Describe cross-feeding between Veillonella and Streptococcus species in dental plaque.

• A. Veillonella uses lactate produced by streptococci as a substrate, converting it to weaker acids, thereby reducing acidity locally and supporting community growth.
• B. Veillonella oxidizes glucose to CO2 and water, increasing acidity.
• C. Veillonella produces lactate that increases plaque acidity.
• D. Streptococcus inhibits Veillonella metabolism.

Answer: (A)

Cross-feeding in dental plaque means one species feeds on the byproducts of another. Streptococcus ferments sugars and makes lactate, which acidifies the local environment. Veillonella, instead of breaking down sugars, uses that lactate as its food source and converts it into weaker acids such as propionate and acetate. By consuming lactate, Veillonella removes a strong acid from the microenvironment, which reduces the overall acidity and helps the community maintain a more favorable pH for continued growth. This cooperative interaction supports coexistence in the plaque. The other ideas—Veillonella making lactate, Veillonella oxidizing glucose to produce more acidity, or Streptococcus inhibiting Veillonella—don’t fit the observed cross-feeding relationship.