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Aseptic Techniques

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  1. Describe and discuss the results of your tube transfer
    The following table shows the observation of the tube transfer



Culture tube

Control tube

After 1 hour

Clear solution. No observable change.

Clear solution. No observable change.

After 2 hours

Slightly cloudy solution

Clear solution. No observable change.

After 2 hours[pic 1]

Obvious cloudy solution

Clear solution. No observable change.

The results of the tube were checked three times. It was first checked after 1 hour of incubation, both the culture one and the control remained clear. Possible explanation of the clearness of the culture tube is that it took time for the growth and development of microorganism to adapt to the new growth condition.

After 2 hours, the culture tube solution turned slightly cloudy, this implies the growth of microorganism. After 2 hours, the culture tube solution turned into cloudy obviously. The degree of turbidity of the solution depends on the amount of inoculum present and the incubated time. If a longer incubating time is allowed, a more significant result should be observed.[pic 2]

For the control tube, it remained clear during the incubation, this implies the absence of the growth of microorganism.

  1. Describe morphologies of the microorganisms on your streak plate
    The following table shows the morphology of the microorganism




Margin (theoretical)

B. subtilis




S. epidermidis




P. aeruginosa




S. cerevisiae




  1. Answer c) Before and after you transfer the culture.
    As the purpose of inoculation is to transfer the microbial culture from one source to another medium. The inoculating loop should be flame sterilized before the transfer to remove any air-borne microorganisms and prevent the non-target microorganisms from contaminating the sample. The inoculating loop should also be flamed after the transfer as the microorganism is a potential hazard, which can cause diseases. So flaming can kill the remaining microorganisms in the loop to prevent the leakage of them.
  2. The correct order should be 4 7 6 1 3 5 2
    The burner should be attached to the gas source to ensure it has optimal source for burning. Next, the air intake should be adjusted to ensure that the air hole was closed. If the air hole remained open, the flame will strike back with the igniting burner. By turning on the gas, there is fuel supply for the burner to burn. One should light the burner with striker immediately to prevent the undesirable leakage of gases. Then, the air supply should be adjusted by opening the air hole of the burner until there is a blue flame with two cones observed. This is crucial because blue flame is of high temperature that can allow effective sterilization. After that, the loop can be heated until the entire wire glows red. This can ensure the entire loop is under flame sterilization and the microorganisms on the loop are killed. Finally, cool the loop so that the high temperature will not directly kill the sample microorganisms.
  3. General properties of microorganisms used
    Escherichia coli
    It is a common group of bacteria. It is a rod-shaped, gram-negative bacterium that can be easily found in the intestines of humans and animals as they grow best at 37 degree Celsius. Each bacterium measures approximately 0.5μm in width by 2μm in length. Most
    E. coli are harmless and actually are an essential part of a healthy human intestinal tract1. For example, it can be found in human intestines and assist with waste processing, vitamin K production, food absorption and pathogenic bacteria prevention. However, some E. coli are pathogenic, they can cause diarrhea or illness outside of the intestinal tract such as kidney infections.

    Bacillus subtilis
    Bacillus subtilis is a rod-shaped, gram-positive bacteria. It can be naturally found in soil and vegetation. The optimum temperature for its growth is in between 25-35 degree Celsius. One special property of this bacterium is that it can form a tough, protective endospore, in order to survive in harsh conditions such as acidic, alkaline, osmotic, or oxidative conditions and heat2. For the medical use of Bacillus subtilis, it is used to produce antibiotics to treat bacterial skin infections and prevent infection in minor cuts and burns.

    Staphylococcus epidermidis
    Staphylococcus epidermidis
     is a gram-positive bacterium. It lives on the human skin and mucosa and the most common infections in catheters and implants. It is one of the five most common organisms that cause nosocomial infections due to the increased usage of biomaterials in the clinical environment3. The nosocomial pathogen causes infections on prosthetic valves, cerebrospinal fluid shunts, joint prosthesis vascular prostheses, valves, and in postoperative wounds and the urinary tract. It is also the most frequent organism found in the blood of bone marrow transplant patients and on central venous catheters for patients of total parental nutrition. Its major application is in food industry as it contains a lipase gene that can increase lipase activity to assist the making of fruit-flavored esters in food. It can produce esters without the use of organic solvents, when the organic solvents are not used, toxicity and flammability can be prevented.

    Pseudomonas aeruginosa
    Pseudomonas aeruginosa
     is a rod-shaped, gram-negative bacterium. It can be widely found in the environments such as soil, water, humans, animals, plants, sewage, and hospitals4. It is about 1-5 µm long and 0.5-1.0 µm wide. It is the leading opportunistic human pathogen at most medical centers killing patients with cystic fibrosis, cancer or ALDS through the transmission by hands and equipment. P. aeruginosa is used in petroleum industry as a solvent for enamels and paints. It can also degrade aromatic hydrocarbons that cause pollution.

    Saccharomyces cerevisiae
    Saccharomyces cerevisiae
     is a globular-shaped, yellow-green yeast that belongs to the Fungi kingdom. They can be found on surfaces of plants, the gastrointestinal tracts and body surfaces of insects and warm-blooded animals, soils from all regions of the world and in aquatic environments5. It is not pathogenic and is a common yeast that is used in fermentation process which converts sugar into alcohol. It is also used in the baking process as a leavening agent that the yeast is able to release gas into their environment, results in the spongy-like texture of breads and cakes.


  1. E.coli (Escherichia coli). (2015). Centers for Disease Control and Prevention. Retrieved from http://www.cdc.gov/ecoli/general/index.html 
  2. Bacillus subtilis. (2015). Microbe Wiki. Kenyon College. Retrieved from https://microbewiki.kenyon.edu/index.php/Bacillus_subtilis
  3. Staphylococcus epidermidis. (2011). Microbe Wiki. Kenyon College. Retrieved from https://microbewiki.kenyon.edu/index.php/Staphylococcus_epidermidis
  4. Pseudomonas aeruginosa. (2012). Microbe Wiki. Kenyon College. Retrieved from https://microbewiki.kenyon.edu/index.php/Pseudomonas_aeruginosa
  5. Saccharomyces cerevisiae. (2010). Microbe Wiki. Kenyon College. Retrieved from https://microbewiki.kenyon.edu/index.php/Saccharomyces_cerevisiae



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