Primary bacteria found below the gum line are primarily what type?

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

Answer: (A)

Beneath the gum line, oxygen is scarce because diffusion into the gingival sulcus is limited and inflammatory fluid uses available oxygen quickly. This creates an environment that favors bacteria that do not require oxygen to grow, or that tolerate very low oxygen levels—anaerobes. So, anaerobic bacteria become the dominant group in subgingival plaque. While spirochetes and Actinomyces can be present in the mouth, their associations are not as defining for the subgingival environment: Actinomyces are often found on the tooth surface and in supragingival plaque and many Actinomyces are facultatively anaerobic. Therefore, the primary bacteria found below the gum line are anaerobic.