Seok-Woo Lee, DDS, MS, PhD 9/16/2004 1 Dental Conference - MID Dental Plaque Biofilm September 30, 2004 Infection as an interaction between organisms SPECIFIC INTERACTION OF MOLECULES WITH EACH OTHER. Interacting molecules interact as pairs, one of which is called the LIGAND and the other the RECEPTOR. Symbiosis Dental disease as an infectious disease Understanding microbial etiology Pathogenicity (virulence) of pathogens Virulence factors Understanding microbial pathogenesis Genetic and Molecular Basis for Virulence Understanding host response Outcome of disease Applying to diagnosis, treatment, prevention Dental Caries Demineralization of the tooth surface caused by bacteria Periodontal Disease
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Seok-Woo Lee, DDS, MS, PhD 9/16/2004
1
Dental Conference - MID
Dental Plaque Biofilm
September 30, 2004
Infection as an interaction between organisms
SPECIFIC INTERACTION OF MOLECULES WITH EACH OTHER. Interacting molecules interact as pairs, one of which is called the LIGAND and the other the RECEPTOR.
Symbiosis Dental disease as an infectious disease
Understanding microbial etiologyPathogenicity (virulence) of pathogens
Virulence factors
Understanding microbial pathogenesisGenetic and Molecular Basis for Virulence
Understanding host responseOutcome of disease
Applying to diagnosis, treatment, prevention
Dental Caries
Demineralization of the tooth surface caused by bacteria
Periodontal Disease
Seok-Woo Lee, DDS, MS, PhD 9/16/2004
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Virulence factors
Gene products that enhance a microorganism’s potential to cause diseaseInvolved in all steps of pathogenicity
Attach to or enter host tissueEvade host responsesProliferateDamage the hostTransmit itself to new hosts
Encoded by virulence genes
Identifying virulence factors
Microbiological and biochemical studiesIn vitro isolation and characterizationIn vivo systems
Genetic studiesStudy of genes involved in virulenceGenetic transmission systemRecombinant DNA technology
Isogenic mutantsA molecular form of Koch’s postulates (Falkow)
Specific Virulence Factors
Adherence and Colonization FactorsInvasion FactorsCapsules and Other Surface ComponentsEndotoxinsExotoxinsSiderophores
Etiology of dental disease is
Dental Plaque
Removal of plaque and calculus
Seok-Woo Lee, DDS, MS, PhD 9/16/2004
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Dental plaque as a biofilmDefinition of biofilm
Matrix-enclosed bacterial populations adherent to each other and/or to surfaces or interfacesMay form on a wide variety of surfaces, living tissues, indwelling medical devices, water system piping, natural aquatic systemsPrevailing microbial lifestyle (vs. planktonic)Like a complex, highly differentiated, multiculturedcommunityOf single or multi-species
Biofilm: analogy to city
Planktonic (nomad) vs biofilm (city)Initial colonization followed by lateral spread, vertical direction growthShared resources and activites only possible through biofilmProtection from other species, host, and harsh environmentNeed communication – quorum sensing, exchange of genetic information
The nature of biofilms
Natural method of growth for microorganismsProvides advantages for colonizing species
Protection fromCompeting microorganismsEnvironmental factors, host defenseToxic substances, such as lethal chemicals, antibiotics
Facilitate processing and uptake of nutrients, cross-feeding, removal of harmful metabolic productsDevelopment of an appropriate physico-chemical environment
Seok-Woo Lee, DDS, MS, PhD 9/16/2004
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Formation of dental plaque
Acquired pellicle formationAdherence of salivary glycoprotein on tooth surface
Rapid colonization by pioneer species (Gram (+) cocci and rods)
S. sanguis, S. oralis, S. mitis, A. viscosus can adhere to pellicle by specificityResisting shear force (saliva) and electrostatic repulsion
Predominance by Gram (-) filaments (in 5 days)Microbial interaction, replacing Gram (+) cocci and rodsEmergence of Gram (-) filamentous bacteria Matrix of microorganisms and a ground substance
Climax Community
Dental pellicle Structure of biofilms
Composed of microcolonies (15-20% by volume) disctributedin a shaped matrix or glycocalyx (75-80% volume)Presence of voids or water channels
Permit the passage of nutrients and other agents, acting as “circulatory” system
Exopolysaccharides (EPS) – the backbone of the biofilm50-95% of the dry weight of the biofilmMaintain the integrity of the biofilmAct as a buffer and a substrate for resident bacteria
Physiological heterogeneity within biofilmspH can vary quite remarkably within a biofilmDifferent chemical and physical microhabitats
Seok-Woo Lee, DDS, MS, PhD 9/16/2004
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Supragingival dental plaque biofilm Dental plaque in health and disease
Pattern of colonization (microbial succession) in dental plaque formationDifference in predominant species
Health-associated dental plaqueDisease-associated dental plaque
Dental plaque hypothesesSpecific plaque hypothesisNon-specific plaque hypothesis
Microbiota associated with periodontal health, gingivitis, and advanced periodontal disease
0%
20%
40%
60%
80%
100%
Healthy -supragingival
Gingivitiscrevicluar
Gram-negative rods
Gram-positive rods
Gram-negativecocciGram-positive cocci
0%
20%
40%
60%
80%
100%
Start Day 1 Day 3 Day 10
Spirochetes
Filamentous forms
Gram (-) rods andcocciGram (+) rods andcocci
Plaque reformation after cleaning
Seok-Woo Lee, DDS, MS, PhD 9/16/2004
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Dental plaque hypothesis
Specific plaque hypothesis A single or limited numbers of specific pathogen within dental plaqueSpecific forms of periodontal disease have specific bacterial etiologies, i.e. LJP
Non-specific plaque hypothesisOvergrowth of dental plaque will lead to diseasePlaque as a relatively homogeneous bacterial massGingivitis
IntermediateQualitatively distinct bacterial composition: healthy vs. disease (subjects, sites)Pathogenic shift; disturbed equilibrium A small group of bacteria: Gram (-), anaerobic
Health vs. disease microflora in dental plaque
Potential pathogens
Understanding dental diseases from ecological perspective
The mouth - a unique microhabitatMulti-species biofilm“Selection” of “pathogenic” bacteria among microbial community
Selection pressure coupled to environmental changes
Therapeutic and preventive measures - by interfering with the selection pressures responsible for their enrichment
Ecological plaque hypothesis
Dental plaque biofilm infection
Ecological point of viewEcological community evolved for survival as a wholeComplex community
Over 400 bacterial speciesAdherence, coaggregation
Dynamic equilibrium between bacteria and a host defenseAdopted survival strategies favoring growth in plaqueDisturbed equilibrium leading to pathology
The dental plaque bacterial composition may result in a destructive inflammatory response
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