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CAN YOU EXPLAIN MORE ABOUT GRAM POSITIVE & GRAM NEGATIVE BACTERIA
Gram-positive bacteria differ from gram-negative bacteria in the structure of their cell walls. The cell walls of gram-positive bacteria are made up of twenty times as much murein or peptidoglycan than gram-negative bacteria.
A Gram positive bacterium has a thick, multilayered cell wall consisting mainly of peptidoglycan (150 to 500 A) surrounding the cytoplasmic membrane. The peptidoglycan is a mesh like exoskeleton similar in function to the exoskeleton of an insect.  However, the peptidoglycan of the cell is sufficiently porous to allow diffusion of metabolites to the plasma membrane. The peptidoglycan is essential for the structure, for replication, and for survival in the normally hostile conditions in which bacteria grow. During infection, the peptidoglycan can interfere with phagocytosis, is mitogenic (stimulates mitosis of lymphocytes), and has pyrogenic activity (induces fever).
      The peptidoglycan can be degraded by treatment with lysozyme.  Without the peptidoglycan, the bacteria succumb to the large osmotic pressure differences across the cytoplasmic membrane and lyse. Removal of the cell wall produces a protoplast that lyses unless it is osmotically stabilized.
      The Gram positive cell wall may also include other components such as teichoic and lipoteichoic acids and complex polysaccharides (usually called C polysaccharides). Proteins such as the M protein of streptococci and R protein of staphylococci also associate with the peptidoglycan. Teichoic acids are water-soluble polymers of polyol phosphates, which are covalently linked to the peptidoglycan. Lipoteichoic acids have a fatty acid and are anchored in the cytoplasmic membrane. These molecules are common surface antigens that distinguish bacterial serotypes and promote attachment to other bacteria as well as to specific receptors on mammalian cell surfaces (adherence). Teichoic acids are important factors in virulence. Lipoteichoic acids are shed into the media and host and, although weaker, can initiate endotoxic-like activities.
 Gram negative cell walls are more complex than Gram positive cell walls, both structurally and chemically. Structurally, a Gram negative cell wall contains two layers external to the cytoplasmic membrane. Immediately external to the cytoplasmic membrane is a thin peptidoglycan layer, which accounts for only 5% to 10% of the Gram negative cell wall by weight. There are no teichoic or lipoteichoic acids in the Gram negative cell wall. External to the peptidoglycan layer is the outer membrane, which is unique to Gram negative bacteria. The area between the external surface of the cytoplasmic membrane and the internal surface of the outer membrane is referred to as the periplasmic space. This space is actually a compartment containing a variety of hydrolytic enzymes, which are important to the cell for the breakdown of large macromolecules for metabolism. These enzymes typically include proteases, phosphatases, lipases, nucleases, and carbohydrate-degrading enzymes. In the case of pathogenic Gram negative species, many of the lytic virulence factors such as collagenases, hyaluronidases, proteases, and beta-lactamase are in the periplasmic space. This space also contains components of the sugar transport systems and other binding proteins to facilitate the uptake of different metabolites and other compounds. Some binding proteins can be components of a chemotaxis system, which senses the external environment of the cell.
In Gram stain reaction  Gram positive bacteria: Retain crystal violet dye and stain dark violet or purple.
Gram negative bacteria : Can be decolorized to accept counterstain (safranin); stain red.


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