1.8. Microbes and biofilm concept

Question 1

describe the composition and structure of a biofilm

Answer 1

1. enclosed by self-produced EPSs matrix
2. irreversibly associated to each other and/or to a surface
3. may form on biotic/ abiotic surfaces –> present in all settings

Question 2

what is a biofilm?

Answer 2

aggregates of micro-organisms

Question 3

what is EPS?

Answer 3

EPS are slime produced for protection

1. extracellular polysaccharides
2. structural proteins
3. lipids
4. nucleic acids (DNA & RNA)

Question 4

list in sequence and describe each step in biofilm formation

Answer 4

1. initial reversible attachment (weak van der Waal forces & hydrophobic effect)
2. irreversible attachment (pili, fimbriae)
3. micro-colony (growth & cell division)
4. maturation (EPS produced)
5. dispersion

Question 5

differentiate planktonic & sessile microbial cells

Answer 5

1. planktonic = free-floating
2. sessile = communities –> more properties than planktonic:
   sessile can up/downregulate gene function–> can save significant amounts of energy

Question 6

describe how biofilm multicellularity protects against antimicrobial agents

Answer 6

1. less susceptible to antimicrobial agents

2. microorganisms protected by multicellular biofilm construct

Question 7

quorum-sensing (communication)

Answer 7

1. auto-inducer concentrations amongst cells in tight-knit biofilm are used as communication
   - ->synchronise activities of large microbe group
   - -> biofilm microbes can alter behaviour on a population-wide scale in response to change in number and/or species present in the community

Question 8

autoinducers

Answer 8

• small, hormone-like molecules
  1. synthesized intracellularly by microbes
  2. actively secreted/ passively released from microbes
  3. [extracellular AI] increases with increase in number of microbes in population
  4. population-wide changes triggered by signal transduction cascade when AIs accumulate above threshold level required for detection & receptors bind the AIs
  5. sessile microbial cells => EPS –> cells in close proximity => [signal molecule] builds up => changes cell behaviour
  6. some bacterial pathogens do not produce toxins until they have large enough population to survive host’s defence mechanisms

Question 9

discuss the importance of biofilms in infectious diseases

Answer 9

1. Device-related biofilm infections
   - Biofilms occur on or within indwelling medical devices
2. Non-device related biofilm infections
   - Biofilms that form directly on host tissues

Question 10

Main nosocomial infections associated with biofilms

Answer 10

1. Bacteraemia
   - 87% of bacteraemias have an indwelling vascular device
2. Urinary tract infections
   - 95% of UTIs are catheter-related
   - Risk of UTI increases by 5% for each day the catheter is in situ
3. Pneumonia
   - Incidence of ventilator-associated pneumonia ranges from 7% to > 40%
4. Surgical wound infections

Question 11

current approaches to management of biofilm-related infections

Answer 11

• Rigorous antisepsis
• Early detection and treatment
• Removal/replacement of foreign bodies/catheters
• Antibiotics
• Anti-quorum-sensing drugs (e.g. Macrolide antibiotics)
• Antimicrobial impregnated devices
• Antimicrobial lock therapy

Question 12

novel & future approaches to management of biofilm-related infections

Answer 12

• Sonication of indwelling devices (implants or prostheses or catheters) from patients with suspected infection to improve the detection rate of bacteria
• Substances able to destroy biofilm EPS matrix (e.g. dispersin B)
• Substances which destroy persister cells
• Quorum-quenching enzymes
• Substances which cause biofilm self-destruction (e.g. phage therapy)
• Strategies to enhance the activity of conventional antimicrobial agents (e.g., electrical current, radiofrequency, electromagnetic fields, ultrasound)