Mannitol Agar Lab Report

The identification of unknown organisms carries important ramifications that can be applied to many real world scenarios. In keeping with quality assurance beverages, food, cosmetics, and other products are frequently inspected for contaminants resulting from a presence of pathogenic bacteria. In medicine, a physician’s diagnosis and consequent treatment is largely determined from samples collected from infection sites that have been analyzed using microbial tests.

The unknown was also tested for catalase. Aerobic bacteria produce the enzyme catalase. It breaks downs hydrogen peroxide into water and oxygen. After smearing an isolated colony of the unknown on a slide, hydrogen peroxide was added and it resulted in bubbling. Bubbling suggests a positive test and if there is no bubbling, it is a negative test. A citrate lyase test was also done using citrate agar. Bacteria

|MSA Agar |For organisms that are |Isolates for mannitol fermentation |Yellow color change in |Staphylococcus aureus |

MSA agar is selective and differential medium which was used to see if the bacteria fermented mannitol or not. Selective because it selects for gram positive bacteria specifically Staph. species and it has 7.59% NaCl which means the bacteria must tolerate high concentrations of salt to grow and differential because it has a mannitol phenol red pH indicator. After running most of the test, I was able to conclude that my gram positive unknown is either Staphylococcus aureus or Staphylococcus epidermis. To differentiate between the two MSA agar was used because Staphylococcus aureus ferments mannitol and should have growth because it is a gram positive bacteria but Staphylococcus epidermis does not ferment mannitol but can have growth on the agar. So, using aseptic technique, I split the plate in half and inoculated my 2 unknowns onto MSA plate, then incubated at 37 for 24 hours. I knew my unknown A would not grow because it is a gram negative bacteria but it was inoculated as a control to make sure the test is running properly. When I came the next day, the gram-positive bacteria of my plate had growth and the color changed from red to yellow indicating that the bacteria fermented mannitol, which produced acid lowering the pH of the medium. Gram-positive bacteria had yellow color growth and it was surrounded by a yellow halo and gram-negative bacteria did not have any growth and the agar was still red in

4) A MSA plate test was run on a sample of the organism and the results were consistent with the given results for M. Luteus. The results showed a fair amount of growth on the plate, and the color of the agar around the growth remained red. The MSA test is selective in that the salt will inhibit most gram negative organisms and select for gram positives. If there is growth and the color of the agar turns yellow around the growth, this would mean that mannitol was fermented by the organism and the acid waste released by the bacterium lowered the pH around the growth. Since there was growth and no color change, the sample is said to be gram positive and unable to ferment mannitol (negative for differential). This result was also consistent with the given test results for M. Luteus.

A total of 13 tests were performed on the unknown bacteria culture #1. Two tests were inconclusive and could not be used. The first test was simply the phenylethyl alcohol agar (PAA) to check for contamination because of its selectivity towards gram-positive bacteria. The alcohol in the agar penetrates the thin peptidoglycan wall of gram-negative bacteria, which results in a slowed and stopped growth. The mannitol salts agar (MSA) is a differential test due to the mannitol sugar. It also has high amounts of salt (7.5% NaCl). If the organism can ferment the sugar, and produce acid as a result, the phenol red pH indicator dye will turn yellow due to the acidic environment. If no change occurred, then it is a negative result meaning that the bacteria

After gaining some knowledge about bacteria, we were giving an investigating bacteria growth lab to do. Our objective was to observe the conditions required for bacteria to grow and to test the effectiveness of substances that may be antibacterial, disinfecting, and or sanitizing. My group and I began our procedure by gathering all the bacteria by swabbing our necks and mouths. After this, we inoculated the culture by rubbing the bacteria on the agar, a nutrient rich gel made from sea kelp, on the bottom side of the container where we grow bacteria, the Petridish. We hoped for the results to come back with little or even no colonies and an immense zone of inhibition around the tiny circle cut out of filter paper covered in toothpaste, Neosporin, and Chlorhexidine Gluconate 4% Solution.

Research Question: How does the size of the cell affect its efficiency in exchanging substances through several ways, like diffusion?

that the bacteria are capable of growing on the agar and that there was nothing

What would it mean if a known catalase positive bacteria did not produce bubbles after the addition of H2O2? It would mean that a different strain of bacteria was used that doesn’t react to hydrogen peroxide.

The Alcohol in the agar interferes with the DNA synthesis of Gram-negative organisms which inhibits growth.

For the final test, two drops of hydrogen peroxide (H2O2) were placed on the isolated colony of the BHIA medium, observed immediate formation of bubbles, as O2 was produced indicating a positive test for catalase.

In the catalase activity there were three different procedures that led to the results that will be discussed. In the first procedure as you can see in table 1, a catalase was used to test what would occur to it when hydrogen peroxide is added. In this particular lab, potatoes were used as the catalase since they’re already buffered at pH 7.4, which will show better results than using any other catalase buffered at pH 7.0. The potato would speed up the breakdown of the hydrogen peroxide, this would result in the water and oxygen molecules being released (Mader, 2013). The cause of the oxygen molecules being released is that bubbling will begin to occur from the result of the hydrogen peroxide breaking apart (Mader, 2013). This explains why bubbles appear after a slice of potato was placed inside the test tube

Test tube 1, had 5 centimeters of distilled water and 8 centimeters of hydrogen peroxide this resulted in no bubbles present. Test tube 2, had 5 centimeters of catalase and 8 centimeters of hydrogen peroxide, 1 centimeter of bubbles were formed. Test tube 3, consisted of 7 centimeters of catalase and 8 centimeters of hydrogen peroxide, 0.5 centimeter of bubbles were formed. Although both tubes 2 and 3 reacted in bubble height, the bubbles size were different. Test tube 2’s bubbles were smaller and many more were present than test tube