Biofilm Formation Flashcards
What is biofilm
Microbial communities that form a slime layer (ECM) via quorom sensing
Define quorom sensing
cell-cell communication that allows bacteria to share info on cell density –> and adjust gene expression accordingly
How does quorom sensing work
- Bacteria produces autoinducers AI (extracellular < intracellular)
- Different bacteria can interpret different types of autoinducers
- AI signals attract other bacteria cells –> produce more AI
- Once extracellular conc of AI > intracellular –> bacteria self-downregulates to stop making AI
What are 3 strategies to overcome biofilm
- Prevent adhesion of biofilm
- Destroy the biofilm matrix
- Action on dormant bacteria
- dormant bacteria will stop quorum sensing during antibacterial treatment
(most vulnerable)
Explain Direct ELISA (antigen detecting, enzyme linked immunosorbent assay)
Antigen binds to primary antibody conjugate –> binds directly to detection molecule
- Good for looking for PURE ANTIGEN
Explain Indirect ELISA
Antigen binds to primary antibody conjugate –> binds to secondary antibody conjugate –> binds to detection molecule
- DOES NOT RELY ON ANTIGEN BINDING, only presence of primary antibody conjugate
Explain Sandwich ELISA
like indirect ELISA, but capture antibody is needed to secure antigen to secondary antibody conjugate
What are the steps for Latex agglutination? (5)
- One drop of positive control is added to circle #1
- One drop of negative control is added to circle #2
- One drop of latex reagent is added to 3 circles
- 2 complete colonies are quickly emulsified into reagent circle #3
- The slide is rocked by hand for 45 secs and placed on a slide rotator for another 45 secs
Explain polymerase chain reaction PCR test
Small amount of DNA needed
- DNA is detected + amplified, analyzed
- selective amplification of bacterial genes to minimize false positive
What is the most important aspect of specimen collection
Selection + collection
What are the 5 rules of specimen collection?
- Enough quantity of material used
- Sample should be drawn from site of infection
- Use sterile equipment
- Examination must occur PROMPTLY afer collection
- Specimens needed to diagnose bacterial infections should be secured before antimicrobial drugs are given
Explain direct specimens
Sample collected from sterile body fluids
eg. (CSF, blood)
Explain indirect specimens
Sample that has passed through body parts that contain bacteria
- need to differentiate between the good and bad
eg. coughed sputum, stool sample, voided urine
What happens if the gram-pos bacteria contains endospores in gram-staining?
Will stain clear
What is the most sensitive and specific method for diagnosing biofilm?
Bacterial cultures
Why are bacterial cultures used?
Most bacteria can be grown in artificial media
- HOWEVER strict intracellular microorganisms (chlamydia, rickettsia) can only be isolated in living eukaryotic cells
In Disk diffusion antibiotic suceptibility test, explain the following areas
Cloudy
Clear
No zone of inhibition
Cloudy = bacterial growth
Clear = bacterial death (due to release of antibiotics)
No zone of inhibition: too low dose, resistance, not effective antibiotic
Define colony-forming unit CFU
The origin of a colony in a pure culture (single or multiple cells)
Explain the streak plate technique
Sterile inoculating loop is used to apply CFUs to culture plate
- observe streaks after some time –> see where bacteria grew
Explain Defined media
You know the exact chemical composition of the media
Explain complex media. give example
You don’t know exact composition.
- Contains more nutrients and growth
eg. yeast, trypticase soy agar, macconkey agar
Yeast breaks things down into smaller components, therefore the final components of the media are not exactly known
When is blood added in a complex media
To provide additional growth factors for fastidious microorganisms
Explain selective media. Provide an example
Contains substances that favour the growth of particular microorganisms OR inhibit the growth of unwanted ones
Eg. Inhibit gram-pos, grow gram negative: Eosin, methylene blue, crystal violet dies, bile salts
Explain differential media. Give an example
Allow growth of multiple bacteria types –> cause visible changes to help differentiate between various bacteria
Blood agar
- used to differentiate bacteria based on their hemolytic properties
- can also be considered an enriched medium for fastidious organisms
