What distinguishes Gram-negative bacteria from Gram-positive bacteria?

What distinguishes Gram-negative bacteria from Gram-positive bacteria?

• A. Presence of a thick peptidoglycan layer
• B. Presence of an outer membrane
• C. Absence of a cell wall
• D. Presence of endospores

Answer: (B)

The presence of an outer membrane is a key feature that distinguishes Gram-negative bacteria from Gram-positive bacteria. In Gram-negative bacteria, the outer membrane sits outside the thin peptidoglycan layer, providing an additional barrier that can restrict the entry of certain substances, including antibiotics, which can contribute to their resistance. This outer membrane contains lipopolysaccharides, which play a crucial role in the immune response and can affect the pathogenicity of these bacteria. In contrast, Gram-positive bacteria are characterized by a thick peptidoglycan layer that retains the crystal violet stain used in Gram staining, resulting in their characteristic purple color under a microscope. They lack an outer membrane, making them more susceptible to certain antibiotics that target the peptidoglycan layer. The other options, such as the absence of a cell wall or the presence of endospores, do not apply to Gram-negative bacteria specifically and are not distinguishing characteristics. Most bacteria, including both Gram-positive and Gram-negative, possess a cell wall, while endospores are a survival mechanism found in some specific genera like Bacillus and Clostridium, regardless of Gram classification.

The presence of an outer membrane is a key feature that distinguishes Gram-negative bacteria from Gram-positive bacteria. In Gram-negative bacteria, the outer membrane sits outside the thin peptidoglycan layer, providing an additional barrier that can restrict the entry of certain substances, including antibiotics, which can contribute to their resistance. This outer membrane contains lipopolysaccharides, which play a crucial role in the immune response and can affect the pathogenicity of these bacteria.

In contrast, Gram-positive bacteria are characterized by a thick peptidoglycan layer that retains the crystal violet stain used in Gram staining, resulting in their characteristic purple color under a microscope. They lack an outer membrane, making them more susceptible to certain antibiotics that target the peptidoglycan layer.

The other options, such as the absence of a cell wall or the presence of endospores, do not apply to Gram-negative bacteria specifically and are not distinguishing characteristics. Most bacteria, including both Gram-positive and Gram-negative, possess a cell wall, while endospores are a survival mechanism found in some specific genera like Bacillus and Clostridium, regardless of Gram classification.