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29 Cards in this Set
- Front
- Back
- 3rd side (hint)
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Classification categories of bacteria according to their shape |
Coccus (spherical) Baccilus (rod-shaped) Spirillum (spiral) |
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Identify bacteria labelled A |
Coccus |
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Identify bacteria labelled B |
Baccilus |
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Identify bacteria labelled C |
Spirillum |
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How can you classify bacteria, if not by shape? |
Gram staining |
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Gram positive bacteria |
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Gram negative bacteria |
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Gram staining procedure |
1. Fixation 2. Stain with crystal violet 3. Treat with iodine solution 4. Decolourisation 5. Counterstain with safranin Gram positive will go purple Gram negative will go red |
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Bacteria cultured on a growth media must have... |
1. A carbon source e.g. glucose or lactose 2. A nitrogen source e.g. ammonium or amino acids 3. A sulphur and phosphorus source 4. Vitamins, minerals and growth factors 5. A suitable temperature e.g. 25°c 6. A suitable pH |
6 |
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3 bacteria which live in different temperatures |
Psychrophiles (arctic soil) Mesophytes (human body) Hyperthermophiles (volcanoes) |
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3 Bacteria with different oxygen needs |
Obligate aerobe growth is inhibited by the absence of oxygen Obligate anaerobe growth is inhibited by the presence of oxygen Facultative anaerobic grow best in the presence of oxygen but can respire anaerobically if needed |
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Bacteria have different oxygen requirements. Identify the bacteria from test tube 1 |
The bacteria are cluster at the top of the tube as they need oxygen (diffuses into growth medium from air) for respiration and growth. Growth is inhibited in the absence of oxygen so they must be obligate aerobes |
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Bacteria have different oxygen requirements. Identify the bacteria from test tube 2 |
The bacteria are clustered at the bottom of the test tube as they do not need oxygen (which diffuses in the growth medium from air at the top of the test tube) to respire or grow. Their growth is inhibited in the presence of oxygen so they must be obligate anaerobes |
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Bacteria have different oxygen requirements. Identify the bacteria from test tube 3 |
Bacteria are spread throughout the test tube, with more clustered at the top. They can respire and grow in the absence of oxygen but grow better in the presence of oxygen found at the top of the test tube where oxygen can diffuse in the growth medium from the air. They must be facultative anaerobes. |
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Why are aseptic techniques used? |
-To prevent the contamination of the environment by the microorganisms being handled -To prevent the contamination of the bacterial cultures by unwanted microorganisms from the environment |
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What must all equipment and growth material that comes in contact with microorganisms being cultured be? |
Sterile |
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4 sterilisation techniques |
1) Pass any metal transfer tools used e.g. inoculating hoop through a blue Bunsen flame until they glow red to sterilise them 2) Use pre-sterilised petri dishes 3) Sterilise any glassware used under high pressure and high temperature in an autoclave for 15 minutes 4) Sterilise nutrient agar used in an autoclave before letting it set into a plate |
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How to prepare a sterile agar plate using aseptic techniques |
1. Open the culture bottle cap using your little finger and do not place the cap or bottle on the bench 2. Flame the neck of the bottle in a blue Bunsen flame 3. Work closely to the flame as the updraft helps to prevent contamination 4. Open the sterile Petri dish lid at an angle 5. Pour in the molten nutrient agar (which has already been sterilised in an autoclave) and close lid immediately. Swirl gently to remove any air bubbles 6. Secure lid with tape |
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How to inoculate a nutrient agar plate with bacteria growing in milk |
1. Sterilise the inoculating hoop in a roaring, blue Bunsen flame until it glows red 2. Dip the inoculating hoop into the milk sample 3. Open the Petri dish lid at an angle (to avoid contamination by microorganisms in the air) and using the inoculating hoop, spread the milk droplet across the surface of the agar in a zig-zag pattern, while rotating the plate 4. Secure the lid with tape but do not completely seal (as anaerobic conditions encourage pathogen growth) and incubate at 25°c (at 37°c pathogen growth is again encouraged) |
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How can bacteria grown in liquid cultures be counted to estimate population size? |
Bacteria grown in liquid cultures can be counted directly (by counting each cell) or indirectly by measuring turbidity (cloudiness of the culture medium) using a colorimeter |
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2 types of counting directly |
1. Total counts which include both living and dead cells 2. Viable counts which include only living or actively growing cells and therefore underestimates population size |
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Viable counts |
Viable counts count living or actively growing cells that grow into visible colonies on an agar plate. If the population density is too high, serial dilution (or dilution plating) is used. |
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Serial dilution method |
1. Fill 5 test tubes with 9cm³ of sterile water using a sterile pipette 2. Add 1cm³ of your sample to the first test tube. This is now a 1 in 10 (10-¹) dilution 3. Mix this test tube thoroughly and pipette 1cm³ into the next test tube. This is now in a 1 in 100 (10-²) dilution 4. Repeat this process until you reach a 10-⁴ dilution 5. Plate each dilution onto nutrient agar using aseptic techniques |
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Describe the plates above |
R and S it is impossible to distinguish individual colonies and therefore its impossible to count them T has too many colonies to count reliably U has distinct colonies that can be counted reliably V not enough colonies for a reliable estimate |
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Equation to calculate no. of bacteria present in original sample |
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Calculate no. of bacteria present in a 0.5cm³ with 69 colonies present in a dilution of 10-⁴ from a 1cm³ sample |
69 × 10,000 = 690,000 690,000 × 2 = 1380,000 |
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Disadvantages of serial dilution |
-Doesn't account for dead bacteria cells so underestimates population size -Cannot be sure each colony came from only one bacteria, they could have clumped together |
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Define colony |
A cluster of cloned cells which have all arisen from a single bacterium or fungal spore |
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Define pathogen |
A microorganism which causes disease in its host |
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