antibiotic-associated diarrhoea, with the hospitalized elderly being at particular risk. The organism makes a crystalline surface protein layer (S-layer), encoded by the slpA gene, the product of which is cleaved to give two mature peptides which associate to form the layer. The larger peptide (high molecular weight; HMW), derived from the C-terminal portion of the precursor, is relatively conserved, whereas the smaller peptide (low molecular weight; LMW), derived from the N-terminal portion of the precursor, is a dominant antigen which substantially forms the basis for serotyping of isolates. PCR ribotyping is a more discriminatory typing method, based on the intergenic rRNA. We obtained the sequence for slpA and some flanking DNA from a collection of C. difficile strains of 14 ribotypes isolated from elderly patients. Sequences from different ribotypes were compared with one another and with published sequences. Sequences from C. difficile ribotypes 046 and 092 were identical. Sequences from ribotype pairs 005 and 054, 012 and 046/092, 014 and 066 and 031 and 094 differed by 1-3 nt in the slpA gene. There were ultimately nine ribotypes or groups of ribotypes with very different slpA sequences, particularly in the region encoding the LMW peptide. The sequence from ribotype 002 was very different from previously published sequences. The DNA segment sequenced included the 59 315 bp of a secA homologue, encoding a putative transport protein required for peptide secretion across the plasma membrane. The amino acid sequences of the predicted HMW peptides were aligned and a neighbour-joining tree was produced using 10 000 bootstrap replicates. The predicted SecA N-terminal region was similarly analysed. For both SlpA and SecA, a strong association was found between ribotypes 012, 046/092, 017, 031 and 094. Ribotypes 001 and 078 formed part of this clade for SlpA but not SecA, indicating independent evolution for slpA and secA, presumably because they come under different selection pressures.
Abstract-Mild hyperhomocysteinemia is a risk factor for atherosclerotic vascular disease. Homozygosity for the C677T mutation in the gene for 5,10-methylenetetrahydrofolate reductase (MTHFR) is frequently associated with hyperhomocysteinemia, particularly in individuals with low levels of serum folate, and has been directly associated with cardiovascular disease in certain populations. The purpose of this study was to establish whether the C677T mutation, which causes thermolabile MTHFR, is a risk factor for ischemic stroke in the Irish population. The homozygous C677T genotype has previously been associated with coronary heart disease in Ireland. We collected blood from 174 individuals (minimum age 60 years) who had suffered an ischemic stroke that was confirmed by computed tomography brain scan. Control subjects (nϭ183) aged Ն60 years, who had never suffered a stroke or transient ischemic attack, were recruited from hospitals and active retirement groups in the same geographical area. MTHFR genotypes were determined and other known risk factors for stroke were documented. In the control group, the frequency of subjects with the homozygous C677T genotype was 10.4%. In patients who had suffered ischemic stroke, the frequency was 15.5%. This difference was not statistically significant. 2 In addition it is associated with thickening of the carotid arterial wall. 3,4 The magnitude of the risk of vascular disease conferred by hyperhomocysteinemia varies between populations. A meta-analysis of the data indicates that hyperhomocysteinemia confers at least a 2.5-fold increased risk of stroke. 5 Homocysteine is a sulphur amino acid generated by the many transmethylation reactions that consume S-adenosyl methionine (SAM) (Figure). Homocysteine is remethylated to methionine (from which SAM is then regenerated) by the vitamin B12-dependent enzyme methionine synthase. This remethylation uses 5-methyl tetrahydrofolate as the methyl donor. 5-methyl tetrahydrofolate is itself generated from 5,10-methylene tetrahydrofolate by the enzyme 5, 10-methylenetetrahydrofolate reductase (MTHFR). Under normal circumstances, homocysteine can be irreversibly degraded by the transsulfuration pathway, the first step of which is catalyzed by the vitamin B6-dependent enzyme cystathionine -synthase (CBS).Plasma homocysteine levels are therefore influenced by both nutritional (folate and vitamins B12 and B6) and genetic factors, including mutations in the genes encoding methionine synthase, CBS, and MTHFR. In particular, a biochemically defined "thermolabile" variant of MTHFR is associated with moderate hyperhomocysteinemia. 6 The genetic change underlying thermolabile MTHFR is a C to T base transition at nucleotide 677 in the MTHFR cDNA, 7,8 which results in the substitution of valine for alanine. 8 The frequency of homozygotes for the thermolabile MTHFR mutation is between 5% and 15% in different European populations. 9 Recently, homozygosity for the thermolabile genotype has been associated with a nearly 10-fold increased risk of an indivi...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.