Periodontal Microbiology Flashcards
What was the mode of early microbiology experiments?
What’s the issue with this?
Growing things on a plate
The problem is the “we know what we can grow” bias
What revolutionized microbiological study?
Molecular appraoaches
How many distinct oral species can be in a person?
40-60
Core microbiome
About 8% of species seen in a person’s mouth are seen in other people’s mouth
These microbiomes can change with ethnicities
The plaque biofilm definition
Organized cooperating community of organisms with specific inter-bacterial and host-bacterial interactions
T/F - you expect to see all 5 stages of biofilm formation in the mouth
False - we can brush and tongue away biofilm
What are the main species of Primary colonizers
Strep sanguis
Actinomyces viscosus
What occurs during the Attachment phase of biofilm formation?
Planktonic bacteria adhere to an acquired pelicle
What is in a pellicle t make bacteria attach to it?
Glycoproteins and antibodies
What bacterial characteristics change following attachment?
Synthesis of outer membrane proteins (this is what our body sees as foreign bodies)
Active cellular growth
What occurs during the growth stage of biofilm formation?
Co-aggregation and Co-adhesion
Co-aggregation
Cell-to-cell recognition of genetically distinct cell types
Cell clumps form and attach to a pellicle
Co-adhesion
Interactions between suspended and already adhering micro-organisms
What influences co-adhesion?
Temperature (no coadhesions below 37 C)
Lactose (more lactose means less co-adhesion)
Most of what we do to prevent caries effects what?
Co-adhesion
What occurs during biofilm maturation?
Increase in diversity
Replication and matrix formation
Ecological succession
Primary colonizers
Gram+ and Gram- streptococci that bind to pellicle proteins form saliva
Secondary colonizers
Gram- species that bind to the bridge species
Why do secondary colonizers need to bind to a bridge species?
They can’t bind to the tooth, so they have to bind to bacteria
What is known as the “bridge species”?
F. nucleatum
Tertiary colonizers
Gram- species that bind
Our body sees these as pathogens
How does the biofilm environment change when it increases in thickness?
Difficulty diffusing things in and out of the biofilm
An oxygen gradient develops
Completely anaerobic conditions emerge in the deeper layers (streps start to die, which allows pathogenic species to come in)
Reverse gradients of fermentation products develop as a result of bacterial metabolism
What provides nutrients to the supragingival plaque?
Dietary products dissolved in teh saliva
What provides nutrients to the subgingival plaque?
Periodontal tissues and blood
bacterial hydrolytic enzumes breakdown host macromolecules into peptides and amino acids
Describe the structure of a biofilm
Microcolonies (15-20% of volume)
Interbacterial matrix
Voids/water channels
Exopolysaccharides provide the backbone of the biofilm
There is a lower layer, loose layer, and a fluid layer
Describe the lower layer of a biofilm
Dense layer of microbs
Polysaccharide matrix
Tightly bound together
Steep diffusion gradient (things can’t get down there)
What’s the best way to remove the lower layer of a biofilm?
Mechanical therapy
Describe the loose layer of a biofilm
Irregular in appearance
Extends into surrounding medium
Describe the fluid layer of a biofilm
Stationary sublayer
Fluid layer is in motion
Nourishes the biofilm by molecular difusion
Describe the structure of supragingival plaque
The shape depends on shear force
The interbacterial matrix is highly variable
What is the shape of supragingival plaque under low shear force?
Towers or muschrooms
What is the shape of supragingival plaque under high shear force?
Elongated colonies capable of oscillation
What is the consistency of a gram+ matrix of supragingival plaque going to be?
Very fibrilar
What is the consistency of a gram- matrix of supragingival plaque going to be?
Very regular
What are the advantages to biofilm living?
Defense
Protection from external changes
Transfer of info and genetic mateiral
What is quorum sensing?
Regulation of expression of specific genes through accumulation of signaling compounds that mediate intercellular communication
Bacteria in biofilms are constantly talking and interacting to see if there’s enough of them to do damage
Why are biofilms more resistant to antibiotics than planktonic bacteria?
Antibiotics depend on cell turnover
Biofilm cells grow slower, so they are not going through DNA replication as often
Slow growing bacteria express ‘non-specific defense mechanisms’ and more exopolymers
Exopolymers
Retard diffusion with an ion exchange mechanism that prevents charged ions from reaching deeper zones
They also have extracellular enzymes that breakdown antibiotics
What is the classic model of a true pathogen?
Microorganism that isn’t normally present and produces virulence factors that damage the host or produces an immune response
Are there true oral pathogens?
No
Oral ‘pathogens’ are normally present throughout life
Damage from oral pathogens require presence in large numbers - ecological shifts lead to changes in proportions/balance which favors pathogens/disease
Auto-inducer 2
AI-2 may determine the switch from commensal to pathogenic community
Can turn on in response to cell density in a biofilm
Commensal bacteria produce and respond to low levels of AI-2
Pathogens produce at high levels of AI-2
What is the clinical significance of the structure of a biofilm?
It changed tooth-brushing paradigm
Non-contact brushing (sonic waves) can remove towers and mushrooms by shear force
What is the clinical significance in the antibiotic resistance of biofilms?
It changed antibiotic sensitivity testing
What is a major target for therapy in biofilms?
Auto-inducer 2
What is the top reason for implant failure?
Active periodontal disease - teeth act as reservoirs for colonization of implants
How can drug-resistant pathogens translocate to neighboring teeth?
Periodontal probing
What will decrease bacterial load more - full mouth scaling, or one quad at a time?
Full mouth scaling and root-planing within 24 hours has been shown to decrease bacterial load better
What gets more care, a live tooth or an implant?
They get the same amount of care (but err on the side of the implant)
