MCB2010L Final Exam questions and
answers
What is fluid thioglycollate broth (FTB)? - ANSWERS 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? - ANSWERS 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? - ANSWERS Oxygen indicator. Pink when oxidized,
colorless when reduced.
What is the application of FTB? - ANSWERS 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? - ANSWERS 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? - ANSWERS -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? - ANSWERS 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? - ANSWERS At the very top of the broth, forming a
band.
Why is the FTB broth pink at the surface of the medium? - ANSWERS 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? -
ANSWERS 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? -
ANSWERS 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? - ANSWERS 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? - ANSWERS 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? - ANSWERS 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? - ANSWERS 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? - ANSWERS 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? - ANSWERS 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? - ANSWERS 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? - ANSWERS 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
