ABP Periodontal Pathogenesis and Host Response 1 — Questions and Answers
Question 1: Which bacterium is considered the 'keystone pathogen' in periodontal disease because it disrupts host immunity disproportionate to its low abundance?
- Tannerella forsythia
- Porphyromonas gingivalis (Correct answer)
- Treponema denticola
- Aggregatibacter actinomycetemcomitans
Correct answer: Porphyromonas gingivalis
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?
- P. gingivalis, A. actinomycetemcomitans, T. denticola
- P. gingivalis, T. forsythia, T. denticola (Correct answer)
- F. nucleatum, P. intermedia, P. gingivalis
- A. actinomycetemcomitans, E. corrodens, C. rectus
Correct answer: P. gingivalis, T. forsythia, T. denticola
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?
- Primary initiator of alveolar bone resorption
- Keystone pathogen that suppresses innate immunity
- Bridge organism linking early colonizers to late-colonizing pathogens (Correct answer)
- Producer of gingipains that degrade host defense proteins
Correct answer: Bridge organism linking early colonizers to late-colonizing pathogens
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?
- Porphyromonas gingivalis
- Treponema denticola
- Tannerella forsythia
- Aggregatibacter actinomycetemcomitans (Correct answer)
Correct answer: Aggregatibacter actinomycetemcomitans
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?
- Primarily aerobic bacterial composition that excludes anaerobes
- Extracellular polysaccharide matrix that limits drug penetration and shields bacteria (Correct answer)
- Absence of quorum sensing communication among species
- High oxygen tension creating an inhospitable environment for pathogens
Correct answer: Extracellular polysaccharide matrix that limits drug penetration and shields bacteria
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.
Question 6: Gingipains produced by Porphyromonas gingivalis primarily function to:
- Stimulate osteoblast matrix synthesis
- Produce volatile sulfur compounds causing halitosis
- Degrade host defense proteins and cleave complement to evade immunity (Correct answer)
- Bridge early and late microbial colonizers in the biofilm
Correct answer: Degrade host defense proteins and cleave complement to evade immunity
Gingipains are cysteine proteases that degrade immunoglobulins, complement proteins, and cytokines, effectively disabling multiple arms of the host immune response.
Question 7: In Socransky's microbial complexes, which complex serves as the 'bridge' between early colonizers and the pathogenic red complex?
- Yellow complex
- Purple complex
- Green complex
- Orange complex (Correct answer)
Correct answer: Orange complex
The orange complex (including F. nucleatum, P. intermedia, P. nigrescens, and others) bridges the early yellow/green colonizers and the late red complex, facilitating ecological succession to a pathogenic biofilm.
ABP Periodontal Pathogenesis and Host Response 1
Which bacterium is considered the 'keystone pathogen' in periodontal disease because it disrupts host immunity disproportionate to its low abundance?