Which statement is true about acid production by health-associated streptococci?

Which statement is true about acid production by health-associated streptococci?

• A. They stop metabolism at pH around 7
• B. They stop metabolism around pH 6 due to acid sensitivity
• C. They stop metabolism around pH 5
• D. They never stop

Answer: (B)

Acid production by health-associated streptococci comes from fermenting carbohydrates to acids like lactic acid, which lowers the plaque pH. But these streptococci are relatively acid-sensitive; their metabolism can be inhibited when the environment becomes too acidic. The typical threshold where metabolic activity declines is around pH 6. This means they generate acid when conditions are near neutral, but as the pH drops toward 6, their enzymes and cellular processes are inhibited, limiting further metabolism. That’s why the statement that they stop metabolism around pH 6 due to acid sensitivity is the best choice. In contrast, stopping at neutral pH 7 isn’t characteristic, stopping only at very acidic pH around 5 would imply greater acid tolerance than these health-associated strains have, and saying they never stop ignores the clear effect of acid on their metabolism.

Acid production by health-associated streptococci comes from fermenting carbohydrates to acids like lactic acid, which lowers the plaque pH. But these streptococci are relatively acid-sensitive; their metabolism can be inhibited when the environment becomes too acidic. The typical threshold where metabolic activity declines is around pH 6. This means they generate acid when conditions are near neutral, but as the pH drops toward 6, their enzymes and cellular processes are inhibited, limiting further metabolism. That’s why the statement that they stop metabolism around pH 6 due to acid sensitivity is the best choice. In contrast, stopping at neutral pH 7 isn’t characteristic, stopping only at very acidic pH around 5 would imply greater acid tolerance than these health-associated strains have, and saying they never stop ignores the clear effect of acid on their metabolism.