The membrane attack complex (MAC) is most effective against which type of organisms?

The membrane attack complex (MAC) is most effective against which type of organisms?

• A. Gram-positive
• B. Gram-negative
• C. Fungi
• D. Viruses

Answer: (B)

The membrane attack complex works by forming pores in the lipid membranes of target cells, causing lysis when the membrane is compromised. It is most effective against Gram-negative bacteria because they present an exposed cytoplasmic membrane beneath a relatively thin layer of peptidoglycan and an outer membrane. The MAC can insert through the outer membrane and disrupt the inner cytoplasmic membrane, leading to cell breakup. In Gram-positive organisms, the thick peptidoglycan wall acts as a robust barrier that impedes MAC access to the cytoplasmic membrane, reducing susceptibility. Fungi have rigid cell walls (chitin and other polymers), and viruses lack a readily accessible cellular membrane in many contexts, so MAC is not as effective against them.

The membrane attack complex works by forming pores in the lipid membranes of target cells, causing lysis when the membrane is compromised. It is most effective against Gram-negative bacteria because they present an exposed cytoplasmic membrane beneath a relatively thin layer of peptidoglycan and an outer membrane. The MAC can insert through the outer membrane and disrupt the inner cytoplasmic membrane, leading to cell breakup. In Gram-positive organisms, the thick peptidoglycan wall acts as a robust barrier that impedes MAC access to the cytoplasmic membrane, reducing susceptibility. Fungi have rigid cell walls (chitin and other polymers), and viruses lack a readily accessible cellular membrane in many contexts, so MAC is not as effective against them.