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Lab Practical #3
Microbiology lab practical #3
Terms in this set (63)
What is the name of the carbohydrate in the MSA media?
Why is mannitol in the MSA media?
It provides the substrate for fermentation and makes the medium differential.
Why is sodium chloride in the MSA media?
It makes the medium selective because its concentration is high enough to dehydrate and kill most bacteria.
What is the pH indicator in MSA media?
Why do the Staphyloccoci thrive in a high salt concentration? (MSA medium)
They're able to adapt to salty habitats such as human skin.
Which organism ferments mannitol?
What is the application of the MSA exercise?
Mannitol Salt Agar is used for isolation and differentiation of Staphylococcus aureus.
of, relating to, or occurring in the intestine.
Define selective media
A media that selects for growth of one type of organism, while inhibiting the growth of others.
In MacConkey Agar Lactose is the
In MacConkey Agar Bile salts and Crystal Violet
inhibit the growth of gram positive bacteria.
In MacConkey Agar, Natural Red Dye is
the pH indicator.
Lactose fermentation turns the media red. Why?
Acid accumulates from lactose fermentation.
What is the application of MacConkey Agar?
MacConkey Agar is used to isolate and differentiate members of the Enterobacteriaceac based on the ability to ferment lactose.
Define complex media
A medium in which at least one nutritional ingredient is of unknown composition or amount. Media with any plant or animal extract are always complex.
What is the function of peptone in the EMB agar?
It provides a complex mixture of carbon, nitrogen, and other nutritional components.
What are the two sugars in the EMB agar?
Lactose and Sucrose.
What are the functions of the sugars in the EMB agar?
They encourage growth of enteric bacteria and to differentiate them based on color reactions created when combined with the dyes.
What are the two dyes in the EMB media?
Eosin Y and Methylene Blue
What are the functions of the two dyes in the EMB agar?
inhibit the growth of Gram positive organisms and they react with vigorous lactose fermenters and (in acidic environment) they turn the growth dark purple or black.
Why would the organism, E. Coli, turn dark or metallic green in EMB agar?
It's a vigorous fermenter and releases acid into the agar.
What is the application of the EMB agar?
EMB agar is used for isolation of fecal coliforms.
In MRVP ____ provides protein.
In MRVP ____ is the fermentable carbohydrate.
What is the buffer in the MRVP medium?
The MR test is designed to detect _____.
Organisms capable of performing a mixed acid fermentation, which overcomes the phosphate buffer in the medium and lowers the pH.
Define mixed acid fermentation.
Accummulation of a variety of acids and a significant drop in the pH of the medium. Less than 4.4.
Methyl Red is red at pH ____ and yellow at pH ____.
Red at 4.4
Yellow at 6.2
The VP test was designed for
organisms that are able to ferment glucose, but quickly convert their acid products to acetoin and 2,3-butanediol.
What is the application of the MRVP exercise?
Used to distinguish between members of the family Enterobacteriaceac and differentiate them from other Gram negative rods.
In the catalase test, how does flavoprotein produce toxins?
By bypassing the next carrier in the chain and transfer electrons directly to oxygen.
Name the two toxins produced in catalase.
Hydrogen peroxide(H2O2) and superoxide radical(O2)
What is the function of superoxide dismutase in catalase test?
It catalyzes conversions of superoxide radicals (the more lethal of the two compounds) to hydrogen peroxide.
_____ converts hydrogen peroxide into water and _____.
Catalase; gaseous oxygen.
What is the application of the Catalase test?
Used to identify organisms that produce the enzyme catalase.
Define utilization media
Highly defined formulations designed to differentiate organisms based on their ability to grow when an essential nutrient is strictly limited.
What is the function of sodium citrate in the citrate media
It's the only carbon-containing compound.
What supplies the sole nitrogen source in the citrate media?
Ammonium phosphate ions.
What is the pH indicator and it's color and ranges in the citrate media.
Bromthymol Blue; Green at pH 6.9 and blue at pH 7.6
What specifically happens for the media to go from green to blue?
Bacteria that survive in the medium and utilize the citrate also convert the ammonium phosphate to ammonia and ammonium hydroxide, both of which tend to alkalinize the agar. As the pH goes up, it changes from green to blue.
How is the citrate test inoculated?
On a citrate slant typically inoculated lightly with an inoculating needle rather than a loop.
What is the application of the Citrate test?
To determine the ability of an organism to use citrate as its sole source of carbon; distinguish between members of the family Enterobacteriaceac and differentiate them from other Gram negative rods.
What are the three sugars in the TSI media?
Glucose, lactose, and sucrose
What is the function of animal protein in the TSI media?
It's the source of carbon.
What are the two sources of oxidized sulfure?
Ferrous sulfur and sodium thiosulfate.
What is the pH indicator of TSI media?
What is the hydrogen sulfide indicator in the TSI media?
as glucose diminshes, the organisms located in the aerobic region (slant) will begin to break down available amino acids, producing NH3 and raising the pH.
When interpreting a tube, if the color of the butt is obscured, what would you assume the slant color to be?(TSI agar)
What is the application of the TSI agar?
TSIA are primarily used to differentiate members of Enterobacteriaceac and to distinguish them from other Gram negative rods.
Define zone of inhibition
zone on an agar plate where bacterial growth won't develop in the area where it is susceptible to the agent.
likely or liable to be influenced or charmed by a particular thing
the ability to not be affected by something especially adversely.
a naturally produced substance made from one microorganism to kill another microorganism.
What organism, according to the lab manual, produces bacitracin?
How does bacitracin work
it inhibits bacterial cell wall synthesis
What is the application of Bacitracin Susceptibility Test?
The bacitracin test is used to differentiate and presumptively identify beta-hemolytic streptococci.
Define hemolytic ability-
ability to lyse red blood cells and hemoglobin
Bloos agar is used to detect the hemolytic ability of
Gram positive organisms, typically Streptococcus species.
exotoxins capable of destroying red blood cells and hemoglobin.
What does alpha hemolytic mean and what would it look like?
partial destruction of red blood cells; greenish discoloration of the agar around the colonies.
What does beta hemolytic mean and what would it look like?
complete destruction of red blood cells and hemoglobin, results in a clearing of the medium around colonies.
What is the application of the Blood agar test?
Blood agar is used for isolation and cultivation of many types of fastidious "picky" bacteria. Especially streptococcus.
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