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MCB2010L Final Exam Questions With
Correct Answers
What is fluid thioglycollate broth (FTB)? - answer✔It is prepared as a basic medium or with a
variety of substances, depending on the needs of the organism being cultivated. It is appropriate
for a broad variety of aerobic and anaerobic, and fastidious (requiring specific nutrients to grow)
and non fastidious organisms. Well adapted for strict anaerobes and microaerophiles.
What are the key components of FTB? - answer✔Yeast extract, pancreatic digest of casein,
dextrose, sodium thioglycollate, L-cystine, and resazurin.
-yeast extract and casein provide nutrients
-sodium thioglycollate and L-cystine reduce oxygen to water
-resazurin is an indicator of oxygen
What purpose does resazurin dye serve in FTB? - answer✔Oxygen indicator. Pink when
oxidized, colorless when reduced.
What is the application of FTB? - answer✔Can be modified to promote growth of a wide variety
of fastidious to non fastidious microorganisms. It can be used to illustrate microbial growth
representing all levels of oxygen tolerance. However, it generally is associated with the
cultivation of anaerobic and microaerophilic bacteria.
Why is it preferred to use fresh FTB medium over old medium? - answer✔Oxygen removed
during autoclaving will diffuse back into the medium as the tubes cool to room temperature. This
produces a gradient of concentrations from aerobic (comparable to air) at the top to anaerobic at
the bottom. Fresh media will appear clear to straw coloured with a pink region at the top, where
the dye has become oxidized. The use of old medium will cause the aerobic region of the tube to
grow, indicating widespread oxidation throughout the tube.
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Where would you expect to see growth on FTB medium of a strict aerobe, anaerobe,
microaerophile, facultative anaerobe, and an aerotolerant anaerobe? - answer✔-Strict aerobe: at
the top of the broth, where oxygen is abundant
-Anaerobe: at the bottom of the broth, where oxygen is not present
-Microaerophile: in the middle of the broth where oxygen is present, but not in large amounts
-Facultative anaerobe: concentrated at the top (grows best when most oxygen is present), but
spread throughout (can grow anaerobically)
-Aerotolerant anaerobe: growth relatively evenly throughout (anaerobic, but tolerates oxygen
presence)
Consider resazurin dye. Considering the major application of this medium, which is more
desirable, a thick coloured or a thin coloured band? - answer✔A thin coloured band would be
more desirable, as it would indicate that the medium is more fresh. The older the medium, the
more oxidation occurs within the media, creating the indicator band to expand. Certain bacteria
will not be able to grow or the results of their growth will become skewed.
Where is the resazurin located in the broth column? - answer✔At the very top of the broth,
forming a band.
Why is the FTB broth pink at the surface of the medium? - answer✔This is where the most
oxygen is present.
Which type of organism would most likely be affected negatively by the use of old FTB media? -
answer✔Strict (obligate) anaerobes; these organisms are inhibited by the presence of oxygen,
therefore an abundance of oxygen in the tube may produce limited growth by these organisms.
Which type of organism would most likely be positively affected by the use of old FTB media? -
answer✔Strict (obligate) aerobes; the abundance of oxygen in the media will provide a
tremendous advantage to these organism's growth, as they need sufficient amounts of oxygen to
produce.
Which type of organism would be least affected by the use of old FTB media? -
answer✔Aerotolerant anaerobes; these bacteria continue their production anaerobically in the
presence of oxygen. Oxygen presence will neither inhibit, nor fuel their growth.
What is the GasPak Anaerobic System? - answer✔A plastic jar in which we create anaerobic,
microaerophilic, or CO2 enriched conditions, depending on the specific needs of the bacteria
being cultivated.
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What components are required for the anaerobic jar? - answer✔Chemical gas generator packet
containing sodium borohydride and sodium bicarbonate, and a paper indicator strip saturated in
methylene blue and resazurin. Palladium acts as a catalyst for the reaction that will produce the
necessary conditions within the jar.
What is the purpose of the indicator strip? How is oxygen presence indicated? - answer✔To
confirm the presence or absence of oxygen within the jar. Methylene blue and resazurin are
colorless when reduced, but are blue and pink, respectively, when oxidized.
What does the gas generator packet do within the anaerobic jar? - answer✔Water is added to the
envelope. Sodium borohydride and sodium bicarbonate react with the water to produce hydrogen
and carbon dioxide gases. Palladium catalyzes a reaction between hydrogen and free oxygen in
the jar to produce water.
How long does it take for the gas generator packet to create anaerobic conditions? What is the
evidence of this? - answer✔Removal of the free oxygen produces anaerobic conditions in the jar
in approximately one hour; this is evidenced by the white indicator strip and moisture inside of
the jar.
Suppose that after incubation, you examine the jar before opening it and see that the methylene
blue strip is blue (or the resazurin strip is pink). What would you guess the internal environment
to be- aerobic or anaerobic? - answer✔Aerobic; the indicator strips should be white when within
the jar, representing an anaerobic environment. If these strips are oxidized, they change colour,
indicating the presence of oxygen within the system.
Suppose that after incubation, you examine the jar before opening it and see that the methylene
blue strip is blue (or the resazurin strip is pink). How would you expect the growth on the plates
inside the jar to differ from the plates incubated outside of the jar? - answer✔The plates inside of
the jar would reflect inhibited growth of anaerobic organisms, while aerobic organisms would be
positively affected. These results will be skewed towards favouring aerobic organisms. Plates
outside of the jar will remain unaffected.
Suppose that after incubation, you examine the jar before opening it and see that the methylene
blue strip is blue (or the resazurin strip is pink). Which organisms would be most affected by the
conditions described? - answer✔Obligate anaerobes would be most affected as they require no
oxygen present in order to grow. The presence of oxygen within the anaerobic environment will
stunt their growth. Obligate aerobes will benefit from the influx of oxygen, causing these
organisms to flourish in an aerobic environment. If the conditions are just right, microaerophiles
may be permitted to grow where they once would not with a small amount of oxygen present.
