ABP Periodontal Pathogenesis and Host Response

Question 1

Which bacterium is considered the 'keystone pathogen' in periodontal disease because it disrupts host immunity disproportionate to its low abundance?

Accepted Answer

Porphyromonas gingivalis

Answer

P. gingivalis is the keystone pathogen that, even at low colonization levels, subverts innate immunity and reshapes the entire subgingival microbiome toward a dysbiotic state.

Question 2

Socransky's 'red complex,' the bacterial group most strongly associated with severe periodontitis, consists of which three organisms?

Accepted Answer

P. gingivalis, T. forsythia, T. denticola

Answer

Socransky's red complex comprises Porphyromonas gingivalis, Tannerella forsythia, and Treponema denticola — organisms consistently co-detected in deep periodontal pockets with bleeding.

Question 3

What is the primary role of Fusobacterium nucleatum within the subgingival biofilm community?

Accepted Answer

Bridge organism linking early colonizers to late-colonizing pathogens

Answer

F. nucleatum acts as a bridge species, co-aggregating with both early colonizers (streptococci) and late-colonizing pathogens (red complex), allowing the mature pathogenic biofilm to assemble.

Question 4

Leukotoxin A (LtxA), a major virulence factor that lyses PMNs and macrophages, is uniquely produced by which periodontal pathogen?

Accepted Answer

Aggregatibacter actinomycetemcomitans

Answer

Aggregatibacter actinomycetemcomitans produces leukotoxin A, which selectively kills human leukocytes bearing the LFA-1 integrin, allowing the organism to evade immune clearance.

Question 5

Which feature of the subgingival biofilm most contributes to its resistance to systemic antimicrobial agents?

Accepted Answer

Extracellular polysaccharide matrix that limits drug penetration and shields bacteria

Answer

The extracellular polymeric substance (EPS) matrix of the biofilm impedes antibiotic diffusion, reduces metabolic activity of embedded bacteria, and enables horizontal gene transfer for antibiotic resistance.

(ABP) American Board of Periodontology Practice Test

(ABP) American Board of Periodontology Practice Test

ABP Periodontal Pathogenesis and Host Response