Which antibiotic class is ineffective against Mycoplasma pneumoniae due to lack of a cell wall?

• A. Macrolide
• B. Tetracycline
• C. Beta-lactam
• D. Fluoroquinolone

Answer: (C)

Mycoplasma pneumoniae lacks a cell wall, having only a cell membrane. Beta-lactam antibiotics—penicillins, cephalosporins, and related drugs—rely on inhibiting enzymes that build peptidoglycan, the structural component of bacterial walls. Without a cell wall, there’s no peptidoglycan target for these drugs, so they’re ineffective against Mycoplasma. Other antibiotic classes that don’t depend on cell wall inhibition—such as macrolides (which block protein synthesis), tetracyclines (also inhibiting protein synthesis), and fluoroquinolones (which inhibit DNA replication)—can still be active against Mycoplasma.