MCB2010L Final UPDATED Actual
Questions and CORRECT 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
