Bacterial cell walls

Full Answer Section

(b) Resistance to Phagocytosis: The thick peptidoglycan layer of gram-positive bacteria can offer some protection from phagocytosis by immune cells [Todar, 2008]. However, gram-negative bacteria's outer membrane with virulence factors can further impede phagocytosis [Tortora et al., 120].

(c) Chemical Composition: Gram-positive bacteria primarily have peptidoglycan in their cell walls, along with teichoic acid [Todar, 2008]. Gram-negative bacteria have a thinner peptidoglycan layer and an outer membrane composed of lipopolysaccharides, lipoproteins, and phospholipids [Murray et al., 61].

(d) Decolorization by Alcohol: During Gram staining, a critical step involves decolorization with alcohol. The thick peptidoglycan of gram-positive bacteria retains the crystal violet stain, appearing purple. In contrast, the alcohol disrupts the outer membrane of gram-negative bacteria, allowing the crystal violet to leach out. These bacteria are then counterstained pink with safranin [Todar, 2008].

References:

• Murray, P. R., et al. Medical Microbiology, Eighth Edition. Elsevier, 2016.
• Tortora, Gerard J., et al. Microbiology: An Introduction, Twelfth Edition. Pearson, 2018.
• Todar, Kenneth. Todar's Online Textbook of Bacteriology. https://scholar.google.com/citations?user=cfVGRAcAAAAJ&hl=en, 2008. Accessed 24 June 2024.

Sample Answer

Gram-Positive vs. Gram-Negative Cell Walls: A Tale of Two Barriers

Gram staining, a cornerstone microbiological technique, differentiates bacteria based on their cell wall composition. This difference significantly impacts how these bacteria interact with antibiotics, immune cells, and staining procedures.

(a) Sensitivity to Antimicrobial Agents: Gram-positive bacteria, with their thick peptidoglycan walls, are generally more susceptible to certain antibiotics like penicillin and vancomycin that target peptidoglycan synthesis [Tortora et al., 117]. Gram-negative bacteria have a thinner peptidoglycan layer and an outer membrane with lipopolysaccharides, which can act as a barrier, hindering some antibiotics [Murray et al., 62].