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A2 BIO UNIT3 > 3.4 Microbiology > Flashcards

3.4 Microbiology Flashcards

1
Q

Draw coccus, bacillus, spirillium and vibrio

A
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2
Q

Draw diplococcua, staphylococcus and streptococcus

A
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3
Q

What is meant by a gram stain?

A

A method of staining the cell walls of bacteria as an aid to their indentification

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4
Q

Function and effect of crystal violet

A
  • basic dye
  • binds to peptidoglycan so all bacteria stains purple
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5
Q

Function and effect of Lugols iodine

A
  • mordant
  • binds the crystal violet to the peptidoglycan more strongly
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6
Q

Function and effect of acetone-alcohol

A
  • decolouriser
  • removes unbound crystal violet and lipopolysaccharide
    —> gram negative bacteria lose stain and become colourless
    —> gram positive bacteria remain purple
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7
Q

Function and effect of counter-stain

A
  • gram negative bacteria stain pink
  • gram positive bacteria remain purple
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8
Q

Describe gram positive bacteria

A
  • purple after staining
  • absence of LPS in cell walls allows them to bind stain efficiently and makes them more susceptible to penicillin and lysozyme
    —> lysozyme hydrolyses bonds holding peptidoglycan molecules together
    —> penicillin prevents the bonds inter-linking peptidoglycan molecules from forming so bacteria burst
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9
Q

Describe gram negative bacteria

A
  • pink
  • LPS layer removed with the dye when washed with acetone
  • LPS protects peptidoglycan so not impact by lysozyme and are resistant to penicillin
  • antibiotics to treat gram negative must interfere with cells ability to make proteins
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10
Q

Describe the method of gram staining

A
  • application of crystal violet
  • application of mordant (Lugols iodine)
  • alcohol wash (acetone)
  • application of counter stain (safranin)
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11
Q

Describe conditions needed for bacterial growth

A
  1. Nutrients
    - carbon and energy source (ie glucose)
    - nitrogen for AA synthesis
  2. Growth factors
    - vitamins
    —> Na+, Mg2+, Cl-, SO42-, PO43-
  3. Temperature
    - bacterial metabolism controlled by enzymes so 25-45 optimum
  4. pH
    - most bacteria favour slightly alkali conditions (7.4)
    - fungi grow better in neutral to slightly acidic conditions
  5. Oxygen
    - some grow best in presence of O2 but can survive without (facultative anaerobes)
    - some can’t grow in O2 (obligate anaerobes)
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12
Q

Explain what is meant by defined, undefined, selective, and complete culture mediums

A

Defined: only known ingredients
Undefined: components not all known
Selective: only certain bacteria grow
Complete: all chemicals needed to support growth

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13
Q

What is meant by aseptic technique?

A

Laboratory practise that maintains sterility in apparatus and prevents contamination of equipment and environment

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14
Q

How do you prevent contamination of cultures and apparatus?

A
  • sterilised all apparatus and media before use to prevent initial contamination
  • handle cultures carefully, flaming necks of culture vessels and using sterile loops
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15
Q

How do you prevent contamination from the environment?

A
  • sterilised work surface before and after using disinfectant
  • use correct handling techniques in inoculation
    —> bottle in one hand
    —> flame mouth of bottle and inoculating loop
    —> secure lid with adhesive tape
    —> incubate at 25°C to prevent pathogenic growth
    —> do not open dish after inoculation
  • use autoclave
  • disposable materials in plastic bags, autoclaved, then binned
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16
Q

Briefly describe the methods of measuring growth

A
  • directly
    —> viable counts by counting colonies describe living cells only
    —> total counts using a haemocytometer describe living and dead cells
  • indirectly
    —> turbidity (cloudiness) of mixture ie light absorption
17
Q

Define a colony

A
  • cluster of cells which arise from a single bacterial or fungal spore by asexual reproduction
    —> produced by serial dilution of culture, plating, then incubation
18
Q

Equation for population size

A

Population size = number of colonies x dilution factor
—————————————————
volume of sample

19
Q

What does it mean if dilution is too great or insufficient?

A

Too great = too few colonies on each plate to be statistically sound
Insufficient = colonies merge and clump leading to inaccurate counting (usually underestimate)

20
Q

Briefly describe how turbidimetry measures growth

A
  • use colorimeter
  • absorbance of suspension, then reading from a standard graph of light absorbance plotted against number of bacterial cells

A2 BIO UNIT3 (8 decks)

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