Biol 251 lab 2
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What does culture media provide microorganisms?
nutrient source to allow microbes to grow
Discuss solid culture media. What makes it solid? What is the advantage for microbial growth.
- Agar (seaweed) that make the media solid in room temperatue
- provides a flat, solid surface for inoculating and growing microorganisms.
Explain four types of media by purpose and explain how blood agar can be both enrichment and
- General purpose media:allow the growth of many microorganisms which do not need special growth factors.
- Enrichment media:contains special growth factors required by some microorganisms to grow.
- Selective media:inhibit the growth of some groups of microorganisms and select for the growth of other microorganisms.
- Differential media:shows differences between microbial colonies based on their cultural characteristics.
- Blood agar:Is Differential as different patterns of hemolysis can be observed and are characteristic for certain bacteria. It's also enrichment because it contains red blood cells which are broken open by some microbes to obtain nutrients, such as heme.
Which environmental sample (s) do you expect to show the most growth? Did the expectation
fit your class results?
- Unwashed hand, unwashed broccoli, and blood agar (throat scrape and hand)
Should one be concerned to find bacterial growth in the throat or on the skin? Explain your
- We covered with bacteria all the time and mot of it is part of our body's natural flora.
Explain the results of your finger sample counts both before and after washing. Which agent
was most effective in reducing colony counts in the class? Why were there growth of colonies
even after the washing was performed?
Some microorganism are resistant to harsh environmental conditions such as soap and we can't wash away all organism.
Should one be concerned to find microorganisms on food samples? Was there a difference
between washed and unwashed fruit? Could this result in food infection? Explain your
- Yes. less cultures in washed broccoli.
- In some cases unwashed fruit can cause food infection. It depends on the type of microbes that are on the fruit.
Explain microbial growth on personal specimens?
Personal specimens such as cell phones are indirect contact with our skin and many times unwashed for long periods therefor, personal specimens are covered with microbes from our skin and the environment
Explain the difference between a bacterial colony and a microbial colony. (Hint: use the demo fungal plates to compare with yours).
- Microbial colony may be any type of microbes
- Bacterial colony is bacteria culture
Explain microbial diversity regarding the results you obtained from all of your samples.
- The SDA agar show only fungi colony because its a selective media.
- The TSA and BAP had diversity of colonies
Based on your results and the results of the rest of the class, discuss the statement
“microorganisms are ubiquitous”.
They can be found in any habitat on erth
Define aseptic technique and explain why it is important to use when handling microbial cultures.
A way to work with microbial culture that insure the environment, personal, and the cultures are not contaminated and the culture stay pure.
Free of living pathogens
List the procedures used in making a streak plate that fulfill aseptic technique.
- 1. Disinfect the work bench and wash your hands
- 2. sterilize the bacteriological loop/needle in the incinerator before collecting the culture.
- 3. Hold the btoth tube, if used, open the cup and hold it with your finger hold the opening of the broth tube in front of the incinerator and turn it to sterilize it.
- 4. Insert the bacteriological loop the the broth and collect sample of the culture close the cup and put the tube in the rack.
- 5. Open the lid of the petri plate on an angle just enough that you be able to spread the culture on the media.
- 6.close the lid of the petri plate and sterilize the bacteriological loop in the incinerator and put it back in its place
- 7.disinfect the bench and wash your hands
What is the purpose of flaming culture tubes prior to entry with loops?
To prevent microbes from the air from entering the culture
A culture with many different species of bacteria is called___________
What is the proper method of labeling and incubating Petri plates?
On the bottom
What will disinfection of the bench kill? Not kill?
- Kill vegetative cells & viruses
- Not kill endospores
What is degerming? Sanitization? Disinfecting? Sterilizing?
- Degerming: Hand washing
- Sanitization:To clean, free of dust and germs
- Disinfecting: Kill vegetative cells & viruses
- Sterilizing: kill all microbes by heat (autoclave steam or incinerator fire)
Name the instrument commonly used in microbiological laboratories to sterilize materials prior to
disposal. How is sterilization accomplished?
- Autoclave (steam)
- incinerator (burning)
Separation of one different species in a sample culture medium from each other
Separation of only one species of bacteria in culture medium
Explain how a colony forms and the relationship to the word clone.
Consist of identical cells which called clones because they duplicated and replicated from a single original cell
Which are the two common way of isolation we use in the lab?
Streak plate & pure plate
Streak plate method
With a bacteriological loop first obtain pure culture from it source and steak it in a designated area on the agar, Using aseptic technique spread the the first culture farther to separate cultures in the petri plate.
How are bacteria “thinned out” so that individual colonies are formed on the streak plate?
In streak plate we use the bacteriological and aseptic technique to keep spread out the original colony. By doing this, we keep thinning out the colonies, as we spreading a smaller amount of the culture each time we streaking the agar.
What is the purpose of describing isolated bacterial colonies?
Isolation of bacterial colonies allow us to separate species of bacteria and grow it as pure culture so we can study this particular bacteria
Why is it important to limit the quantity of cells used to prepare a negative stain?
It will able us to see individual bacteria. If we use large quantity the bacteria will overlap and it will be hard to identify its shape
What causes a stain to adhere to bacterial cells? Why did the cells not stain with negative dye?
- Positive charge chemical cause stain to adhere to bacteria. because bacteria is negatively charged (due to the teichoic acid on Gram positive bacteria, and the lipopolysaccharide on the Gram negative bacteria)
- Negative dye is negatively charged due to chromogen
What are the practical uses of a negative stain for studying bacteria?
for observing morphology, size, and arrangement of bacterial cells
Different shapes of bacteria
What is the purpose of determining the shape and arrangement of a bacterial culture?
To allow us to tell the different between species of bacteria (each species has its own shape and organization)
A bacterium is viewed on a slide using the microscope. It is spherical and arranged in twos.
What is the classification of their bacteria?
Material from a bacterial culture is stained and viewed on a slide. Long rods and very short
coccobacillary rods are observed. Give an explanation.
Pleomorphism: A variety of shapes seen in a given sample (slide)
What is one type of culture medium that may have an effect on the shape and arrangement?
Broth medium: Sometimes microorganisms take odd shapes in broth medium such as very long rods or cocci appear as single, pair and chains.
What is the measurement used for most bacteria? What is this measurement?
Micrometer: also expressed as μm, 10-6 , or a millionth of a meter.
Can rod shaped bacteria look like cocci in some cases?
Yes. sometimes if it's standing on its head or tail. we can see it as a spherical shape (cocci)
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