Biofilm och kliniska fall

Question 1

Define biofilm

Answer 1

A community of bacterial cells + their secreted extracellular polymeric substances (EPS)

EPS=polysaccharides + extracellular DNA + supportive proteins

Question 2

What are the 5 characteristics of biofilm?

Answer 2

1. Complex and dynamic community structures
2. Bacteria in biofilm show different gene expression than planktonic bacteria
3. Bacteria can communicate inside the biofilm using quorum sensing
4. Biofilm bacteria are less susceptible to antibiotics
5. Biofilm bacteria are protected from the host defenses

Question 3

Define planktonic

Answer 3

Bacteria that exist outside of biofilm, as free individual cells

Question 4

What are the 4 steps of biofilm formation?

Answer 4

1. attachment (the planktonic bacteria attaches to the surface and starts excreting EPS)
2. accumulation (the biofilm is growing)
3. maturation (the biofilm has reached a good size)
4. dispersal (the biofilm has become too large and starts breaking apart)

Question 5

Define quorum sensing

Answer 5

It is signals that bacteria send in a biofilm that count how many bacteria there are inside the biofilm

Question 6

Name some strategies for prohibiting biofilm (5)

Answer 6

1. Stop adhesion
2. inhibit quorum sensing
3. enzymes to break down EPS
4. eradicate persistors
5. bacteriophages

Question 7

Why can’t we stop biofilms using antibiotics?

Answer 7

The problem is twofold: because antibiotic resistance is already a global problem, and we don’t want to increase it, and also beacuse biofilms are extra resistant to antibiotics due to their inherent characteristics.

Question 8

Define MBEC

Answer 8

Minimum biofilm eradication concentration

Question 9

How does MBEC compare to MIC?

Answer 9

Usually higher values, since biofilms are inherently more resistant to antibiotics than planktonic bacteria (which is what MIC is measured for)

Question 10

Compare resistance vs tolerance

Answer 10

Resistance: resistant microorganisms can grow in the presence of AB

Tolerance: the ability of a microorganism to survive (not growing or dying) in the presence of AB

Question 11

How does the biofilm matrix/barrier help the bacteria in the biofilm survive antibiotics?

Answer 11

Certain antibiotics have a hard time penetrating through the barrier, which means that some of the bacterial cells within the biofilm never will be exposed to high enough concentrations of AB to kill them

Question 12

How can polysaccharides in the biofilm help it against antibiotics?

Answer 12

Certain species, such as ps.aeruginosa, can excrete polysaccharides that bind the AB and sequester it so it does not affect the bacterial cells

Question 13

How does extracellular DNA help the biofilm against antibiotics?

Answer 13

It is thought that the extracellular DNA can be involved in horizontal gene transfer of AB-resistance genes between bacterial cells.

Question 14

How do enzymes in the biofilm help against antibiotics?

Answer 14

Antibiotic-degrading enzymes such as betalactamases accumulate in the biofilm and break down the antibiotic upon it entering the biofilm, ensuring it does not reach the bacterial cells

Question 15

How does the nutrition gradient in the biofilm help against antibiotics?

Answer 15

Because there are more nutrients on the outside of the biofilm, that get used up the closer to the center you get, it means that the cells at the center are less metabolically active - ”sleeping” - which makes them more tolerant to AB.

Question 16

How does the oxidative stress response play a role in protecting against antibiotics?

Answer 16

Bactericidal antibiotics work through introducing the production of lethal levels of reactive oxygen species (ROS). In a biofilm, bacterial cells can detoxify ROS.

Question 17

Define small colony variance

Answer 17

A different phenotype to the wildtype bacterial cells, with reduced colony size, slow growth and therefore higher tolerance to AB

Question 18

What are persistor cells and what role do they play in the biofilm?

Answer 18

Bacterial cells that are not growing and therefore can survive antibiotic treatment, to then reconstitute the biofilm once treatment ends. Contribute to the establishment of chronic infection.