Which of the following is an example of aciduric bacteria?

• A. S mutans and Lactobacilli
• B. Veillonella
• C. Streptococcus pneumoniae
• D. Actinomyces naeslundii

Answer: (A)

Aciduric bacteria are those that not only survive but continue to metabolize and produce acid even when the environment becomes acidic. In dental plaque, a drop in pH after sugar intake is quickly tolerated by certain bacteria, allowing them to keep generating acid that demineralizes enamel. S. mutans and Lactobacilli are classic examples of these aciduric organisms: they thrive at low pH and remain active in acid conditions, contributing prominently to caries progression by producing lactic acid from sugars and sustaining the acidic environment.

Veillonella, while present in plaque, consumes lactate produced by others rather than producing acid itself, so it doesn’t act as an aciduric driver of caries. Streptococcus pneumoniae is more associated with respiratory infections than with the cariogenic dental biofilm. Actinomyces naeslundii tends to be an early colonizer and is not the primary aciduric force driving caries, though it can tolerate some acidity.

Thus, the pairing of S. mutans with Lactobacilli best exemplifies aciduric behavior relevant to dental caries.