What type of organism primarily carries out nitrate to nitrite conversion in the oral cavity?

• A. Commensal bacteria
• B. Fungi
• C. Viruses
• D. Eukaryotic cells

Answer: (A)

Nitrate to nitrite conversion in the mouth is done by bacteria that are part of the normal oral microbiota. These commensal, resident bacteria on the tongue and in dental biofilms use nitrate as an alternative electron acceptor in their anaerobic metabolism, converting it to nitrite through nitrate reductase enzymes. This microbial process is why nitrite appears in saliva after dietary nitrate intake and is not driven by human cells. Fungi, viruses, and human (eukaryotic) cells do not play the primary role in this conversion in the oral cavity, so the correct answer highlights the commensal bacteria as the main performers of this reaction.