![]() You will learn more about the strategies antibiotics use to cross the cell wall in Week 3. In contrast, the thick, porous peptidoglycan layer in the cell wall of Gram-positive bacteria gives greater access to antibiotics, allowing them to more easily penetrate the cell and/or interact with the peptidoglycan itself. In terms of bacteria: Gram positive bacteria have a thick peptidoglycan layer and no outer lipid membrane whilst Gram negative bacteria have a thin. This second, outer membrane of Gram-negative bacteria is an effective barrier, regulating the passage of large molecules such as antibiotics into the cell. Using a particular staining process the bacteria could be determined either gram-positive or negative, depending on whether they retained (positive) or lost (negative) a violet color during this. Gram Staining Gram-positive bacteria have a thick peptidoglycan layer which is dehydrated by ethanol, trapping the crystal violet stain Gram-negative bacteria. YM (yeast and mold) which has a low pH, deterring bacterial growth. Eosin methylene blue (EMB) that contains methylene blue toxic to Gram-positive bacteria, allowing only the growth of Gram negative bacteria. Figure 10 Arrangement of the cell wall in (a) Gram-positive and (b) Gram-negative bacteria. In 1884 a Danish physician, Christian Gram, discovered that bacteria could be separated into two distinctive groups, gram-positive and gram-negative. While the plate on the right selectively only allows the bacteria Neisseria gonorrhoeae, to grow (white dots). The inner membrane in (a) and (b) (shown as a double green line) is separated from the peptidoglycan layer by the periplasmic space. In the Gram-positive bacteria in (a) the peptidoglycan is a thick external layer shown in brown, while in the Gram-negative bacteria in (b) the peptidoglycan layer is much thinner and is surrounded by an outer membrane of lipopolysaccharide and protein (as a green wavy line). Learn the characteristics, types, and treatment of gram-positive and gram-negative bacteria, which are bacteria with thick peptidoglycan and a hard outer shell. This diagram shows the differences in cell wall structure between Gram-positive and Gram-negative bacteria.
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