biofilms Flashcards
define biofilm; 2 marks
state why the 3 describing words are used; 3 marks
a coordinated and organised heterogeneous community of bacterial cells surrounded by a self produced polysaccaride martrix
- the biofilm is coordinated because the cells communicate
- organised because different regions of the biofilm perform different tasks
- heterogeneous in that different regions exist
how is culturing microbes in the lab different to how microbes exist in real life; 2
- cells in real life are stuck to surfaces where as cells in the lab are suspended in liquid (planktonic)
- in a lab a single species in usually grown where as in real a multi species situation often exists
what 3 things are needed for a biofilm to grow
- a surface to stick on; skin, teeth, pipes, rocks
- a source of nutrients; they can survive on very few nutrients
- moisture
discuss the 4 stages of biofilm formation
1)attachment; a free living cell attaches reversibly to a surface using flagella and performs twitching motility with pili before attaching more firmly. growth and division into a mass occurs
2) exopolysacarride production; cells sense that a quorom has been reached (minimum number of individuals needed) via acyl homoserine lactone and then bind firmly to eachother and the surface and begin producing extracellular polysaccaride substances which contain polysaccarides, proteins and nucleic acids.
- the biofilm is now firmly cemented irriversibly
3) maturation; further cell grwoth occurs leading to a complex structure which nutrition sticks to.
- tunnels through the biofilm exist so gas exchange can occur
- those in the middle of the biofilm but those on the outside have best access to nutrients
- growth rate oscillates between fast and slow; if the cells on the inside have poor nutrients that decrease production of ammonium so that the outer growth is slowed so that nutrients can diffuse to the centre
- two biofilms in close proximity coordinate their oscillation so that while one is growing quickly the other is going slowly; the nutrients are fully utilised
- expression of flagellin is decreased
4) dispersal involves part of a biofilm moving to a new envirnment;
- may be passive such as fluid in a pipe, abrasion on a rock etc
- may be active;starvation activates enzymes to break down the biofilm from within so that a better environment can be found.
which enzymes are used for biofilm active dispersal
Dispersin B, Alginate lyase, NucB, DNase
why are biofilms hard to remove
because often only the outside is removed which leaves the inner microbes which are most resistant and can grow the quickest
state 4 examples of heterogeneity in biofilms
- pH difference of as much as 1
- different nutrient availability
- substrate/product concentration
- different gene expression
discuss 6 reason biofilms being hard to remove
discuss one way of successfully eliminating biofilms
- biofilms are 500 times less susceptible to antibiotics, physical forces and disinfectants than planktonic cells
- often antibiotics stimualte the biofilm to lay down more matrix making them harder to remove
- heterogeneity in pH means when an antibiotic travels through the biofilm it is antagonised chemically so that it has reduced function.
- the matrix means antibiotics diffuse slowly so have the gradients have time to degrade the antibiotics
- antibiotics normally target growing cells, but many cells in a biofioms arent growing so cell cell growth cant be disrupted
- the cells at the bottom of the biofilm are already in a stressful environment so have a resistance phenotype
-quorum sensing is thought to be key to this resistance because inhibiting quorum sensing leads to higher sensitivity to antibiotics
define persister
a cell with a very resistant phenotype despite having the same genotype as a less resistant phenotype
discuss medical impacts associated with biofilms; 3 marks
discuss biofilms in the mouth; 6 marks
- 80% of bacterial infections are biofiom associated
- infections involve seeding; cells disperse from primary area
- formation on medical devices like contact lensesm pacemakers, cathaters
- dental plaque is a biofilm; can cause gum disease
- 500 oral bacteria have been identified (mostly unique to the mouth)
- its not the amound of plaque but the composition; which bacteria are present
- the mouth is a unique environment due to fluctuating temperature, nutrient availability and presence of different surfaces (gums, teeth, saliva)
- highlights flaws in Koch’s postulates; multiple species cause caries (tooth decay)
- mouth cuts can cause microbes to enter bloodstream and cause heart problems
discuss industry associated cases of biofilms causing problems; 4
- pipeline growth reduces diameter and causes corrosion because bacteria convert sulphates into sulphides which corrodes steel parts in pipes
- growth on ship hulls causes drag
- growth in malfunctioning air conditioning units causes respiritory disease
- food poisoning strain of E.colu can form biofilms 400 times larger than it normally would when grown with A. calcoaticus (a commensal organism which forms biofilms in meat factories which are non harmful)
discuss strategies against biofilms
1) removal;
- toxic nanoparticles
- surfactin antibiotic
2) prevention; makes sense to do this because biofilms are so hard to remove
- block signals leading to matrix formation
- interfere with qurom sensing
- create surfaces that bio films cant stick to; very smooth surfaces such as SLIPS or sharklet complex pattern inspired by shark skin (no microbes live here)
discuss benefits biofilms can have to human life; 3
gut biofilms produce vitamin B and K12 and stop bad microbes colonising
rumen biofilms digest cellulose
sewege treatment
discuss the differences between flagella and pilli
- function; flegaella used for initial attachment wheres as pili are used for twitching motility
- size;flagella are much longer than pili
- location; flagella are usuall found in one part of the cell; polar/peritichous. pili are found all over the cell
- assembly; new subunits added to the end of flagella, to the base of pili
- movement mechanism; flagella bunch together counter clockwise before rotating clockwise (running and tumbling. pili movement involves extension then retration via quick deconstruction
