oral bacteria A Flashcards
Sampling oral bacteria- niches?
distinctive communities in different niches tongue, teeth, buccal mucosa, gingival crevice, etc.
sampling methods
collect saliva, tongue blade, scrape from tooth surface, wick fluid from deep pockets (endodontic paper)
for molecular ID what is often the main target
16s RNA genes which possess both variable and common regions
Identifying oral bacteria: Molecular techniques
PCR
hybridization assays
16S sequence analysis
microscopy
dental plaque
- Biofilm on tooth surface
* One of the highest concentrations of bacteria in the body
colonizing bac of plaque interact with?
acquired pellicle
steps to plaque formation
bac contact acquired pellicle / passive transport of bac to pellicle surface coaggregation supportive microenvironment glucan production O2 drops some species detatch
acquired pellicle
A. Bacteria never come in contact with a clean tooth surface. Tooth surface is coated with an acquired pellicle
•film deposited on tooth surface
•film composition = molecules in saliva (predominant), material shed from bacterial cell surfaces, polymers from gingival crevicular fluid
initial colonation/ passive transport what species? what binds? binds to? irreversible?
Initial colonization is by Streptococcus species Streptococcus gordonii Streptococcus oralis Streptococcus mitis Streptococcus sanguis (now sanguinis)
Adhesins on bacterial surface bind to receptors in the pellicle.
Streptococcus: Antigen I/II are important adhesins
Bind human salivary glycoproteins, other bacteria and calcium
Pellicle receptors = polymers from saliva and bacteria
Adhesion is usually irreversible
coaggregation
mportant species at this stage?
Subsequent attachment of these species and other bacterial species occurs by coaggregation
•bacteria binding to other bacteria
•additional bacteria bind to early-binding bacteria and to each other
•multiple species coaggregate
Important species at this stage:
Actinomyces naeslundii
Actinomyces viscosus
Streptococcus gordonii
supportive microenvironment, strains supported by this?
D. Microenvironment created that supports additional species: Streptococcus mutans and Streptococcus sobrinus
Bacteria multiply in the developing biofilm
glucan production
Streptococci produce glucosyltransferases
•extracellular enzymes which polymerize the glucose moiety of sucrose into glucan polymers and other polysaccharides
Glucans = branched-chain polysaccharides
Alpha(1-6) linkage
Alpha(1-3) linkage
Glucans are like cement
Bacteria bind to glucans
Bacteria are bound to each other and to matrix of glucans
O2 dropping levels
allow what strains to colonize?
where does this occur especially?
Oxygen levels drop: Late colonizers include obligate anaerobes.
Prevotella melaninogenicus
Prevotella oralis
Veillonella spp.
Especially between teeth and dental gingival crevice
detatchment of some species, how they detatch
Get some detachment of bacteria and colonization of new sites
Some bacteria will shed or degrade their adhesins to facilitate release
Altered properties of bacteria in a biofilm
- Up-regulation of genes for extracellular polysaccharide synthesis
- Increased resistance to antimicrobial agents
- Metabolic interaction between closely spaced bacteria
Increased resistance to antimicrobial agents found in biofilm due to?
a. restricted penetration of agent into biofilm (due to polysac)
b. inactivation of agents by enzymes concentrated in biofilm
c. slow growth rate of bacteria in biofilm
d. expression of novel surface-associated phenotypes
Metabolic interaction between closely spaced bacteria of biofilm
Synergistic - degradation of complex nutrients
Antagonistic - bacteriocins (exclude susceptible strains)
plaque eventually reaches?
Plaque eventually reaches a microbial homeostasis = stability in bacterial composition
Breakdown of homeostasis will?
alters bacterial composition
can be due to:
•reduction in saliva flow
•increased consumption of sucrose
Caries can result
main bacterial strains of caries
Mutans streptococci:
Streptococcus mutans (mainly)
Streptococcus sobrinus
Fermentation in biofilm produces:
acids: lactic acid, will demineralize teeth
acid is produced from the metabolic activities of the bacteria using saccharides produced with GTF
metabolic acid effect on teeth, what molecule is affected?
result of increased pH?
Solubilizes calcium and phosphate (produced from hydroxyapatite)
Get reprecipitation when pH increases (becomes less acidic)
prolonged acidic environments created by?
causes?
Prolonged acidic environment created by regular snacking on high sucrose foods
demineralization > remineralization
enamel and dentin dissolving, results?
Enamel dissolves slowly
Dentin more easily attacked and colonized by bacteria
Dentin is protein rich/many different bacteria can grow: Then disease rapidly progresses
Root canal becomes invaded and Abscess form
Age and root surface caries
likely causative strains?
Gingival recession occurs with age: This fact changes the microbial homeostasis
Cementum surface of the root is exposed and made vulnerable to bacterial colonization
60% of individual >60 years old have root caries
MS and lactobacilli likely pathogens, Actinomyces viscosus and Actinomyces naeslundii.
(Both of these Actinomyces species had been shown toproduce root surface caries in experimental animals)
Pathogenic properties of cariogenic bacteria
Rapidly transport fermentable sugars/convert to acid
Production of extracellular and intracellular polysaccharides
Ability to maintain sugar metabolism under extreme conditions
Rapid transport of fermentable sugars/convert to acid of cariogenic bacteria
•Rapidly transport fermentable sugars/convert to acid
Rapid compared to other plaque bacteria
Cariogenic bacteria have multiple sugar transporters
Including PEP-PTS systems (group translocation system)
Group translocation - molecule transported into the cell while being chemically altered
Production of extracellular and intracellular polysaccharides of cariogenic bac
Glucans and Fructans (extracellular)
Intracellular storage - allows acid production even
when sucrose in not available
how oral bac maintain sugar metabolism under extreme conditions of cariogenic bacteria?
spp?
Acidic conditions more tolerated by MS and lactobacilli (so they are both acid-producing and acid-tolerant)
a. maintain a favorable intracellular environment (pump out protons even into acidic surroundings) ATP usage is coupled to protons being pumped out (using ATP synthesized by glycolysis)
b. bacterial enzymes have more acidic pH optima
c. produce acid-stress response proteins to protect cell contents
Notable property of noncariogenic bacteria
Alkali production
Urea and arginine are the major substrates for alkali production via the generation of
ammonia (NH3), using enzymes urease and arginine deiminase
virulence factors of s mutans
Ag I/II GTFs GBPs fructanse dextranase intracell polysac PEP-PTS H-ATPase acid tolerance
Ag I/II of s mutans
adherence to salivary pellicle
GTFs of s mutans
production of glucan polymers from sucrose, used for adherence and accumulation
GBPs of s mutans
binding to glucans, adherence
fructanase of s mutans
hydrolysis of fructan polymers, produces acid
dextranse of s mutans
cleavage of glucans/ relase glucose to be used= produces acid
intracellular polysaccharides of s mutans
can be used when exogenous stores of saccharides are depleted
PEP-PTS of s mutans
catalyzes high affinity uptake of multiple different sugars
H-ATPase of s mutans
use of ATP to move protons out of cell in acidic environment
Basis for periodontal disease, hypothesis?
non-specific plaque
specific plaque
Non-specific plaque hypothesis of periodontitis
disease is due to the host response to non-specific growth of bacteria on tooth surfaces
(inflammatory disease)
Traditional view
Bacterial complexity of dental plaque
Non-specific mechanisms of generating inflammatory response: LPS and volatile fatty acids
Specific plaque hypothesis of periodontitis
disease is due to a limited number of species which produce biologically active molecules that are proinflammatory or antigenic (infection)
Non-specific plaque hypothesis treatment
failure?
Treatment dictates that flora be suppressed continuously or periodically
Sometimes traditional debridement fails leading to:
refractory periodontitis
give broad-spectrum antibiotics
Specific plaque hypothesis Key illustrative examples:
Localized juvenile periodontitis
Acute necrotizing ulcerative gingivitis
Localized juvenile periodontitis
strain?
mechanism?
treatment?
1-5 out of 1000 teenagers
Aggregatibacter actinomycetemcomitans can invade gingival tissues and produces a leukotoxin (LT) that inhibits neutrophils
locally delivered antimicrobial agents or systemic tetracycline treatment
Acute necrotizing ulcerative gingivitis
strain?
treatment?
Trench mouth of World War I
Spirochetes and Fusobacterium nucleatum
controlled by antibiotic mouth rinses with oxidizing agents also systemic metronidazole (antibiotic) treatment
Specific plaque hypothesis early and adult form considerations
important strains?
Consider both early-onset and adult forms of disease No single bacterial species uniquely involved= polymicrobial infection
Porphyromonas gingivalis
Tannerella forsythia
Treponema denticola (& other spirochetes)
Porphyromonas gingivalis Virulence Factors and their functions
• Fimbriae allows adhesion to:
– Saliva-coated hydroxyapatite
– Human oral epithelial cells
- Hemagglutinins
- Capsule prevents phagocytosis
• 3 major proteolytic activities:
– Trypsin-like
– Collagenolytic
– Glycylprolyl peptidase activity
Porphyromonas gingivalis as a “keystone pathogen”
Current model for periodontal disease, In between specific and nonspecific plaque hypotheses
Low-abundance bacteria with community wide effects that are critical for the
development of dysbiosis is now known as keystone pathogens, the best documented example of which is Porphyromonas gingivalis.
Aggregatibacter actinomycetemcomitans important Virulence Factors
leukotoxins invasins bacteriocin PLC capsular polysac
Leukotoxin of Aggregatibacter actinomycetemcomitan
Cytotoxic to human PMNs, monocytes, and T-lymphoctyes
• Invasins of Aggregatibacter actinomycetemcomitan
– Aids in bacteria penetrating eukaryotic cells
• Bacteriocin of Aggregatibacter actinomycetemcomitan, target spp?
• Inhibition of growth or killing of other bacterial species: streptococcus sanguis and actinomyces viscosus
• Capsular polysaccharide of Aggregatibacter actinomycetemcomitan
• Capsular polysaccharide • Resistance to phagocytosis by PMNs, reduction in complement dependent response by PMNs, increase In bone resorption
• Phospholipase C of Aggregatibacter actinomycetemcomitan
• Hydrolyzation of host cell membrane
Fusobacterium nucleatum Virulence factors
capsule
• Hemolysin
• Leukocidin(leukotoxin)
• Superoxide dismutase
Prevotella intermedia Virulence factors, actions?
• The brown or black pigment
§ metabolic end-product of hemin, acts as a defensive barrier that protects the bacteria from the toxic effects of oxygen
• Collagenase, hyaluronidase, and protease
§ Degrade host tissues and cleave other host derived molecules
• Hemolysin
§ Enhanced by the action of proteases
§ Favors the acquisition of iron, which is an essential nutrient to their metabolism and their survival
Modified Koch’s postulates
- Association of microorganism with periodontitis
- Elimination of bacteria reduce the disease
- Evidence of host response to pathogen
- Ability of pathogen to cause disease in animal model
- Evidence that pathogen produces virulence factors that contribute to disease.
