Biological Media Lab Report

Lab Report 2
Biological Media
Meva Tinsley
Georgia State University

Lab Report 2
Introduction: Biological Media
Microorganisms require nutrients and certain environmental conditions in order to thrive. In the lab, we use a Biological Media to aid in growth reproduction. Also referred to as a culture medium, a Biological Media is a substance used to support the growth of microorganisms. The two types of media most commonly used in Microbiology are selective media and differential media. Selective media are used to encourage the growth of specific or desired microbes. Differential media on the other hand are used to distinguish colonies of microbes as well as identify different bacteria. When growing
bacteria there are many growth conditions one must be aware of such as temperature, nutrients, water supply, and oxygen supply. These growth conditions can be the be all and end all of the bacteria. This week in the lab we used TSA, EMB, MSA, and a SIM tube. Trypticase soy agar serves as a general-purpose medium because it allows for the growth of a wide variety of microorganisms. TSA is also used in the isolation of pure cultures. Robert Koch was the first to use agar in the microbiological world. Eosin Methylene Blue Agar is another media we used in the lab. EMB is selective for Gram-negative bacteria, and it also can distinguish if Gram-negative organisms can use lactose. Mannitol Salt Agar is both a selective and differential media. The purpose of this media is to detect mannitol fermenters. We also used SIM (Sulfur, Indole, and motility) tube, which is differential media. This media detects sulfur reduction.
Procedures: Biological Media I started off my lab as I usually would, by washing my hands and putting on my lab coat and gloves. With my hands sterile and my lab coat on I was ready to begin the lab. On my lab counter were four TSA plates, one EMB plate, one MSA plate, and three SIM tubes. I also had the organisms Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, and Citrobacter freundii. Using the aseptic technique, I first sterilized my inoculation loop by running it through the flame of the Bunsen burner.
I also sterilized the top of the test tube just for contamination purposes. Next I dipped my inoculation loop into the test tube to gather a sample of Staphylococcus aureus. Once I had my sample, I then began using the strike method to inoculate my TSA plate. I made sure to flame sterilize my loop between each strikes. I continued on using this same process to inoculate the three remaining TSA plates with the other three bacteria. After all of my TSA plates were inoculated with each bacteria, I move on to the second part of my experiment, which involved the EMB and MSA plates. My lab partner and I were required to take a marker and on the back of our EMB and MSA plates section each plate into four quarters. We then labeled each quadrant of both plates with one organism that we were given at the beginning of the lab. Next we labeled our plates with our names and lab times. We were then prepared to inoculate our plates. Starting with the EMB plate, I first sterilized my inoculation loop and dipped it into the test-tube. Gathering a light sample, I began to inoculate one quadrant of my EMB plate with a zigzag line. I made sure to start from the edge of the
quadrant and work my way towards the center. I continued on using this same process with the remaining organisms making sure to flame sterilize my loop between each organism. Next, using my MSA plate I sterilized my inoculation loop and dipped it into the test-tube. Gathering a light sample, I followed the same steps used with inoculating my EMB plate. I inoculated each quadrant with a different organism and used the same zigzag formation. Also, I started from the edge of the quadrant and worked my way towards the center. Once I was done with the second part of the experiment, I moved on to the final part of the experiment, which required the use of the SIM tubes. My partner and I were told to chose an organism to test with the SIM tubes. We chose the organism Pseudomonas aeruginosa. Next we labeled our tubes with our names, the organism, and the time. After, I proceeded to flame sterilize my loop and then I gathered a sample of my organism. With my sample of Pseudomonas, I inoculated my green citrate tube using a zigzag line. Next I sterilized my loop through the Bunsen burner and gathered another sample of the bacteria. With another sample of Pseudomonas on my inoculation loop, I then dipped my loop into the phenol red tube. After I was done with the phenol red tube I then sterilized my loop and put it back into its box. Then, I took my inoculation needle and sterilized it through the flames of the Bunsen burner. Following the sterilization of my needle, I began to inoculate my SIM tube with the sample of Pseudomonas. I stabbed my needle into the SIM tube and pulled it straight out. Last but certainly not least, I placed all of my plates and tubes inside of a refrigerator for incubation.
Results: Biological Media After two days of incubation, I was able to review my results.
I gathered all of my plates and tubes from the refrigerator and began my observation. At first glance, I noticed that TSA plate containing the bacteria Escherichia coli displayed the most colonies. The colonies were smaller and more clumped towards the edges. Towards the center of the TSA plates were larger colonies and they appeared to be a little bit more spread apart than the colonies around the edges. I counted about 38 larger colonies. Next I looked at the TSA plate containing the bacteria Pseudomonas aeruginosa. This TSA plate displayed larger colonies around the edges and in the center. The colonies were more attached which made counting the colonies a bit difficult; however I was able to count about 33 colonies. Following, I moved on to my next TSA plate, which had the bacteria Citrobacter freundii on it. This bacterium contained the largest colonies. The colonies were pretty close, and I was able to count about 25 colonies. The last TSA plate I examined contained the bacteria Staphylococcus aureus. This plate contained a lot of colonies however they were very tiny. It also contained about 10 larger colonies. After reviewing all of my TSA plates, I moved on to observe my MSA plate. Staphylococcus was the only bacteria that grew on my MSA plate. This bacterium was also the only one that changed colors. It became a neon yellow color while all of the other bacteria stayed a pink color. Next I moved on to my
EMB plate. All of the quadrants were a purplish color meaning that there was a strong positive result of lactose formation. Staph’s quadrant was white, meaning that there was a negative formation of lactose present. Also, Staph was unable to grow on the EMB plate meaning that it was a gram-positive bacterium. Lastly I observed my test tubes. Our first test tube that contained citrate displayed a color change from green to blue. This meant that the bacteria Pseudomonas aeruginosa was positive for citrate. Our second test tube filled with the phenol red remained red, meaning that Pseudomonas aeruginosa was not able to produce glucose. The last test tube, which was the SIM tube, had developed a dark ring around the top. This meant that the bacteria Pseudomonas aeruginosa was positive for sulfur reduction.
Conclusion: Biological Media Media are usually fixated with the required nutrients for bacteria to survive. Media can also tell you if lactose is present or if a bacterium is gram positive or negative. In this lab, I was able to learn about what each media represented. I learned that TSA media are general media and usually allow for the growth of various bacteria. I also realized that each media served as an indicator as to what was in each bacterium. Like in the bacteria Staph I was able to tell that it was gram-positive bacteria because it was unable to grow on the EMB plate.