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.

Screening of Probiotic Activities of Forty-Seven Strains of Lactobacillus spp. by In Vitro Techniques and Evaluation of the Colonization Ability of Five Selected Strains in Humans

Abstract: It is well known that the presence of lactobacilli is important for the maintenance of the intestinal microbial ecosystem (39). They have been shown to possess inhibitory activity toward the growth of pathogenic bacteria such as Listeria monocytogenes (3, 25, 36, 42), Escherichia coli, Salmonella spp. (8, 16, 27), and others (4, 13, 37). This inhibition could be due to the production of inhibitory compounds such as organic acids, hydrogen peroxide, bacteriocins (30), or reuterin (4) or to competitive adhesion to the epithelium. In order to survive in and colonize the gastrointestinal tract, probiotic bacteria should express high tolerance to acid and bile and have the ability to adhere to intestinal surfaces (31, 34). Survival in and temporary colonization of the human gastrointestinal tract have been demonstrated for some lactic acid bacteria (1, 23, 29). However, in vivo testing is expensive and time consuming and requires approval by ethical committees. Therefore, reliable in vitro methods for selection of promising strains are required. Enterocyte-like Caco-2 cells (38) have been successfully used for in vitro studies on the mechanism of cellular adhesion of nonpathogenic lactobacilli (10, 24, 40, 43) and bifidobacteria (5, 15). Moreover, this cell line has been used to examine the mechanism of cellular adhesion and invasion of pathogenic bacteria such as L. monocytogenes (21), Salmonella typhimurium (20), and E. coli (32). Recently, Caco-2 cells have been used to examine the antimicrobial activity of lactobacilli (6, 13, 27) and bifidobacteria (5) against pathogenic bacteria. Antimicrobial properties of lactobacilli have been determined by using three methods: inhibitory activity toward the growth of test bacteria in vitro (7, 13, 14), inhibitory activity toward cell association, and invasion of pathogens using cultured human intestinal cells (6, 7, 12–14, 27), as well as protection of conventional or germfree mice against bacterial infection (7, 13, 14, 27). These showed how antimicrobial activities observed by in vitro methods could be confirmed in vivo as well. In the present study, the Caco-2 cell line was used to study the adhesive properties of 47 potentially probiotic cultures in vitro. The cultures were also examined for antimicrobial properties toward pathogenic bacteria along with tolerance to low pH and bile salts. Among these cultures, five promising strains were examined by in vivo studies. The abilities of the selected strains to survive passage through the gastrointestinal tract and maintain colonization was tested in fecal samples using API 50CHL and internal transcribed spacer PCR (ITS-PCR) for primary selection of strains and restriction enzyme analysis (REA) combined with pulsed-field gel electrophoresis (PFGE) for confirmation of isolates recovered from fecal samples during and after administration. It was the main objective of this study to compare the in vitro evaluation of certain properties of various Lactobacillus spp. that are important for their survival in the gastrointestinal tract with their actual ability to survive in vivo.

The purification of eukaryotic polypeptides synthesized in Escherichia coli.

Abstract: Over the last 13 years, manipulation of DNA in vitro has developed from the transfer of genetic information between prokaryotic organisms (Cohen et al., 1973) to a technology which facilitates efficient and controlled production of proteins in foreign hosts. A significant feature of these developments is the ability to express eukaryotic genes in prokaryotes such as Escherichia coli (Harris, 1983; Wetzel & Goeddel, 1983). The supply of many eukaryotic polypeptides which have potential clinical or industrial use is often limited by their low natural availability. Gene cloning and expression in E. coli can provide a more abundant source of these polypeptides. The mode of gene expression affects the location of the proteins produced. The proteins may either be located in the cytoplasm of E. coli or secreted through the cell membrane. Eukaryotic genes cloned in frame with synthetic or bacterial nucleic acid sequences can be expressed as hybrid products in the cell cytoplasm. Transcription, from bacterial promoters, and translation, yield fusion proteins which include bacterial or synthetic polypeptide sequences in addition to the eukaryotic polypeptide. An alternative approach which locates proteins in the cytoplasm is direct expression, where bacterial promoters and terminators are used in the transcription of the foreign gene alone. In E. coli an ATG, or occasionally a GTG, sequence must precede the gene coding sequence, for translation initiation. Thus the primary products oftranslation possess an N-terminal methionine residue. E. coli possesses enzymes which catalyse the efficient removal of the methionine residues from natural proteins when required, but these enzymes do not work with the same efficiency on recombinant polypeptides and therefore directly expressed proteins may possess an unnatural N-terminal methionine residue. Finally, gene sequences which include a leader or signal sequence cloned in frame with the eukaryotic genes, when transcribed and translated can direct secretion of the eukaryotic polypeptides through the bacterial cell membrane. From the increasing number of reports of eukaryotic polypeptide synthesis in E. coli it is clear that the mode ofexpression affects not only the efficiency ofproduction, but the nature of the polypeptide product itself. In general, recombinant polypeptides accumulate to higher levels of total cell protein when expressed intracellularly than when secreted, but many of the polypeptide products located in the cytoplasm are insoluble and aggregated. The consequent isolation and purification techniques required are the subject of this Review.

Test for Escherichia coli Enterotoxin Using Infant Mice: Application in a Study of Diarrhea in Children in Honolulu

Abstract: In a new test for detection of Escherichia coli enterotoxin, supernates of broth cultures were injected into the stomachs of infant mice and fluid accumulation in the intestine was measured after 4 hr by weighing. Results with known positive and negative strains were comparable to those obtained with the rabbit-loop test, and the mouse test was easier to perform. Cholera toxin, unlike E. coli enterotoxin, did not dilate infant mouse intestine significantly, even in high concentrations. Use of the infant-mouse test in a study of 37 children with diarrhea in Honolulu revealed no enterotoxin-producing coliform bacteria in the stools. This is in contrast to studies reported from India, where such strains were found in a large proportion of undifferentiated cases of acute diarrhea in adults. None of 15 stock strains of E. coli serotypes generally thought to be enteropathogenic produced significant amounts of enterotoxin as measured by the test in mice.