Q.80 Which of the following Gram-positive cocci are found in biofilm of dental
plaque?
(A) Gonococcus
(B) Streptococcus mutans
(C) Streptococcus sobrinus
(D) Fusobacterium species
Streptococcus mutans and Streptococcus sobrinus are the correct Gram-positive cocci found in dental plaque biofilms. Both options (B) and (C) contribute to plaque formation and dental caries through glucan production and adhesion to tooth surfaces. Gonococcus and Fusobacterium species do not qualify as they are Gram-negative.
Option Analysis
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(A) Gonococcus (Neisseria gonorrhoeae): This pathogen causes gonorrhea and appears as Gram-negative diplococci, not associated with oral biofilms like dental plaque.
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(B) Streptococcus mutans: Gram-positive coccus that initiates dental plaque biofilms by producing glucosyltransferases, forming sticky glucans from sucrose for adhesion and caries development.
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(C) Streptococcus sobrinus: Gram-positive coccus similar to S. mutans, frequently isolated from plaque, enhances biofilm via extracellular polysaccharides and contributes to tooth decay.
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(D) Fusobacterium species: Gram-negative anaerobic rods (e.g., F. nucleatum) that bridge early and late plaque colonizers but fail Gram-positive criteria.
Dental plaque biofilm harbors complex microbial communities where Gram-positive cocci dental plaque biofilm players drive pathogenesis. Streptococcus mutans and Streptococcus sobrinus dominate early colonization, producing virulence factors key to caries.
Biofilm Formation Process
Dental plaque starts with salivary pellicle adhesion by Gram-positive cocci like streptococci. S. mutans synthesizes glucans from dietary sucrose via glucosyltransferases, creating a matrix for biofilm stability. S. sobrinus amplifies this through similar polysaccharide production, enhancing acidogenic environments.
Pathogenic Contributions
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S. mutans adheres via surface proteins (PAc, Gbps), tolerates low pH, and resists antimicrobials in biofilms.
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S. sobrinus co-occurs in caries-active plaque, boosting demineralization.
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Later Gram-negative species like Fusobacterium join, but initial layers remain Gram-positive dominated.
Clinical Relevance for CSIR NET
These Gram-positive cocci dental plaque biofilm agents are exam favorites in microbiology. Their exclusion of Gonococcus (genital pathogen) and Fusobacterium (rods) tests Gram staining and ecology knowledge. Prevention targets sucrose reduction and mechanical disruption.
