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EOS Principles of diseases > growth & nutrition of bacteria > Flashcards

growth & nutrition of bacteria Flashcards

1
Q

define bacterial growth

A
  • growth is an increase in the number of cells (not an increase in size)
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2
Q

define generation time?

A
  • is the time it takes for a cell to divide & the bacteria population to double
  • bacteria divide by binary fission
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3
Q

list the 4 phases of the bacterial growth curve?

A
  1. lag phase
  2. logarithmic phase
  3. stationary phase
  4. death or decline phase
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4
Q

describe the lag phase of the bacterial growth curve

A
  • lag phase occurs immediately after inoculation into fresh medium
  • bacteria increase in size not number as they are increasing their metabolic activity
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5
Q

what does the length of the lag phase depend on?

A
  • size of inoculum
  • time to recover from transfer into medium
  • time for synthesis of coenzymes or division factors
  • time for new enzyme synthesis needed for metabolising substrates is media
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6
Q

describe the log phase of the bacterial growth curve?

A
  • in log phase, cells divide at a constant rate by binary fission
  • rate is dependent on: composition of growth medium & conditions of generation time
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7
Q

describe the stationary phase of the bacterial growth curve

A

bacterial growth plateaus due to:

  • exhaustion of essential nutrients
  • increase in toxic metabolites
  • exhaustion of space
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8
Q

describe the death or decline phase in the bacterial growth curve

A
  • during decline phase viable cell count population declines

viable count = just alive cells, total count = alive & dead cells

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9
Q

what is the use of a continuous culture?

A
  • prevents death & decline phase
  • bacterial cultures are maintained in a state of exponential growth over a long period of time
  • uses a chemostat
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10
Q

causes of variations in generation time for different pathogens (2)

A
  1. serum resistance - allows some pathogens to have higher doubling times in host tissue
  2. virulence factors - allows some pathogens to have a long generation time (host immune system not triggered quickly by these bacteria)
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11
Q

what does measuring bacterial growth involve? what are the 3 methods for measuring bacterial growth?

A
  • involves estimating the number of cells that arose from binary fission during growth phase
  • methods:
    1. viable count
    2. total cell count (direct microscopic count & turbidity)
    3. real-time PCR
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12
Q

what does a viable count involve for measuring bacterial growth?

A
  • involves serial dilutions plated onto solid media

- only living bacteria will divide & form a visible colony on agar plate that can be counted to estimate bacteria growth

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13
Q

what are the advantages & disadvantages of using a viable count to measure bacterial growth?

A

advantages

  • quantitative
  • can identify the bacteria

disadvantages

  • only living cells develop colonies that are counted
  • clumps of cells can develop into a single colony - reduces accuracy
  • need correct culture conditions
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14
Q

when measuring bacterial growth, what does a direct microscopic count involve?

A
  • estimating the concentration of bacteria in media
  • counts all cells both living & dead (total count)
  • uses a cell counting chamber
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15
Q

when measuring bacterial growth, what does the turbidity method involve?

A
  • turbidity method estimates large numbers of bacteria in a clear liquid media & broth
  • optical density of suspension is directly related to cell number
  • spectrophotometer can be used to count cells
  • McFarland turbidity standard can be used to estimate number of cells in suspension
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16
Q

what are the requirements for bacterial growth

A
  • physical requirements - temp, pH, osmotic pressure, oxygen
  • chemical requirements - carbon, nitrogen, sulphur & phosphorous, trace elements & growth factors
17
Q

what are the requirements for different anaerobes? (obligate anaerobes, facultative anaerobes, aerotolerant anaerobes)

A
  • obligate anaerobes = die in presence of O2
  • facultative anaerobes = can grow with or without oxygen
  • aerotolerant anaerobes = can survive in presence of O2 but do not use it for metabolism
18
Q

what is the optimum growth temperature, pH & osmotic pressure for MOST pathogenic bacteria?

A
  • most pathogens are mesophiles: grow at 15-45C with optimum around 37C
  • most bacteria prefer a neutral pH
  • require isotonic osmotic pressure -> hypertonic environment cause plasmolysis of bacteria (increased salt or sugar)
19
Q

what are growth factors?

A
  • organic compounds obtained from the environment (vitamins, amino acids, purines & pyrimidines)
  • must be supplied by environment for cell to survive & reproduce as cell cannot synthesise them
20
Q

what are fastidious organisms?

A
  • bacteria that require a medium with various growth factors or other components & are hard to grow
21
Q

what does the aseptic technique involve for growing bacteria in the laboratory?

A
  • sterile media

- sterilisation & disinfection to prevent contamination

22
Q

what are the 6 different type of growth media for growing bacteria?

A
  1. solid media - for isolation of single colonies
  2. liquid media - for growing large numbers of bacteria
  3. semisolid media - for
    demonstration of motility
  4. routine media - basic nutritive media capable of growing less fastidious bacteria
  5. enrichment media - permits growth of a specific bacteria
  6. enrichment broth - used for organisms in low numbers or swapped by other bacteria
23
Q

what is selective media?

A
  • media that select for particular groups of bacterial pathogens
  • contains inhibitors which suppress the growth of unwanted bacteria
24
Q

what is differential media used for?

A
  • for differentiation of 2 species or groups

- makes it easy to distinguish colonies of different microbes

25
Q

what is MacConkey Agar used for?

A

it it selective

  • contains components that inhibit growth of some bacteria & promotes growth of other
  • most gram +ve will not grow
  • enterobacteria will grown

it is differential

  • bacteria that ferment lactose will be pink
  • backer that cannot ferment lactose will be yellow
26
Q

what is blood agar used for?

A

is an enrichment media (blood for fastidious organism)
it is differential
- certain bacteria produce enzymes that lyse red blood cells
& produce a colour change

not selective
- supports growth of a wide range or organisms

27
Q

define a strict bacterial parasite

A
  • bacteria that can only use a small number of substrates
28
Q

define an opportunist bacterial organism

A
  • bacteria that can utilise many substrates

EOS Principles of diseases (12 decks)

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