Microbiology Flashcards
Transmission of bacteria
• Vertical: parent to child • Horizontal: - Non-parent transfer - Between spouses • The most common vehicle is saliva
Window of infectivity for transmission of bacteria
- From 19 to 30 months of age
- Has been found in children as young as 10 months
- One study found Streptococcus mutants in 53% of 6 to 12 months children
Adhesin
- A surface structure or macromoleture that binds a bacterium to a specific surface.
- Antigen I/II or SpaP.
- Attaches to salivary pellicle receptors, salivary agglutinate, and other bacteria.
- Also provides mechanism fo binding salivary agglutination glycoprotein to the streptococcal cell surface-generates receptor for other bacteria to adhere.
- Enables P. Gingivalis to adhere to streptococci, enabling secondary colonizers to be incorporated into plaque communities.
Glucans
- Tooth adherence
- Promotes aggregation
- Biofilm accumulation
- Retention of bacterial nutrients
Lipoteichoic Acid (LTA)
- Lipoteichoic acid is an amphipathic constitutions of the gram-positive bacteria outer-envelope.
- Can stimulate inflammation - TLR2.
- Analogous to LPS in gram negative bacteria.
- May help in adherence
- Key in virulence
Etiological factors in dental caries
1) Microorganisms - some oral flora are carcinogenic, others protective
2) Host factors (saliva, tooth anatomy, oral hygiene, etc.)
3) Substrate (fermentable carbohydrate)
4) TIME: the more often the above factors are in contact, the more damaging the effect
What are con founders?
An outside factor that correlates (positively or negatively) with the independent variable and the dependent variable.
3 major hypotheses regarding the etiology of caries
1) Specific plaque hypothesis: proposes that only certain species of bacteria are involved in the caries process
2) Nonspecific plaque hypothesis: assumes all plaque/bacteria is pathogenic
3) Ecological plaque hypothesis: suggests that shifts in the pH of the biofilm cause a shift toward carcinogenic bacteria (Streptococci mutants) in the balance of resident oral flora, resulting in disease
Extended caries ecological hypothesis (what we now believe)
- Low pH non-mutans strep include Streptococcus mitis, oralis, and sanguine.
- These bacteria are pioneer bacteria and early colonizers of tooth structure, binding to the pellicle first.
- They have long been thought to be benign and perhaps helpful in preventing caries via competitive inhibition (they compete for nutrients and space in the biofilm, thus leaving little for mutants strep to love on ).
- Given the right environment, even these “good” bacteria can cause demineralization and destruction of tooth structure.
- Our efforts to eradicate caries should not be aimed at a caries vaccine or targeted antimicrobial, but at changing the environment of the biofilm and maintaining a neutral pH.
Paradigm regarding etiology of the carious lesion
- Old paradigm: the carious lesion is an irreversible manifestation of the disease and is the result of progressive demineralization of tooth structure.
- New paradigm: carious lesions represent an imbalance in the ongoing remineralization/demineralization cycle that continuously occurs.
- When demineralization exceeds remineralization, a carious lesion forms.
Composition of enamel
- 95% Hydroxyapatite
- 4.5% water
- 0.5% organic matrix (proteins—amelogenins, enamelins)
Various ions (such as fluoride) can be incorporated into the HA crystals
Chemistry of demineralization/remineratlization
- Neutral conditions: a dynamic equilibrium exists between the mineral content of enamel and the oral fluid.
- When the oral environment is acidic, the H+ ions in the oral fluid react with the phosphate ions and hydroxyl ions in the enamel. The oral fluid is now unsaturated with phosphate ions, so these ions are leached from the enamel in an effort to re-establish equilibrium.
