Topics: Bacteria, Escherichia coli, Microbiology Pages: 5 (1193 words) Published: February 22, 2015
Microbiology: ‘The Correct handling of Micro-organisms’ 1. Devise a title for each of the two experiments you did :
(i), Experiment 1 demonstrated the growth of bacteria when placed in liquid nutrient broth culture, the number of species present had increased in growth. .(1)
(ii) Experiment 2 illustrated the growth of bacteria when placed on different surfaces of solid agar plates which included: nutrient agar, CLED agar and MacConkey agar; the number of species present also had increased in growth. (1)

2(A). Experiment 1: Choose 2 words that describe the appearance of the pre –incubation broth: (i) Straw yellow (½) (ii) Transparent .(½) 2 (B). Choose two words that describe the appearance of the post-incubation broth: (i) Turbidity .(½) (ii) Pellicle formation (½) 3. Complete the table below to show your post-incubation observations in Experiment 2

Nutrient Agar


MacConkey Agar

Appearance of agar before incubation
Pale yellow

Appearance of the colonies for each species on each type of agar

E.coli – Shiny white/clear with rough outer edges.

P.aeruginosa – Matte white/clear with smooth outer edges

B.subsilis – Matte white/clear with rough outer edges.
E.coli – opaque yellow colony produced.

P.aeruginosa – green colony produced

B.subsilis – pale blue colony produced
E.coli – orange colony produced

P.aeruginosa – white colony produced

B.subsilis – pale orange colony produced.

Appearance of Agar surrounding each species following incubation

E.coli – Yellow
P.aeruginosa – Blue
B.subsilis – Pale Blue
E.coli – Orange
P.aeruginosa – Orange
B.subsilis – Orange
4 (A). Describe what is meant by the term aseptic technique: Aseptic technique is any technique that ensures asepsis (such that no contamination of the culture) occurs and thus prevents the risk of infection. (1)

4 (B). Briefly describe 5 aseptic procedures you used during the experiments, emphasising in each example you give, how you reduced potential contamination to your cultures by unwanted micro-organisms: (i) First, we must sterilise the inoculating loop by heating it until the colour reached a distinct red hot in the hottest part of a blue flame on a Bunsen burner. This was done before and after use; this ensures that any bacteria which may have been left on the loop were destroyed and so asepsis is achieved. (1)

(ii) The inoculating loop was held at a steep angle that is somewhat close to vertical. This ensures that any liquid that is present on the loop will flow downwards and into the flame, where it will be completely destroyed and so asepsis is established. (1)

(iii) Another technique included flaming the necks of bottles using the Bunsen burner. This ensures that any microorganisms present will be destroyed and not able to enter thereby preventing contamination of the culture(s).


(iv)We had to perform the transfer of each microorganism on the cultures as quickly and efficiently as possible. The cultures were exposed to air for a minimal amount of time; otherwise risk of contamination would have occurred. .(1)

(v) During experiment 1, we had to lift the cap of the bottle and hold it in our little finger, taking care not to place it on the worktop. Then using the rest of our fingers, we would hold the bottle and use our free hand to complete the rest of the procedure. Once the experiment was completed we used our little finger to place the cap back onto the bottle. (1)

5 (A). The formation of aerosols in the microbiology laboratory should be avoided. What does a microbiologist mean by an aerosol? This is the dispersal of...
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