Dental Plaque and Biofilms (4) Flashcards
Do biofilms create their own environment?
yes
What are 2 types of biochemical interactions n a biofilm?
synergistic
antagonistic
What are examples of synergistic biochemical interactions of bacteria in a biofilm?
enzyme complementation
food chains
coaggregation/coadhesion
cell-cell signalling
gene transfer
What are examples of antagonistic biochemical interactions of bacteria in a biofilm?
bacteriocins
hydrogen peroxide
organic acids
low pH
nutrient competition
What is enzyme complementation?
Some oral bacteria possess different but overlapping patterns of enzyme activity
division of labour
What does this diagram represent?
enzyme complementation
bacteria may rely on other bacteria in the biofilm to get in there first and cut off an end sugar from an oligosaccharide side chain to expose a new sugar and allow it to metabolise
Does enzyme enzyme complementation allow?
Avoid competition for nutrients and can therefore co-exist
Where does supragingival plaque gain most of its nutrients from?
saliva - not diet unless sucrose intake is high
What bacteria does sucrose favour?
streptococci
What does streptococci metabolising sucrose form?
both intra and extracellular
polysaccharides for use as a nutrient supply when sucrose is not available
What do streptococci use as a nutrient supply when sucrose is not available?
both intra and extracellular polysaccharides
What are the early colonisers e.g. S. sanguins equipped to do?
equipped to break down salivary glycoprotein
a reliable source of nutrient in the pellicle and plaque matrix
Where does the GCF come from?
rich and constant source
from the connective tissue under gums, through the junctional epithelium and into the gingival crevis
What do some bacteria in the subgingival plaque require?
growth factors
What is a primary feeder?
feeds first
What is a secondary feeder?
the products of metabolism of one microorganism (Primary Feeder) become the main source of nutrients for another organism (Secondary Feeder)
the growth of some species being dependant on the metabolism of other organisms
Describe a simple food chain between S. mutans and Veillonella
How do secondary colonisers attach to primary colonisers?
by intra- and inter-genetic Coadhesion/Coaggregation (lectin mediated)
This can also facilitate metabolic interactions
between mutually-dependant strains
Can genes for fructan andglucan synthesis be differenentially regulated?
yes
Genes involved with glucan (gtfBC) and fructan (ftf) synthesis in S mutans are
differentially regulated during biofilm formation:
Early plaque formation – no change
Late plaque formation (7 days) - gtf expression is markedly upregulated and ftf supressed
What molecules are involved in quorum sensing?
These include Acyl-homoserine Lactones (AHL) produced by G-ve bacteria and small peptides secreted by G+ve bacteria
What is quorum sensing?
cell density dependent growth
What type of gene transfer occurs in biofilms?
horizontal gene transfer
What types of sensing can induce gene transfer?
Signalling molecules such as those involved in QS can markedly increase the ability of recipient cells to take up DNA
What is an example of successful gene transfer?
Resident S mitis and S oralis and pathogenic S pneumoniae bacteria isolated from the naso-pharyngeal area possess genes conferring penicillin resistance that display a common mosaic structure
common goods
What is an example of an antagonistic interaction?
Bacteriocins or bacteriocin-like substances (BLIS) are high molecular weight proteins which can inhibit the growth of related bacteria while the producer strains are resistant to the actions of the bacteriocins they produce
Do both gram - and + bacteria have anatagonsistic interacting species?
Produced by most species of oral streptococci and are broad-spectrum, inhibiting species belonging to the G+ve and G-ve genera
What advantage will bacteriocins give bacteria?
The production may give strains a competitive advantage during colonisation
Other than bacteriocins, what other inhibitory factors can bacteria produce?
Hydrogen Peroxide
Organic Acids
Enzymes
What can antagonisms result in?
Antagonism can also result in the prevention of exogenous bacteria from colonising the oral cavity
Do the antagonistic factors always lead to exclusion of species?
no, but can prevent exogenous bacteria from colonising oral cavity
What is the ability to maintain stability in a variable environment called?
microbial homeostasis
Bacteria can maintain homeostasis, but what are some challenges presented form the body?
- host defences
- environmental stresses
What are examples of environmental stresses that the body poses?
Saliva composition and flow
GCF composition and flow
Diet
Challenge by exogenous species
Hormone levels
Antimicrobials in toothpaste and mouthwashes
Physical disturbance
What is the essential mechanism of microbial homeostasis?
When the environment is disturbed, self-regulatory mechanisms (homeostatic reactions) come into force to restore the balance
An essential component of this mechanism is negative feedback, whereby a change in one or more organisms results in a response by others to neutralise or oppose the change
When is microbial homeostasis greatest?
in communities that shown the greatest diversity
When can microbial homeostasis breakdown?
immunological disorders
non-immunological factors
What are examples of immunological disorders which breakdown microbial homeostasis?
slgA-deficiency
Neutrophil dysfunction
immunosuppression
What are examples of non-immunological factors which breakdown microbial homeostasis?
Xerostomia
increased GCF flow
diet - high in refined carbohydrates
hormones
