Antibiotics assays

Several workers (28-29) reported an increase in the methylene blue reduction time when 0.05-0.5 lU Penicillin were present per milliliter of milk. Similarly, Manokidis et al. (30) noted that Penicillin and Oxytetracycline were responsible for a false positive phosphatase test in pasteurized or partially pasteurized milk while Streptomycin, Erythromycin and Neomycin inhibited the phosphatase test to some extent in partially pasteurized milk, but not in raw milk. Although raw milk containing antibiotic residues was never mistakenly identified as pasteurized, these authors suggested that as a "precaution" antibiotic assays be run in conjunction with the phosphatase test. 

The Court s opinion on outliers was that since, for chemical testing, the USP does not provide for outliers, the use of outlier testing for chemical analyses is prohibited. The Court also agreed that the USP specifically allows outlier testing for biological and antibiotic assays. (This opinion has been challenged a number of times on scientific grounds.)... 

There are a number of chemical and physical requirements for bacterial growth, such as carbon and nitrogen sources, pH, and temperature (see Chapter 1). Some antibiotic assay organisms, such as Bacillus subtilis and Escherichia coli, grow on simple media, others, such as the lactobacilli used for vitamin assay, need an enriched medium containing a wide range of nutritional supplements. Many media are commercially available in the dehydrated form from various suppliers. 

Antibiotic assays can be carried out in the form of agar diffusion assays, or as tube assays in liquid media. ... 

Tube assays of disinfectants are considered in Chapter 10 under the heading of MIC values. The principles for antibiotic assay using these methods is the same. 

These are basically the same as the antibiotic diffusion system, except that a zone of growth is formed. A series of high and low standards and tests are prepared and the calculations are identical to those carried out in the antibiotic assays (Figure 11.9). 

Vial, J. L., and Preib, F. B., 1967, Antibiotic assay of dermal secretions from the salamander, Plethodon cinereus, Proc. Mo. Acad. Sci., 1 37. 

A casual examination of the current literature indicates that there is considerable confusion regarding antibiotic assay standards with regard to the terms unit and microgram used to indicate potency. Bacitracin and polymyxin are defined in terms of antimicrobial units which are not directly expressible in terms of weight of the compounds since these antibiotics have not been isolated in pure form penicillin originally fell into this category until its crystallization. For others which have been isolated in pure... 

Precautions and Special Recommendations. Logically enough, success or failure in the laboratory performance of antibiotic assays is determined by the care with which the specimen is obtained, the time interval which elapses between acquisition of the specimen and performance of the test, and the background information supplied with the specimen. 

The cup plate method of assay (51) is similar to the widely used method of antibiotic assay except that a vitamin Bts deficient medium is employed and zones of stimulation rather than zones of inhibition are measured. The method described in this section is that of Harrison, Lees, and Wood (15). 

In practice, both the plate-diffusion and the turbidimetric tube-dilution methods are used for antibiotic assays but for vitamin assays the tube-dilution method is preferred. The recommended methods for the antibiotics and vitamins, together with the suggested media, organisms, etc., are given in Tables 64 to 66. 

Culture Media and Buffer Solutions for Antibiotic Assays ... 

Luciferin includes a whole family of compounds whose heterocyclic structures vary fix>m one organism to another. Most luciferase enzymes use the same cofactors as metabolic processes (ATP, FMN, NADH), and bioluminescence is easily associated with other types of Inological reactions for analytical applications. Firefly ludferase is used tt> follow processes that use adenosine triphosphate (ATP) as a cofactor, for example, the measurement of biomass, the detection of a bacterial infection, antibiotic assays, and the monitoring of other enzymatic reactions that consume or produce ATP. Luciferase catalyses all these reactions according to the following overall reaction scheme ... 

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