Diffusion, agar

Assay Methods. The primary assay for the streptovaricins is the microbiological assay using the agar diffusion method or a turbidimetric procedure (60). The streptovaricins can also be identified by paper (60,88) or thin-layer chromatography (3). 

First of all, the allelopathic activity of a compound (or of a mixture of compounds) isolated as per the above methods should be tested in agar diffusion assays using different algal strains The selection of an assay alga depends primarily on its ability to grow satisfactory under the chosen... 

The first study was performed by Venturini [97, 98] in both rats and dogs by using a microbiological assay (i.e. agar diffusion test and S. aureus 209 P FDA as test organism). Conversely from rifampicin, whose serum levels were already detectable 30 min after the administration and still measurable after 48 h, only trace amounts (i.e. 0.2 pg/ml) of rifaximin were detected in serum of fed rats 4 h later (fig. 6). The amount of detectable antibiotic was reduced by 50% in fasted animals. Similar results have been obtained in dogs after oral administration of 25 mg/ kg of both rifamycin derivatives [97, 98], No detectable amount of rifaximin was found in serum at any time. 

The microbiological methods used for the determination of CTC potency in body tissues and fluids, bulk products, and pharmaceutical formulations can be separated into two testing procedures (1) agar diffusion plate method (cylinder-plate) and (2) turbidimetric method. 

Agar diffusion plate method (cylinder-plate) This method is employed for determining the... 

Since gramicidin is not very soluble in aqueous solution, relatively few agar diffusion assays have been reported. 

Ceriotti has reported an agar diffusion assay for gramicidin utilizing Micrococcus lysodeikticus 1. ... 

Kreuzig has studied the agar diffusion assay for tyrocidine in detail using gel chromatography as an analytical technique146. 

A comparison of the G.L.C. and microbiological (agar-diffusion) assays has been reported by Tsuji et al239 who showed the neomycin content of neomycin sulphate powders determined by the G.L.C. method, to correlate well with values obtained by the microbiological assay when it is assumed neomycin C has 35% of the biological activity of neomycin B. 

In the simpler agar-diffusion technique the relative distances of the HpHb lines and the HBG line from the serum and antiserum wells are used as a basis for typing. 

Si assays utilizing the agar diffusion systems (1 ). Microbiological... 

The agar diffusion method is the typical choice for bioassays of antibiotics, but is unsuitable for antibiotics consisting of heterogeneous mixtures of closely related compoimds, which are scarcely soluble in water and diffuse poorly in agar gel. In addition, those antibiotics that are unstable in bright sunlight and produce zones of inhibition that may be neither clear nor proportional in size to the logarithm of the antibiotic concentration are difficult to assay by this method. 

Antimicrobial activity of the medication was determined by the agar diffusion method [4, 5]. A wide spectrum of pyogenic microflora (Table 16.1) as well as Candida spp. and Helicobacter pylori were studied as test cultures. 

Agar-diffusion tests with the anti-isomaltose, myeloma protein and several dextran preparations showed that the protein does indeed combine with a number of dextrans. Results of gel electrophoresis of the sample showed that the purified myeloma protein consisted of several multimolecular forms.107 This observation is at variance with a report that the W3129 myeloma protein isolated from the same type of serum was homogeneous.168 Additional studies are needed in order to establish whether the anti-isomaltose, myeloma protein is synthesized as a homogeneous protein or in multimolecular form. 

The BR-test constitutes a nonspecific screening assay for the systematic control of raw milk, which combines principles of both agar diffusion and color reduction procedures (36). In this test, the sample is introduced into a microtiter... 

Over the years, numerous methods have been developed for detecting antibacterial residues in animal tissues. Most of these methods are agar diffusion... 

To overcome this problem, an agar diffusion test has been developed to detect chloramphenicol residues in the urine of slaughtered animals (87). The principle of the test is based upon incorporation of -glucuronidase in an agar medium shown with Bacillus subtilis. With this test, the glucuronide of chloramphenicol, which is the major metabolite in urine, is hydrolyzed and the antibacterial activity is demonstrated according to the usual microbiological detection assays. 

Miscellaneous. A manometric technique utilizing a Warburg apparatus has been used to follow esterase activity. The carbon dioxide liberated from sodium bicarbonate by the fatty acids is measured (Willart and Sjostrom 1959). An agar diffusion procedure has been utilized for screening microorganisms for lipolyptic enzymes. The presence of lipase is indicated by clear zones in the turbid media (Lawrence et aL 1967). 

By the dialysis method, the protein binding of moxalactam was 43 percent and by the agar-diffusion method, 40 percent (6). By an ultrafiltration method, the binding of moxalactam in pooled fresh human plasma was 50.7 percent at physiologic temperature and pH (38). 

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