EX 1- Biology of Infectious Agents- Igboin

Question 1

Organized multicellular community of bacteria, attached to a living or inert surface, surrounded by a self produced extracellular, polymer matrix

Answer 1

Biofilm

Question 2

What are biofilms role in infections?

Answer 2

• most bacteria in nature exist in biofilms
• form in diverse environments w/ fluid flow
• 60-80 % of microbial infections caused by biofilm bacteria

Question 3

What are the steps in formation of a biofilm?

Answer 3

• Attachment
• Colonization
• Growth and maturation
• Dispersal

Question 4

What are the steps in the formation of a biofilm according to time?

Answer 4

• Reversible adsorption of bacteria (sec.)
• Irreversible attachment “Sessile” (sec-min)
• Bacteria multiply, microcolonies: cell division (attached bacteria) recruitment of other bacteria (hrs-days)
• Exopolymer production by microcolonies, biofilm establishment (quorum sensing) (hrs-days)
• Incorporation of other bacteria into growing biofilm. (days- months)

Question 5

______ is important for biofilm formation

Answer 5

Surface conditioning

Question 6

Adsorption of organic molecules onto a clean surface forms a ______ film to which bacteria adhere

Answer 6

conditioning (ie salivary proteins on teeth surface)

Question 7

For this to occur surface conditioning is important.

Answer 7

Attachment

Question 8

_______ attach to conditioned surface

Answer 8

Pioneer bacteria/Primary colonizers

Question 9

Bacterial cell surface proteins involved in the attachment to surfaces: other bacteria, host surfaces. Attach to other molecules, receptors, specific interaction

Answer 9

Adhesion molecules

Question 10

______ bind to primary colonizers (adhesion molecules).. Some require waste/ by-products of primary colonizers.

Answer 10

Secondary colonizers

Question 11

“Bridge species” that bridges the gap btw early and late colonizers

Answer 11

F. nucleatum

Question 12

What can develop under an aerobic biofilm? Which causes bacteria to interact (cooperative consortia) with different species?

Answer 12

Anaerobic biofilm bc of decreasing O2 concentration

Question 13

What is the structure of a mature biofilm?

Answer 13

• “web”
  numerous bulbous microcolonies w/ fluid filled channels
• 75-95% extracellular polymer
  -5-25% bacteria

Question 14

What do the fluid filled channels in mature biofilms carry?

Answer 14

Nutrients, bacterial molecules, and waste

Question 15

What are the two ways that bacteria spread from a mature biofilm (biofilm dispersal)?

Answer 15

1. Active- enzyme degradation of ExoP (bacteria can detach)
2. Passive- fluid flow, collision, human intervention ( brush teeth)
   Once released new pioneer cells establish a biofilm downstream

Question 16

What are the advantages of a biofilm to microbes?

Answer 16

• Resistant to antimicrobials ( chronic infections)
• Resistant to host defenses (chronic infections)
• Resistant to mechanical removal
• Nutritional advantages- pool resources to digest nutrient sources, some species utilize waste of others

Question 17

What are the advantages of a biofilm to a host?

Answer 17

• prevent colonization by harmful organisms
  –occupy space
  –produce molecules that kill other species
  ie S. sanguinis produces H2O2 which inhibits growth of S. mutans

Question 18

Process of cell-cell communication by which bacteria monitor the density of members of their species and other species in an environment

Answer 18

Quorum sensing

Question 19

What is the purpose of quorum sensing in bacteria?

Answer 19

synchronize behaviors that cannot be accomplished by individual bacteria working alone (strength in numbers)
ie biofilm formation, virulence (host invasion), conjugation

Question 20

What is the general quorum sensing circuit in gram -ve bacteria?

Answer 20

LuxI/LuxR sensing ciruit

Question 21

What are the 2 main components in the LuxI/LuxR quorum sensing circuit of gram -ve bacteria?

Answer 21

• Signal molecule
• -autoinducer (AHL-acyl homoserine lactone) made by Lux I
• Receptor/Response regulator
• -Lux R

Question 22

How does the LuxI/R sensing circuit in gram -ve bacteria work?

Answer 22

• When there is enough LuxI made outside the cell, it diffuses into the cell.
• Inside the cell, it binds to signaling receptor (luxR), which binds to the DNA/Target gene causing different processes (ie light)
• Species specific

Question 23

What is the general mechanism for quorum sensing in gram +ve bacteria?

Answer 23

Oligopeptide mediated quorum sensing

Question 24

What are the 3 main components of the oligopeptide mediated quorum sensing circuit in gram +ve bacteria?

Answer 24

• signal mol: oligopeptide
• receptor (R)
• response regulator/gene expression activator (RR)
• -species specific

Question 25

How does the oligopeptide mediated quorum sensing circuit in gram +ve bacteria work?

Answer 25

• Oligopeptide on the outside of the cell binds to a surface receptor
• When bound, the surface receptor activates a gene expression activator protein
• The gene expression activator protein binds to the DNA and expresses a gene

Question 26

What is the proposed mechanism for interspecies communication?

Answer 26

LuxS/AI-2 based quorum sensing

• Sugnaling molecule: autoinducer-2 (AI-2) made by LuxS
• -made by > 30 different G+ and G- species

Question 27

What are the three classes of signaling molecules for quorum sensing?

Answer 27

1. Acyl homoserine lactone (AHL), (gram -ve)
2. Oligopeptides (gram +ve)
3. AI-2 (multi-species)

Question 28

What cellular processes are regulated by quorum sensing?

Answer 28

• Biofilm Formation
• Expression of virulence genes
• Motility (flagella gene expression at high cell density)

Question 29

How is quorum sensing targeted to block biofilm formation?

Answer 29

• Block synthesis of signaling molecule
• Degrade the signaling molecule
• Block the receptor form binding to the signaling molecule