Manipulation of Microbial Growth

Topics: PH, Petri dish, Agar plate Pages: 9 (2765 words) Published: September 5, 2013
Year 12 Nutrition Stage 2 SACE: Practical – Manipulation of Microbial Growth| August 25 2013

The hypothesis for this particular practical experiment is that, as the pH decreases or increases from neutral pH of approximately 7, the amount of microbial growth on the agar solution will decrease

Agar Solution Preparation:
*hand sanitizer/ hand wash soap
*small container
*1g of agar powder
*0.25g of beef extract stock
*60mL of heated water
*electronic balance
*small spoons (2x)
*teaspoons (2x)
*0.2M Acetic Acid Solution (pH of 3)
*0.2M Sodium Hydroxide Solution (pH of a 11)
*100mL beaker (3 x)
*Bunsen burner
*heat-proof mat
*gauze mat
*stirring rod
*Petri dishes (6x)
*small wooden blocks
*fine black marker

Agar Plate Inoculation:

*fine black marker
*sticky tape
*sterilized cotton bud (6x)

*paper towels
*meat extract stock
*pipette dropper
*50mL conical flask

Agar Solution Preparation:
1. Hands were first washed with soap or sanitizer.
2. Then using a small spoon, 1g of agar powder was measured onto the small container provided using the electronic balance. 3. With the use of another spoon, 0.25g of beef extract broth was then measured into same small container containing agar powder. 4. 60mL of heated water was then added into a 100mL beaker. Exactly one teaspoon of the water was then removed from the beaker. 5. Teaspoon of water removed is then replaced with exactly one teaspoon of Acetic Acid solution which was added directly into the beaker. 6. Contents of the small container (agar powder and beef broth) were then emptied into the 100mL beaker containing 60mL of solution. 7. Apparatus required for heating the contents of the 100mL beaker was set up afterwards. This included the Bunsen burner, tripod, gauze mat and heat-proof mat. 8. Beaker was then placed on top of tripod and gauze mat apparatus; lighter was used to ignite Bunsen burner and then initiate heating of agar solution. 9. Solution was allowed to heat whilst continually stirred and mixed using stirring rod Heat 60mL of water with agar and beef extract whilst continually stirring and mixing until contents have dissolved and the solution comes to boil. 10. The heated beaker was then allowed to cool until its surface was able to be handled. 11. The contents of the agar solution were poured into the two petri dishes provided for the particular sample. This was done by tilting the lid at a 30° angle and steadily pouring the contents evenly to both petri dishes. Then each dish was covered with the lid immediately afterwards. 12. The solutions were allowed 10-15 minutes, for the mixture to cool down and set into a firm jelly. 13. Steps 2 until 12 above were then repeated two times, replacing Acetic Acid Solution with Sodium Hydroxide for a solution; and the exclusion of addition of Acetic Acid or Sodium Hydroxide solution and instead the use of 60mL of heated water only for the other solution. 14. Work station allocated was cleaned up afterwards and apparatus used for the agar solution preparations were put away. 15. After agar jelly has set, all agar plates were inverted upside down.

Agar Plate Inoculation:
1. Hands were washed with soap or sanitizer once again.
2. With the use of a black marker, the agar plates were labelled with appropriate labels so that the distinctions of the agar solutions were easily made. The agar plates were labelled, ‘Acidic,’ Alkaline and ‘Neutral’ correspondingly. 3. All six agar plates were gathered along with a paper towel, and then six sterilized cotton buds were gathered. Then the cotton buds and agar plates were placed on top of paper towel laid on bench or work place. 4. The nutrients were then introduced onto the agar plates by dipping a cotton bud into the meat extract solution provided, at the same time ensuring the removal excess of meat broth on the bud, after...
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