BIOL123
LEPHON
LAB4.1correction.docxLab 4 Selective Media & Agar BIO250L”
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“Pre-Lab Questions”
1. What is the difference between chemically defined and chemically complex media? Give either a clinical or environmental research example for which each media type would be the most appropriate choice for culturing microorganisms. In chemically defined media, the chemicals that comprise the chemical media are known and can be recognized, as well as the quantity known; such a medium is used to identify the least amount nutrients that a microorganism need to thrive. The chemical composition of chemically complex medium is unknown. The components in this medium are organic. Blood and animal or human tissue, for example can be added to a culture to allow a pathogen to proliferate in animals or humans.
2. Why is differential media typically inoculated with isolated colonies that have been previously cultured on general growth media? Differential media is used to identify individual bacteria in previously isolated colonies based on the properties of that bacterium. One example is how agar can distinguish between bacteria that are hemolytic and bacteria that are not hemolytic.
3. Use a textbook or a reputable internet source (such as www.cdc.gov) to research and describe a scenario in a lab or clinical setting in which a selective and/or differential test would be necessary. When a bacterium becomes residtant to an antibiotic, a selection test may and has been used on a culture that is already resistant. This enables the cells to be used; this have already developed an antibiotic resistance that must be discovered and marked. This was performed on neomycin-resistant cells. A differential test detects the presence of a specific organism, allowing it to be eliminated as soon as it is detected.( https://bio.libretexts.org/Bookshelves)
“EXPERIMENT 1: Bioprospecting for Starch Degrading Bacteria
Data Tables
Table 3: Starch Agar and Gram Iodine Results
|
Sample |
Growth on Starch Agar? (Yes or No) |
Clear area around colonies? |
Do these bacteria contain amylase? |
|
A |
|
NO |
Y |
|
B |
|
YES |
YES |
|
C |
|
YES |
YES |
|
D |
|
NO |
NO |
Post-Lab Questions
1. Why is cow manure used as a potential source of starch-degrading bacteria? (If you are not familiar with the process of digestion in cows, use a reputable internet source to inform your answer.) Amylase, which is required to breakdown starch, is present in the mouth
2. What are some other potential sources of starch-degrading bacteria? Fermenting foods such as hops used in beer manufacturing, kombucha, and milk kefir are all possible sources of starch-degrading bacteria
3. What component makes starch agar selective for starch-degrading bacteria? Because starch agar often contains bacteria that digest starch, it makes an excellent selective medium because it acts as a selective nutrient to stimulate the development of these degrading bacterium.
4. Why were each of the following steps performed in this experiment?
a. Serial dilution: To function as a dilutant for bacteria such that they may be counted. The stock solution contains far too many microorganisms to be useful in the other procedure of microbial identification by isolation.
b. Growth on the nutrient agar plates: This was done for the goal of isolating bacteria and then transferring a single kind of bacterium so that they could be identified.
c. Streak on the starch agar plates: This was done for the goal of isolating bacteria and then transferring only one type of bacterium so that they could be identified.
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“EXPERIMENT 2: Selection and Differentiation of Body Inhabiting Gram-Positive Bacteria
Data Tables
Table 4: Experiment 2 MSA Growth Observations
Post-Lab Questions
1. What chemical in MSA confers selectivity? How? The high sodium chloride concentration promotes the development of microorganisms such as staphylococcus which other types of this organism cannot ferment MSA. The staphylococcus does.
2. What chemical makes MSA differential? How? Sugar mannitol is the difference in chemical presence between organisms that can use sugar mannitol as a source of sustenance and those that can't. Sugar mannitol ferments, causing it to become acidic, which changes the PH. When this type of bacterium is present, the ph changes, which accounts for the color shift.
3. Why are the nutrient agar plates used in this experiment? The agar plates are used to compare the rates of growth in MSA and Agar.
4. Was there any growth on you MSA plates? Did any of the colonies change the color of the MSA? What does this tell you about the bacteria taken from each area of your body? Yes, there was a change in hue, indicating that there were bacteria present that allowed MSA to ferment, causing the setup to become acidic. The acidity is what caused the cosmos to form.
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EXPERIMENT 3: Selection and Differentiation of Body Inhabiting Gram-Negative Bacteria from Liquid Samples
Data Tables
Table 5: MacConkey Agar Results
|
Sample |
Growth? (Yes or No) |
Colony Color (Clear or Red) |
Analysis |
|
TAP WATER |
|
|
CLEAN |
|
SPRING WATER |
|
|
SEEMS SAFE AND CLEAR |
|
POND WATER |
|
|
VERY DIRTY |
Experiment 3 Post-Lab Questions
1. What types of bacteria are inhibited on MacConkey agar? What ingredient(s) in MacConkey agar selects against those bacteria? MacConkey agar are inhibited by Gram positive bacteria the ingredients that allow for for selection are crystal violet and salts .
2. What ingredient(s) makes MacConkey agar differential? MacCoknkey agar is a differentiating agent. Due to the presence of lactose. When bacteria break down lactose, acidic waste is released, changing the ph and giving it the red-pink appearance.
3. Using a textbook and a reputable online source (such as the CDC), research and describe some potentially pathogenic members of the intestinal bacteria family Enterobacteriaceae. Which pathogenic species are lactose fermenters that will grow on MacConkey agar? I'll ferment the lactose on the MacConkey agar with Salmonella typhimurium. E. coli is a lactose fermenting bacterium as well.
4. Use a reputable internet source to research and describe some potentially pathogenic intestinal bacteria that do not ferment lactose that will grow on MacConkey agar. C-Legionella, Bordetella, and Helicobacter are bacteria that do not digest lactose.
5. Use a reputable internet source to research and describe what variations of MacConkey agar can be used to detect other species of bacteria. There is a MacConkey Agar variant that does not include Crystal Violet and detects Gram-Positivecocci. - There is also MacConkey Agar, which contains Violet and is used to suppress bacteria such as Proteus, which can conflict with other results.
6. How would you verify that the colonies that grew on a MacConkey agar plate were Gram-negative? The use of crystal violet and bile salts together helps to identify gram-negative bacteria. halt the development of gram-positive bacteria, leaving only gram-negative bacteria in the sample.
7. Look up the formula for MacConkey agar either in a microbiology textbook or online. Is this a chemically defined or a chemically complex media? Why is that important? MacConkey agar is a chemically defined complex medium because it contains chemicals that promote the growth of some bacteria while inhibiting the development of others.
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