8. Microbial biofilms Flashcards
1
Q
Define ‘biofilm’
A
- community of microbial cells
- encased within a matrix of polymers
- associated with an interface
2
Q
What kind of interface are biofilms found at?
A
- can be air-liquid
- or liquid-solid
3
Q
Biofilms have emergent properties. What does this mean?
A
- not simply a sum of microbes within them
4
Q
Explain planktonic biofilms
A
- in liquid
- homogenous
- single species
- nutrient rich
5
Q
Explain surface-associated biofilms
A
- cultures on agar plate
- limited heterogeneity
- single species
- nutrient rich
6
Q
Explain natural biofilm
A
- in wildlife
- heterogenous
- mixed species
- limited nutrients
7
Q
4 stages of biofilm growth
A
- attachment
- colonisation
- development
- dispersal
8
Q
In the mouth, how are most cells transported?
A
- saliva
- sloughing of epithelial cells
9
Q
What happens in attachment of a biofilm?
A
- cells swim or passively reach surface
- non-specific and specific attachment forces
10
Q
What happens in colonisation of biolfilm?
A
- adherent cells start to grow
- cell-cell communication
11
Q
What happens in development of a biofilm?
A
starts to form 3D structure
12
Q
What happens in dispersal?
A
active or passive sloughing
13
Q
Pseudomonas aeruginosa is a … pathogen
A
opportunistic
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
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
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
17
Q
Macromolecules such as … form the basic structure of a biofilm
A
- polysaccharides
- proteins
- nucleic acids
18
Q
Small molecules can be trapped in the … of biofilms e.g …
A
- matrix
- nutrients
- metals
- signalling molecules
19
Q
How to prepare a biofilm for EM scanning?
A
- have to dehydrate and remove water
20
Q
What percentage of human infections can be attributed to biofilms?
A
65-80%
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
What did Bill Costerton do?
- 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
How does 'antimicrobial resistance occur?
- genetic changes
- transmitted to progeny during cell division (vertical transmission)
- transmitted between resistant and sensitive strains of species or between species (horizontal transmission)
27
How does antimicrobial tolerance occur?
- 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
Why are biofilm bacteria so tolerant to antimicrobials?
- 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
Studies on synchronous populations of cells show that antibiotic sensitivity varies with ...
stage of growth
30
How does growth rate link to antibiotic resistance?
- 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
Antibiotics that target cell walls are less effective against biofilms than?
planktonic cells
32
Explain persister cells
- 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
Antibiotics targeting protein or RNA synthesis were ... effective against planktonic and biofilm cells
equally
34
Biofilms are highly resistant to ...
phagocytosis
35
Why are biofilms resistant to phagocytosis?
- inflammatory cells can't penetrate the matrix which encapsulates bacteria
- even if they can penetrate channels, they don't digest bacteria effectively
36
Antibodies penetrate biofilms well/poorly
poorly
37
Adaptive responses in biofilms can ... bacteria e.g?
- 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
Role of efflux pumps
- pumps things out of cells
- important in chemo as cancer cells become more tolerant as up regulate the pumps
- pumps drugs out
39
Antibiotic efflux pumps are up-regulated in biofilms formed by ...
- E.Coli
- P.aeruginosa
- Candida albicans
40
Efflux pumps are effective against all antibiotics?
no
- upregulation of them is not universal
41
How can you measure mass transfer in biofilms?
- using fluorescently labelled latex beads, dyes or labelled proteins
42
Diffusion may be impeded by the biofilm matrix but ...
- not significant for small molecules
- even large molecules like IgG are weakly limited
- molecules are carried through water channels
43
For mass transfer in biofilms, what's more important than diffusion being impeded?
- 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
Positively charged tobramycin is impeded whereas ... is not
ciprofloxacin (neutral)
45
Reduced penetration occurs in non-mucoid stains. Why?
do not produce the carb alginate
46
Adding extracellular DNA to biofilms enhances ...
protection vs tobramycin
47
What hypothesis is created with tobramycin and negatively charged DNA?
negatively charged DNA in the biofilm matrix retards tobramycin
48
A biofilm is not just a trap but a ...
3D sticky web
49
3 stages of bacterial cell cell interactions in oral biofilms
- signalling
- synergism
- antagonism
50
2 relations of biofilms to dentistry
- cross-contamination (surfaces in clinic, dental unit waterlines, can harvest respiratory viruses)
- dental plaque
51
What is the predominant mode of bacterial growth?
biofilms
