Biofilms

Question 1

Bacteria exist in two basic states. What are these?

Answer 1

Planktonic - free swimming

Sessile - adherent bacteria

Question 2

All antimicrobials are tested on planktonic bacteria. What is MIC and MBC?

Answer 2

MIC - Minimum Inhibitory Concentration

MBC - Minimum Bactericidal Concentration

Question 3

Define biocide.

Answer 3

A physical or chemical agent which kills all viable microorganisms.

Question 4

Define microbicide.

Answer 4

An agent which specifically kills microorganisms.

Question 5

Define bacteriostatic agent.

Answer 5

An agent which inhibits growth of bacteria.

Question 6

Define bactericidal agent.

Answer 6

An agent which kills viable bacteria.

Question 7

Define Minimum Inhibitory Concentration (MIC).

Answer 7

The lowest concentration of antimicrobial which will inhibit the visible growth of an overnight culture of a microorganism.

Question 8

Define Minimum Bactericidal Concentration (MBC).

Answer 8

The lowest concentration of antimicrobial that will prevent the growth of an organism after sub-culture on to an antibiotic free media.

Question 9

What does MBEC stand for? Define this.

Answer 9

Minimum Biofilm Eradication Concentration.

- The minimal concentration of antibiotic required to eradicate the biofilm.

Question 10

Define biofilm.

Answer 10

A biofilm is a microbially derived sessile community characterised by cells that are irreversibly attached to a substratum or interface.

• Found embedded within a matrix of extracellular polymeric substances that have they have produced.
• Exhibit altered phenotype with respect to growth rate and transcription.

Question 11

Give the 5 simple steps of biofilm formation (detail in book).

Answer 11

1. Planktonic cells begin to absorb/adhere.
2. Irreversibly attaches to surface.
3. Colony formation.
4. Maturation/extracellular polymeric layer formation.
5. Dispersal = biofilm phenotype to planktonic.

Question 12

Why do biofilms affect immuno-suppressed patients and allow for recurrent exacerbation of infection and infections on indwelling medical devices? (2)

Answer 12

1. Inherent tolerance to antimicrobials and host defense mechanisms.
2. The expression and production of virulence factors responsible for the host’s symptoms.

Question 13

Persister cells aid in the tolerance of biofilms. Explain how.

Answer 13

Persister cells are a specialised subpopulation of microbial cells which can repopulate the surface of biofilms. These do not grow or die in presence of antimicrobial ie they stay dormant but once antimicrobial therapy has stopped, persister cells becomes activated and can repopulate the surface giving rise to reinfection.

Question 14

A mechanism of tolerance for biofilms is having a slow growth rate. How does this help?

Answer 14

Slow growth rate due to nutrient limitation and hypoxia.

Slow growing means reduced metabolic rate therefore reduced susceptibility to antimicrobials.

Question 15

Cell-to-cell communication works as a mechanism of tolerance. How?

Answer 15

Cell-to-cell communication involve intercellular signals which alter the physiology of the biofilm.
Causes upregulation of molecular efflux pumps which can then expel antimicrobials from the cell.
So allows microbe to grow in presence of antimicrobial agent.

Question 16

Mechanism of tolerance - slow penetration of antimicrobials. Outline mechanism.

Answer 16

Slow penetration of antimicrobials.
Extracellular polymeric substances (ETS) - able to reduce penetration of antibiotics into biofilm.
Occurs physically and chemically.
The -vely charged EPS remove the +vely charged antimicrobials.

Question 17

Mechanism of tolerance - genetic diversity. Outline mechanism.

Answer 17

Hypermutations occur - in response to environmental and physiological stress.
Stress increases mutation rates in subpopulations within biofilm.
- allows for increased antimicrobial resistance
- cells can be shed from biofilm which are more fit to live in a changing environment.

Question 18

What is a nosocomial infection?

Answer 18

Hospital acquired infection.

Question 19

Describe the 5 mechanisms of tolerance.

Answer 19

1. Cell-to-cell communication
2. Genetic diversity
3. Presence of persister cells
4. Slow growth rate
5. Slow penetration of antimicrobials