Identification of regions of the Escherichia coli chromosome specific for neonatal meningitis-associated strains.

Specific virulence factors associated with the pathogenesis of Escherichia coli strains causing neonatal meningitis (ECNM), such as the K1 capsular polysaccharide, the S fimbriae, and the Ibe10 protein, have been previously identified. However, some other yet unidentified factors are likely to be involved in the pathogenesis of ECNM. To identify specialized unique DNA regions associated with ECNM virulence, we used the representational difference analysis technique. The genomes of two strains belonging to nonpathogenic phylogenetic group A of the ECOR reference collection were subtracted from E. coli strain C5, isolated from a case of neonatal meningitis. Strain C5 belongs to the phylogenetic group B2 as do the majority of ECNM. We have isolated and mapped 64 DNA fragments which are specific for strain C5 and not found in nonpathogenic strains. Of these clones, 44 were clustered in six distinct regions on the chromosome. The sfa and ibe10 genes were located in regions 2 and 6, respectively. A group of genes (cnf1, hra, hly, and prs) known to be present in a pathogenicity island of the uropathogenic strain E. coli J96 colocalized with region 6. The occurrence of these DNA regions was tested in a set of meningitis-associated strains and in a control group composed of non-meningitis-associated strains belonging to the same B2 group. Regions 1, 3, and 4 were present in 91, 82, and 81%, respectively, of the meningitis strains and in 40, 13, and 47% of the control strains. Together, these data suggest that regions 1, 3, and 4 code for factors associated with the ability of E. coli to invade the meninges of neonates.

Plasma concentration, kinetic constants, and gene polymorphism of angiotensin I-converting enzyme in centenarians.

We have determined serum activity and kinetic constants of angiotensin I-converting enzyme (ACE), parallel to an insertion/deletion (I/D) polymorphism in its gene, in French centenarians and controls 20-70 years of age because this enzyme could have an impact on cardiovascular risk, and thus on longevity. Both the ACE D allele and ACE D/D genotype were more frequent in centenarians in comparison with controls, without sex-related differences nor significant correlation with a cardiovascular pathology. In centenarians, I/D polymorphism was correlated with circulating ACE activity (D/D genotype, 89.0 +/- 36.8 U/L; I/D genotype, 63.5 +/- 26.0 U/L; and I/I genotype, 55.1 +/- 39.4 U/L). The Michaelis constants for two substrates were identical whatever the genotype and were not different between centenarians and controls, i.e., 0.30 +/- 0.03 mmol/L for furylacryloyl-phenylalanyl-glycyl-glycine and 1.35 +/- 0.05 mmol/L for hippuryl-histidyl-leucine; for the latter, the optimal pH and activating concentration of chloride did not depend on I/D polymorphism. The maximal velocities with both substrates reflected the distribution of serum ACE activity as a function of the genotypes, in centenarians and in controls. In conclusion, plasma ACE activity is subject to a similar genotypic influence in centenarians as in adults 20-70 years of age; however, ACE itself appears to be functionally similar for each genotype. Furthermore, the D allele as well as the higher serum ACE activities associated with the D/D genotype cannot discriminate individuals at high risk for cardiovascular diseases, major causes of mortality before the age of 100 years.

Indication for genetic linkage of the phosphoenolpyruvate carboxykinase (PCK1) gene region on chromosome 20q to non-insulin-dependent diabetes mellitus.

There is strong evidence that non-insulin-dependent-diabetes mellitus (NIDDM) has a polygenic mode of inheritance. Nevertheless, major gene effects may be involved in its pathogenesis, especially in forms with an early age of onset. We performed linkage analyses between 4 candidate genes for insulin resistance and NIDDM in a set of 55 multigenerational French Caucasian families, using the affected sib-pair approach. No significant results were obtained with glycogen synthase (GSY), insulin receptor substrate-1 (IRS-1) and apolipoprotein C-II (APOC-II) genes. However, a significant trend towards linkage was found between NIDDM and the phosphoenolpyruvate carboxykinase gene (PCK1) located on chromosome 20q (p = 0.005 for the mean estimated proportion of alleles shared identically by descent, mean IBD = 0.55), particularly among sib-pairs with diabetes diagnosed before the age of 46 years (p = 0.0003, mean IBD = 0.66). These results suggest that the PCK1 gene or a nearby locus contributes to the development of NIDDM in the French population.