Hey there! Sign in to join this conversationNew here? Join for free
x Turn on thread page Beta
    • Thread Starter
    Offline

    1
    ReputationRep:
    Is anyone able to comment on the sources of anomalies in this experiment procedure and apparatus?



    Provided with: 5 sterile petri dishes, 5 test tubes of liquid agar, a slope of Micrococcus luteus bacteria, 5 antibiotic discs in a sterile petri dish.

    Method:

    1. Label each petri dish appropriately.

    2. Take 5 test tubes of molten agar from the oven and allow to cool until hand hot.

    3. Using sterile techniques inoculate one test tube of agar with the bacteria and pour into one of the petri dishes. Ensure the agar covers the base of the petri dish. Put the lid on and leave to set.

    4. Repeat instruction 3 with the remaining 4 tubes of agar.

    5. When the plates have set, transfer one the of antibiotic discs into the centre of each plate, using sterile technique at all times.

    6. Tape up the plate.

    7. Invert and place the plates in an incubater.

    8. The plates will be incubated for 72 hours, after which you must measure and record the diameter of the ring of clearance around the antibiotic disc.
    Offline

    15
    ReputationRep:
    well for starters...."hand hot" you may have different interpretations as to when exactly the test tube will become hand hot
    Offline

    2
    ReputationRep:
    I would say that poor aseptic technique would be the most likely cause of anomalies. For example, if you contaminated one of the plates, you won't actually be measuring the effectiveness of the antibiotic against the bacteria that you thought you were!
    • Thread Starter
    Offline

    1
    ReputationRep:
    This is what I have thus far:

    • "Hand hot" -- Subjective, varying temperatures may result in more or less bacteria present initially to grow, so some agar plates may have more bacteria to kill.
    • Difficulty in measuring the diameter of the inhibition zone. Rarely a perfect circle and therefore it's difficult to establish which diameter should be measured.
    • No mention of volume of agar in each test tube, therefore there could be varying quantities of agar, resulting in a different thickness of agar; the agar plates are thus not standardised. Increased culture medium will contain more nutrients etc, leading to increased growth of bacteria, compared to other plates.
    • Possibility of varying concentrations of antibiotics, no mention in the method.
    • With this method, there may not be uniform growth, another technique such as swabbing could ensure there is uniform growth.
    • Poor aseptic technique - antibiotics working on the wrong bacteria.
    Offline

    2
    ReputationRep:
    (Original post by tetedupet)
    This is what I have thus far:

    • "Hand hot" -- Subjective, varying temperatures may result in more or less bacteria present initially to grow, so some agar plates may have more bacteria to kill.
    • Difficulty in measuring the diameter of the inhibition zone. Rarely a perfect circle and therefore it's difficult to establish which diameter should be measured.
    • No mention of volume of agar in each test tube, therefore there could be varying quantities of agar, resulting in a different thickness of agar; the agar plates are thus not standardised. Increased culture medium will contain more nutrients etc, leading to increased growth of bacteria, compared to other plates.
    • Possibility of varying concentrations of antibiotics, no mention in the method.
    • With this method, there may not be uniform growth, another technique such as swabbing could ensure there is uniform growth.
    • Poor aseptic technique - antibiotics working on the wrong bacteria.
    Sounds good to me
    • Thread Starter
    Offline

    1
    ReputationRep:
    Any ideas for apparatus? Or is that irrelevant here? In order to get 6/6:

    "Anomalies in results identified and explanations suggested. Describes most of the unavoidable sources of error associated with the apparatus used and procedure adopted, discussing their relative influence and suggesting methods of overcoming them."
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: April 10, 2006
Poll
Do you like carrot cake?

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Write a reply...
Reply
Hide
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.