What is the role of Lactobacillus species in caries progression?

• A. Lactobacillus spp. are aciduric and contribute to progression by surviving at low pH and continuing acid production.
• B. Lactobacillus spp. neutralize pH and prevent demineralization.
• C. Lactobacillus spp. produce antibiotics to kill Streptococcus mutans.
• D. Lactobacillus spp. only colonize healthy enamel and do not contribute to caries.

Answer: (A)

Lactobacillus species contribute to caries progression because they are both acidogenic and highly aciduric. When a cavity begins, sugars fermented by bacteria lower the local pH; many bacteria can’t tolerate this drop, but lactobacilli thrive in these acidic conditions and continue producing acid, especially lactic acid, even as the environment stays harsh. This ongoing acid production deepens demineralization and helps lesions advance from early signs to more extensive decay, particularly in dentin. They’re not the primary initiators of caries—that role is more associated with other acidogenic bacteria like Streptococcus mutans—but once a lesion is established, lactobacilli amplify progression by sustaining low pH and acid attack. They do not neutralize pH, they do not kill S. mutans with antibiotics, and they do contribute to caries rather than just colonizing healthy enamel.