Which statement best describes a bactericide?

• A. A substance that inhibits the growth or reproduction of bacteria
• B. A substance that inhibits the growth of bacteria without killing them
• C. A substance that kills bacteria e.g. antibiotic
• D. A substance that kills fungi

Answer: (C)

A bactericide is an agent that actively kills bacteria. The key idea is the difference between killing and merely inhibiting growth. Bacteriostatic agents stop bacteria from growing or reproducing but don’t kill the cells, so they aren’t bactericides. An agent that kills fungi would be antifungal, not bactericidal. Many antibiotics are bactericidal and therefore fit this description, though some are bacteriostatic depending on the drug and conditions. So the best description is a substance that kills bacteria, with antibiotics provided as a common example.