Gram cell wall structure

Fig. 2. Cell wall structure of (a) Gram-positive and (b) Gram-negative bacteria.

Fig. 1.6 Schematic drawing of the cell wall structure of Gram-positive bacteria.

The mechanism of antibacterial activity is through inhibition of gram-positive bacterial cell-wall synthesis thus, the penicillins are most effective against actively multiplying organisms. Because mammalian cells do not have a definitive cell-wall structure as do bacteria, the mammalian toxicity of the penicillins is low. Allergic phenomena in patients following sensitization may occur. 

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

The different result in the Gram test observed between these two types of bacteria is due to differences in their cell wall structure. These differences in cell wall structure have important consequences in the sensitivity of the two types of bacteria to certain types of antibacterial agents. It is believed that Gram-negative bacteria have an extra outer layer. 

Bacteria are classified into two groups on the basis of a staining reaction discovered by Gram in 1884. In this reaction, the cells do or do not retain a crystal violet-iodine dye complex after an alcohol wash. Cells that retain the stain are gram-positive those that do not are gramnegative. This empirical classification divides bacteria into two classes that differ in cell wall structure. 

The antibacterial properties of penicillin were discovered by Alexander Fleming in 1929. These natural penicillins produced by several species of the mold Penicillium, had a number of drawbacks. They were effective only against a type of bacteria referred to as Gram positive because of a staining reaction based on their cell wall structure. They were also very susceptible to destruction by bacterial enzymes called (l-lactamases, and some were destroyed by stomach add and had to be administered by injection. 

The bacterial cell wall is the first line of defense against environmental stress in gram-positive bacteria. Thus, selection schemes that change the cell wall structure can potentially make cells more resistant to environmental stress. D-cycloserine is an antibiotic that inhibits alanine racemase and D-alanine D-alanine ligase, both involved in cell wall biosynthesis. Mutants resistant to this antibiotic have been isolated in a number of gram-positive species and shown to have differences in surface properties (Clark Young, 1977 Reitz, Slade, Neuhaus, 1967). We have used D-cycloserine as a selective agent to directly select mutants in a variety of strains and found that the mutants obtained have properties useful in industrial fermentation processes. 

In this paper, we show how the nmr resonances of one cellular organelle, the gram positive bacterial cell wall, can be studied in vivo. Although these measurements are far from complete, vivo nmr has begun to provide insights into the physico-chemical basis of cell wall structure and function, which cannot be obtained from other spectros-cqpic measurements, electron microscopy, or biochemical analyses. 

Gram-negative bacteria with their complex cell wall structure are much more resistant to cationic microbicides such as QACs than are Gram-positive bacteria. It is assumed that the cationic surface-active QACs form clumps... 

Gram negative and Gram positive refer to whether a stain is lost or retained by microbes after application and destaining procedures, respectively. The difference in stainability relates to the cell wall structure, which, in turn, provides a means for contrasting different types of bacteria. 

GRAM-POSITIVE (NEGATIVE) Refers to a property of bacteria to accept and retain (or reject) a stain in the cell wall. Retention of the stain indicates the presence of certain cell wall structures, which serves to help identify the strain of bacteria. 

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

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