microlab exam 2
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microlab exam 2
exam 2 microlab critical thinking questions
What is the component in the SIM deep tubes that makes this medium suitable to detect the production of indole by bacteria?
What organic molecule is necessary to detect mixed acid fermentation by bacteria?
why is a chemically defined medium necessary for the detection of citrate utilization by bacteria
because the citrate converts to CO2 and if the proper medium insn't there for sodium to bind and oxygen to be used, it will simply escape and you won't be able to tell
Indole test uses what to detect ph
medium for methyl red test
medium fo rvoges proskauer test
medium for citrate teset
sodium citrate, o2
what is the importance of catalase to certain bacteria?
catalyzes the destruction of peroxide
do anaerobic bacteria require catalse? explain
strict ones don't because there is not o2 present to generate the toxins
what is the substrate of the catalase reaction?
what metabolic property characterizes bactera that posses oxidase activity?
Do anaerobic bacteria require oxidase? explain
no because they don't use o2
what is the function of the test reagen in the oxidase test
it acts as an artificial substrate getting oxidized by cytochrome oxidase
the oxidase test is used to differentiate amound which groups of bacteria
those that use oxidase and those that don't
what is the purpose of the phenol red in the urea broth medium
detects the ph of the medium
when would you use the urease testq
to find bacteria that passes the enzyme urease.
why does the urea disk change color
increase in ammonia cause the phenol red to change color since ammonia is alkaline
what is the urea broth
a medium with urea and phenol red
explain what occurs during decarboxylation
decarboxylase enzyme removes a carboxyl group from an organic molecule and produces an amine with co2
why does the LDC broth or lysine iron agar turn purple when lysine is decarboxylated
the decarboxylase enzyme turns the lysin into an amine and neutralises the ph
why does the LDC medium always turn yellow regardless of the ability of the bacteria to produce lysine decarboxylase
because the fermentation of glucose raises the ph of the medium turning it yellow
why is the lysine decarboxlase tset negative if both LDC and DC broths turn purple
because it cannot be proven that the purple color is due to lysine being used
why is sterile mineral oil added to LDC test media
to preven O2 from reacting with the medium
how does the pH indicator bromcresol purple indicate a change in ph
by chaning from yellow to purple or vice versa
what is the purpose of the ferric chloride in the phenylaline deamination test
it reacts iwth phenylpyruvic acid which is the product of phenylaamine danimation
name some bacteria that can deaminate phenylalanine
p. vulgarus, proteus, morganella, providencia
describe the process of deamination
the enzyme catalyzes the removal of an amino group from phenylalanine. this produces orgainc acids water and ammonia
describe the color of an uninoculated tube of phenlalanine agar
from your results which bacteria are negative for nitrate reduction? which are positive?
Negative are s. epidermus. all the others are positvie
why is the development of a red color a negative test when zinc is added?
because the zinc reacts with the no2 to push it back to no3
how would you perform a complete test for the presence of nitrate reduction?
ad the a and b and then zince to see if it changes back