MCB2010L Final EXAM QUESTIONS AND ANSWERS
What is fluid thioglycollate broth (FTB)? - CORRECT 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? - CORRECT 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? - CORRECT ANSWER✅✅Oxygen indicator. Pink when
oxidized, colorless when reduced.
What is the application of FTB? - CORRECT 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? - CORRECT 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.
Where would you expect to see growth on FTB medium of a strict aerobe, anaerobe, microaerophile,
facultative anaerobe, and an aerotolerant anaerobe? - CORRECT 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? - CORRECT 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? - CORRECT ANSWER✅✅At the very top of the
broth, forming a band.
Why is the FTB broth pink at the surface of the medium? - CORRECT 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? -
CORRECT 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? - CORRECT
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? - CORRECT
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? - CORRECT ANSWER✅✅A plastic jar in which we create
anaerobic, microaerophilic, or CO2 enriched conditions, depending on the specific needs of the bacteria
being cultivated.
What components are required for the anaerobic jar? - CORRECT 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? - CORRECT
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? - CORRECT 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? - CORRECT 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? - CORRECT 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? - CORRECT 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? - CORRECT 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.
What is fluid thioglycollate broth (FTB)? - CORRECT 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? - CORRECT 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? - CORRECT ANSWER✅✅Oxygen indicator. Pink when
oxidized, colorless when reduced.
What is the application of FTB? - CORRECT 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? - CORRECT 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.
Where would you expect to see growth on FTB medium of a strict aerobe, anaerobe, microaerophile,
facultative anaerobe, and an aerotolerant anaerobe? - CORRECT 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? - CORRECT 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? - CORRECT ANSWER✅✅At the very top of the
broth, forming a band.
Why is the FTB broth pink at the surface of the medium? - CORRECT 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? -
CORRECT 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? - CORRECT
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? - CORRECT
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? - CORRECT ANSWER✅✅A plastic jar in which we create
anaerobic, microaerophilic, or CO2 enriched conditions, depending on the specific needs of the bacteria
being cultivated.
What components are required for the anaerobic jar? - CORRECT 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? - CORRECT
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? - CORRECT 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? - CORRECT 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? - CORRECT 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? - CORRECT 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? - CORRECT 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.
