Gram positive cell

FIGURE 9.22 (a) The cross-link in Gram-positive cell walls is a pentaglycine bridge. 

The complex outer layers beyond the peptidoglycan in the Gram-negative species, the outer membrane, protect the organism to a certain extent from the action of toxic chemicals (see Chapter 13). Thus, disinfectants are often effective only at concentrations higher than those affecting Gram-positive cells and these layers provide unique protection to the cells from the action of benzylpenicillin and lysozyme. 

Glntaraldehyde also owes part of its mode of action to its ability to react with, and provide irreversible crosslinking in, the cell wall. As a result, other cell functions are impaired. This phenomenon is especially found in Gram-positive cells. 

The disaccharide fragments listed in this Table are not found in the polysaccharides of Gram-positive cell-walls. For references on the structures of O-specific and capsular polysaccharides mentioned in this Table, see Refs. 98 and 276. b The total number of isomeric, disaccharide fragments identified in different polymers is shown in parentheses. 

Carbohydrate chains of teichuronic acids and neutral polysaccharides linked to the carbohydrate chains of peptidoglycans are fragments of macromolecules of Gram-positive cell-wall. Only two examples of the biosynthesis of these polymers have been studied in detail. Evidence for both block and monomeric mechanisms of the chain assembly was obtained. 

Biosynthetic type of the main chain 1 O-Specific polysaccharides Exopoly- saccharides Gram-positive cell-wall Mechanisms of the chain... 

Abbreviations for biosynthetic types are composed from abbreviations of nucleoside residues of activated forms of the monosaccharide components. 6 See footnote a to Table VI lin. and br. mean linear and branched polysaccharides. c Including other bacterial amphi-philes of Gram-negative, outer membranes. d Including amphiphiles of Gram-positive cell-membranes. 

Flood the smear with 95 percent ethyl alcohol for 10 to 20 seconds and rinse the slide with water. Gram-positive cells will remain violet, but gram-negative cells will be colorless. 

Fig. 4.9 Illustration of the gram positive cell wall and membrane...

Vancomycin, a natural product that was first approved in 1955, is still the prototype for structural variations with the same mechanism of action the binding to the terminal L-Lys-D-Ala-D-Ala tripeptide in Gram-positive cell wall biosynthesis. The compounds below are semi-synthetic modifications of the same basic structural class (glycopeptides) as the prototype vancomycin, thus following in the chemical footsteps of the (1-lactams currently, there are three semi-synthetic glycopeptides, oritavancin 39, telavancin 40 and dalba-vancin 41, in late stage clinical development. 

The bacteriostatic activity of a series of substituted trans-3-benzoylacrylic acids has been successfully correlated by Hansch linear free energy relations involving polar and partition substituent constants. The activity-lipophilicity relations for this series closely parallel those found previously for other antibacterial agents, with an ideal lipophilic character for gram-positive cells of 6.1 and, for linear dependence, a slope of 0.7. A polar reaction constant, p, of about —0.6 to —0.7 is given. A possible mode of action for these acids and their related substituted cis- and trans-3-benzoyl acrylic acids and esters is discussed as an enzyme-inhibitor interaction. 

Feature Gram-positive cells Gram-negative cells... 

Invaginations of the cytoplasmic membrane are referred to as mesosomes. Those that form near the septum of Gram-positive cells serve as organs of attachment for the bacterial chromosome. 

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