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243: Medical Microbiology > 5. Biofilms > Flashcards

5. Biofilms Flashcards

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USMLE® Step 1 flashcards Biology 101 flashcards
1
Q

what is a biofilm

A

a highly concentrated conditioning film of nutrients which draws bacteria to them

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2
Q

when bacteria arrive at a biofilm and attach what do they adapt?

A

a sessile phenotype

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3
Q

what are the three methods that bacteria arrive at a biofilm through

A
  1. diffusion
  2. chemotaxis
  3. turbulence impaction
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4
Q

explain how bacteria arrive at a biofilm through chemotaxis

A

bacteria are drawn towards a surface, they use their flagella to propel them towards the surface

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5
Q

explain how bacteria arrive at a biofilm through turbulence impaction

A

turbulence brings the bacteria right to the surface

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6
Q

bacteria exist in laminar flow,, what is this?

A

particles flow in smooth, distinct layers where there is no mixing

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7
Q

what does the boundary layer do

A

here there is no flow, it facilitates diffusion of bacteria that drop out of laminar flow

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8
Q

what occurs during turbulent flow

A

there is lots of mixing, the boundary layer is disturbed bringing the liquid right to the surface = binding

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9
Q

what type of surface does turbulent flow work better with, why?

A

rough surfaces over smooth surfaces

  • there is more surface area = more binding opportunities
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10
Q

describe the mechanism of bacterial attachment to a surface

A

both molecules are negatively charged and so bacterial cell gets repelled

bacterial cell then hovers over the surface

bridging structures called adhesins then connect the bacterium to the surface

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11
Q

name 4 adhesins

A

flagella, pili, fimbriae, stalks, adherence proteins

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12
Q

what do bacteria produce that prevents them from being flushed following attachment

A

their own glue rich in sugars

  • this is termed the matrix
  • and is the beginning of the biofilm
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13
Q

what happens following attachment

A

adoption of a sessile phenotype

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14
Q

what does adoption of a sessile phenotype mean

A

50-60 changes in genes:

  • down regulation of planktonic genes
  • up-regulation of sessile genes
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15
Q

what are planktonic genes

A

swimming genes (e.g. flagella)

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16
Q

what are sessile genes

A

genes that help you live in a biofilm, e.g. stress proteins, capsule

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17
Q

what genes are involved in producing this glue

A

Alg genes

18
Q

what % of the biofilm matrix is water

A

98%

19
Q

what provides structure and integrity to the matrix

A

exopolymeric substances (EPS)

20
Q

what do channels in the biofilm allow

A

allow fresh liquid into the biofilm (nutrients/ oxygen)

removes waste products

21
Q

how do top-heavy biofilm stacks form

A

disproportionate levels of oxygen and nutrients reach the top layer = higher bacterial growth + EPS production

22
Q

what happens to a biofilm with low flow & low nutrients

A

slow compact growth

23
Q

what happens to a biofilm with high flow & high nutrients

A

rapid growth, prone to sloughing. (unstable)

24
Q

what are cells embedded in the matrix protected from

A

predation (macrophages)
antimicrobial compounds
increased flow rates

25
Q

what messaging molecules do cells in a matrix use

A

N-acyl-homoserine lactones (AHLs)

26
Q

describe AHLs: N-acyl-homoserine lactones

A

lipid, long chain molecules = easy to get through biological membranes

27
Q

when do AHLs work

A

when there is sufficient number of cells and the threshold is reached, they can coordinate a response

28
Q

what happens when there are sufficient AHLs

A

genes that code for virulence factors are expressed, making the pathogen dangerous

29
Q

how are cells lost from biofilms

A

via programmed detachment or sloughing

30
Q

what type of bacteria use AHLs

A

gram negative

31
Q

what do gram positive cells use to communicate

A

signalling peptides

32
Q

what is the max height of bacterial biofilms

A

200 um

33
Q

why do cells detach

A

insufficient nutrients = cell death

34
Q

what slough’s cells from a biofilm

A

phagocytes (grazing on the biofilm)

35
Q

bacteria regenerate can regenerate their flagella, what does this mean

A

they can signal to lysogenic bacteria blocking them in the matrix to open - allowing them to leave

36
Q

how many genes does P. aerugniosa have that are sensitive to autoinducers

A

616

37
Q

what is an autoinducer

A

signalling molecules that communicate with other bacteria

38
Q

what two proteins control the amount of autoinducer and the transcription of the operon

A

lux I and lux R

39
Q

what does Lux R do

A

recruits RNA polymerase to transcribe the operon when bacteria and autoinducer conc is high

40
Q

what does Lux I do

A

produces the autoinducer

243: Medical Microbiology (27 decks)

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