These bacterial may not be initial harmful, however if they enter our petri dish, they may find the conditioned to grow, results in;
- The unknown bacteria could mutant, perhaps resulting in the mutation of harmful pathogens.
- In general, the unknown bacteria could interfere with the experiment, giving incorrect results.
Method:
Washed your hands with bacterial soap, and then cleaned the working area with a paper towel that had been soaked in a disinfectant solution. This is to maintain a sterile environment and to kill any other potentially harmful bacteria.
In a water bath, set at 50-60’c, I placed a bottle containing some solid agar. This was then given time to melt and become a liquid. It was important that the nutrient agar was also sterile.
While the agar is melting, take the two petri dishes, and label the LOWER side of the dish. You must include your name, the date, and the name of the bacterium. The reason we label on the base is because it is possible for the lids to be transposed. Also write the information at the edge of the dish, so that it is possible to still see the bacteria, after growth, clearly.
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.úúúúÙProducing a pure culture of bacteria form a mixture.
Ishita Patel 09/10
/02
The bacterium that we are sub culturing is called Bacillus Subtilis. The aim of the experiment is to isolate pure cultures, as individual colonies.
Apparatus:
Two sterile petri dishes 1) containing
a pre-set layer of sterile nutrient agar
2) An unfilled, sterile petri dish
The petri dishes used to subculture bacteria are disposable.
Inoculating loop
Bunsen Burner
Disinfectant solution, i.e. Dettol
Paper towels
“BIOHAZARD TAPE”
Marker pen
Fresh, warm (50’c - 60’c), sterile nutrient agar. ( Agar is a mixture of seawee
d and nutrients)
Aseptic techniques:
Thought out the experiment we followed various aseptic techniq
ues.
The aim of these aseptic techniques was to avoid contamination from other sources of bacteria, i.e. pathogens
These bacterial may not be initial harmful, however if they enter our petri dish, they may find the conditioned to grow, results condition will become anaerobic. Anaerobic conditions are perfect for some human bacteria’s; especially bacteria form the human gut. If these bacteria get the correct condition to cultivate they could become harmful. e.g. if the bacteria then grows and gets in contact with us, there might be a large amount of it to make us ill or it may have mutated into an more dangerous form.
This petri dish can then be incubated in an warm oven at 30’c. This is not the optimum temperature of the bacteria, infact the optimum temperature for the bacteria would b 35’c-45’c. However this is dangerous as this is also the optimum for many human pathogenic bacteria. And if they have some how entered the plate they could begin to cultivate. Human bacteria have , however a narrow temperature range for there optimum, and so we can use a close enough temperature to the optimum for the bacteria, and this temperature would not act as a n optimum for the human bacteria.
Also turn the plate upside down, so the lid acts as the base. So that as the warm agar causes condensation within the closed petri dish, the water droplets don’t fall onto the bacteria, and cause any individual colonies of bacteria to merge together.
By now, your agar should have set. Repeat the steps mention above following the same aseptic technique. However this time when streaking the plate simply swipe the inoculating loop across the agar.
