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Bacterial cell walls
Compare and contrast gram-positive and gram-negative cell walls with regard to (a) sensitivity to antimicrobial agents, (b) resistance to phagocytosis, (c) chemical composition, and (d) decolorization by alcohol.
Sample Answer
Comparison of Gram-Positive and Gram-Negative Bacterial Cell Walls
Gram-positive and gram-negative bacterial cell walls exhibit distinct characteristics that influence their sensitivity to antimicrobial agents, resistance to phagocytosis, chemical composition, and decolorization by alcohol.
(a) Sensitivity to Antimicrobial Agents:
Gram-positive bacteria are generally more susceptible to antimicrobial agents compared to gram-negative bacteria. This is attributed to the differences in cell wall structure, with the thick peptidoglycan layer of gram-positive cell walls being more permeable to antibiotics, facilitating their entry and action on the bacterial cell.
(b) Resistance to Phagocytosis:
Gram-negative bacteria are typically more resistant to phagocytosis compared to gram-positive bacteria. The outer membrane of gram-negative cell walls, composed of lipopolysaccharides and porins, acts as a barrier that protects the bacteria from engulfment by phagocytic cells of the immune system.
(c) Chemical Composition:
Gram-positive cell walls have a thick layer of peptidoglycan that retains the crystal violet dye in the Gram staining process, giving them a purple color. In contrast, gram-negative cell walls have a thinner peptidoglycan layer surrounded by an outer membrane containing lipopolysaccharides, which contributes to their pink color after decolorization.
(d) Decolorization by Alcohol:
During the Gram staining procedure, alcohol decolorizes the bacterial cells to differentiate between gram-positive and gram-negative bacteria. Gram-positive bacteria retain the crystal violet stain due to their thicker peptidoglycan layer and lack of an outer membrane, while gram-negative bacteria are decolorized and counterstained with safranin.
In summary, the structural differences between gram-positive and gram-negative bacterial cell walls influence their responses to antimicrobial agents, susceptibility to phagocytosis, chemical composition, and decolorization characteristics during laboratory staining procedures. Understanding these distinctions is vital for effective diagnosis and treatment of bacterial infections.
References:
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