Kimsey Cooper Microbiology 210 Lab Final Unknown Report Section#006/ Radha
Report on Identification of Mixed Culture Unknown Lab Exercise 33 Introduction
The purpose of this experiment is to apply app ly the knowledge gained from the entire semester in the Microbiology Lab and apply ap ply it to be able to identify bacteria. Each student was given a tube that had a mixture of two different types of bacteria inside. The tube used in this experiment was tube number fourteen. Inside the tube was one gram negative and one gram positive organism. The bacteria of which we learned about and of which were possibilities to be inside the test tubes include: Corynebacterium xerosis, Enterococcus faecalis, Staphylococcus aureus, Staphylococcus epidermis, Clostridium perfringens, Enterobacter aerogenes, Pseudomonas aeruginosa, Neisseria flavescens, Proteus vulgaris, and Moraxella catarrhalis. The organisms in the test tubes must be streaked for isolation for oxygen requirements and followed with additional tests based on results. Materials and Methods
The first steps taken in lab were to conduct co nduct a gram stain from the organisms o rganisms in the mixed culture using the techniques and steps in exercise seven. Using aseptic techniques from exercise 5 in the lab manual, I then inoculated the mixed culture onto two Tryptic Soy Agar, TSA, plates and incubated them for 24 hours in 37C in both aerobic and anaerobic conditions. The next week, I aseptically streaked the mixed culture from the tube again with an inoculating loop onto two different types of agar. One agar used was Columbia CNA agar with 5% sheep’s blood for gram positive organisms and the other agar was MacConkey agar, MAC. I inoculated both plates for 24 hours in 37C. After that, I aseptically conducted another gram stain test using lab exercise seven to be sure of the morphology of my organisms. On the CNA agar I checked for hemolysis and on the MAC agar I checked for a difference in colony color. The next route I took was for gram positive organisms. For the gram positive organisms I first conducted a Carbohydrate Fermentation and Hydrogen Sulfide production test. I used Triple Sugar Iron, TSI, agar slants. I aseptically streaked the top of the agar aga r slant and stab inoculated the agar ¾ of the way down. I then incubated it for 24 hours at 37C. The next test I conducted was the Catalase test. For this test I needed two clean glass slides and a bottle of 3% H2O2. I aseptically mixed a bacterial colony onto a clean glass slide with a drop of water. Then I put one or two drops of % H2O2 directly on top of the organism and watched for bubbling. Another
test that I conducted was on the Mannitol Salt Agar, MSA. For this test I aseptically streaked for isolation and incubated the agar for 24 hours at 37C. After that I conducted a Coagulase test. This test used citrated rabbit plasma as the medium. I aseptically inoculated a loop full of the bacteria into the tube and inoculated it for 24 hours in 37C. Finally, the last test I conducted for the gram p ositive organisms was the DNase test. This test was for my organism because it was Catalase p ositive. For this test I aseptically heavily spot-inoculated my organism onto two methyl green agar plates and incubated for 24 hours in 37C. For my gram negative organisms, I conducted totally different tests. The first test I conducted was the Oxidase test. For this test I aseptically transferred an individual bacterial colony onto a glass slide and added a drop of water, and mixed them together. I then transferred with my loop a small amount o nto the oxidase test strip and the results were instantaneous. The next tests I conducted were more complicated and known as the Methyl Red Vogues Proskauer, MRVP, tests. The first step for this test was to aseptically transfer part of my bacterial colony into a broth tube and incubate for 48 hours at 37C. After that, I transferred 2.5 mL of the MRVP results to a clean test tube and added ad ded 0.6mL of α-naphthol and 0.2 mL of 40% Potassium Hydroxide to the solution. I vortexed the solution and added 5 drops of Methyl Red indicator and waited for a color change. After that test I conducted the IMVic Series of tests. This series also included the MRVP test. First came the Indole test. For this test I used the Sulfide-Indole-Motility deep agar, SIM, I aseptically stab inoculated the medium ¾ of the way down and incubated for 24 hours at 37C. After that I added 5-10 drops of Kovac’s Reagent and observed for a color change. The next test out of that series I conducted was the Simmons Citrate test. For this test I used the Simmon’s Citrate agar and I aseptically streaked the top of the slant and incubated for 24 hours at 37C. After this test I conducted the Urease test. For this test I used the urea agar slants. I aseptically streaked the agar on the top of the surface and incubated for 24 hours at 37C. The last test I conducted for my gram negative organism was the Nirtrate Reductase test. For this test I aseptically inoculated the nitrate broth with my organism and incubated the tubes for 48 hours at 37C. After that I added 5-10 drops of sulfanilic acid and α-naphthylamine to the tube for a color change. I did not have to add the zinc dust. Results
The results for my gram positive bacteria were first of all, gram positive cocci. The results from the CNA agar showed that I had γ hemolysis and I saw no zones of clearance. The results that I obtained from the TSI slant were KA--. This means that after incubation, the slant of the agar turned pink (alkaline), the butt of the agar turned yellow (acidic), and the butt of the agar did not have any cracking or any blackening in the medium. The results for the Catalase test were a bubbling over the bacteria on the glass slide which means a positive reaction for catalase. The results for the MSA were negative for mannitol fermentation. The colonies remained translucent. The results for the Coagulase test negative and no n o clotting was found in the citrated rabbit plasma. Finally,
the results for the DNase test were negative as well. There was no zone of clearance around the spot inoculated bacteria. The results for my gram negative bacteria were first of all, g ram negative rods. The results from the MAC agar were negative n egative and I the colonies remained translucent. The results I obtained from the oxidase test were positive. The end of the test strip turned to a blueish/ purple color. The results for the Methyl Red test were positive and the medium turned a red color. co lor. The results for the Vogues Proskauer test were negative an d the medium did not impart a rose color. The results for the Indole test were positive and the medium turned a cherry che rry red color. The results for the Simmon’s Citrate test were positive for citrate permease and the medium changed from green to blue after incubation. The results for the Urease test were positive as well and the agar changed c hanged from a salmon-orange to a fuchsia fuchsia color. The final test I conducted was the Nitrate Reductase test. The results for this test were positive as well. The liquid broth turned red and created a red precipitate. Discussion
I will now discuss the purpose of inoculating all of the tests chosen for my gram positive organism. The first test conducted was on the CNA agar. This tested for the hemolysis pattern of my organism. The agar plate showed no zone of clearance and thus resulted in γ hemolysis. The purpose of conducting c onducting this test is because it enabled me to differentiate between the degrees of which the hemolysins lysed red blood cells. The incubation times for all of the organisms for 24 hours and the temperature at 37C is important because this is the optimal temperature to maintain agar state and also the perfect temperature that provides the right conditions for most microbial growth. In these tests, most of the incubation times and temperatures were the same for basically the same reasons. The second test conducted was on the TSI agar. This agar differentiates between the ability of organisms to ferment glucose, sucrose, or lactose and to liberate hydrogen sulfide gas from sodium thiosulfate. My gram positive organism was KA- - which meant that the slant was alkaline (pink), the butt was acidic (yellow), and it did not liberate the gas (were no cracks in medium). These results showed that my organism ferments glucose only. The third test conducted was the Catalase test. This test was to check for the presence of the catalyst catalase which wh ich liberates molecular oxygen. This catalyst is necessary for organisms to be able to survive in aerobic conditions. After the experiment, it was seen that my gram positive organism did in fact bubble, and utilize catalase. The fourth test conducted was on the MSA agar. This test was conducted for the purpose of selective and differential halophiles. It is based on mannitol fermentation. The phenol-red indicator helps to identify the bacteria. My colonies were shown not to ferment mannitol and they remained translucent. The fifth test conducted was the Coagulase test. The coagulase test is important for distinguishing between species of Staphylococci that a re catalase positive, which is why I conducted it. Coagulase is an extracellular protein involved in blood clotting which is why the rabbit plasma was provided as the medium. The plasma is a source of fibrinogen, citrate and EDTA which are needed to form clots. My organism did not form a clot and an d therefore was negative. The last test conducted con ducted for
my gram positive bacteria was the DNase test. This test is also conducted for catalase positive organisms. DNases aid in the spread of b acteria throughout tissues. The soy and peptones in the media provide p rovide nutrients and the sodium chloride provides the osmotic equilibrium for this test. The 0.2% polymerized DNA and methyl green gives the medium a 7.5 pH. The DNase positive organisms produce a zone of clearing around the organism. My organism did not produce that and therefore does not contain DNase. Based on all of the results from these tests, my conclusion is that my gram positive cocci organism is, Staphylococcus Epidermis. I will now discuss the purpose of inoculating all of the tests chosen for my gram negative organism. The first test conducted was o n the MAC agar. This tested for the organism’s ability to ferment lactose. The neutral red indicator serves to contrast the lactose-fermenting from the non lactose-fermenting organisms. I observed that my bacterial colonies remained translucent and the medium stayed a redish/ purple color. This result means that my organism does not ferment lactose. The incubation times for all of the organisms for 24 hours and the temperature at 37C is important because this is the optimal temperature to maintain agar state and also the perfect temperature that provides the right conditions for most microbial growth. The second test conducted was the Oxidase test. This test was looking for the p resence of cytochrome c oxidase which is important in the determination of aerobic cond itions. Without this enzyme, an organism cannot survive around oxygen. If the organism is positive for this enzyme, the enzyme oxidizes and produces indophenol indophen ol blue which causes the test strip to turn blueish/ purple. I observed this reaction so my organism utilizes oxidase an d is aerobic. The second test I performed was the MRVP test. This test differentiates between organisms by detecting fermentative end-products following growth in a buffered peptone- glucose broth. In the Methyl Red test, the low pH of 4 is indicated by a red medium. In the Vogues Proskauer test, acetonin is shown by imparting a rose color to the medium after addition of 40% 40 % KOH. My organism tested positive for the mixed-acid fermentation with the red color, but tested negative for the 2,3-butanediol fermentation. This test needed to be incubated for 48 hours instead of 24 hours to allow for extra time for growth of the bacteria and because it is a broth medium. However, it was incubated at the same temperature. The third test conducted was the Indole test. This test was performed to detect the presence of tryptophanase which hydrolyzed tryptophan into indole, pyruvic acid, and ammonia. The medium contains peptones rich in tryptophan and the Kovac’s Reagent allows for detection of production of indole as the waste product. A positive reaction, which is what I obtained, results in the medium turning a cherry red color. A second result from the SIM deep agar is used to test for cysteine desulfurase or thiosulfate reductase which produces hydrogen sulfide gas and a blackening color. A third result is testing for motile bacteria and produces cracks in the agar. My organism did not produce the gas and was not motile. The fourth test conducted was the Simmon’s Citrate test which determines if the organism can use citrate as the sole source of its carbon. It also tests for the presence of citrate permease. To detect for a pH shift, which is an indicator of the enzyme, bromthymol blue is added to the medium. The agar changes from a green to blue color if the enzyme is present which is what I observed in my test. The fifth test I conducted was the Urease test. The urease test detects the degradation of proteins, and the utilization u tilization of
this as a nitrogen source. If urea is present, alkaline ammonia accumulate and rises the pH turning it from salmon-orange to fuchsia which is what I observed. The last test conducted for my gram negative organism was the Nitrate Reductase test. This test was looking for the utilization of the enzyme enz yme nitrate reductase. This enzyme allows for the organism to undergo the nitrogen cycle and utilize ammonia as their nitrogen source. The nitrogen broth used contains nutrients that contain KNO3 as the source of nitrate. Durham tubes also trap the nitrogen gas produced during the reaction. The medium is evaluated for the presence of reduced forms of nitrates by adding the nitrate reagent A and B. If nitrates are present, the broth turns a red color and produces a red precipitate. This is the reaction that I found. This test was also incubated for 48 hours h ours compared to 24 hours because it was a broth and it allowed for the extra time for the reactions. It was still incubated at 37C. From all of these tests I concluded that my gram negative bacillus organism is, Pseudomonas is, Pseudomonas Aeruginosa The purpose for conducting this experiment was obtained. Both organisms were correctly identified and all of the skills learned throughout the semester in lab were put to use in determining the individual bacteria bac teria of the mixed culture. Some sources of error that may have occurred would definitely be in the aseptic techniques performed. Any number of contaminants may have gotten into the tests and slightly messed up the results. Another possible source of error would be that lab was only held once a week and results were not readily available to look at and describe by the specified incubation incuba tion periods.
