Nutrient Agar Streak Plates Lab Report

The three organisms that were identified in my unknown tube were Citrobacter freundii, Corynebacterium xerosis, and Micrococcus. The first step of this project involved isolating the three organisms that were within the mixed culture. Once I successfully isolated them, I was able to do specific colony morphologies for each of the organisms. The characteristics of Citrobacter freundii includes butyrous, opaque, circular, convex, and beige. Corynebacterium xerosis is white, small, punctiform, circular, dry, and brittle. Micrococcus is white, large, opaque, butyrous and circular.

This experiment was given to us to utilized previous knowledge learned throughout the semester to identify a gram negative unknown bacterium. We had to first learn the difference between a gram negative and a gram positive organism. We started off with doing gram stains to determine whether it was positive or negative. Based on the gram stains, a gram positive stains purple and a gram negative stains pink. A gram positive stains purple because the cell walls is made of a thick peptidoglycan layer and doesn’t

There are many reasons for identifying an unknown bacterium. The purpose of this exercise was to identify an unknown bacterium from a liquid culture. We chose our unknown bacteria from a rack of test tubes with several different species of bacteria inside. I wanted to pick an unknown bacteria with a number easy to remember so I pick the test tube labeled “745”. Procedures were followed as stated in the lab manual written by Dr. Pedro J.A. Gutierrez.

The purpose of this experiment is to distinguish and indentify an unknown bacterium. There are several tests that can help one eliminate and narrow down the options. The most useful test, and the very first one done, is a gram stain. This test will tell whether the bacterium is gram-positive or gram-negative. After the type of gram stain is identified, the tester has a wide array of differentiating tests at their disposal. Based on the results from these tests, and the numerous others that are available, one can accurately establish the identity of an unknown bacterium.

The purpose of this lab was to isolate and identify the microbes from the randomly assigned mixed culture in test tube number # 10. In order to achieve identification of the microbes the mixed culture will be inoculated on various media, and subjected to biochemical tests in order to differentiate and identify the microbes. These experiment were carried out over the course of five days in a microbiology lab. Isolation of two microbes for a pure culture of each was achieved by the streak plate method, and gram staining identified a gram-positive (+) microbe and a gram-negative (-) microbe. A blood agar plate was inoculated with the gram (+) microbe to reveal it was beta hemolysis.

I performed a gram stain on my unknown 7. It appeared to be purple and round shaped. I came to the conclusion that my bacterium is gram-positive, cocci. A gram stain is a differential test. It allows recognizing the difference between two cell walls structures. In a gram-positive cell wall contains a thick peptidoglycan layer covering the plasma membrane (2). The purple staining is retained around the cell

Figure 3. The isolated colonies from figure 2 are viewed under the microscope at the 100x objective after gram staining. In this figure, you can see both gram-negative and gram-positive microorganisms. The gram-negative are the Rhodospirillaceae and they are pink rod-shaped bacteria. The

I began to make gram stains for both colony 2 stock and reserve culture. The goal for this gram stain technique was to determine weather or not the organism is gram positive or gram negative. The reason two gram stains were necessary was to make sure the slants were identical in both the stock and reserve cultures. I ran out of lab time and was not able to view the gram stains under the microscope, but will continued on Monday.

Introduction: A frequent matter in the science, medical and pharmaceutical world is identifying unknown bacteria. Throughout the past months of this class we have learned lab technique and how to do a variety of different tests on bacteria. Microbiology is not only an academic understanding of microorganisms but learning how to practically use lab procedures to properly identify and test organisms. There are several reasons one might need to identify a bacteria. It could be to find out the causative agent in a patients disease or to figure out the antibiotics that need to be administered.

Plate B incubated at 25oC produced a white, opaque, waxy, and spreading bacteria colonies while plate A incubated at 37oC produced a white, thin spreading bacteria colonies (Figure 1.). Gram staining revealed that plate B contained a rod-shaped bacterium having partial pink and purple coloration with endospores. This suggests that the bacteria is a gram positive bacteria. Gram positive bacteria typically have a thick cell wall which traps the crystal violet making them appear purple. Conversely, plate A is a rod-shaped bacterium but with pink coloration.

The objective of these “unknown” experiments was to take a mixed culture, which contains two unknown species, and identify those species through a series of tests. The group was informed that one species of bacteria would be a gram-negative bacillus and the other would be a gram positive coccus. The tests to be conducted ranged from streak plate isolation to biochemical tests. Each test to be conducted was discussed and agreed upon by all group members. The results of each test were analyzed by the group and led to selection of the next test that would further narrow the possible identity of the unknown species.

The first day an unknown sample was assigned to each group of students. The first test applied was a gram stain to test for gram positive or gram-negative bacteria. The morphology of the two types of bacteria was viewed under the microscope and recorded. Then the sample was put on agar plates using the quadrant streak method for isolation. There were three agar plates; one was incubated at room temperature, the second at 30 degrees Celsius, and the third at 37 degrees Celsius. By placing each plate at a different temperature optimal growth temperature can be predicted for both species of bacteria.

The identification of bacteria is a fundamental objective of microbiologists. It is essential to distinguish specific bacterial properties to understand the environment, physiology and disease. As new bacterial species emerge and existing ones evolve into different strains, it is imperative that microbiologists continue to isolate bacteria from the field, identify their findings and research newly discovered forms. Their discoveries can then be used to evaluate the types of microbial life that may be found in certain environments and the corresponding benefits or risks to those that dwell in those areas.

We began the experiment with conducting a Gram Stain to be able to differentiate if our organism is gram negative or gram positive. The Gram Stain also allows to determine the size of the cell, the cell’s morphology, and arrangement of the cell. Gram negative cells have a LPS outer layer and an inner thin peptidoglycan layer and the gram-positive cells have a

After heat-fixing, I stained with Crystal Violet for 1 min, rinsed with distilled water, stained with Gram Iodine for 1 minute, rinsed with distilled water, gently rinsed with 95% ethanol, rinsed with distilled water again, stained with Safranin for 1 minute, rinsed with water, and dried the slides with bibulous paper. I checked the bacteria with Microscope 90. For the rest of the lab, I performed different tests on the two different bacteria.