Antibiotics surface activity

The mechanisms by which antibiotics exert their phytotoxic effects are for the most part unknown. There are doubtless many mechanisms. However, Brian (1957a) states that in the case of polymyxin this antibiotic appar tly disorganizes the cell membranes of surface root cells, possibly as a result of its marked surface activity, and the cell contents leak out. Whether other polypeptide antibiotics produce root injuries by the same mechanism is not known. 

Although the alkylphenols, the quaternary amines, and the polypeptide antibiotics are surface-active, this property alone cannot cause biological action (Luduena et al., 1955). Ordinary surface-active substances of the three charge-types (cationic, anionic, and neutral) are highly antibacterial, slightly anti-... 

Polyene antibiotics have slight surface-active properties and, although this property has been shown to play no role in the mechanism of action [103,345], the ability of polyenes to spread at surfaces makes them ideal drugs for topical... 

Differences in surface activity of antibiotics are of special interest, in view of the nephrotoxicity of the aminoglycosides, which has been... 

The cases mentioned above are typical of simple liquid-liquid extraction systems, which can be found in the traditional chemical industries. However, extraction systems in the biotechnological industries are more complicated because of the presence of microbial cells and surface active compounds produced during fermentation. The adsorption to the interface of soluble and insoluble surface-active compounds present in the fermentation broth usually causes a mass transfer resistance that reduces the transfer rates (Pursell et al., 2003a, 2003b, 2003c). This is in agreement with what has been found (Pursell et al., 1999) for the case of the extraction of the antibiotic erythromycin-A from a buffer solution and from filtered fermentation broth into 1-decanol the presence of the naturally occurred soluble surface active compounds in the filtered broth led to a 45% reduction in... 

Gradient epoxy rq)licas (five replica substrata per time period) were placed in 24-well plates together with epoxy replicas of SLA (sandblasted and acid etched) cpTi discs (Institut Straumann, Basel, Switzerland) [20] and titanium-coated Thermanox discs (Nunc, Wiesbaden, Germany) as reference surfaces. Substrata were sterilized and the surface activated by oxygen-plasma treatment (Harrick Plasma, Ithaca, USA) for 4min. Immediately after the plasma treatment, the substrata were covered with media (a-DMEM with 10% foetal bovine serum and 1% antibiotics). 

Note that complete baseline resolution has Rg > 1.5, and this level can be achieved for each analyte with at least one selector. In general, the best results are observed with ristocetin A, and teicoplanin is the most distinct of the three. This last antibiotic has particular aggregation properties. It is surface active due to the presence of a long hydrophobic chain in the radical R in the acyl group of jS-o-glucosamine (see above) and forms micellar aggregates above the critical micelle concentration of O.lSmM. Apparently, this may affect its recognition properties. 

There are various modes of action of antibiotics, such as inhibition of the biosynthesis of the bacterial cell wall, action as a surface-active agent on the bacterial cell membrane, inhibition of the formation and function of bacterial enzymes by trapping metal ions, which are normally enzyme activators, inhibition of the synthesis of proteins and bacteria, action on mitochondria, and so on. 

The plate assay method for antibiotics is the most widely used and accepted method employing the diffusion technique. Its advantages lie in its simplicity as to labor and equipment. It has definite disadvantages in that the assay is affected by various salts, surface active agents, and solvents which tend to change diffusion characteristics of the antibiotics. With alterations in the diffusion characteristics the dose response curves of the sample and standard will no longer be parallel and the assay itself would be invalid. 

The turbidimetric technique has advantages and disadvantages as in the case of the plate diffusion assay. It is fortunate that some of the disadvantages of one method are found to be no problem in the other. Within limits, turbidimetric methods are not affected by most solvents, surface active agents, organic salts, and impurities which may change an antibiotic s diffusion characteristics. Interference is encountered with highly... 

The polymyxins are a group of closely related lipopeptide antibiotics produced by B. polymyxa and related bacilli. As seen in O Fig. 10.5, polymyxin B is a decapeptide in which amino acids 3 through 10 form a cyclic octapeptide. A branched-chain fatty acid is connected to the terminal 2,4-diaminobutyric acid (DAB). The structures of polymyxins differ in substituents at residues 3 (DAB or D-Ser), 6 (o-Leu or L-Ileu), or 7 (d- or l-DAB) (Suzuki et al. 1965). The cationic 7y-amino groups of the DAB residues, together with the hydrophobic side chain of the fatty acid, give these antibiotics the surface-active properties of a cationic detergent. Pseudomonas strains produce viscosin, a peptidolipid biosurfactant which lowers surface tension of water to 27 mN/m (Neu et al. 1992). 

The study of the colloidal properties of many of the antibiotics is complicated by difficulties of purification and the results of some of the earlier work must be regarded critically. This is particularly so of the measurements of surface properties which are susceptible to error arising from the presence of low concentrations of surface active impurities. The effect of impurities on the bulk properties is not so serious, although the release of even small amounts of solubilized water-insoluble material as the solutions are diluted below the CMC can be a problem in such techniques as light scattering. 

The critical concentration for the association of many naturally occurring compounds is high and often is greater than circulating levels of the compound. This does not diminish the significance of association, for many hormones and other substances are concentrated in cells or special organelles. For example, the surface-active steroidal antibiotic, fusidic acid, is concentrated approximately fifty times inside E. coli in solutions of 2 x 10" gml" [333] and adenosine... 

Foam dressings are typically composed of polyurethane, but can also be constructed from rubber, acrylic, polyethylene, neoprene, etc. The value of urethane foams is derived from their well-established biocompatibility. Further to this, by suitable choice of diisocyanate and polyol combination, they can be tailored to be hydrophilic or hydrophobic. The former is useful in exudate reduction, while the latter may have lower adherence to the wound surface. These foams can be impregnated with pharmaceuticals, such as antibiotics, or activated carbon to reduce odor. 

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