Most broad-spectrum antibiotics act by:

• A. stimulating host immune response
• B. inhibiting cell wall synthesis
• C. increasing bacterial motility
• D. disrupting viral replication

Answer: (B)

Verified step by step guidance

1. Step 1: Understand the term 'broad-spectrum antibiotics' — these are antibiotics effective against a wide range of bacteria, both Gram-positive and Gram-negative.
2. Step 2: Review the common mechanisms of action of antibiotics, which include inhibiting cell wall synthesis, protein synthesis, nucleic acid synthesis, and disrupting metabolic pathways.
3. Step 3: Recognize that stimulating the host immune response or increasing bacterial motility are not typical mechanisms of antibiotic action.
4. Step 4: Recall that most broad-spectrum antibiotics, such as beta-lactams (e.g., penicillins), work by inhibiting bacterial cell wall synthesis, which weakens the bacteria and leads to their death.
5. Step 5: Conclude that among the options given, 'inhibiting cell wall synthesis' is the correct mechanism by which most broad-spectrum antibiotics act.