Plaque Biofilms/Dental bacteria Flashcards
Discuss dental plaque biofilm?
Dental plaque is a central component of periodontal health and has a lot in common with
biofilms that occurs elsewhere.
What are biofilms?
Biofilms are complex biological structures that occur everywhere in nature. It could broadly
be described as a slime composed of proteins and sugars with complex populations of
bacteria embedded in it. Biofilms are adapted to survive in very challenging environments
and in living organisms, are often involved in many chronic inflammatory disease
processes.
What is Extracellular Polymeric
Substance (EPS)?
The largest component of the organic matrix is secreted by the micro organisms and is
composed of glycoproteins, proteins, polysaccharides. DNA released from dead or living
microbes form important structural components of the Extracellular Polymeric
Substance (EPS). EPS attaches the biofilm either inanimate or living surfaces. It also
forms a significant part of the protection of the microbes from antibiotics or disinfectants.
EPS assists as a medium for communication between the different microorganisms: so called quorum sensing. Channels within EPS assist with the removal of waste products
and act as supply channels to the microbe community.
What is Quorum sensing?
Quorum sensing is the mechanism that bacteria within a biofilm use to communicate and
coordinate their activities and physiological processes. This occurs by means of the
release and sensing of defusable signal molecules. Plasmid transfer is a valuable method
of passing important information, like antibiotic resistance, between organisms within the
community. This effective communication between microbes within a biofilm allows these
organisms to behave like a multicellular organism, to
the benefit of all involved.
How does a biofilm form?
Stage I: Reversible Attachment
Planktonic bacteria in an environment attaches to the
surface by means of surface adhesions or fimbrae.
Stage II: Permanent Attachment
The primary coloniser bacteria multiply and become
more firmly attached to the surface. They are now
described as sessile. Quorum sensing starts and this
induces changes in their gene expression. This also
induces phenotypic change that improves survival.
Stage III: Protective Matrix
Once these microbes have attached firmly to the surface, they start to produce EPS and
forms the slimy matrix that further assist other colonies to adhere to the surface. This initial
population changes the environment within the EPS and encourages different organisms
to join.
Stage IV: Maturation
Once mature the biofilm supports shedding of planktonic bacteria to start the process
elsewhere. Complete fragments of this biofilm can be shed to colonise new areas.
Swarming is another interesting phenomenon that occurs in response to quorum sensing.
The behaviour of the colony changes and suddenly starts to actively migrate or spread
across the surface.
Discuss canine biofilm early colonisers?
How does e Extracellular Polymeric
Substance (EPS) protect planktonic bacteria?
Biofilms, by their very nature, provide significant protection for the participating microbes.
Conditions that cause environmental stress (e.g. nutritional or oxygen limitation) that would
kill planktonic bacteria, often has no noticeable effect on these same organisms within a
biofilm. The buffering effect of EPS appears to act as a protective buffer.
How does Extracellular Polymeric
Substance (EPS) block antibiotics?
EPS can protect organisms in a biofilm, by limiting access to them, by large molecules like antibiotics. To achieve effective antibiotic levels to kill susceptible bacteria within a biofilm,
much higher concentrations have to be present, than those required to kill the same
bacteria in planktonic state. Antibiotic levels to achieve effective antibiosis of organisms
within a biofilm often requires doses that exceed safe dose levels.
EPS acts as a medium to transfer genes (for example antibiotic resistance) between species.
How does hibernation help with antibiotic resistance within the biofilm?
Some organisms within biofilms become metabolically inactive, called hibernation. Some
of these organisms regain their activity once released as planktonic forms. In this
hibernation state, these organisms could be resistant to the effect of antibiotics.
Discuss the speed of biofilm formation?
Planktonic bacteria attach to
the surface within a few minutes and forms strongly attached micro colony forms within 2
to 4 hours. EPS formation occurs within 6 to 12 hours and the increased tolerance to
biocidal chemicals, improves as the EPS develops. Mature biofilms are highly resistant to
biocides and biofilm colonies starts shedding planktonic bacteria, within 2 to 4 days.
How quickly can a biofilm reform after mechanical disruption?
If a mature biofilm is mechanically disturbed, it can reform within 24 hours. This rapid
recovery is achieved by rapid regrowth of remaining fragments. It might also recover
rapidly by planktonic spread of opportunistic microbes to a susceptive environment.
Discuss dental plaque?
Plaque is a biofilm that occurs in the oral cavity. The formation of plaque is not related to
the ingestion of specific foods. It occurs most rapidly at night and also during parenteral
feeding methods.
What is a pellicle?
The dental pellicle, or acquired pellicle, is a protein film that forms on the surface enamel, dentin, artificial crowns, and bridges by selective binding of glycoproteins from saliva that prevents continuous deposition of salivary calcium phosphate.
When does the pellicle form?
The pellicle forms extremely rapidly after any cleaning process on the surface of the tooth
crown. This thin layer of glycoproteins covers the entire oral cavity and is derived from
saliva and gingival crevicular fluid (GCF). The composition of the pellicle varies from these
sources though, and this might indicate the selective adhesion of macromolecules from
this environmental source.
What are primary colonisers of a biofilm?
This describes the initially reversible and later permanent attachment of planktonic
bacteria to the surface of the pellicle. It therefore represents stages one and two of the
biofilm formation described above.
What are Secondary colonisers?
Secondary colonises cannot adhere to the pellicle themselves but attaches to the
primary colonisers. This adherence is called co-aggregation.
What is Maturation of a biofilm?
As the EPS (Extracellular Polymeric
Substance) accumulates plaque biofilm matures and individual micro colonies benefit and
thrive within the new environment. At this stage the biofilm supports shedding of planktonic
bacteria but also the potential release of micro-colonies or small fragments of biofilm. This
represents stages three and four in biofilm formation and promotes the spread of plaque.
What are the key primary colonisers of the canine pellicle?
Gram-negative Neisseria (a diplococcal species) predominates. This study identified
key primary colonisers:
*Neisseria zoodegmatis
*Neisseria animolaris
*Corynebacterium
*Stenotrophomonas
What bacteria does Canine & Feline Plaque have in Health & Disease?
HEALTH = GRAM NEGATIVE + AEROBIC
DISEASE= GRAM POSITIVE + ANAEROBIC
“Healthy” Canine Plaque
is Dominated by?
Gram-negative bacteria Streptococcus species are rare when compared
with human Plaque.
Both Morexella and Bergeyella and Porphyromonas predominates in
healthy gingiva states
“Diseased” Canine Plaque is
Dominated by?
Gram-positive anaerobic bacteria.
Peptostreptococcus and other
Peptostreptococcaceae, and Actinomyces predominates during mild periodontitis.
What is “Healthy” Feline Plaque Dominated by?
Gram-negative bacteria.
Like Porphyromonas, Morexella and Fusibacterium
Compare oral microbial communities in humans cats and dogs?
What is “Disease” Feline Plaque
Dominated by?
Gram-positive anaerobic bacteria. Peptostreptococcaceae predominates in
mild periodontitis.
