Microbiology 3 - Biofilms

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  1. What is a biofilm?
    Microbial community forming at a phase boundary (generally, but not always, at a liquid:solid interface)

    • Environmental
    • -Drain surfaces
    • -River beds
    • -Water storage (cooling, heating)
    • -Ship hulls

    • Medical
    • -Catheters, implants
    • -Dental plaque
  2. What kind of microbial diversity is there in the mouth?
    Oral cavity contains >750 species of bacteria.An individual has about 100 species in their oral cavity.

    50% cannot be cultured.

    Streptococcus, Actinomyces, Veillonella, Fusobacterium, Porphromonas, Prevotella, Treponema, Neisseria, Haemophilis, Eubacteria, Lactobacterium, Capnocytophaga, Eikenella, Leptotrichia, Peptostreptococcus, Staphylococcus, and Propionibacterium
  3. What diseases can oral biofilms lead to?
    Plaque can lead to gingivitus, periodontitis and caries.
  4. What are some common constituents of a biofilm?
    • Bacteria
    • Fungi
    • Algae
    • Protozoa
    • Bacteriophages
    • Environmental debris
    • (Host components)
  5. In which layers might a biofilm accumulate on a ship's hull?
    Molecular fouling - conditioning film

    Microfouling - bacteria, microalgae, fungi

    Macrofouling - Macroalgae, invertebrates
  6. What are common features of biofilms?
    May be spatially and temporally heterogeneous

    May have specific mechanisms for attachment to a surface

    • Generate extracellular polysaccharide (EPS)
    • - adhesion
    • - protection
    • - facilitates community interactions

    Resistance to antimicrobials

    Altered metabolic requirements
  7. Are biofilms smooth and of an equal depth?
    No, more like a city, peaks and troughs
  8. What are the two different terms for cells growing in a liquid suspension and for cells attached to a surface or to a preformed biofilm?
    Planktonic and Sessile
  9. What changes in gene expressions can occur from a change from planktonic to sessile lifestyle?
    Morphology may change - lengthen, shorten

    Motility - may lose flagella - less need to move

    Growth rate (metabolism) - may have access to different nutrients because of the biofilm ecosystem

    Signalling - may begin to communicate with other bacteria

    Antibiotic and disinfectant tolerance - may be gained from other bacteria etc
  10. What are some of the advantages of a biofilm lifestyle?
    Stability – adhesion

    Utilise available nutrients in liquid phase or from surface

    Proximity of diverse range of other bacteria providing metabolic interactions and protection

    Habitat diversity – gradients, surface type

    Evasion of host responses

    Antimicrobial resistance
  11. Describe an example of a model for dental plaque formation.
    Nutrients on the surface of the tooth, to which some bacteria attach

    Other bacteria can then attach to these bacteria using adhesin to receptors on other bacteria
  12. How does activity and environment vary at diffferent gradients of the biofilm?
    Image Upload 1
  13. What is Marsh's Ecological plaque hypothesis?
    Potential pathogens may be present in low numbers in plaque, or transmitted in low numbers to plaque; both situations may be compatible with health.

    A major ecological pressure will be necessary for such pathogens to outcompete other members of the resident microbiota and achieve the levels needed for disease to occur.

    Image Upload 2
  14. What are two fermenter systems for studying biofilms?
    Chemostat for studying planktonic bacteria

    • Constant Depth film fermenter (CDFF)
    • (Biofilm disks with indents containing bacteria which is scraped to a constant level)
  15. What are the relative locations of live and dead bacterial cells
    There are more dead bacterial cells deeper in the biofilm
  16. What are some biofilm community interactions?
    Foodwebs and concerted (coordinated) actions - Some bacteria feeding of the products released by others

    Cells density dependent signalling - Certain genes and signals turned on at specific densities

    Group protection - One bacteria type may make an enzyme (like beta-lactamases) which diffuses to produce a zone of protection

    Gene Transfer - genes can be shared between bacteria in the biofilm.
  17. What evidence is there of gene transfer in plaque biofilm?
    Grow plaque biofilm in CDFF

    Introduce Bacillus subtilis carrying the transposon Tn5397 (Tetracycline resistance)

    Select with Tetracycline

    Found some oral streptococci became TcR and carried Tn5397

    Indicated transfer of Tn5397 from B. subtilis to oral streptococci
  18. Why do biofilms need to be controlled?
    • Biofilms cause:
    • -Equipment damage
    • -Product contamination
    • -Energy losses
    • -Medical infections

  19. Why are antibiotics and disinfectants often ineffective against Biofilm control?
    Huge doses required

    Undesirable environmentally

    Undesirable ecologically

    Impractical medically (may kill patient!)
  20. Why are biofilms resistant to antimicrobials?
    • Transport Limitations
    • -antimicrobial agent is reactively neutralized in the surface layers of the biofilm faster than it diffuses into the biofilm

    • Physiological Limitations
    • -nutrient-deprived cells are forced into a slow-growing or non-growing state that are much less susceptible to a variety of antimicrobial challenges

    • Spread of Resistance Phenotype
    • -antimicrobial resistance genes may be upregulated or spread from resistant to previously susceptible cells through a variety of mechanisms
Card Set
Microbiology 3 - Biofilms
Microbiology 3 - Biofilms
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