Question

Medical Microbiology Tutorial: Biofilms

Answer 1

\({\bf{Definition:}}\)
biofilm: a thin, slimy structure composed of a community of bacteria; adheres to a surface and is surrounded by an extracellular polymeric substance matrix (hereafter EPS)



\({\bf{Stages~of~Biofilm~Formation:}}\)
1. attachment/adherence to the surface
2. EPS synthesis/colony formation
3. Maturation
4. Dispersal

\({\bf{Examples~of~Biofilms:}}\) two broad categories: biofilms on medical devices, and biofilms on natural tissue. know a few examples of each.

devices: catheters, grafts, fillers, prosthetics
tissue: cystic fibrosis, dental plaque, some tract infections

Answer 2

Why study biofilms in the context of medicine? Biofilms can greatly enhance the ability of bacteria to survive antibiotics. The biofilm can persist even after symptoms stop, so patients will take antibiotics, stop when symptoms stop. The biofilm allows the population to rebuild.

\({\bf{Antibiotics~vs.~Biofilms:}}\)
Biofilms increase tolerance, or a phenotypic quality that increases the time that a bacterial population can survive antibiotic treatment. This is not the same as resistance, which is an inherited characteristic such as increased efflux or target modification, that allows survival regardless of treatment length.

Mechanisms:
1. the EPS matrix is a physical barrier that stops antibiotics from reaching their targets
2. dormancy. biofilms maintain a population of dormant cells that are not metabolically active. therefore, antibiotics that target metabolically active cells are not effective.
3. persistors cells with a tolerant phenotype maintain the biofilm
4. cells that antagonize antibiotics (efflux, degradation, etc.)

Answer 3

\({\bf{Antibiotic~Strategies:}}\) can be categorized by what part of the biofilm synthesis stage they target
- attachment: can synthesize surface coatings that are inhospitable to biofilm attachment/growth
- colony formation: traditional antibiotic methods (target cellular structures or syntheses)
- maturation/dispersal: QS inhibitors

alternatively:
physical methods: physically breaking the biofilm through debridement/sonication or through enzymes

Answer 4

\({\bf{Studying~Biofilms:}}\)


- Crystal Violet staining: Culture cells, isolate the biofim, stain the biofilm with crystal violet dye, measure intensity w/ spectroscopy. Higher absorbance is proportional to higher biofilm density



- Flow cytometry: Culture cells, dissolve in solution, pass individual cells through the flow cell, expose each cell to a laser, detect the change in absorbance and scattering. Measures general physical properties of biofilms

- Cell microscopy. There are a lot of microscopic techniques but the general mechanism is that some kind of beam passes through the sample and the change in the beam's properties is detected. Gives information about physical properties of biofilms.

Answer 5

\({\bf{Sources:}}\)
- lecture notes
- https://www.pnas.org/content/116/29/14734
- https://www.livescience.com/57295-biofilms.html
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2732559/
- https://www.ncbi.nlm.nih.gov/pubmed/28362216