Gram-negative cells

The Gram-negative cell envelope (Fig. 1.4) is even more complicated essentially, it contains lipoprotein molecules attached covalently to the oligosaccharide backbone and in addition, on its outer side, a layer of lipopolysaccharide (LPS) and protein attached by hydrophobic interactions and divalent metal cations, Ca and Mg. On the inner side is a layer of phospholipid (PL). 

Gram-negative cell walls are generally richer in lipides than Grampositive bacteria. 

Beveridge TJ (1999) Structures of Gram-negative cell walls and their derived membrane vesicles. J Bacteriol 181 4725 1733... 

The addition of polar groups to the R group, i.e. the group directly linked to the amide carbonyl, generally allows the penicillin molecule, e.g. amoxicillin, to more easily pass through the Gram-negative cell waU, and thus increases antibacterial activity. 

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. 4.12 Composition of typical gram negative cell wall and membrane...

Osborn, M.J. Studies on the Gram-Negative Cell Wall. I. Evidence for the Role of 2-Keto- 3-Deoxyoctonate in the Lipopolysaccharide of Salmonella Typhimurium. Proc Natl Acad Sci USA 50 (1963) 499-506. 

Methods of isolating bacterial cell-walls have been used mainly in studies of Gram-positive bacteria, but hydrolysates of similar preparations from Gram-negative cells reveal the sugar components of the somatic antigens. It was from cell-wall preparations of Escherichia coU that l-glycero-T)-manno-heTptose was isolated. ... 

Bacteria, gram-negative, cell-wall structure of, 273... 

The region between the outer surface of the cytoplasmic membrane and the inner surface of the outer membrane is called the periplasm. This occupies a distance of about 12-15 nm, is gel-like in consistency and, in addition to the peptidoglycan, contains sugars and an abundance of proteins including hydrolytic enzymes and transport proteins. Table 3.2 summarizes the major differences in wall composition between Gram-positive and Gram-negative cells. 

Table 3.2 Gram-positive and Gram-negative cell wall composition...

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

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