Selective media

The rationale for the selective media used in the isolation of the TK variants is discussed in Sections III and IV. Basically, the TK locus appears diploid, and the three possible genotypes—the (TK- 

Donald Clive, W. Gary Flamm, and James B. Patterson 

TK-deficient cells grow in media supplemented with 50 

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The varying metabolic activities of bacteria and their response to immediate environmental factors have been exploited in the design of special diagnostic and selective media. Recipes for these run into many hundreds such media are used in hospital and public health laboratories for identifying organisms found in samples believed to be contaminated by them, and as an aid to diagnosis and treatment. In addition they are used to detect contaminants in pharmaceutical products (British Pharmacopoeia 1993). A few examples will be given to illustrate the principle. 

Selective media for staphylococci. It is often necessary to examine pathological specimens, food and pharmaceutical products for the presence of staphylococci, organisms which can cause food poisoning as well as systemic infections. 

Selective media for pseudomonads. These media depend on the relative resistance of pseudomonads to the quaternary ammonium disinfectant cetrimide. In some recipes the antibiotic nalidixic acid (Chapter 5) is added, to which pseudomonads are also resistant. 

Selective media for legionellas and listerias. Such have been devised. 

Frisvad J C, Filtenborg O, Lund F and Thrane U (1992), New selective media for the detection of toxigenic fungi in cereal products, meat and cheese , in Samson R A, Hocking A D, Pitt J I and King A D Modem Methods in Food Mycology, Elsevier Science Publishers, Amsterdam, 275-285. 

Trust in risk information about food-related hazards is an important determinant of public reactions to risk information. One of the central questions addressed by the risk communication literature is why some individuals and organizations are trusted as sources of risk information whereas others are not. Industry and government often lack public trust, whereas other sources are highly trusted (such as consumer organizations, selected media, and physicians). Their analyses indicate that knowledge in itself does not make one a trusted source, but that trusted sources are characterized by multiple positive attributes. 

Once the recombinant vectors have been produced, they are used to transform host cells. In the example of the plasmid pBR322, the host cells are bacteria. Once transformed, the bacteria are plated on selective media so that bacteria transformed with a recombinant plasmid can be easily identified. In the case of plasmid pBR322 shown in Figure 1-6-3, bacteria with recombinant plasmids would be resistant to ampicillin but sensitive to tetracycline. 

Resistance Tests. Several transformants were tested for their ability to grow on all three selective media. These transformants were streaked onto nutrient agar plates containing 0.1% naphthalene, dibenzofuran, or... 

Recommended Feed Volumes. Both feed volume and magnetic solids discharge rate should be balanced in selecting media recovery drum size. The feed rates typically recommended for single and double wet drum separators depend on drum diameter. For a 762 mm dia single drum, the recommended feed rate is 50—55 m3/(hrn) for either a 914 mm dia single drum or a 762 mm dia double drum, 55—70 m3/(h-m) for a 914 mm dia double drum, 70—95 m3/(h-m). 

Figure 16.1. Schematic representation of the yeast two-hybrid system for evaluation of protein-protein interactions. Haploid yeast of a and a cells can mate to form (a/a) diploid cells. (A) If two test proteins, PT1 and PT2—expressed in (a/a) diploid cells as fusion proteins of DNA binding domains (DAB) and activation domains (AD) of yeast gene-transcript activator proteins—bind to each other, the binding interaction allows the diploid cells to grow in histidine selection media. Histidine selection media is permissive for diploid cells that express the HISS reporter gene only if PT1 and PT2 interact. (B) If PT1 and PT2 do not interact, no HISS gene product is expressed and the hybrid cell cannot grow in histidine media.

Any general purpose, solid bacteriological medium, such as tryp-ticase soy agar or blood agar, can be used. Selective media are... 

Methods that require the re-isolation and growth of cells encounter a separate series of problems. Cells isolated from environmental sources do not always grow up on minimal or selective media as do lab-cultured cells. Environmental isolates... 

Of the various media used in thin-layer chromatography, many are adaptable to the deoxy sugars and their derivatives. Some selected media, solvent systems, and types of derivatives are listed in Table II. 

Different selective media may enhance growth of different sorts of epithelial cells from such cultures (Chung et al., 1982) but the differentiated functions are rapidly lost if serum is added to the medium (Lieberman and Ove, 1958 Becker and Willis, 1979). The selectivity of particular defined media can be a disadvantage in that each individual cell type requires a different defined media. 

For selective media used and details regarding soil treatments see Blum and Shafer.7 Selective media used glucose as the carbon source. b Bacteria —fast growing bacteria that produce colonies > 1 mm diameter in 6 days c pmol/g phenolic acid treatments... 

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