Presence-absence test

Semi-quantitative tests Most probable number (MPN) tests These are based on the presence/absence test. Decimal dilutions of the test sample are inoculated into a set number of tubes of liquid media. Bacterial densities can be determined from... 

If the number of target organisms in a sample is too low to be detected directly with one of these tests or if their growth is suppressed by competitive (non-target) microorganisms, it is necessary to carry out a pre-enrichment culture of the target organisms in a selective broth. This will never be a quantitative test, but more a presence/absence test. 

In microbiology two fundamental types of measurements are used by the analyst. The simplest ones consist in counting colonies on culture media in a Petri dish. Another principle consists in evaluating the most probable number of microbes by inoculating sub-samples into multiple tubes. The result of the latter is given by statistical tables. For both types of methods results are only available after a few days. For the presence of very few microbes, so-called presence/absence tests have been developed by microbiologists. They are mainly used for the detection of pathogenic microbes. For the last two types... 

In principle, the theory used for the presence-absence testing is the same as for counting large numbers of cfp, but differs in its application. Low count materials are characterised by the fact that some capsules contain no organisms. Because the certified value is in reality a fraction of negatives (capsules without bacteria), the fraction of negative isolations in the laboratory will be compared to the certified number of negatives. 

The objective of the presence-absence test is not to determine the concentration of microorganisms present in a sample, particularly drinking water sample, but to know simply whether the organism is present or absent. After inoculation in a suitable medium and incubation, a positive result is indicated by changes or growth in the medium. The test is usually used to examine on a routine basis samples (100 mL in a single culture container) from water treatment plants or distribution systems. It should be followed with further tests to determine the densities of the organism of interest, if a positive test is obtained. 

Four methods may be used to detect and enumerate total coliforms, fecal coliforms, and E. coli in water samples. These are grouped as (a) multiple tube fermentation technique also known as the MPN technique, (b) membrane filtration technique, (c) presence/absence test, and (d) use of the enzymatic substrates test also known as the chromogenic-fluorogenic substrate test. 

Presence/absence test for total coliforms This test uses P-B broth and is intended for obtaining qualitative information on the presence or absence of coliform bacteria in samples, particularly drinking water samples. The test is usually used to examine on a... 

This test may be in form of a presence-absence test, i.e., single 100 mL sample or multiwell or multitube. Several chromogenic and fluorogenic liquid and solid media have been developed and are commercially available for simultaneous detection of conforms and E. coli (Table 4.11). 

Clinical tests are targeted to measure the concentration of different sets of compounds, such as small molecules (e.g., amino acids, fatty acids, organic acids, steroids) and peptides and proteins (e.g., thyroid stimulating hormone, hemoglobin A 1C) and oligonucleotides (e.g., DNA, RNA, SNPs). The presence, absence, or altered concentrations of a diagnostic compound or compounds may indicate the presence of a disease, type and severity of a disease, risk factors for disease, what is the basis for... 

Component or group of components of which the presence/absence or mass fraction/concentration is to be determined in the test sample. 

The solution resulting from dissolving the test portion and treating it according to the analytical procedure. The test solution may be used directly to determine the presence/absence or the mass fraction or mass concentration of the analyte without attributable sampling error. Alternatively, an aliquot (2.2.9) may be used. 

When the experiments were performed at the same pressure, temperature, and moisture content but with toluene as modifier and with a static extraction time of 15 or 30 min prior to the dynamic extraction step, then recovery was most affected by moisture content (sum of ranks 88) followed by pressure (sum of ranks 70) and the toluene volume (sum of ranks 68). The fourth variable to influence was the static extraction time (sum of ranks 57). Temperature, volume of collection solvent, and the presence/absence of glass beads were the least important. Figure 6 shows the relative changes in recovery for each compound and for each of the seven variables investigated in Test 2. 

PDK-1 and a peptide substrate were incubated with Mg and ly- P]ATP in the presence of test agents using a range of concentrations. Inhibition of kinase activity was assessed by comparison of phosphorylated versus total substrate in the presence and absence of the test molecules. Results from these screens identified three inhibitors with IC50 values in the low nanomolar range. 

When a compound was identified at least in most samples of a group, an analysis of variance with interaction by the General Linear Model procedure was performed to check the effect of salt content (lower and higher), sodium nitrite (presence, absence), added amino acids (control, cysteine and proline) and reaction time (7, 14 and 21 days). When significant and more than two levels in an effect, multiple comparison by the Tukey test were carried out to compare means. Statistic analyses were performed by means of the SPSS version 11.0. 

In section 2.3.3.1 the existence of methods giving a presence/absence result are mentioned. With the results from such tests a breakdown of the overall error becomes quite complicated. Only two types of error can be clearly discerned, either the method incorrectly identifies a sample as positive (false positive) or it incorrectly identifies a sample as negative (false negative). A method is fully accurate if it avoids both types of error. 

The presence/absence procedure was based on the ISO method for the detection of Salmonella (ISO 6579) which is summarised as follows (1) pre-enrichment in Buffered Peptone water (incubation time (18 2) h at (37 1)°C) and (2) selective enrichment in broth of own choice (incubation time and temperature according to own procedure). The detailed procedure is described elsewhere [37]. Each laboratory determined the presence or absence of Salmonella in 50 capsules. Four of these individually identified capsules were negative control capsules. The numbers of these capsules were unknown to the laboratories at the time of analysis. For the presence/absence procedure, all capsules showing typical colonies on the isolation agar were subjected to a confirmation for Salmonella. At least two colonies per capsule were used for this confirmation. All colonies (>1000 colonies) tested by the laboratories gave a positive Salmonella identification. The type of confirmation test used is described elsewhere [37]. 

CO/H7 and H7yCO coadsorption. The presence/absence of multiple-vacancy Pt sites in the absence/presence of Ce02 in the support has been also checked through the competitive adsorption of other probe molecules, among which H2 (normally used to test the dispersion of supported Pt) and CO. Some quantitative aspects of the competitive adsorption of these probes was reported in table 2 here the spectroscopic aspects of their coadsorption will be dealt with. 

The standard deviations can be compared with the precision achieved by testing one factor at a time 1.414a. Precision is clearly much improved over that obtained with the "one factor at a time" technique. (The standard deviations for the "presence-absence" forms of the coefficients - see chapter 2, section II.B - defined... 

Re-suspend in Cl /I free medium (in the absence or presence of test compounds)... 

For qualitative (presence-absence) or semiquantitative determinations of cyanide, the easiest and most reliable method is a simple test with either Feigl-Anger or sodium picrate paper. The reactions on which these tests are based as well as other methods for detection of cyanogenic glycosides are described by Hegnauer (1986). 

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