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Microbiology for Dentists > 8. Microbial biofilms > Flashcards

8. Microbial biofilms Flashcards

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Biology 101 flashcards
1
Q

Define ‘biofilm’

A
  • community of microbial cells
  • encased within a matrix of polymers
  • associated with an interface
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2
Q

What kind of interface are biofilms found at?

A
  • can be air-liquid
  • or liquid-solid
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3
Q

Biofilms have emergent properties. What does this mean?

A
  • not simply a sum of microbes within them
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4
Q

Explain planktonic biofilms

A
  • in liquid
  • homogenous
  • single species
  • nutrient rich
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5
Q

Explain surface-associated biofilms

A
  • cultures on agar plate
  • limited heterogeneity
  • single species
  • nutrient rich
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6
Q

Explain natural biofilm

A
  • in wildlife
  • heterogenous
  • mixed species
  • limited nutrients
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7
Q

4 stages of biofilm growth

A
  • attachment
  • colonisation
  • development
  • dispersal
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8
Q

In the mouth, how are most cells transported?

A
  • saliva
  • sloughing of epithelial cells
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9
Q

What happens in attachment of a biofilm?

A
  • cells swim or passively reach surface
  • non-specific and specific attachment forces
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10
Q

What happens in colonisation of biolfilm?

A
  • adherent cells start to grow
  • cell-cell communication
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11
Q

What happens in development of a biofilm?

A

starts to form 3D structure

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12
Q

What happens in dispersal?

A

active or passive sloughing

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13
Q

Pseudomonas aeruginosa is a … pathogen

A

opportunistic

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14
Q

How does pseudomonas aeruginossa link to biofilms?

A
  • commonly found in water systems
  • usually harmless but can cause UTIs, wound infection or lung infections in CF patients
  • can cause outbreaks in hospitals e.g ear piercing clinics
  • forms thick biofilms in labs and is studied as a model in biofilm processes
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15
Q

Explain why biofilms are heterogenous

A
  • biofilms are 3D
  • open structures with channels permeating the matrix
  • they’re heterogenous as cell distribution is not uniform and microcolonies are often seen
  • nutrients and waste products not uniformly distributed either due to matrix impeding mass transfer
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16
Q

Biofilms contain a range of different niches. Explain

A
  • anaerobic bacteria can grow in some parts containing less oxygen
  • more oxygen rich parts would encourage growth of aerobes
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17
Q

Macromolecules such as … form the basic structure of a biofilm

A
  • polysaccharides
  • proteins
  • nucleic acids
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18
Q

Small molecules can be trapped in the … of biofilms e.g …

A
  • matrix
  • nutrients
  • metals
  • signalling molecules
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19
Q

How to prepare a biofilm for EM scanning?

A
  • have to dehydrate and remove water
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20
Q

What percentage of human infections can be attributed to biofilms?

A

65-80%

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21
Q

Examples of human issues caused by biofilms

A
  • CF
  • dental disease
  • chronic wounds
  • kidney stones
  • endocarditis
  • atherosclerosis
22
Q

Diagnostic criteria for biofilm infections

A
  • pathogenic bacteria associated with surface
  • direct exam of infected tissue shows aggregated cells in cell clusters encased in a matrix (of bacterial or host origin)
  • infection confined to particular site on host
  • recalcitrance to antibiotic treatment despite demonstrated susceptibility of planktonic bacteria
23
Q

Infections are harder/easier to treat when in a biofilm

A

harder

24
Q

Who investigated Pseudomonas aeruginosa?

A

Bill Costerton

25
Q

What did Bill Costerton do?

A
  • followed observations that catheter infections are often recalcitrant to antibiotics
  • used model of artificial urine flowing over discs of catheter material
  • inoculated with Pseudomonas aeruginosa (common cause of UT catheter I)
  • tested antibiotic sensitivity in biofilm bacteria and compared with planktonic cells
26
Q

How does ‘antimicrobial resistance occur?

A
  • genetic changes
  • transmitted to progeny during cell division (vertical transmission)
  • transmitted between resistant and sensitive strains of species or between species (horizontal transmission)
27
Q

How does antimicrobial tolerance occur?

A
  • environmental adaptation e.g biofilm formation or change in growth rate
  • transient reduction in antimicrobial sensitivity (not directly through cells but traits can be passed on)
  • responsible for treatment failure
28
Q

Why are biofilm bacteria so tolerant to antimicrobials?

A
  • slow growing
  • presence of dormant ‘persister’ cells
  • sequestration from immune system (important for bacteriostatic antibiotics that work with host immunity)
  • elevated expression of efflux pumps
  • poor penetration of antibiotics
29
Q

Studies on synchronous populations of cells show that antibiotic sensitivity varies with …

A

stage of growth

30
Q

How does growth rate link to antibiotic resistance?

A
  • growth as in cell wall synthesis may play a role but not just growth rate
  • slow growing cells in biofilms should be more resistant to RNA synthesis inhibitors
31
Q

Antibiotics that target cell walls are less effective against biofilms than?

A

planktonic cells

32
Q

Explain persister cells

A
  • all populations of bacteria (planktonic or biofilm) have a small proportion of inactive/dormant cells
  • antibiotics are ineffective against them because they’re asleep
  • very difficult to kill and therefore they become a significant proportion of biofilm bacteria
  • form small colonies on agar and may be responsible for infections on replacement hips 15-20 yrs after operation
33
Q

Antibiotics targeting protein or RNA synthesis were … effective against planktonic and biofilm cells

A

equally

34
Q

Biofilms are highly resistant to …

A

phagocytosis

35
Q

Why are biofilms resistant to phagocytosis?

A
  • inflammatory cells can’t penetrate the matrix which encapsulates bacteria
  • even if they can penetrate channels, they don’t digest bacteria effectively
36
Q

Antibodies penetrate biofilms well/poorly

A

poorly

37
Q

Adaptive responses in biofilms can … bacteria e.g?

A
  • protect
  • pseudomonas spp. produce rhamnolipids in biofilms which can kill neutrophils
  • interactions with oral strep induce production of a complement evading protein
  • up regulation of efflux pumps
38
Q

Role of efflux pumps

A
  • pumps things out of cells
  • important in chemo as cancer cells become more tolerant as up regulate the pumps
  • pumps drugs out
39
Q

Antibiotic efflux pumps are up-regulated in biofilms formed by …

A
  • E.Coli
  • P.aeruginosa
  • Candida albicans
40
Q

Efflux pumps are effective against all antibiotics?

A

no
- upregulation of them is not universal

41
Q

How can you measure mass transfer in biofilms?

A
  • using fluorescently labelled latex beads, dyes or labelled proteins
42
Q

Diffusion may be impeded by the biofilm matrix but …

A
  • not significant for small molecules
  • even large molecules like IgG are weakly limited
  • molecules are carried through water channels
43
Q

For mass transfer in biofilms, what’s more important than diffusion being impeded?

A
  • electrostatic or van der Waal’s interactions
  • matrix acts as an ion exchange resin e.g metal cations are trapped in an ionic matrix
  • reaction also matters as reactive molecules like peroxide are inactivated by the matrix
44
Q

Positively charged tobramycin is impeded whereas … is not

A

ciprofloxacin (neutral)

45
Q

Reduced penetration occurs in non-mucoid stains. Why?

A

do not produce the carb alginate

46
Q

Adding extracellular DNA to biofilms enhances …

A

protection vs tobramycin

47
Q

What hypothesis is created with tobramycin and negatively charged DNA?

A

negatively charged DNA in the biofilm matrix retards tobramycin

48
Q

A biofilm is not just a trap but a …

A

3D sticky web

49
Q

3 stages of bacterial cell cell interactions in oral biofilms

A
  • signalling
  • synergism
  • antagonism
50
Q

2 relations of biofilms to dentistry

A
  • cross-contamination (surfaces in clinic, dental unit waterlines, can harvest respiratory viruses)
  • dental plaque
51
Q

What is the predominant mode of bacterial growth?

A

biofilms

Microbiology for Dentists (37 decks)

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