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.

High-affinity binding of the bactericidal/permeability-increasing protein and a recombinant amino-terminal fragment to the lipid A region of lipopolysaccharide.

Abstract: Bactericidal/permeability-increasing protein (BPI) is a 55-kDa cationic protein (nBPI55) elaborated by polymorphonuclear neutrophils (PMN). BPI has potent bactericidal activity against a wide variety of gram-negative organisms and neutralizes endotoxin activities. An N-terminal fragment of nBPI55 exhibits the bactericidal and antiendotoxin properties of the holoprotein. To further characterize the biological activities of the N-terminal fragment, a recombinant protein (rBPI23) corresponding to the first 199 amino acids of human BPI was produced and purified. rBPI23 had antibacterial activity equivalent to that of nBPI55 against Escherichia coli J5. Furthermore, both rBPI23 and nBPI55 bound identically to a broad range of R- and S-form lipopolysaccharides (LPS) and to natural and synthetic lipid A. Binding of radiolabeled nBPI55 to LPS was inhibited in an identical fashion by either nBPI55 or rBPI23. The binding of both proteins to immobilized E. coli J5 lipid A was inhibited in a comparable fashion by long- or short-chain LPS or lipid A. The binding of both rBPI23 and nBPI55 was specific, saturable, and of high affinity, with an apparent Kd of approximately 2 to 5 nM for all ligands tested. These results demonstrate that BPI recognizes the highly conserved lipid A region of bacterial LPS via residues contained within the amino-terminal portion of the BPI molecule.

Vesicle-Mediated Transfer of Virulence Genes from Escherichia coli O157:H7 to Other Enteric Bacteria

Abstract: Many gram-negative bacteria produce membrane vesicles, suggesting that vesicle production is not purposeless; indeed, studies during the last two decades have presented strong evidence supporting the importance of vesicles. Typical vesicles released from the surfaces of gram-negative bacteria are 50 to 250 nm, spherical, and made up of outer membrane and encapsulated periplasmic components (4, 26). Vesicle components include outer membrane proteins, lipopolysaccharide, periplasmic proteins, phospholipids, DNA, and RNA (9, 12, 15, 22, 34, 40). Vesicles from gram-negative bacteria were reported to fuse to both gram-positive and gram-negative bacteria and in some instances to promote lysis of the target cell (28). Moreover, vesicles may function as an alternative secretory pathway (3, 23) and promote adherence of the parent cell to host cells (17, 32). By virtue of their small size, bilayer protecting envelope, and ability to integrate into the membranes of foreign bacteria and to adhere to or be engulfed by eukaryotic cells, a potential role of vesicles in delivery of virulence factors, including enzymes and toxins, is not unlikely (23). In fact, virulence factors associated with the parent strain, including proteases, phospholipases, autolysin, hemolysins, and Shiga toxins, have been isolated from vesicles (3, 22, 26, 28). Aside from toxic compounds, DNA has also been isolated from vesicles. Vesicles produced by Pseudomonas aeruginosa were reported to contain DNA (22). Vesicles released by Neisseria gonorrhoeae harbor both linear and circular DNA, including 4.2- and 7.1-kb plasmids (12). Chromosomal and bacteriophage-associated virulence genes were detected in Escherichia coli O157:H7 vesicles (26). Moreover, this research demonstrated that DNA was protected from digestion by DNase, suggesting that DNA is packaged within vesicles (26). Bacterial evolution often proceeds by horizontal gene transfer between different genera and species (1, 7). Antibiotic resistance genes and pathogenicity islands have been acquired by a variety of pathogens, including E. coli, Salmonella enterica serovar Typhimurium, Yersinia pestis, Dichelobacter nodosis, and Helicobacter pylori (19). Virulence factors contributing to the pathogenicity of E. coli O157:H7, including Shiga toxins (45, 46) and intimin (31, 44), are encoded on pathogenicity islands in the O157 chromosome and are thought to have been acquired by horizontal transfer. Results of previous studies suggest that vesicles may be involved in the transfer of genetic material among similar bacterial species (8, 12, 26). The hypothesis has been put forth that vesicles influence antibiotic resistance in other bacteria in two ways: by physical dissemination of preformed antibiotic-inactivating enzymes into the recipient periplasm and by delivery of antibiotic resistance plasmids (3, 12). Competent Haemophilus influenzae produces vesicles which are released into the medium when cells are returned to normal growth conditions or a noncompetent state (8). Specific DNA-binding peptides were reported to be present on the surfaces of H. influenzae vesicles (24, 25) and to be associated with vesicles from N. gonorrhoeae (11). Previously, it was reported that vesicles released by E. coli O157:H7 into culture medium contain virulence genes and Shiga toxin (26). In the present study, we demonstrate that E. coli O157:H7 vesicles mediate the transfer of virulence genes, which are subsequently expressed by recipient enteric bacteria. Moreover, the origin of the DNA in E. coli O157:H7 vesicles is elucidated. Observations show that in addition to bacteriophage-associated genes, E. coli O157:H7 vesicles contain plasmids and fragments of chromosomal DNA.

Construction of broad-host-range plasmid vectors for easy visible selection and analysis of promoters.

Abstract: We have constructed a series of broad-host-range plasmids which use "visual screens" to detect promoter activity. These plasmids contain the pMB1 and pRO1600 origins of replication and are capable of replicating in a wide range of gram-negative bacteria. The genes encoding beta-galactosidase and alkaline phosphatase from Escherichia coli and bacterial luciferase from Vibrio harveyi supply the promoterless indicator genes. The constructs were tested in E. coli and Pseudomonas aeruginosa.

Cloning and sequencing of a Shiga-like toxin type II variant from Escherichia coli strain responsible for edema disease of swine.

Abstract: A Shiga-like toxin type II variant (SLT-IIv) is produced by strains of Escherichia coli responsible for edema disease of swine and is antigenically related to Shiga-like toxin type II (SLT-II) of enterohemorrhagic E. coli. However, SLT-IIv is only active against Vero cells, whereas SLT-II is active against both Vero and HeLa cells. The structural genes for SLT-IIv were cloned from E. coli S1191, and the nucleotide sequence was determined and compared with those of other members of the Shiga toxin family. The A subunit genes for SLT-IIv and SLT-II were highly homologous (94%), whereas the B subunit genes were less homologous (79%). The SLT-IIv genes were more distantly related (55 to 60% overall homology) to the genes for Shiga toxin of Shigella dysenteriae type 1 and the nearly identical Shiga-like toxin type I (SLT-I) of enterohemorrhagic E. coli. (These toxins are referred to together as Shiga toxin/SLT-I.) The A subunit of SLT-IIv, like those of other members of this toxin family, had regions of homology with the plant lectin ricin. SLT-IIv did not bind to galactose-alpha 1-4-galactose conjugated to bovine serum albumin, which is an analog of the eucaryotic cell receptor for Shiga toxin/SLT-I and SLT-II. These findings support the hypothesis that SLT-IIv binds to a different cellular receptor than do other members of the Shiga toxin family but has a similar mode of intracellular action. The organization of the SLT-IIv operon was similar to that of other members of the Shiga toxin family. Iron did not suppress SLT-IIv or SLT-II production, in contrast with its effect on Shiga toxin/SLT-I. Therefore, the regulation of synthesis of SLT-IIv and SLT-II differs from that of Shiga toxin/SLT-I.

Genetic characterization of highly fluoroquinolone-resistant clinical Escherichia coli strains from China: role of acrR mutations.

Abstract: The genetic basis for fluoroquinolone resistance was examined in 30 high-level fluoroquinolone-resistant Escherichia coli clinical isolates from Beijing, China. Each strain also demonstrated resistance to a variety of other antibiotics. PCR sequence analysis of the quinolone resistance-determining region of the topoisomerase genes (gyrA/B, parC) revealed three to five mutations known to be associated with fluoroquinolone resistance. Western blot analysis failed to demonstrate overexpression of MarA, and Northern blot analysis did not detect overexpression of soxS RNA in any of the clinical strains. The AcrA protein of the AcrAB multidrug efflux pump was overexpressed in 19 of 30 strains of E. coli tested, and all 19 strains were tolerant to organic solvents. PCR amplification of the complete acrR (regulator/repressor) gene of eight isolates revealed amino acid changes in four isolates, a 9-bp deletion in another, and a 22-bp duplication in a sixth strain. Complementation with a plasmid-borne wild-type acrR gene reduced the level of AcrA in the mutants and partially restored antibiotic susceptibility 1.5- to 6-fold. This study shows that mutations in acrR are an additional genetic basis for fluoroquinolone resistance.