Bacteria Chapter 5: Biofilm

Question 1

What is a biofilm?

Answer 1

organized community of bacteria adhered to a surface and surrounded by (enmeshed in) a matrix of extracellular polymeric substances (EPS)

Question 2

What is EPS?

Answer 2

slimy, film-like substance produced by bacteria of the biofilm

composed of polysaccharides, proteins and nucleic acids

Question 3

What initiates biofilm formation?

Answer 3

coordinated chemical signalling between cells (quorum sensing)

Question 4

What molecules does quorum sensing use?

Answer 4

autoinducers (signalling molecules) produced by bacteria

bacteria have receptors for these molecules

Question 5

Quorum Sensing Process

Answer 5

1. Elevated number of bacteria are present in close proximity to each other
2. Autoinducer concentration increases
3. Once binding of autoinducers exceeds a certain threshold, signalling cascade is initiates
4. Cascade modulates gene expression, which modulates bacterial physiology to encourage community development

Question 6

Biofilm Formation Process

Answer 6

1. Bacteria attaches to surface
2. EPS is produced, resulting in much stronger (often irreversible) attachment/colonization
   - structure influenced by environmental factors
3. Single cells detach from biofilm

Question 7

Do bacteria in biofilm behave as a group?

Answer 7

yes – they sense and respond to stimuli in a coordinated manner

Question 8

Are bacteria deep inside the biofilm the same as bacteria closer to the surface?

Answer 8

have different physiologies – due to different O2 and nutrient availability

Question 9

What are some benign (non-disease causing) environmental biofilms?

Answer 9

• slippery coatings on rocks in streams

- coatings on ship hulls

Question 10

What are some pathogenic biofilms on implanted medical devices?

Answer 10

(Gram-negative and Gram-positive bacteria)

• urinary catheters
• heart valve implants
• hemodialysis equipment
• dental implants

Question 11

What are some pathogenic biofilms on human body surfaces?

Answer 11

• cystic fibrosis (CF) infections in lung, caused by Pseudomonas aeruginosa
• tuberculosis infections, caused by Mycobacterium tuberculosis
• urinary tract infections, caused by Escherichia coli
• ear infections (variety of bacteria)
• tonsillitis (variety of bacteria)
• oral biofilms

Question 12

What are many biofilm infections on human body surfaces caused by?

Answer 12

opportunistic pathogens that are also human commensals

• often results in chronic disease that is difficult to treat with antibiotics

Question 13

What do oral biofilms cause?

Answer 13

• dental caries

- gingivitis

Question 14

What might benign biofilms do?

Answer 14

attract, recruit, and concentrate pathogenic bacteria that might not form a biofilm on their own

Question 15

Are biofilms more or less resistant to antibiotics compared to planktonic bacteria?

Answer 15

more resistant to antibiotics

also more resistant to antimicrobial stressors, including those mounted by natural host responses (ie. immune system)

Question 16

What are the 3 biofilm properties that contribute to antimicrobial resistance?

Answer 16

• EPS matrix
• nutrient and O2
• persister cells

Question 17

How does the EPS matrix contribute to biofilm antimicrobial resistance?

Answer 17

complex enmeshing can impede penetration of antimicrobial agents to bacteria buried deep into the biofilm

Question 18

How do nutrients and O2 contribute to biofilm antimicrobial resistance?

Answer 18

• bacteria closer to surface have better access to nutrients and O2
• bacteria deeper into the biofilm are often metabolically inactive
• antibiotics are most effective against metabolically active cells –bacteria in the biofilm interior are protected

Question 19

How do persister cells contribute to biofilm antimicrobial resistance?

Answer 19

• persister cells remain viable despite prolonged exposure to antimicrobial or increased dosage
• they confer no heritable resistance to progeny once the selective pressure is removed
• allows cells in biofilm to survive for extremely long periods of time

Question 20

What are 3 new pharmaceutical approaches to anti-biofilm therapy?

Answer 20

• interfering with EPS synthesis
• inhibiting adherence of biofilms to their surface substrate
• targeting autoinducers