Microbiology 3 - Biofilms
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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
- -Catheters, implants
- -Dental plaque
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
What diseases can oral biofilms lead to?
Plaque can lead to gingivitus, periodontitis and caries.
What are some common constituents of a biofilm?
- Environmental debris
- (Host components)
In which layers might a biofilm accumulate on a ship's hull?
Molecular fouling - conditioning film
Microfouling - bacteria, microalgae, fungi
Macrofouling - Macroalgae, invertebrates
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
Are biofilms smooth and of an equal depth?
No, more like a city, peaks and troughs
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
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
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
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
How does activity and environment vary at diffferent gradients of the biofilm?
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.
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)
What are the relative locations of live and dead bacterial cells
There are more dead bacterial cells deeper in the biofilm
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.
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
Why do biofilms need to be controlled?
- Biofilms cause:
- -Equipment damage
- -Product contamination
- -Energy losses
- -Medical infections
Why are antibiotics and disinfectants often ineffective against Biofilm control?
Huge doses required
Impractical medically (may kill patient!)
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
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