Plaque is a Biofilm

Question 1

what is a biofilm

Answer 1

a surface-associated organic film consisted of microbial cells and materials from the microbes and hosts/environment
bacteria growing on a surface instead of growing in liquid
can be very thick
often, the microbes are multi-species

Question 2

most bacteria in the environment are ____ and growing on a surface, not _____

Answer 2

sessile
planktonic

Question 3

metabolic changes of biofilms

Answer 3

changes in gene expression and production of extracellular matrix or extracellular polymeric substance

Question 4

how are biofilms important in systemic bacterial infecitons

Answer 4

S. aureus (skin infections, sepsis, endocarditis)
P. aerugenosa (cystic fibrosis)
C. albicans can also make a biofilm, which resemble bacterial biofilms

Question 5

what are biofilms made of

Answer 5

live and dead bacteria and an organic matrix
EPS
GCF proteins in gingival crevice
salivary glycoproteins
protein and lipids from dying bacteria

Question 6

EPS

Answer 6

polymer - often carbohydrates, some proteins and DNA
EPS produced varies with species

Question 7

a biofilm is not a homogenous slime or smear; they have

Answer 7

organisation and structure - water channels

Question 8

how do biofilms form

Answer 8

reversible attachment of planktonic cells
first colonizers become irreversibly attached
growth and cell division
production of EPS and formation of water channels
attachment of secondary colonizers and dispersion of microbes to new sites

Question 9

how do dental plaques form

Answer 9

acquired pellicle formation: salvatory glycoproteins, net negative charge
transport: bacteria arrive at the site, random contact, sedimentation, chemotaxis, saliva
initial adhesion: reversible and then irreversible attachment of bacteria to acquired pellicle
growth of micro-colonies
co-aggregation and co-adhesion

Question 10

co-aggregation

Answer 10

specific interaction between different bacteria species or strain - receptor mediated

Question 11

co-adhesion

Answer 11

ability of bacteria to adhere to surfaces - both abiotic and biotic

Question 12

reversible initial adhesion

Answer 12

mostly physics - long-range and short-range molecular forces (van der Waals interactions, electrostatic, hydrophobicity)
bacteria are very small - changes and molecular interactions can exert significant force

Question 13

electrostatic interaction

Answer 13

both bacteria and acquired pellicle have a negative charge
cations (Ca2+ divalent) in saliva bridge the charges
reversible

Question 14

hydrophobic interaction

Answer 14

lipoteichoic acid (LTA) in the cell wall of gram positive bacteria is hydrophobic
reversible

Question 15

lectin-like interaction

Answer 15

bacterial adhesins (proteins) interact with receptors (carbohydrate groups from glycoproteins) in pellicle
reversible

Question 16

specific irreversible adhesion and co-aggregation

Answer 16

irreversible attachment
co-aggregation
bridging

Question 17

irreversible attachment

Answer 17

strong, specific interactions (hydrogen bonding, covalent, ionic)
adhesin - receptor interactions
fimbria often act as adhesins
numerous receptors available on the pellicle

Question 18

co-aggregation

Answer 18

bound bacteria provide new receptors for other bacteria adhesins
some bacteria cannot bind directly to pellicle, but can bind to bacteria already bound to pellicle

Question 19

bridging

Answer 19

pellicle-bacteria-bacteria-bacteria

Question 20

biofilms form in what manner

Answer 20

in a consistent stepwise manner

Question 21

natural succession of plaque fora

Answer 21

after first bacteria adhere to teeth there is co-adhesion of other bacteria

Question 22

primary colonizers

Answer 22

gram positive cocci (Streptococcus spp.) and rods (aerobes)
use oxygen, lower redox potential of the environment

Question 23

secondary colonizers

Answer 23

gram negative rods (anaerobes)
e.g. Porphyromonas gingivalis, Fusobacterium nucleatum, Prevotella intermedia
community gains complexity over time

Question 24

early colonizers bridge what to the what

Answer 24

bridge late colonizers to the pellicle