ORAL MICROBIOLOGY

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ORAL MICROBIOLOGY
Normal oral flora Diverse organisms, including
bacteria, fungi, mycoplasmas, protozoa and
viruses 350 cultivable species Unculturable
flora (identified by molecular techniques)
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ORAL MICROBIOLOGY
Normal oral flora Streptococci are the
predominant supra-gingival bacteria Four main
groups mutans salivarius anginosus mitis
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Primary enemy of the teeth Lennart
Nilsson The Body Victorious Streptococcus mutans
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ORAL MICROBIOLOGY
Normal oral flora Predominant cultivable species
in sub-gingival plaque Actinomyces Prevotella
Porphyromonas Fusobacterium Veillonella
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NORMAL ORAL FLORA
Gram-positive bacteria Actinomyces
Filamentous bacteria A. israelii -gt Dental
plaque associated with dental calculus
formation A. naeslundii -gt Dental plaque
associated with root surface caries (debated)
gingivitis
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NORMAL ORAL FLORA
Gram-positive bacteria Streptococcus (Viridans
Streptococci) mutans group (mutans
streptococci) On tooth surfaces produce acid
rapidly can grow in acid conditions S. mutans
Primary pathogen in enamel caries in children
young adults, root surface caries in elderly S.
sobrinus
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NORMAL ORAL FLORA
Streptococcus salivarius group Mucosal
surfaces, esp. tongue initial colonizer
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NORMAL ORAL FLORA
Streptococcus mitis group May act as
opportunistic pathogens may cause infective
endocarditis S. sanguis Found in plaque
produces IgA protease S. oralis Found on tongue,
cheek, plaque, saliva produces IgA protease
glucans initial colonizer S. mitis On soft
hard tissues initial colonizer (S. Pneumoniae is
also in this group)
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NORMAL ORAL FLORA
Streptococcus anginosus group (Group A
streptococci) Dental plaque mucosal
surfaces Dentoalveolar endodontic
infections Abscesses of internal organs esp.
brain liver
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NORMAL ORAL FLORA
Gram-positive bacteria Anaerobic
streptococci Peptostreptococcus species Carious
dentine, pulp chambers, root canals,
advanced periodontal disease Lactobacillus L.
casei, L. fermentum, L. acidophilus 1
of microflora increases in advanced
caries lesions of the enamel and root surface
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NORMAL ORAL FLORA
Gram-positive bacteria Eubacterium Pleomorphic
rods or filaments, -gt caries periodontal
disease 50 of anaerobes of periodontal
pockets Propionibacterium Strict anaerobic
bacilli (root surface caries plaque)
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NORMAL ORAL FLORA
Gram-positive bacteria Rothia Branching
filaments (saliva plaque) BifidobacteriumStric
t anaerobic bacilli (plaque)
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NORMAL ORAL FLORA
Gram-negative bacteria Haemophilus Facultativ
e anaerobes (plaque, saliva mucosal surfaces) -gt
acute bacterial epiglottitis, pneumonia, sinusiti
s, meningitis
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NORMAL ORAL FLORA
Gram-negative bacteria Actinobacillus A.
actinomycetemcomitans (coccobacilli) subgingival
plaque, -gt juvenile periodontitis, -gt adult
periodontitis Eikenella E. corrodens
(coccobacilli) plaque -gt dentoalveolar abscess,
chronic periodontitis, infective endocarditis
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NORMAL ORAL FLORA
Gram-negative bacteria Capnocytophaga CO2-depende
nt, fusiform rods, 'gliding' motility plaque,
mucosal surfaces, saliva -gt destructive
periodontal disease
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NORMAL ORAL FLORA
Gram-negative bacteria Fusobacterium Strict
anaerobe gingival crevice or tonsils Remove
sulfur from cysteine and methionine to produce
hydrogen sulphide and methyl mercaptan
(halitosis) -gt acute ulcerative gingivitis
Fusospirochaetal Complex -gt dentoalveolar
abscess
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NORMAL ORAL FLORA
Porphyromonas P. gingivalis, P. endodontalis
(pleomorphic rods) Strict anaerobes (vitamin K,
hemin) Gingival crevice, subgingival plaque -gt
chronic periodontitis, dentoalveolar
abscess Prevotella P. intermedia, P.
melaninogenica (pleomorphic rods) Strict
anaerobes (vitamin K, hemin) dental plaque, -gt
chronic periodontitis, dentoalveolar abscess
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NORMAL ORAL FLORA
Wolinella W. recta (curved bacilli, flagellae)
Strict anaerobe, gingival crevice, -gt destructive
periodontal disease Treponema T. denticola, T.
macrodentium (motile, helical cells) Strict
anaerobes, difficult to culture, gingival
crevice, -gt acute ulcerative gingivitis,
destructive periodontal disease
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ORAL ECOSYSTEM
Oral flora Sites of the oral cavity where they
grow (habitats) Associated surroundings
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THE ORAL ECOSYSTEM AND DENTAL PLAQUE
Oral habitats Buccal mucosa and dorsum of
tongue Tooth surfaces Crevicular epithelium
and gingival crevice Prosthodontic and
orthodontic appliances
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Factors affecting microbial colonization of
the oral mucosa
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THE ORAL ECOSYSTEM AND DENTAL PLAQUE
Adherence of a microorganism is a
prerequisite for colonization and subsequent
infection Saliva modulates bacterial growth
Provides pellicle for bacterial adhesion
Nutrient source Co-aggregates bacteria
Defense factors Non-specific (lysozyme,
lactoferrin, histatins) Specific (IgA)
Maintains pH
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THE ORAL ECOSYSTEM AND DENTAL PLAQUE
Microbial factors Competition for receptors
for adhesion Production of bacteriocins
Antagonistic metabolic end-products
Co-aggregation with same or different species
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THE ORAL ECOSYSTEM AND DENTAL PLAQUE
Dental plaque Microorganisms surrounded by
organic matrix derived from host and
microorganisms (food reserve and cement) An
example of a natural biofilm Supragingival
Subgingival Appliance-associated plaque
(denture, orthodontic appliance-related)
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THE ORAL ECOSYSTEM AND DENTAL PLAQUE
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THE ORAL ECOSYSTEM AND DENTAL PLAQUE
Main stages of plaque formation Transport Initia
l adhesion/co-adhesion Irreversible
attachment Colonization
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Smooth surface plaque
Mature plaque with calcification at the base
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THE ORAL ECOSYSTEM AND DENTAL PLAQUE
Plaque formation Pellicle (primarily salivary
glycoproteins) deposited on the tooth
surface Pioneer organisms adhere to the
pellicle Colonies grow synthesize an
extracellular matrix composed of microbial
polysaccharides and layers of salivary
glycoproteins
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THE ORAL ECOSYSTEM AND DENTAL PLAQUE
Plaque formation (contd.) New organisms inhabit
the plaque as the microenvironment is
changed Growth of microbial complexity, size and
thickness
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Predominant organisms in the pioneer and climax
communities of plaque
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THE ORAL ECOSYSTEM AND DENTAL PLAQUE
Plaque formation (contd.) Climax community
Balance between the deposition and loss of plaque
bacteria Degenerating bacteria in a climax
community act as nucleation points for
mineralization, forming a calcified mass called
calculus
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MICROBIAL INTERACTIONS IN PLAQUE
Synergistic interactions Degradation of salivary
proteins and glycoproteins by glycosidases and
proteases Experiment Subgingival bacteria
grown on human serum (analog of
GCF) Carbohydrate side chains removed by S.
oralis, E. saburreum and Prevotella spp., each
with complementary glycosidase activity
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MICROBIAL INTERACTIONS IN PLAQUE
Experiment contd. Hydrolysis of protein core by
anaerobes, including P. intermedia, P. oralis, F.
nucleatum and Eubacterium Some amino acid
fermentation and carbohydrate side chain
metabolism occurred and led to the emergence of
Veillonella spp.
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MICROBIAL INTERACTIONS IN PLAQUE
Experiment contd. Final phase progressive
protein degradation and extensive amino acid
fermentation -gt Increase in Peptostreptococcus
and E. brady Individual species grew only poorly
in pure culture in serum Different species avoid
direct competition for nutrients, and hence
co-exist
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MICROBIAL INTERACTIONS IN PLAQUE
Bacterial polymers are also targets for
degradation Fructan of S. salivarius and other
streptococci Glycogen-like polymer of
Neisseria Streptoccocal glucans Metabolized by
S. mitis group, S. salivarius, A. israelii,
Capnocytophaga and Fusobacterium
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MICROBIAL INTERACTIONS IN PLAQUE
Metabolic products of one organism (primary
feeder) becomes the main source of nutrients for
another (secondary feeder) Experiment Studies
with gnotobiotic animals Fewer carious lesions
were obtained in rats inoculated with either S.
mutans or S. sanguis and Veillonella than in
animals infected just with the individual
streptococci.
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Potential nutritional interactions between plaque
bacteria
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MICROBIAL INTERACTIONS IN PLAQUE
Experiment contd. Lactate produced by various
species can be utilized by Gram-negative,
anaerobic Veillonella spp (which cannot
metabolize glucose and fructose) and be converted
to weaker acids
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THE ORAL ECOSYSTEM AND DENTAL PLAQUE
Plaque formation (contd.) Bacteria near the
enamel surface reduced cytoplasmcell wall ratio
(metabolically inactive) Predominant flora
cocci, bacilli filaments (in the outer layers)
occasionally spiral organisms Cocci attached to
filamentous microorganisms (outer surface of
plaque) -gt 'corn-cob' structure
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THE ORAL ECOSYSTEM AND DENTAL PLAQUE
Plaque can be defined as A tenacious, complex
microbial community on tooth surfaces, containing
living, dead and dying bacteria and their
products, embedded in a matrix of polymers
mainly derived from saliva
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Toothbrush vs plaque