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Lab 4 Selective Media & Agar BIO250L”

Student Na

e: Click here to enter text.
Access Code (located on the underside of the lid of your lab kit):

“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 ingredients that make up the chemical media are know

and can be identified and quantity known such a medium is use to determine the least

amount of nutrients that a microbe needs to survive In chemically complex media the

chemical composition is unknown.the ingredients in this media have an organic origin for

instance, blood, and animal or human tissue can be added to a culture to enable a

pathogen to grow. The reason these organic ingredients are added is because the

pathogen is already know to grow in an animal or a human being

2. Why is differential media typically inoculated with isolated colonies that have been previously

cultured on general growth media?

Differential media is used in previously isolated colonies to identify specific microbes on

basis of the characteristics of that mircorogranism. One example is how agar can

differentiate between hemolytic and non hemolytic bacteria

–

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.

In the case where a microbe is resistant to an antibiotic, selective test can and have

been used on a culture that is already resistant to anti-biotic.this allows for the cells that

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Lab 4 Selective Media & Agar BIO250L”
have already grown a resistance to the antibiotic to be identified and marked. This was

done to cells that were resistant to neomycin. In a differential test, pin points the

presenceof a certain organism this makes it possible to eliminate this organism as soon

as it has been spoted https://bio.libretexts.org/Bookshelves/Microbiology/Book

%3A_Microbiology_(Boundless)/6%3A_Culturing_Microorganisms/6.3%3A_Culturing_B

acteria/6.3C%3A_Selective_and_Differential_Media

“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
Yes no y

B
Yes yes- yes-

C
Yes y- -yes

D
No 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.)

Because of the presence of Amylase which is needed to digest starch in the mouth

2. What are some other potential sources of starch-degrading bacteria?

potential sources of starch degrading bacteria can be found in fermenting food like hops

in the process of beer making, kombucha, and milk kefir

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Lab 4 Selective Media & Agar BIO250L”
3. What component makes starch agar selective for starch-degrading bacteria?

Because starch agar usually has in it the bacteria that degrades starch, it makes a good

selective media because it is will act as a selective nutrient to promote the growth of this

degrading bacteria

4. Why were each of the following steps performed in this experiment?

a. Serial dilution:

To act as a dilutant of microbes so that they it is possible to count them The

stock solution has too many microbes to be effective in the other process of

microbe identification thought isolation.-

b. Growth on the nutrient agar plates:

this was for purpose of bacteria isolation then transfer a single type of bacteria

hence being able to identify them

c. Streak on the starch agar plates:

to introduce a different media that would identify the presence of starch

degrading bacteria

Insert a photo of your plates. Include your name and access code handwritten in the background of

your photo.

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Lab 4 Selective Media & Agar BIO250L”

“EXPERIMENT 2: Selection and Differentiation of Body Inhabiting Gram-Positive Bacteria

Data Tables
Table 4: Experiment 2 MSA Growth Observations

Surface
Tested

Growth (Yes
or No) –

Nutrient Agar

Growth (Yes or
No) – MSA Agar

MSA color around
colonies (Red or

Yellow)

Other
Observations

Face Yes Yes Yellow Cfogged up –

nose Yes Yes Yellow
Thick and
droppy-

Controller Yes Yes Yellow
Many organisms

–

Control No No Select one: clear –

Post-Lab Questions
1. What chemical in MSA confers selectivity? How?

The HIGH concentration of sodium chloride allows for the growth of microgranisms like

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Lab 4 Selective Media & Agar BIO250L”
staphylococcus which while other types of this organism cannot ferment MSA, The

staphylococcus does

2. What chemical makes MSA differential? How?

Sugar mannitol is the differential chemical presence of organisms that can use sugar

mannitol as a source of nutrition will ferment it causing to become acidic which in turn

change the ph .This change in ph accounts for color change when this kind of bacteria is

present.-

3. Why are the nutrient agar plates used in this experiment?

The agar plates are serve to help compare the growth rates 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 color which serves as confirmation that there were bacteria

that allowed for MSA to ferment hence making the set up acidic. The acidity is what

made the co

Insert a photo of your plates. Include your name and access code handwritten in the background of
your photo.
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Lab 4 Selective Media & Agar BIO250L”

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

CTap water- Yes Select one: Cpretty clean-

Spring water – Yes Select one: C pure and seems extremely safe –

Pond water – Yes Select one: extremely 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 .

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Lab 4 Selective Media & Agar BIO250L”
2. What ingredient(s) makes MacConkey agar differential?

MacCoknkey agar is a differential Because it contains lactose. When bacteria works on

lactose to break it down, there is a release of acidic waste which changes the ph and

gives it the red-pink look

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?

Salmonella typhimurium- i will ferment lactose that is on the MacConkey agar.E-coli is

also a lactose fermenting bacteria.

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, Helicobacter are non lactose fermenting bacteria

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 variation of MacConkey Agar without Crystal Violet it detects Gram-Positive

cocci.- There there is MacConkey Agar that has Violet it is used to control t bacteria

like Proteus which interfere with other results.:

6. How would you verify that the colonies that grew on a MacConkey agar plate were Gram-

negative?

Crystal violet and bile salts usage helps identify gram negative colonies because they

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Lab 4 Selective Media & Agar BIO250L”
stop the growth of gram-positive bacteria thus all that is left in the sample are gram

negative bacteria

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 complex chemically defined media because within it there

ingredients that propagate the growth of some bacteria while other ingredients inhibit the

growth of othes.

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Lab 4 Selective Media & Agar BIO250L”
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Lab

Culturing & Aseptic Technique

PRE-LAB QUESTIONS

. Proper aseptic technique is crucial to ensuring growth of pure bacterial colonies. What is

one experimental way you can test your practices to confirm that you are using proper

aseptic technique?

a. One way I could test to see if my aseptic technique is working would be when

transferring the bacteria from one plate to another, if there are bacteria on the

plate that I didn’t place there, I will know there was a contamination from either

the air or the method of transfer.

2. In a laboratory setting, what are three ways you can properly sterilize culturing

equipment?

a. Wet heat, such as an autoclave, is one way to sterilize equipment. You can also

use dry heat such as a flame or by baking the equipment first. Another way you

can sterilize equipment is by using chemical solvents like bleach.

. For each inoculation tool, give one scenario in which use of that tool would be

appropriate.

a. Inoculation loops would be used when transferring microbes from one plate to

another. Sterile cotton swabs are usually used when collecting microbial samples

from surfaces, Inoculation needles are used when collecting microbes from a

defined region. Sterile plate spreaders are used to transfer an even bacterial

lawn.

4. Why don’t microorganisms in cultures exhibit constant exponential growth? What are some steps you could take to extend the lifespan of a microbial culture?

a. Microbes growing on the medium eventually will either run out of nutrients, become poisoned by the buildup of waste, or alter the pH of their environment so much that they can no longer continue to survive. In order to extend the lifespan of a microbial culture, I would replenish growth medium through transfer to a new plate or replace the liquid medium

5. Using a textbook or a reputable online source, describe how lab cultures are maintained in a continual pattern of growth. Focus particularly on those used in biotechnology, such as E. coli, which is used to make human insulin.

a. Growth media helps to maintain a continual pattern of growth. Some common growth media for microorganisms are nutrient broths and agar plates; specialized media are required for some microorganisms

6. Which of these has a constant growth pattern: an open system or a closed system?

a. An open system provides unlimited nutrient allowing microbes to grow constantly. There is a limited nutrient in a closed system, where microbes no longer continue to grow.

7. A human patient represents what kind of system for bacterial infections?

a. A human represents an open system for bacterial infections. We continuously get rid of waste products while consuming fresh nutrients, providing bacteria to grow

8. You’re a physician trying to isolate bacterial colonies from the human gut in attempt to diagnose a gastrointestinal infection. You streak your sample on a growth media containing glucose, amino acids, and salts that contain both sulfur and phosphorous with a pH of 7. You incubate the plates in aerobic conditions at 37 ˚C for three days, at which point you can see clear bacterial colonies forming on the plate. Would you feel confident in stating that you had successfully cultured all the bacteria from your gut sample? Why or why not?

a. There may be bacteria that was not able to grow into a culture because they cannot survive in the pH or the temperature. Also, some colonies take longer than 3 days to be visible.

9. Do some research and try to identify one to three types of microbes cultured on your plates. Using any resources available to you (i.e., a textbook or internet sources such as the CDC website), look up what bacteria are usually found on the areas from which you obtained your samples and the morphological characteristics of their colonies. Describe what morphological traits (i.e., size, shape, arrangement, color, margin,

etc.)

led to your hypothesized species identification. Be as specific as possible in the microbe type.

a… Shoe from work; Besides E. coli, which is known to cause intestinal and urinary tract infections, the soles of the shoes picked up Klebsiella pneumonia bacteria, a source of wound and bloodstream infections as well as pneumonia, and Serratia ficaria, a rare cause of infections in the respiratory tract and wounds. Yikes! Morphological Traits: Size: Large. Shape: Round (Coccus), morphed (Staphylococcus) (streptococcus), sporadic colonies of (E-Coli Salmonella), Color: Opaque/Tan, Margin: Lobate with raised elevation, and circular/irregular form.

10..For the colonies hypothesized in Question 1, specify which plate and source the microbes came from. Are you surprised to find this type of microbe on this surface? (5 points) Plate #1 and Plate #3 had the most growth with different colonies of bacteria as well as E-coli

a.. I used plate #1 (My Shoe from work) because it mortified me to know how disgusting and dangerous the bottom of my shoes are. I clean and disinfect them all the time, but the sample was taken after one 12hr night shift. Yes, I am very surprised to find these types of microbes on the surface of my shoe. Although this is an expected outcome due to the fact I work in a very busy hospital setting.

11..Looking at your control, did you perform proper aseptic technique or were your plates contaminated? If contamination did occur, list the possible sources and how you can prevent contamination in the future.

a… My plate looked a little bit contaminated. The possible source was that the cotton swab was not sterol even before I opened it form the package, or the prepackaged deionized water that I dipped the cotton swab in wasn’t sterol. I came to these conclusions because in experiment #2 my control samples were clear of contamination.

12.. Was there a large risk for airborne contamination of your experimental plates? Based on the colonies that grew on your plates, do you think any of your experiment plates received airborne contamination?

a… Yes, there is usually a large risk for airborne contamination in these experiments, but this was not the case of my experiment. I had No Growth, No Color, No Amount, No Shape. Clean Clear Plate. Which tells me my experiment was successful.

13.. Were all of your colony transfers successful? Explain what could have been the cause of any unsuccessful transfers.

a.. Yes, all of my colony transfers were successful.

14.. Did you have any growth that was different in appearance from the initial plates? What might account for any differences in growth on the transfer plate/tube?

a.. Yes, all my plates had different growth appearances from the initial plate #1 sample. I believe the differences in growth and shape were due primarily to the different method of transfer used in this experiment. The purpose was to isolate different individual colonies.

15.. Describe why an unsuccessful transfer or growth of the transfer plate/tube differing from the initial plates would be a problem if this experiment were placed in a larger context (i.e., only one step in a longer experiment).

a.. An unsuccessful transfer will show the absence of colonies on the plate and in the stab tube. Overheating can be a factor that can destroy the organism and the morphology of the cell can also be changed in an unsuccessful transfer.

16.. Do some research and describe two or three scenarios in which it would be preferable to use a stab tube vs. a growth plate. (Hint: What do bacteria use to help them move? Can motility be used to help identify many medically important pathogenic bacteria such as the Enterobacteriaceae?)

a. An inoculation needle is used to isolate individual colonies, the needle picks up less microbes, so there is less of a chance of picking up more than one microorganism/bacterium vs. a growth plate sample. The most common methods of transport for bacteria is with the aid of flagella. Many bacteria also use appendages called Pilli to move along a surface. Species are identified in the clinical laboratory by morphological traits and biochemical tests, some of which are supplemented by serologic assessments (e.g., identification of Salmonella and Shigella species). Because of differences in pathogenicity (Escherichia coli) or the necessity to characterize a disease outbreak (Vibrio cholerae, methicillin-resistant Staphylococcus aureus), strains of medical interest are often classified below the species level by serology or identification of toxins. Yes, motility can be used to identify medically important pathogenic bacteria. https://www.ncbi.nlm.nih.gov/books/NBK8406/

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Table 1: Experiment 1 Colony Growth

Plate Number Source Growth (color, amount, shape,

etc.)

1 Cellphone

There are many colonies all the

same yellowish white color. They

are circular with a translucent look

on the outside and opaquer in the

middle

2 Foot

Many colonies, some are yellow,

and some are white. All the

colonies are round and small

3 Table

There are 3 noticeably different

colors. There is white, light yellow,

and a deep yellow or gold. Half of

the culture are very small round

and defined circles; the other half

are very spread out and in almost

a water spill shape

4 Airborne Contamination

There are two different colors,

white, and translucent yellow. The

colonies are very spread out unlike

the first 3 plates. The white

colonies are in a circle, and the

yellow colonies do not have a

distinct shape.

Control

No growth

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Table 2: Initial Reserved Plate Colony Growth Observations

Plate Sample Sample Appearance (morphology, etc.)

1 White, circular, opaque

2 Gold/Orange, smeared look, translucent

3 Light yellow, circular, opaque

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Table 3: Final Plate and Stab Tube Growth Observations

Sample Form Growth

(yes or no)

Same Appearance

as Initial Plate?

(Yes or No)

Successful

Transfer?

(Yes or No)

Plate Yes No Yes

Stab Tube Yes Yes Yes

2
Plate Yes No Yes

Stab Tube No Yes No

Plate Yes Yes Yes

Stab Tube Yes Yes Yes
Control

Plate No Yes Yes

Stab Tube No Yes Yes

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“Lab

Culturing & Aseptic Technique BIO2

0L”

Student Name: Click here to enter text.

Access Code (located on the underside of the lid of your lab kit): Click here to enter text.

“Pre-Lab Questions”

. Proper aseptic technique is crucial to ensuring growth of pure bacterial colonies. What is one experimental way you can test your practices to confirm that you are using proper aseptic technique?
While moving bacteria from a given plate to the other, one way to whether if the aseptic method is working properly is to check for bacteria on the plate that was done not put there. If the bacteria is in the plate, I will absolutely identify there was infection from the air or the way of moving.

2. In a laboratory setting, what are three ways you can properly sterilize culturing equipment?

a. The ways to properly sterilize equipement is application of wet heat, like an autoclave.

b. Dry heat, such as a flame, can also be utilized, or the apparatus can be baked beforehand.

c. Chemical solvents like bleachcan also be utilized to sterilize culturing equipment.

. For each inoculation tool, give one scenario in which use of that tool would be appropriate.
While moving microbes from one bowl to another, immunization loops may used. Innoculation needles are used to gather germs from a designated zone and sterile cotton swabs are used to collects microbial from surfaces. To transmit an even bacterial lawn, sterile plate apreaders are used.

. Why don’t microorganisms in cultures exhibit constant exponential growth? What are some steps you could take to extend the lifespan of a microbial culture?
Microorganisms budding on the agent will eventually exhaust nutrients, get polluted by waste buildup, or modify the PH of its environments to the extent where they cannot thrive. To extend life of a bacterial culture, I would replace the growth media by moving it to a new plate or replace the liquid agent.

Growth

culture contributes in the maintenance of a steady pattern of growth. Nutrient potages and agar bowl are common microbe growth medium; nevertheless, certain germs require specific media.

6. Which of these has a constant growth pattern: an open system or a closed system?
An open system offers an unlimited source of nutrients, letting bacteria to flourish indeterminately. In a locked system, where bacteria will never grow, there is a restricted source of nutrients.

7. A human patient represents what kind of system for bacterial infections?
A person is an open system for bactierial diseases. We are contimually removing surplus while eating new nutrients, which allows bacteria to grow.

“EXPERIMENT 1: Agar

Plate

Preparation and Bacterial Inoculation

Data Tables

Table 1: Experiment 1 Colony Growth

Plate Number

Source

Growth

(Color, Amount, Shape, etc.)

CONTROL

NONE GROWTH FOUND

AIRBORNE-CONTAMINATION

SMALL WHITE ROUND GROWTH

BATHROOM DOOR KNOB

MANY SMALL AND WHITE SPOTS IN THE BOWL

TRASH CONTAINER COVER

BIG SPIDERWEB AT THE CENTER

CAR GEARSHIFT

LARGE WHITE GROWTH. IT APPEARS TO BE CONSTANT OF SNOT.

Post-Lab Questions

1. Do some research and try to identify one to three types of microbes cultured on your plates. Using any resources available to you (i.e., a textbook or internet sources such as the CDC website), look up what bacteria are usually found on the areas from which you obtained your samples and the morphological characteristics of their colonies. Describe what morphological traits (i.e., size, shape, arrangement, color, margin, etc.) led to your hypothesized species identification. Be as specific as possible in the microbe type.
For example, work shoes, in addition to E coli, which can cause intestinal and urinary tract infections, Klebsiella pneumonia bacteria, which can cause wound and bloodstream infections as well as pneumonia, and Serratia ficaria a rare cause of infections in the respiratory tract and wounds, were found on the soles of the shoes.

2. For the colonies hypothesized in Question 1, specify which plate and source the microbes came from. Are you surprised to find this type of microbe on this surface?
Plate # 1 ( work shoe) because it mortified me to know how disgusting and dangerous the bottom of my shoes are. The sample was taken from my work shoes, I am so surprised to find these types of microbes on the bottom surface of my shoe. Althought this is expected outcome due to the fact I work in a very busy office area.

3. Looking at your control, did you perform proper aseptic technique or were your plates contaminated? If contamination did occur, list the possible sources and how you can prevent contamination in the future.
My dish appeared to be polluted; The cotton swab may have been sterol free even before I opened the container, or the supplied deionized water in which I dipped the cotton swab could have been sterol free. These conclusions were reached because my control samples in experiment # 2 were free of contamination.

4. Was there a large risk for airborne contamination of your experimental plates? Based on the colonies that grew on your plates, do you think any of your experiment plates received airborne contamination?
Yes, there is normally a significant danger of airborne contamination in these tests, however that was not the case in my situation. I didn’t have any growth, color, quantity or shape. Plate should be clean and clear. Therefore my experiment was a success.

Insert a photo of your plates after incubation. Include your name and access code handwritten in the background of your photo.

“EXPERIMENT 2: Bacterial Transfer to a

Stab Tube

and an Agar Plate

Data Tables

Table 2: Initial Reserved Plate Colony Growth Observations

Plate Sample	Appearance (morphology, etc.)
Light orange, round small
A spiderweb like
Light yellowish, round milky shape, large

Table 3: Final Plate and Stab Tube Growth Observations

Sample

Form

Growth (Yes or No)

Same Appearance as Initial Plate (Yes or No)

Successful Transfer? (Yes or No)

Plate 1

Stab Tube 2

Plate

Stab Tube

Plate

Stab Tube

Control

Plate

Control

Stab Tube

Post-Lab Questions

1. Were all of your colony transfers successful? Explain what could have been the cause of any unsuccessful transfers.
Yes, All the colony transfers became successful

2. Did you have any growth that was different in appearance from the initial plates? What might account for any differences in growth on the transfer plate/tube?
Yes, all of my plates development patterns differed from the first plate # 1 sample. The changes in development and morphology, I assume, were caused mostly by the various technique of transfer utilized in this experiment. The goal was isolate several individual colonies.

3. Describe why an unsuccessful transfer or growth of the transfer plate/tube differing from the initial plates would be a problem if this experiment were placed in a larger context (i.e., only one step in a longer experiment).
The absence of colonies on the plate and in the stab tube indicates a failed transfer. In a failed transfer, overheating can be a component that kills the organism, and the shape of the cell can also be altered.

4. Do some research and describe two or three scenarios in which it would be preferable to use a stab tube vs. a growth plate. (Hint: What do bacteria use to help them move? Can motility be used to help identify many medically important pathogenic bacteria such as the Enterobacteriaceae?)
An inoculation needle is used to isolate individual colonies, the needle picks up less microbes, so there is less of a chance of picking up more than one microorganism/bacterium vs a growth plate sample. Therefore the most common methods of transport for bacteria is with the aid of flagella. Many bacteria also use appendages called Pilli to move along a surface. Species are identified in theclinical laboratory by morphological traits and biochemical tests, some of which are supplemented by serologic assessments( e.r., identification of Salmonella and Shigella species). Because of differences in pathogenicity( Escherichia coli) or the necessity to characterize a disease outbreak( Vibrio cholerae, methicillin resistant Staphylococcus aureus). Strains of medical interest are often classified below the species level by serology or identification of toxins. Yes, motility can be used to identify medically important pathogenic bacteria.

Insert a photo of your plates and stab tubes after incubation. Include your name and access code handwritten in the background of your photo.

Lab 4 Selective Media &

gar

IO250L”

Student Name:

lick here to enter text.

Access Code (located on the underside of the lid of your lab kit): Click here to enter text.

“Pre-Lab Questions”

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?

ifferential 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

YES

Sample	Growth on Starch Agar? ( Y es or No)	Clear area around colonies?	Do these bacteria contain amylase?
A			NO	Y
B				YES
C
D

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

Surface Tested

Growth (Yes or No) – Nutrient Agar

Growth (Yes or No) – MSA Agar

MSA color around colonies (Red or Yellow)

Other Observations

Face

Fogged up

Nose

Thick & Droppy

Controller

Many organisms

Crontrol

Clear

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

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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