Unrelated concentrations

Many of the by-products of microbial metaboHsm, including organic acids and hydrogen sulfide, are corrosive. These materials can concentrate in the biofilm, causing accelerated metal attack. Corrosion tends to be self-limiting due to the buildup of corrosion reaction products. However, microbes can absorb some of these materials in their metaboHsm, thereby removing them from the anodic or cathodic site. The removal of reaction products, termed depolari tion stimulates further corrosion. Figure 10 shows a typical result of microbial corrosion. The surface exhibits scattered areas of localized corrosion, unrelated to flow pattern. The corrosion appears to spread in a somewhat circular pattern from the site of initial colonization. 

The limitations of ELISA methods include the specificity of antibodies, the concentrations of primary antibody and antigen, and the type of reaction solution. Nonspecific binding of either of the antibodies to related antigens, unrelated proteins of other bacteria, or even the microtiter plate may lead to false positive reactions.49,52 57 Use of a monoclonal antibody may decrease crossreactivity with other antigens. For detection of low numbers of bacteria, as in drinking water, the sample may be filtered to concentrate the cells or cultured in a selective broth until it reaches the minimum detection limit for ELISA.49,58 Commercial test kits using dipsticks, immunoblots, and sandwich ELISA methods have been developed for the identification of pathogenic bacteria.58,59... 

When the bacteria to be detected are less than 1% of the total population in a sample, IFAs cannot be used because of interference from unrelated particles that are concentrated when large volumes of sample are filtered. To overcome this problem, the organism of interest may be concentrated by immunomagnetic separation.10,51 62 For this procedure magnetic beads coated with monoclonal or polyclonal antibodies are mixed with the sample. The beads are collected with a magnet, and the cells attached to the beads then are removed, enumerated, and identified by IFAs. 

The method described here provides a convenient means of determining the specific filtration resistance of fairly dilute suspensions. Results for clay suspensions flocculated by cationic polymers show that the specific resistance gives a sensitive indication of flocculation and is a useful guide in the selection of optimum flocculant concentrations. In a series of trials not reported here, it has been shown that the specific resistance results are very well matched by re-filtration rate data, as expected. The results also agree well with other, unrelated techniques. For more concentrated suspensions, some discrepancies have been found between permeability methods and other measures of flocculation (4). 

Current methods for DNA detection usually require enzymatic amplification of the target DNA sequence prior to analysis. For example, the PCR technique selectively increases the concentration of the target sequence relative to unrelated sequences. PCR methods, however, introduce ambiguities resulting from contamination by different DNA sequence. Therefore, a definitive method is required for the analysis of a single, original DNA sequence. To achieve this objective, the sensitivity and speed of the chemiluminescent enhancement techniques described in this chapter must be improved. 

Growth hormone. Mood disorders have been related to alterations in the activity of the growth-hormone axis. A blunted growth-hormone response to clonidine, an a2 receptor agonist, has been consistently found in depression. Increased growth-hormone secretion during the day and decreased nocturnal growth-hormone secretion have also been observed in depressed patients. Depressed patients have lower CSF concentrations of somatostatin, compared to those with schizophrenia and normal controls. While lower CSF somatostatin is a state-dependent marker of depression, it occurs in a number of unrelated nonpsychiatric conditions, and thus appears to be relatively nonspecific. 

In a monograph of this kind it has not been possible, nor indeed is it desirable, to segregate completely synthetic chemical methods from biological action. Such a separation would inevitably lead to a catalogue of entirely unrelated facts. Nevertheless, some effort has been made to concentrate particular aspects of the subject in different sections or chapters but the interrelationships of chemical constitution with biological activity, have always been kept in mind. 

It is important to note that not all of the variability in Lp(a) levels can be explained by isoform size variability in Caucasians, only 40-70% of the variation results from differences in the numbers of kringle IV repeats in the gene (B15, B16). Interindividual variation (—22%) also occurs as a result of as yet undefined cis-acting sequences at the apo(a) locus (B15). In some cases, unrelated individuals with the same-sized apo(a) gene and protein have been shown to possess markedly different plasma Lp(a) concentrations (B15, L5) within families, however, the relationship between apo(a) gene size and plasma Lp(a) con-... 

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