Escherichia coli

About: Escherichia coli is a research topic. Over the lifetime, 59041 publications have been published within this topic receiving 2050337 citations. The topic is also known as: E. coli & E coli jdj.

Cloning and expression of an adhesin (AIDA-I) involved in diffuse adherence of enteropathogenic Escherichia coli.

Abstract: The adherence of enteropathogenic Escherichia coli (EPEC) to the small bowel mucosa is an important step in the pathogenesis of diarrheal diseases. It has been shown that many EPEC strains adhere to HEp-2 and especially HeLa cells in characteristic patterns termed localized adherence (LA) and diffuse adherence (DA). A plasmid-derived DNA fragment encoding a factor specific for LA hybridized only to EPEC strains expressing LA, which demonstrated that LA and DA are mediated by two genetically distinct adhesins. EPEC strain 2787 (O127:H27), isolated from a case of infantile diarrhea, exhibited three major properties: (i) it showed DA to HeLa cells, (ii) it carried two large (ca. 100-kilobase [kb]) plasmids and one small plasmid of about 3 kb, and (iii) no fimbriae could be detected by electron microscopy in organisms grown on agar plates or in liquid cultures. Whole isolated plasmid DNA was partially digested with EcoRI and cloned into the vector pBR322. One recombinant clone (pIB6) was found to exhibit the same DA pattern on HeLa cells as did the parent strain. This clone contained an 11-kb DNA fragment derived from the largest of the three plasmids, as shown by Southern hybridization. By deletion analysis, a 6.0-kb DNA fragment was shown to be sufficient for expression of the DA phenotype. This insert encoded the production of a 100,000-dalton protein mediating adhesion to HeLa cells.

Characterization, sequence determination, and immunogenicity of a 64-kilodalton protein of Mycobacterium bovis BCG expressed in escherichia coli K-12.

Abstract: We report the DNA sequence of a previously cloned Mycobacterium bovis BCG gene encoding an immunogenic 64-kilodalton protein. This protein, MbaA, was purified from overproducing Escherichia coli K-12 cells, and the presence of antibodies to MbaA in human sera was determined by an enzyme-linked immunosorbent assay. In about 80% of serum samples from tuberculosis patients and in about 60% of samples from BCG-vaccinated individuals, significant levels of anti-MbaA antibodies were found. Surprisingly, in about 30% of the control serum samples obtained from children, anti-MbaA antibodies were also observed. Guinea pigs sensitized with M. bovis BCG or MbaA showed a delayed-type hypersensitivity reaction after challenge with purified MbaA, supporting the previously observed strong reactivity of human T-cell clones with this, for mycobacteria, common antigen.

Antisense inhibition of gene expression in bacteria by PNA targeted to mRNA

Abstract: Peptide nucleic acid (PNA) is a DNA mimic with attractive properties for developing improved gene-targeted antisense agents. To test this potential of PNA in bacteria, PNAs were designed to target the start codon regions of the Escherichia coli beta-galactosidase and beta-lactamase genes. Dose-dependent and specific gene inhibition was observed in vitro using low nanomolar PNA concentrations and in vivo using low micromolar concentrations. Inhibition was more efficient for a permeable E. coli strain relative to wild-type K-12. The potency of the anti-beta-lactamase PNAs was abolished by a six base substitution, and inhibition could be re-established using a PNA with compensating base changes. Antisense inhibition of the beta-lactamase gene was sufficient to sensitize resistant cells to the antibiotic ampicillin. The results demonstrate gene- and sequence-specific antisense inhibition in E. coli and open possibilities for antisense antibacterial drugs and gene function analyses in bacteria.

Nitric oxide, nitrite, and Fnr regulation of hmp (flavohemoglobin) gene expression in Escherichia coli K-12.

Abstract: Escherichia coli possesses a soluble flavohemoglobin, with an unknown function, encoded by the hmp gene. A monolysogen containing an hmp-lacZ operon fusion was constructed to determine how the hmp promoter is regulated in response to heme ligands (O2, NO) or the presence of anaerobically utilized electron acceptors (nitrate, nitrite). Expression of the phi (hmp-lacZ)1 fusion was similar during aerobic growth in minimal medium containing glucose, glycerol, maltose, or sorbitol as a carbon source. Mutations in cya (encoding adenylate cyclase) or changes in medium pH between 5 and 9 were without effect on aerobic expression. Levels of aerobic and anaerobic expression in glucose-containing minimal media were similar; both were unaffected by an arcA mutation. Anaerobic, but not aerobic, expression of phi (hmp-lacZ)1 was stimulated three- to four-fold by an fnr mutation; an apparent Fnr-binding site is present in the hmp promoter. Iron depletion of rich broth medium by the chelator 2'2'-dipyridyl (0.1 mM) enhanced hmp expression 40-fold under anaerobic conditions, tentatively attributed to effects on Fnr. At a higher chelator concentration (0.4 mM), hmp expression was also stimulated aerobically. Anaerobic expression was stimulated 6-fold by the presence of nitrate and 25-fold by the presence of nitrite. Induction by nitrate or nitrite was unaffected by narL and/or narP mutations, demonstrating regulation of hmp by these ions via mechanisms alternative to those implicated in the regulation of other respiratory genes. Nitric oxide (10 to 20 microM) stimulated aerobic phi (hmp-lacZ)1 activity by up to 19-fold; soxS and soxR mutations only slightly reduced the NO effect. We conclude that hmp expression is negatively regulated by Fnr under anaerobic conditions and that additional regulatory mechanisms are involved in the responses to oxygen, nitrogen compounds, and iron availability. Hmp is implicated in reactions with small nitrogen compounds.