Oral Ecology and Microbial Diversity Flashcards
What are the “Traditional Methods” of detecting bacterial species?
Microscopy
Cultivation
What is a problem with Microscopy?
Difficult to distinguish between similar morphotypes
What are some problems with microbial Cultivation?
There are special nutrient requirements
Inhibition of some species by others
Minor species can get overgrown
Slow growing species can get overgrown
What is the 16S Sequencing?
The new method to detecting bacterial species
-rDNA gene alignments and construct phylogenetic trees
T/F - All oral bacteria have been cultivated
False - only about half the species found in the oral cavity have been cultivated
How many organisms are present in the oral cavity?
Lots
- 300+ by cultivation
- 700 by 16S sequence diversity
How many species of oral microbes does an individual harbor?
100-200
What is the effect of the mouth being an open system?
Contact with water, soil, plants, animals, other humans, other body sites leads to transient species and true resident species
What were the goals of the Human Microbiome Project?
Determine whether individuals share a core humane microbiome
Understand whether changes in the human microbiome can be correlated with changes in health
Develop new technologies to support these goals
Addressing the ethical, legal, and social implications raised by microbiome research
Do we have more human cells or bacterial cells in our system?
Bacterial cells
And that microbiota contains many-fold more DNA variety than our humane genome
T/F - Microbial communities are the same throughout the body
False - Each body site harbors a distinct microbial community, including the oral cavity
T/F - Everyone has the same microbiota
False - Individuals differ amongst each other, although some core species are shared
What does Bray-Curtis show us?
A graph that shows diversity among subjects by body habitat
Where do humans acquire their human oral microbiome?
Parents kissing them
What is the hygeine hypothesis? Why is it wrong?
It says “don’t kiss babies or share utensils to avoid transmission of S. mutans”
It’s wrong because otherwise babies don’t develop normal microbiota as well
How do home-reared babies v babies in the NICU develop oral microbiota?
They both develop the same microbiota, but babies that were in the NICU take a little bit longer to develop it
Ecology
The study of interrelationships of organisms and their environment
Niche
The specific combination of conditions that are necessary for the survival of a particular organism
These parameters may be physical, chemical, and biological
Mutliple niches can be found in the oral cavity. Where would different niches be found?
In different oral sites - they can harbor different bacterial species
What are the two most noticeable niches in the oral cavity?
Non-shedding, hard tooth surface - where biofilm/plaque can accumulate
Soft tissues - micro-organisms can invade and cause periapical and odontogenic infections
How can oral ecology change over time?
Oral structure change:
- Teeth erupt and are lost
- Pockets can form
- Injuries occur
- biofilm thickness changes
- If surfaces are cleaned, succession occurs
What are some examples of soft-tissue surfaces?
Sulcus
Tongue
Mucosa
Gingiva
What are the supra-gingival hard surfaces where biofilm can accumulate?
Fissures Proximal surfaces Buccal and lingual enamel surfaces Cementum Restorations Calculus
What are the sub-gingival hard surfaces where biofilm can accumulate?
Enamel
Cementum
Restorations
Calculus
Planktonic bacteria
Bacteria floating in water
Most of the bacteria that cause dental/medical issues are in what form?
Sessile - Attached to surfaces in a biofilm
What are biofilms made up of?
Adherent microorganisms and ECM in an aqueous environment
What is the purpose of the ECM in a biofilm?
It is the sticky material that holds the biofilm together
The reason biofilms are hard to get rid of
Contains water flow through channels that act like a circulatory system
What is the biofilm lifecycle?
Attachment
Growth to mature biofilm community
Detachment of cells to seed new biofilm formaiton
Polymicrobial communities
Can be formed by a single bacterial species
Biofilms are an example
May also include other micro-organisms such as fungi, algae, protozoa
Why are biofilms more complex than planktonic bacteria?
They turn on a different set of genes
Multiple species cooperate
Highly resistant to antibiotics
When are biofilm adaptive genes turned on?
When bacteria detect surfaces
When bacteria detect each other (quorum sensing)
Signals pass between bacteria
What can bacteria in a biofilm do to co-exist and cooperate?
Provide nutrients to each other (food chains)
Remove toxins
Inter- and intra- species signaling
“Division of labor”
What are biofilms highly resistant towards?
Antibiotics
Host defenses
Mechanical disruption
T/F - You need more antibiotics to kill biofilms than planktonic bacteria?
True - up to 1000-fold, which ends up being toxic to the host
What are the factors that contribute to the environment in the oral cavity and create specific niches?
Bacterial adherence Oxygen tension pH Bacterial food supply or substrate Bacterial community interactions
What effect does saliva have on bacterial adherence?
Promotes by providing binding sites
Inhibit by agglutinating and clearing
How much oxygen is in an open mouth?
21%
How much oxygen is in a closed mouth?
12-14%
How much oxygen is in the periodontal pocket?
1-2%
How much oxygen is in supragingival plaque?
1-20% depending on the age of the plaque
(newer, thin plaque has more)
(older, thicker plaque has less)
What is Oxidation-reduction potential?
Electrical potential or tendency to oxidize or reduce (aka the oxygen level)
Positive Eh aerobes = high oxygen
Negative Eh anaerobes = low oxygen
Obligate aerobes
Require O2 at atmospheric levels for growth
Facultative anaerobes
Can switch between aerobic and anaerobic metabolism
Microaerophilic
Require low levels of O2
Aerotolerant anaerobes
Anaerobic metabolism, but tolerate the presence of O2
What can oxygen toxicity cause?
Oxidation of membrane lipids and destruction of cell integrity
Oxidaiton of sulfhydryl groups in enzymes resulting in cross-linking and inactivity (damage proteins)
This is done by oxygen free radicals
What makes anaerobes sensitive to oxygen?
Genetic inability to make enzymes such as superoxide dismutase (SOD), catalase, or various peroxidases
What is the action of superoxide dismutase?
Take superoxides and converted them to O2 and peroxide
What is the action of peroxidases?
Take oxygen and peroxide and convert them to 2 H20 molecules
What is the action of catalase?
Take oxygen and two peroxide and make water and oxygen
What happens to older plaque?
It gets thicker and becomes sheltered from oxygen. This lowers Eh and has a corresponding shift in microflora (succession)
Where is the mouth are anaerobic species found?
In oxygen-protected sites such as the sulcus and mature plaque
Where in the mouth are facultative anaerobes and microaerophilic species found?
Supragingival plaques
What is the significance of Fusobacterium species?
Scavenge oxygen and help provide an anaerobic environment for other species
What is normal oral pH?
7.0-7.2
How can ingested foods directly affect pH?
Carbonated drinks have a pH of 3 and can drop it
How can ingested foods indirectly affect pH?
Bacterial fermenting of sugars to lactic acid has a pH of about 5
What can periodontal pocket pH of 7.5 be a result of?
Inflammaiton
What are the critical ecological determinants of caries?
Bacteria
Substrate
Vulnerable tooth
What are the two MAJOR nutrient niches in the oral cavity?
Supragingival
Subgingival
Where do supragingival environment nutrients come from?
Saliva (endogenous) Ingested food (exogenous)
Where do nutrients in the subgingival environment come from?
Crevicular fluid and cells (endogenous)
What does it mean for ingested nutrients to be ‘bioavaliable’?
Low molecular weight
Soluble carbohydrates and amino acids are readily taken up
What is in saliva that can be used for nutrients?
Glycoproteins Inorganic salts Amino acids Glucose Vitamins
What are examples of endogenous nutrient sources
Saliva
Shed host cells
Gingival crevicular fluid
Breakdown products of perio tissues
What is in crevicular fluid that can be used for nutrients?
Serum proteins Amino acids Glucose Vitamins Hemin Hormones
sIgA
Secretory immunoglobulin A
In the saliva
Prevents adhesion
IgG
In gingival crevicular fluid
Directed against periodontally important organisms
What role do antibodies play in the oral cavity?
Inhibit colonizaiton
Act as opsonins (mark bacteria for targeting)
Activate compliment system
What makes up the innate immunity in the oral cavity?
Epithelial barrier Desquamation of soft tissues Neutrophils Complement proteins in crevicular fluid Antimicrobial peptides
What are the major salivary proteins?
a-amylase
mucins
a-amylase
Digests starches and binds bacteria
Mucins
lubricant in saliva
What are salivary defenses (minor proteins)
Salivary lysozyme Salivary lactoferrin Serum transferrin Sialoperoxidase system Antimicrobial peptides Acidic proline-rich proteins
Salivary lysozyme
Digests peptidoglycans in bacterial cell wall leading to osmotic disruption and cell death
Salivary lactoferrin and serum transferrin
Proteins that bind iron so that it is not bioavailable to bacteria
Sialoperoxidase sustem
Generates superoxide radicals which inactivate bacterial enzymes leading to bacterial death
What mechanisms are used to maintain the integrity of the tooth?
Pellicle proteins/salivary minerals
Salivary buffering
What do pellicle proteins do?
Keeps the tooth from getting dissolved
What bacterial products can be used as nutrients for microbes?
Lactic acid
Vitamin K3
What bacterial products can alter the environment?
Carbon dioxide
Removal of oxygen by Fusobacterium
