Introductory to Microbiology Essay Assignment
* 20 marks will be allocated for formatting and English proficiency.
* 10 marks will be deducted each day for late submissions.
- Agarwood, also known as gaharu, is a resin that can be extracted from agarwood-producing trees like Aquilaria. This commercially important resin is extensively used in perfumery, medicine and in religious rituals. It is believed that Aquilaria trees produce agarwood only when their trunks and branches are injured and infected by microorganisms.
You are interested in finding out the microorganisms responsible for the production of agarwood.
As a scientist with a fully equipped laboratory at your disposal, you set off by heading to a nearby gaharu plantation to collect specimens.
(a) You came across an Aquilaria tree trunk which harbors agarwood (Note: agarwood is usually
found in the heartwood). Initially you have decided to chop down the tree to get to the agarwood within, and then you realized that this was a bad idea. Give TWO reasons why this is so. (4 marks)
(b) Suggest a method in detail how you could properly retrieve the microorganisms in the agarwood and maintain them in the lab. (8 marks)
(c) After 48 hours of incubation in nutrient agar at 37 ?, you noticed that colonies of bacteria and fungi are appearing on the surface of the medium.
(i) How do you quickly distinguish a bacterial colony from a fungal colony growing on nutrient agar? (4 marks)
(ii) Is this method of identification accurate? Explain your answer. (1, 2 marks)
(d) You have decided that it is essential to isolate axenic cultures from the mixture of microbes in the nutrient agar in (c) prior to subsequent analyses.
(i) Define axenic culture. (1 mark)
(ii) Explain how axenic cultures can generally be produced from the microbial mixture in
(c). (4 marks)
(iii) Why is an axenic culture important? (2 marks)
(e) Antimicrobial compounds can also be added to eliminate undesirable contaminants in the preparation of axenic cultures.
(i) Name ONE antimicrobial agent that can be used to minimize both Gram-positive and Gram-negative bacteria. What is the mode of action of this agent? (2, 4 marks)
(ii) Name ONE antimicrobial agent that can be used to minimize fungal growth. What is the mode of action of this agent? (2, 4 marks)
(f) Using the method described in (d) and (e), you finally end up with two bacterial (B1 and B2)
and two fungal (F1 and F2) isolates. Name FIVE differences between a bacterium and a fungus. (5 marks)
(g) You have decided to identify the bacteria first by running some tests.
(i) The bacteria cultures were incubated in an incubator for 48 hours at 37? before Gram staining was performed. Results have indicated that both bacteria isolates B1
and B2 were Gram negative. Is the result reliable? Explain. (1, 4 marks)
(ii) Staining with malachite green has revealed green-colored entities in isolate B1 under the microscope. What does this mean? (1 mark)
(iii) A simple literature review has revealed that isolate B1 is likely Bacillus or Clostridium. Devise an experiment to identify B1. (6 marks)
(iv) With the help of a fellow microbiologist, you have managed to identify isolate B2 as Vibrio cholera. List the fundamental differences between isolate B1 and B2.
(6 marks) (1 mark)
(h) Design an experiment that allows you to reliably identify fungal specimens F1 and F2 down to a generic level. (4 marks)
(i) Suggest a suitable nutrient agar each for the axenic cultures of bacteria and fungi to facilitate their growth. (2 marks)
(j) In the course of bacterial media preparation, you noticed that the usual nutrient powder has been borrowed by a colleague of yours and you are left only with MacConkey agar. Would using this agar affect your experiment? Explain. (1, 2 marks)
(k) You have successfully cultured fungi F1 and F2 using the media suggested in (h). However, you think that it is best to assess whether these are truly fungi which induces the formation of agarwood and not undesired contaminants introduced during the experiment.
(i) Suggest a plan of action for this assessment. (6 marks)
(ii) This assessment is associated with a theory in microbiology (covered in class). Explain this theory and why it is important. (4 marks)
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