Bacteriology/Food Science 324:
1999 QUIZ NO. 3

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I. MULTIPLE TRUE/FALSE (16 points). In the blank by each statement, place a + for a true statement or a O for a false statement. There can be any number of + or O statements. Do not change or qualify the wording of any statement in any way. Each is either true or false as stated. (1/2 point for each blank.)

EXAMPLE:   When communicating with other microbiologists about organisms with which you work, the correct way(s) to indicate a scientific name is (are) shown as follows:

        Bacillus cereus
        bacillus cereus
        Bacillus cereus
        Bacillus Cereus

1.  On occasion, one may heat a food sample to 70-80°C for 10-15 minutes in order to assist the isolation of endospore-forming bacteria.

        This is done routinely to force the cells to produce endospores.
        This is done routinely when one suspects an actively-growing population of Bacillus cereus or Clostridium perfringens in a protein and carbohydrate-rich food.
        The more that one can treat a sample such that the desired organism's isolation is enhanced, the less selective the isolation medium needs to be.
        In a non-heat-treated food sample, vegetative cells of endospore-forming and non-endospore- forming species of bacteria can initiate colony formation (which means they can serve as "colony-forming units").

2.  When testing for nitrate reduction,

        a positive reaction for nitrite formation is indicated for an organism if a red color is obtained only after the addition of the reagents and the zinc.
        a positive reaction for nitrate reduction for an organism determined to be a "strict aerobe" infers that organism's ability to grow anaerobically if nitrate is present in its medium.
        a Durham tube detects formation of nitrogen gas.

3.  When testing a culture for amylase,

        one can use a plate of any all-purpose medium.
        iodine reacts with amylase to produce a blue color.
        one looks for a positive reaction in the area surrounding the growth on the plate, not just in or under the growth.

4.  A black colony on Baird-Parker Agar

        is always assumed to be Staphylococcus aureus.
        must be analyzed for gram reaction, catalase reaction, morphology and cellular arrangement before being identified as a member of the genus Staphylococcus.
        must be tested for coagulase before being identified specifically as Staphylococcus aureus.
        indicates hydrogen sulfide production.

5.  The following assist(s) in the selective isolation of molds and yeasts:

        a "nutritionally-poor" medium
        a low pH in the medium
        incubation at 45°C
        the use of Baird-Parker Agar

6.  Yeasts and molds

        can be differentiated from each other by their abilities to grow aerobically or anaerobically.
        are discrete taxonomic groups.
        are the chief spoilage agents of acidic foods along with lactic acid bacteria.

7.  A food-borne intoxication (as opposed to a food-borne infection)

        can be the result of an organism growing in a food and subsequently dying out before the food is eaten.
        can be caused by certain molds.
        can be caused by Staphylococcus aureus.
        only applies to fermented foods where ethanol is a microbial end-product.

8.  When one considers the growth of molds on petri dish media,

        one may consider spores as potential CFUs (colony-forming units).
        one may consider clusters or fragments of filaments as potential CFUs.
        one calls a mold colony by the term "mycelium."

9.  The use of Dextrose Tryptone Agar (in tubes)

        can involve mixed or pure cultures.
        can distinguish between "strict aerobes," "facultative anaerobes," and "aerotolerant anaerobes" when one observes the pattern of growth in the tubes.
        can determine whether or not acid is produced from the catabolism of glucose.
        can sometimes detect acid produced in respiration, and in this way the medium is similar to Glucose O/F Medium.

II. MATCHING (11 points). Place the letter of the correct item from column b in the blank by each statement in column a. Only one letter per blank. Some statements have two blanks; therefore two letters are needed. Any letter may be used any number of times or not at all. (One-half point for each blank.)

III.  SHORT ANSWER (5 points).

1.  (2 points) By what two ways were we able to grow strictly anaerobic bacteria in the lab?

2.  (2 points) List two ways one can differentiate between molds and yeasts in the laboratory – other than by the determination of "oxygen relationship."

3.  (1 point) How can one can differentiate between yeasts and bacteria in the laboratory?

IV.  EXERCISE 26 (8 points). Very briefly summarize (by the use of a flow chart) your isolation procedure and (by the use of an appropriate table) the observations of your isolates. You may attach extra sheets as you see fit.