Plaque Biofilm Microbiology II Notes

Plaque Biofilm

Definition

  • Plaque biofilm is composed of living and dead bacteria, their extracellular products, and host compounds, primarily from saliva.
  • The matrix serves as a food reserve and binds organisms to each other and to various surfaces.

Composition

  • Composition varies widely between individuals:
    • Some are rapid plaque formers, others are slow.
  • Significant variations exist within an individual:
    • Different sites on the same tooth.
    • Same site on different teeth.
    • Different times on the same tooth site.

Distribution

  • Found on dental surfaces and appliances, especially with poor oral hygiene.
  • Categorized by site of origin:
    • Supragingival:
      • Fissure plaque: mainly in molar fissures.
      • Approximal plaque: at contact points of teeth.
      • Smooth surface: buccal and palatal surfaces.
    • Subgingival:
    • Appliance-associated:
      • Full and partial dentures (denture plaque).
      • Orthodontic appliance-related plaque.

Microbial Adherence and Biofilm Formation

  • Adherence to an oral surface is essential for colonization and biofilm formation.
  • It's the initial step leading to subsequent infection and tissue invasion.

Intrinsic Host Factors

  • Several factors prevent microbial colonization on oral surfaces:
    1. Mucosal barrier removes attached organisms from soft-tissue surfaces.
    2. Dynamic salivary flow patterns in different oral niches.
    3. Muscular movements of the tongue and cheeks physically displace biofilms.
    4. Non-specific and specific defense factors (e.g., IgA) in saliva.
    5. Resident community of microbiota offers ‘colonization resistance’ to invading extraneous organisms.

Plaque Biofilm Formation - Stages

  • A complex process with several stages:

    1. Pellicle Formation:

      • A thin layer of salivary glycoproteins is deposited on the tooth surface within minutes of saliva exposure.
      • Oral bacteria initially attach to the pellicle, not directly to enamel.

    2. Transport:

      • Bacteria approach the tooth surface prior to attachment.
      • Via natural salivary flow, Brownian motion, or chemotaxis.

    3. Long-range interactions:

      • Initial weak forces (electrostatic or Van der Waals) attract bacteria to the pellicle from a short distance.
      • These interactions do not involve direct bonding.

    4. Short-range interactions:

      • Stereochemical reactions between adhesins on the microbial cell surface and receptors on the acquired pellicle.
      • Irreversible phase where polymer bridging anchors the organism, followed by multiplication on the surface.

    5. Coaggregation or co-adhesion:

      • Fresh bacteria attach to the already attached first generation of cells (pioneer or initial colonizers).
      • These may be bacteria of the same genus or different but compatible genera.

  • Pioneer colonizers:

    • Gram-positive cocci and rods initially.
    • Followed by Gram-negative cocci and rods.
    • Finally, by filaments, fusobacteria, spirilla, and spirochetes.

The Climax Community

  • A stable, mature, highly resistant, and organized bacterial ecosystem that's difficult to disrupt without professional intervention.
  • Characteristics:
    1. Microbial Diversity
    2. Layered Structure
    3. Extracellular Matrix Production:
      • Bacteria produce an extracellular polymeric substance (EPS), creating a protective and cohesive matrix.
    4. Resistance and Resilience:
      • Highly resistant to removal by mechanical (brushing) and chemical (antimicrobial) means.
    5. Efficient Nutrient Cycling:
      • Metabolic byproducts from one bacterial species serve as nutrients for others, enabling interdependent survival.
    6. Pathogenic Potential
    7. Quorum Sensing and Communication
    8. Stable Ecosystem:
      • Remains in a balanced, stable state over time, as long as the environment is undisturbed.

Detachment

  • Bacteria from the climax community may detach and enter the planktonic phase (suspended in saliva).
  • They can then be transported to new colonization sites, restarting the cycle.

Calculus Formation

  • Calcium and phosphate ions from saliva may be deposited within deeper layers of plaque biofilm.
  • Undisturbed plaque biofilm leads to degenerating bacteria acting as seeding agents of mineralization.
  • Bacterial phosphatases and proteases accelerate the process by destroying calcification inhibitors in saliva.
  • This leads to insoluble calcium phosphate crystals coalescing into a calcified mass called calculus.
  • Many toothpastes contain pyrophosphate compounds (anti-tartar) that adsorb excess calcium ions, reducing intraplaque mineral deposition.

Structure of Calculus

  • Predominant flora: cocci, bacilli, and filaments (especially in the outer layers), and occasionally spiral organisms.
  • 'Corn-cob' arrangement: cocci attach and grow on the surface of filamentous microorganisms, especially on the outer surface.
  • Some bacteria (mainly cocci) may contain glycogen-like food storage granules for use during periods of adversity.
  • Calculus has a rough and porous surface.
    • Serving as an ideal reservoir for bacterial toxins (e.g., lipopolysaccharides (LPSs)) harmful to the periodontium.
  • Removal of calculus is essential for maintaining good periodontal health.