35-year-old patient with generalized periodontitis. Which microorganism is LEAST likely involved?

Correct answer: D. Aggregatibacter actinomycetemcomitans (Aa)

• A. P. gingivalis is one of the 'red complex' organisms strongly associated with chronic/generalized periodontitis.
• B. T. forsythia is also part of the 'red complex,' strongly associated with generalized periodontitis.
• C. T. denticola is part of the 'red complex' as well, strongly associated with generalized periodontitis.
• D. Correct. Aa is more classically associated with aggressive/localized (not generalized chronic) periodontitis, particularly in younger patients, making it the least likely organism among these choices for a 35-year-old with generalized disease.

Note: Aa is more associated with aggressive/localized periodontitis in younger patients, not typical generalized periodontitis.