Microbiology Case

Lab 1 Part A-E: Prevention of contamination is crucial while performing an experiment. In lab today, I was able to perform the basic microbiology lab techniques that allows us to prevent contamination. Although I feel that I have mastered these techniques, I still have to practice more because I catch myself touching the unsterilized portion of inoculating loop with the test tube. I also sometimes forget to sterilize the inoculating loop before transfer.

Some things to watch out for is making sure that we hit the adjustment lock before adjusting the volume on the pipettes to prevent breaking the pipettes. Also, it is important to not talk or walk around the room while performing aseptic transfer. By talking and walking around the room with the agar plate, contamination may occur.

A useful technique that I learned was testing if the inoculating loop was too hot or not. To test this, gently place the inoculating loop on the agar. If it makes a "sizzle" noise, then it's too hot. Another technique that I learned was how to effectively hold an agar plate with its lid. Place the agar plate on the palm of your hand and hold it was the last three fingers. Hold the lid in a position where it semi-covers the agar plate using your thumb and index finger. This placement of the agar plate and lid not only allows efficient streak plating, but it also prevents contamination because the lid is semi-covering the agar plate.

Lab 1 Part F: The purpose of this lab was to be able to demonstrate proper usage of pipettes, perform aseptic transfer, streak plating, and spread plating. I believe that I am able to competently perform these techniques because I was able to observe single colonies on my agar plate. However, single colonies were only observed at the end of the first streak and at the beginning of the second streak. No visible colonies were observed in the third and fourth streak. A plausible explanation for this is not cooling the inoculating loop long enough. The inoculating loop may have been too hot at the beginning of the second streak, killing the bacteria, thus showing no visible colonies. Another possibility of the lack of visible colonies is the complete transfer of bacterium by the accidental stabbing of the soft agar. These possible reasons show that I still a need a bit more practice to refine my skills.

The purpose of using streak and spread plating is to obtain a pure culture, which is a culture that contains one type of organism. Streak plating can be used for a liquid or solid medium, but spread plating is only used for liquid mediums. The advantages of streak plating is that it is easier to obtain single colonies because the concentration of organisms decreases as each "streaking" occurs. Spread plating is much more difficult because we don't know the initial concentration of organisms in the sample, so we must perform multiple serial