Lecture 4 Flashcards
what are the studies done on plaque formation?
adhesive tape samples from the tooth’s surface
plaque grown on epoxy resin crowns worn for different time periods
in vitro studies of attachment and aggregation between different bacterial species
experimental gingivitis models
what is the definition of plaque biofilm?
organized cooperating community of organisms with specific inter bacterial and host bacterial interactions
what is the attachment stage of biofilm formation?
planktonic bacteria adhere to acquired pellicle
salivary glycoproteins and antibodies in pellicle
alteration in surface charge and free energy
bacteria vary in attachment ability( rapid attachers- specific attachment structures-fimbriae, extracellular polymers, glycocalyx + slow attachers- no specific mechanism)
bacterial characteristics change following attachment- synthesis of new outer membrane proteins, active cellular growth
what is the growth stage of biofilm formation?
coaggregation, coadhesion
what is coaggregation?
cell to cell recognition of genetically distinct cell types
mediated by protein or glycoprotein receptors on one cell and carbohydrates on the other
all cells are suspended
clumps form which then attach to pellicle
what is coadhesion?
interactions between suspended and already adhering micro organisms
influenced by temperature (no co adhesion > 37 degrees), lactose (increase lactose, decrease in co adhesion)
what is the maturation phase of biofilm formation?
increase in diversity
replication and matrix formation
ecological succession
what are tertiary colonizers?
gram -
porphyromonas gingivalis
what are the secondary colonizers?
bridge species- f. nucleatum (prolific coaggregator)- bind other bacteria
what are the primary colonizers?
gram + and some gram -
streptococci bind pellicle proteins from saliva
what happens when biofilm environment increase in thickness?
difficulty in diffusion in and out of the biofilm
an oxygen gradient develops
completely anaerobic conditions emerge in deeper layers
reverse gradients of fermentation products develop as a result of bacterial metabolism
what nutrition is in supragingival plaque?
dietary products dissolved in saliva
what nutrition is in subgingival plaque?
periodontal tissues and blood
bacterial hydrolytic enzymes breakdown host macromolecules into peptides and amino acids
what is the structure of the biofilm?
microcolonies (15-20% volume) + interbacterial matrix
presence of voids or water channels
exopolysaccharides- the back bone of the biofilm
what are the three sources of matrix?
dead bacterial cells
saliva
gingival exudate
what is the structure of the lower layer of the biofilm?
dense layer of microbes
polysaccharide matrix
tightly bound together
steep diffusion gradients
what is the structure of the loose layer of the biofilm?
irregular in appearance
extends into surrounding medium
what is the structure of the fluid layer of the biofilm?
stationary sublayer
fluid layer in motion
nourishes the biofilm by molecular diffusion
in supragingival plaque what does the shape of microcolonies depend on?
shear force
towers or mushrooms- low shear force
elongated colonies capable of oscillation- high shear
what is the interbacterial matrix of supragingival plaque like?
very variable
what are the characteristics of gram positive matrix?
very fibrillar due to dextrans and levans
what are the characteristics of gram negative matrix?
very regular
contains trilaminar vesicles
filled with endotoxins and proteolytic enzymes
probably involved in adherence
what are the interbacterial carbohydrates?
energy source- dextrans, fructans
skeleton of plaque- mutans
what forms the primary attachment in subgingival plaque?
cuticle
origin: epithelial attachment? crevicular fluid? secreted by adjacent epithelium
what is the structure of subgingival plaque similar to?
supragingival plaque
how are bacterial layers near sulcular epithelium different from tooth attached?
no interbacterial matrix
more spirochetes and flagellated bacteria
what is bacterial collaboration used for?
necessary for succession
what is streptococcuscristatus
facultative species, can live with or without oxygen
uses up oxygen when available
what is fusobacterium nucleatum?
robust anaerobe
binding to strep improves survival when o2 is present
what is porphyromonas gingivalis?
microaerophilic, obligae anaerobe
coaggregation essential to survival when o2 is present
how does. s. cristatus, f. nucleatum, and p. gingivalis form robust biofilms in the presence of oxygen?
f. nucleatum invades epithelial cells
s. cristatus does not invade cells
after coaggregation, s. cristatus is carried inside by f. nucleatum
what are the advantages to biofilm living?
defense-presence of concentrate bacterial enzymes, interbacterial matrix
protection from external changes- diffusion minimal in interior regions, antibiotic and antimicrobial resistance, protection from friction and shearing forces, attachment
transfer of info and genetic material- signaling (quorum sensing), conjugation, transformation, plasmid transfer, transposon transfer
what is quorum sensing?
regulation of expression of specific genes through accumulation of signaling compounds that mediate intercellular communication
how does quorum sensing work?
depends on cell density
autoinducer 1 or 2 turns on in response to cell density
antibiotic resistance in dense biofilms
encourages growth of beneficial species
commensal bacteria produce and respond to low levels to A1-2
pathogens produce A1-2 in high levels
A1-2 may determine switch from commensal to pathogenic community
what are the mechanisms of antibiotic resistance?
biofilm bacteria 1000-1500 times more resistant than planktonic
biofilm bacteria grow more slowly- antibiotics depend cell turnover for efficacy, slow-growers express non specific defense mechanisms, and slow growers make more exo-polymers
exo-polymers retard diffusion- ion exchange mechanism prevents highly charged molecules from reacher deeper zones, extracellular enzymes inactivate antibiotics
biofilm bacteria express different genes- gene transfer, phenotypic expression of biofilm existence
what is the classic concept of a pathogen?
not normally present
produces virulent factors– damage host directly (eg toxins), induce host to damage itself (immune responses)
does oral pathogens fir the classic concept?
no because normally present throughout life and damage requires presence in large numbers
what is the ecological concept of oral microbial diseases?
ecological shifts lead to changes in proportions
balance shifts in favor of pathogens/ disease
periodontal disease is an example of ecological catastrophe
what is the clinical significance of the structure of biofilm
changed tooth brushing paradigms
hard to reach interproximal and fissures
non-contact brushing can remove towers and mushrooms by shear force
what is the clinical significance for antibiotic resistance?
change in antibiotic sensitivity testing- planktonic versus biofilm bacteria
what is the clinical significance of targets for therapy
A1-2
vaccines that target common resistance genes
what is the clinical significance of translocation and transmission of bacteria
perio probe can translocate pathogens from pockets to healthy sites
drug resistant strains can translocate to neighboring teeth
teeth act as reservoirs for colonization of implants
bacteria can infect membranes in GTR
rationale for one stage, full mouth disinfection-
full mouth scaling and root planing within 24 hrs, subgingival irrigation with 1% chlorhexedine, tongue brushing, oral microbial rinse
what is periimplant plaque?
plaque can form on implant abutments
implants that fail have a microbial composition similar to perio disease
