How is C. botulinum affected by pH?

• A. Requires high acid environment to grow
• B. Prefers a low acid environment
• C. Germinates best at pH above 7
• D. Is unaffected by pH

Answer: (B)

The main idea here is how pH affects the growth of Clostridium botulinum. This organism grows best when the environment is not highly acidic; in other words, it prefers a low acid (higher pH) setting. Acidic conditions (low pH) inhibit its growth and toxin production, which is why foods with pH at or below 4.6 are kept to prevent botulism. So the statement that fits best is that it prefers a low acid environment. The other options misstate its relationship to pH: it does not require high acidity to grow, it is not defined by germinating best at alkaline pH, and its growth is indeed affected by pH.