Which type of bacteria is predominantly found in subgingival plaque?

• A. Aerobic
• B. Anaerobic
• C. Spirochetes
• D. Actinomyces

Answer: (C)

Subgingival plaque exists in a low-oxygen pocket beneath the gum, so the bacteria that thrive there are anaerobes. Within this anaerobic environment, spirochetes—thin, spiral-shaped and highly motile—are a hallmark group, especially in areas of active periodontal disease with deep pockets. Their ability to penetrate tissues and produce proteolytic enzymes drives destruction and inflammation, so their presence is strongly associated with disease progression. This makes spirochetes the best descriptor of the predominant bacterial population found under the gum line in diseased sites. While a range of anaerobes is present subgingivally, the distinctive, disease-associated signature often centers on spirochetes.