Microbiology Unknown Lab Report Essay

The purpose of this lab was to identify two unknown bacteria cultures using various differential tests. The identification of these unknown cultures was accomplished by separating and differentiating possible

Please explain the purpose of this lab. Include in your explanation the major concepts you learned and any safety concerns associated with the lab.

I inoculated a T-Soy agar with bacteria number 118, for this I used a streak isolation method. Next, in order to distinguish between Gram positive and Gram negative I used a streak isolation technique on a CNA plate, then performed the same exact procedure on a MacConkey plate. The results from the CNA plate showed the Gram Positive bacteria was an Alpha hemolyzer. Next, I used a P Disc on a T-Soy agar inoculated with bacteria 118 and determined the Gram Positive bacteria was not sensitive to P Disc antibiotics. This revealed the Gram Positive bacteria to be Streptococcus Mitis. The results from the MacConkey plate proved the Gram Negative bacteria to be a lactose fermenter. With the Gram Negative bacteria I performed a lysine test with positive results. Next, I performed an ornithine test on the Gram Negative bacteria, with negative results, therefore I concluded the Gram Negative bacteria was Klebsiella pneumoniae.

The unknown bacteria B22 contained an opaque white, circular colony, along with an irregular margin on the initial inoculated agar plate. The broth characteristics included growth with the presence of a flocculent and all around cloudiness; however, the slant characteristics included just a spreading edge. After the bacterium identified to be gram positive, a blood agar plate identified the bacteria to have gamma hemolysis capabilities; additionally, the mannitol salt agar identified the bacterium to indeed ferment the mannitol and the urease enzyme was as well identified from the urea agar. Subsequently, the phenol red mannitol broth showed no mannitol fermentation and the phenol red glucose broth showed fermentation with acid and no gas

In the Sugar Fermentation experiment I ended up with three negatives, being Mannitol, Sorbitol, and Arabinose, and four positives, Lactose, Glucose, Sucrose, and Maltose. In the Litmus milk project, my bacteria turned out to be top neutral with reduction in the bottom. I had no coagulation, no peptonization, negative for Acid, and negative for Alkaline. A few other tests indicated I was positive for Arginine and Lysine, but I had tested negative for Bile Esculin. The bacterium tested was positive for all of the salts as well as for the TSI agar and the

Escherichia coli is a Gram-negative rod that was tested on ten different biochemical testing procedures. The Escherichia coli culture on the MacConkey agar had growth and experienced fermenting of lactose (color change to yellow). This is an expected result because this agar only grows Gram-negative bacteria so it is a selective media. The bile salts and crystal violet are the agents that make the agar select against Gram- positive species. The pink tint is probably from the precipitation of bile salts. The Bacillus subtillis is a Gram-positive bacterium so it was not supposed to show growth or fermentation, but it showed growth without a color change (no lactose fermentation). This was due to the over streaking of maybe Escherichia coli or Enterococcus durans, which are Gram-negative species. Staphylococcus epidermis had a growth along with a yellow to orange color change. Media too was clear.

Sample number 32 displayed beta hemolysis on the blood agar plate it was cultured on. I proceeded to gram stain the sample on a slide, and observed it at 1000x magnification. The organism is rod shaped, with no particular arrangement, and is gram negative. The appropriate identifying tests for this type of bacteria were performed, including the use of SIM agar, Urease, Citrate and OF Glucose tests. Once inoculated, these tests are incubated at 37 degrees Celsius for 24-48 hours. The findings of these tests revealed that the organism is motile, positive for indole production, negative for sulfur, negative for urease, negative for citrate and is a fermenter. The characteristics displayed are indicative of Escherichia coli.

Mac Conkey Agar is selective and differential culture medium for bacteria, which is designed to selectively isolate gram-negative and gram-positive bacteria and also differentiate groups of gram-negative bacteria based on lactose fermentation. The crystal violet and bile salts in Mac Conkey agar is used to inhibit the growth of gram-positive organisms which allows for the selection and isolation of gram-negative bacteria. However, for differential medium Mac Conkey agar will contain lactose, a fermentable carbohydrate, and the pH indicator neutral red. When, bacteria utilize lactose as carbon source the acid products will produce and change neutral red from yellow in neutral solution into pinkish red in the present of acidic environment. Based on the experiment, Mac Conkey agar is used to differentiate and distinguish between two groups of gram-negative bacteria which are Pseudomonas Putida and Escherichia Coli either it is lactose-fermenting bacteria or lactose

On the second day of the unknowns experiment, the TSA plates were observed and their results were recorded. The aerobic TSA plate had a medium amount of growth and the colonies were an off-white color, had irregular shape, undulate margins, and umbonate elevation. The anaerobic TSA plate had less growth, but there was still growth present; the colonies on this plate were transparent, had irregular shape, undulate margins, and raised elevation. The largest colony from each plate was sub-cultured and prepared to be smeared onto a slide for viewing under the microscope. Once the organism had dried, the slide was heat fixed and gram stained. The colony obtained from the aerobic TSA plate showed gram positive bacillus and gram negative bacillus. The colony that was acquired from the anaerobic TSA plate only had the gram negative bacillus. This showed that the gram positive organism was an obligate aerobe and that the gram negative organism was a facultative anaerobe. After the results of the gram stain, the gram negative organism was sub-cultured

Most bacteria are classified as either gram positive or gram negative. Gram positive is a purple stain and gram negative will appear pink or red. Gram negative can cause many kinds of infections. One type of bacteria is Escherichia which is a rod shaped bacteria. A Gram stain is used in lab setting to identify what type of bacteria is present. A sample is placed in a nutrient media and incubated. This media will encourage bacteria growth present. This process allows for further testing and to identify what kind of bacteria is present to allow for appropriate treatment.

The most common medium is blood agar. P. aeruginosa has very simple nutritional requirements. When grown on blood agar, it is known to form round colonies with a fluorescent greenish color under ultraviolet light due to the production of pyocyanine. It also gives off a sweet odor and shows a B-hemolysis. P. aeruginosa is known to produce acid, but no gas when in glucose. It is not an active fermenter of carbohydrates. The optimal growth is 37˚ C. It is oxidative and non fermentative. Although an aerobic atmosphere is necessary for optimal growth, it sometimes can be grown anaerobically if nitrates are present in the medium. It is easily differentiated from other bacteria when grown properly with no

Step 1. Prepare a slide with the positive culture results by transferring the sample to be examined onto a drop of suspension medium such as distilled water using a sterile inoculation loop.

The blood agar petri dish was stored in a refrigerator prior to the start of the experiment. Before the experiment could begin, the agar was left to sit in order to allow it to return to room temperature. Using a marker, four test tubes were then labeled A, B, C, and D. Using a syringe, 5 ml of whole milk was measured and poured into each test tube. Then, small samples of the e. Coli specimen were added to test tubes B, C, and D using a sterilized paper clip which was bent into the shape of a loop. After each use, the loop was promptly sterilized. Test tubes A, B, C, and D were then inverted three times. After inverting test tubes B, C, and D, half a teaspoon of raw, ground garlic was added to test tube C using a standardized measuring

In order to isolate fecal coliforms, Eosin Methylene Blue agar, which contains peptone, lactose, sucrose, and the dyes eosin Y and methylene blue, is used. These sugars provided encourage growth of fecal coliforms while the dyes inhibit growth of Gram-positive organisms. As a result, EMB agar allows the inoculation of Escherichia coli, Enterobacter aerogenes, Salmonella typhimurium, and Enterococcus faecalis. To identify E. coli strains on EMB agar, the cultivated bacteria must appear green, black, or have colonies with dark centers (5).

After inoculating two cultures from a liquid test tube that was given by the instructor, several different test were performed in order to identify the each culture's characteristics. By comparing all the results to the unknown key chart, Unknown #1 concluded to be Staphylococcus epidermidis. It ended up negative results for gelatinase test, casein hydrolysis, oxidase test and motility test; while positive results for catalase test, nitrate reduction and MSA plate. The phenol red broths test showed that S. epidermidis had the ability to ferment when glucose, lactose or sucrose is present; however it did not have the ability to perform fermentation with the presence of mannitol. Unknown #2 concluded to be Shigella flexneri since it tested negative