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Biology🧬 > Microbiology🔬 > Flashcards

Microbiology🔬 Flashcards

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1
Q

What are the different bacteria shapes?

A
  • Cocci - spherical
  • Bacilli - rod
  • Spirilla - spiral
  • Vibrios - comma
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2
Q

What are archaebacteria?

A

Bacteria which thrive in extreme environments

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3
Q

What are eubacteria?

A

Found in all BUT extreme environments

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4
Q

What is gram staining?

LOOK AT DIAGRAMS

A
  • Heat fixed smears of bacteria are stained with crystal violet solution and then washed in ethanol
  • Decolourises gram-negative bacteria
  • Smears are stained with safranin (counterstain)
  • Stains gram-negative bacteria pink/red
  • Stains gram-positive purple (retains crystal violet)
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5
Q

How do bacteria multiply?

A

•Binary fission - asexual reproduction
•Keep doubling each generation
- exponential growth

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6
Q

What do bacteria need to have when grown?

A 
•Suitable physical conditions 
-temperature (usually >_ 25’C)
-suitable pH (usually 7.4)
•Water
•Nutrients
-carbon, glucose, nitrogen, amino acids, inorganic ions, vitamins
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7
Q

What are obligate aerobes?

A

Require oxygen for metabolism/growth

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8
Q

What are obligate anaerobes?

A

Can only survive in the absence of oxygen

-oxygen inhibits growth and metabolism

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9
Q

What are facultative anaerobes?

A
  • Grow better in presence of oxygen but can slowly grow without
  • Make ATP by anaerobic respiration of oxygen is present - but able to switch to fermentation or anaerobic respiration if oxygen is absent
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10
Q

What happens in the lag/latent phase?(1)(Population growth curve for bacteria grown in a culture)

A
  • Cells are active but bacteria are unable to divide
  • Cells take in water and synthesise ribosomes and enzymes
  • Length of phase depends on medium used and whether cells were growing in a similar medium before
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11
Q

What happens in the exponential/log phase?(2)(Population growth curve for bacteria grown in a culture)

A
  • Nutrients are plentiful
  • Cells are very active and reproduce at fastest rate
  • When cells are multiplying at max rate they are ‘in a state of balanced growth’
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12
Q

What happens in the stationary phase?(3)(Population growth curve for bacteria grown in a culture)

A
  • Cells alter the culture medium as they grow
  • Nutrients become depleted and there is a fall in pH - build up of CO2, acids and other metabolites
  • Reproductive rate falls and cells did in greater numbers
  • Limiting factor
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13
Q

What happens in death phase?(4)(Population growth curve for bacteria grown in a culture)

A 
•More cells die than are produced
•Number of living cells declines
-starvation
-shortage of oxygen 
-toxicity of waste products
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14
Q

What is a haemocytometer? (Total count)

A
  • Special slide developed for blood cell counts

* Able to count bacterial cells in known volume of liquid and therefore calculate concentration ->no. per cm3

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15
Q

What is turbidity? (Total count)

A
  • Cloudiness of culture

* Degree of cloudiness as measured with colorimeter proportional to concentration

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16
Q

What is the assumption of serial dilution? (Viable count)

A

•That one colony is produced from one bacteria
•This may underestimate the number of bacteria
-clumping if cells causes colonies to merge

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17
Q

How do you ensure that only the microorganism under investigation is cultured?

A

•Aseptic technique
-involves handling cultures in a way to prevent contamination by unwanted organisms
•Also prevents contamination of personnel and the immediate environment

18
Q

Key points - Aseptic technique

A
  • Hands and surface cleaned before and after
  • Sterile agar and Petri dish
  • Work by a bunsen burner to give updraft->helps prevent airborne particles landing on agar
  • Mouth of culture bottle is flamed to kill unwanted microbes
  • Lift petri dish lid at shallow angle to protect agar surface
  • Flame sterilise inoculating loop/use sterile equipment
  • Autoclave plates/equip to sterilise at end of work
19
Q

What is asepsis?

A

State of being free from disease-causing microorganisms

20
Q

What is sterilisation?

A

Removal or destruction of all living organisms, including spores

21
Q

How are bacteria grown?

A
  • Cultured in a liquid broth or on solid agar
  • Medium is sterilised and contains specific nutrients
  • Inoculation - sterile loop is dipped into bacteria source and then into culture medium
22
Q

What is total count?

A
  • Includes both living and dead cells
  • Can be measured by haemocytometry
  • Numbers can be overestimated in a population due to inclusion of dead cells
23
Q

What is viable count?

A
  • Includes only living cells
  • Involves growing bacteria to form distinct colonies that can be counted
  • Numbers can be underestimated because of clumping of cell’s when the plates are made - serval cell’s forming a single colony
24
Q

SEE DIAGRAMS FOR SERIAL DILUTION

A

SEE NOTES

25
Q

Both gram positive and gram negative bacteria stain purple. Why do gram negative bacteria not appear purple?

A

Their cell walls do not retain the crystal violet stain.

Instead, they are stained red by the counter-stain safranin

26
Q

Why is it important to not completely seal the inoculated plates with adhesive tape and to incubate the plates at a lower temperature, usually 25’C?

A

Human pathogenic bacteria grow best under anaerobic conditions at 37’C

27
Q

Factors affecting growth

A
  • Nutrients
  • Temperature
  • pH
  • Oxygen
28
Q

How do nutrients affect growth?

A

Microorganisms require:
•Source of carbon, nitrogen and phosphorus
•A respiratory substrate (glucose)
•Vitamins and minerals to act as coenzymes
•Water to carry out metabolic reactions

29
Q

How does temperature affect growth?

A
  • Growth is coordinates by enzymes
  • Enzymes work most efficiency over a narrow range of temperatures
  • Too low - rate of enzyme-catalysed reactions becomes to low to sustain life
  • Too high - denaturation of enzymes causes cell death
30
Q

Mesophiles optimum temperature

A

20-45’C

31
Q

Thermophiles optimum temperature

A

Above 45’C

32
Q

Psychrophiles optimum temperature

A

Below 20’C

33
Q

How does pH affect growth?

A
  • Enzymes only work efficiently within a narrow range of pH
  • For most - ph5-pH7.5
  • Microorganisms can tolerate a wider range of pH than plant and animal cells
34
Q

How does oxygen affect growth rate?

A
  • Obligate aerobes require oxygen for metabolism at all times
  • Obligate anaerobes find oxygen toxic and cannot grow in its presence
  • Facultative anaerobes can grow rapidly in presence of oxygen but can also survive without it (slower growth rate)
35
Q

What is serial dilution? (General)

A
  • Pure cultures of microorganisms contain too many cells to allow an accurate count to be made
  • Original culture is diluted down, usually in ten-fold steps
  • Provides a final number within a countable range
36
Q

What is serial dilution (process)

A
  • 1cm3 of original culture is transferred to 9cm3 of sterile nutrient medium/sterile water
  • Mixed to ensure an even distribution (10^-1 dilution)
  • 1cm3 of mixture is transferred into 9cm3 of sterile nutrient medium and mixed (10^-2 dilution)
  • Repeated a number of times to produce further 10-fold dilutions
  • In order to carry out a viable count, a known volume of each bacterial culture, usually 1cm3 or 0.1cm3 is added to agar plates and incubated
37
Q

What are gram-positive bacteria?

A

Have a thick cell wall consisting of peptidoglycan

38
Q

What are gram-negative bacteria?

A

Have a thin layer consisting of peptidoglycan covered by a layer containing lipopolysaccharides

39
Q

What do lipopolysaccharides do?

A

Provide some protection against antibiotics and lysozyme, making gram-negative bacteria more difficult to kill

40
Q

Why do gram-negative not retain crystal violet?

A
  • Acetone removes lipopolysaccharide membrane
  • This washes crystal violet stain from the cell
  • This exposes the inner peptidoglycan layer which statins fed with safranin
41
Q

Why might numbers of colonies be converted to logarithms before being plotted on a graoh?

A
  • Large numbers/large range of numbers
  • Would be difficult to plot
  • Log scale increases by a factor of 10 for each number

Biology🧬 (24 decks)

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