Microbiology Exam #2-2012
Name___________________________
Multiple choice. Choose the best answer (2 points each)
1.__D___Despite incubating an organism at its optimum temperature of 37 C on
tryptic soy agar for 24-48 hours you cannot get your organism to grow. The most
likely explanation is that the organism is: a) a mesophile; b) a capnophile; c) a
facultative anaerobe; d) fastidious; e) an obligate aerobe.
2.____A_An organism that used CO2 as its carbon source and nitrate as its energy
source would be classified as a(n): a )chemo(litho)autotrophs; b) photoautotroph;
c) photoheterotroph; d) chemo(litho)heterotroph; e) chemo(organo)autotroph.
3.___E__A microorganism that has an optimum growth temperature of 37 C, but can
survive short exposure to high temperatures is called a/an: a) extremophile;
b)thermophile; c) psychrophile; d) facultative psychrophile; e) thermoduric.
4.___C__The only type of organism on the planet that does not rely either directly or
indirectly on sunlight: a) photoautotroph b) chemo(organo)heterotroph
c) chemo(litho)autotroph d) chemophototroph e) chemo(litho)heterotroph
5.___D__ If your unknown grows better in a candle jar at 37 C than it does in an
incubator at 37 C, it is a(n): a) facultative anaerobe; b) obligate aerobe; c) obligate
anaerobe; d) a capnophile; e) a microaerophile.
6. __C___The enzymes superoxide dismutase and catalase would most likely be
absent in this type of organism: a) facultative anaerobe; b) obligate aerobe; c)
obligate anaerobe; d) a capnophile; e) a microaerophile.
7.___C__Tissue culture media containing animal sera is particularly sensitive to heat.
The most appropriate method to sterilize this media is: a) autoclaving;
b) pasterurization; c) filtration; d) UV treatment; e) sonication.
8.__B___You are doing research with an organism that only has one photosystem.
What other attribute is it most likely to have? a) it is a chemoheterotroph; b) it has
bacteriachlorophyll; c) it is an obligate aerobe; d) it is an extreme thermophile;
e) it produces oxygen as it photosynthesizes.
9.___B__This class of bacteria does not use oxygen in its metabolism but can survive
in the presence of harmful byproducts derived from oxygen: a) microaerophile;
b) aerotolerant; c) facultative anaerobe; d) obligate aerobe; e) obligate anaerobe.
10.__D___Clostridium rubrum is an obligate anaerobe and E. coli is a facultative
anaerobe. Which of the following statements is true? a) E. coli would be less likely
than Clostridium to have the enzyme superoxide dismutase; b) E. coli would be less
likely than Clostridium to grow in a candle jar; c) E. coli would grow at the bottom of
a thioglycollate tube while Clostridium would grow at the top; d) E. coli would be
more likely to reduce nitrate to nitrite than Clostridium; e) E. coli would be typically
found under deep sediment layers under bodies of water while Clostridium would
be typically found in surface waters.
11.__A___Suppose that you are keying your unknown using Berey’s Manual and it
asks you whether your organism has the protein cytochrome a-3. The test you
would do to obtain this information would be: a) the oxidase test; b) Gas-Pac; c)
phenol red glucose broth test; d) nitrate utilization test; e) Voges-Proskauer test.
12.__C___Both of these metabolic sequences can use an organic compound as a final
electron acceptor: a) fermentation and aerobic respiration; b) obligate anaerobic
and aerobic respiration; c) fermentation and facultatively anaerobic respiration;
d) facultatively anaerobic and aerobic respiration.
13. __B___Part of the process of phagocytosis of bacteria by white blood cells
involves rapid oxygen uptake by the lysosomes of the white blood cell (a respiratory
burst). The reason that this happens is: a) engulfed bacteria cause the white blood
cell to become anaerobic; b) it produces more toxic oxygen byproducts that can kill
the engulfed bacteria; c) it stimulates the production of superoxide dismutase which
kills the engulfed bacteria; d) it allows the white blood cell to be more motile;
e) it prevents the white blood cell from switching to fermentative metabolism which
routinely happens following phagocytosis.
14.__A___Deamination reactions are commonly associated with the: a) catabolism of
amino acids; b) symbiotic nitrogen fixation; c) nonsymbiotic nitrogen fixation;
d) nitrification; e) denitrification
15.__E___ The methanogens (a type of chem(litho)autotroph) are producers of
methane gas and require environments that : a) have sunlight; b) are very acidic;
c) have abundant oxygen and CO2; d) are extremely cold; e)are anaerobic with high
levels of hydrogen gas and CO2.
16.__A___Your instructor asks you to conduct methyl red and Voges-Proskauer tests
on your unknown to help you identify it. The information he is hoping you will
obtain is: a) fermentation byproducts produced; b) oxygen requirements;
c) osmotic tolerance; d) temperature optimum; e) whether your organism has
cytochrome a3 in its electron transport system.
17.__D__Heating a solution at a specified temperature for a specified time (time and
temperature chosen to kill a specific organism in the solution), describes this
process: a) tyndallization (intermittent sterilization); b) disinfection; c) antisepsis;
d) pasteurization; e) degermination.
18.__C___ All of the following pertain to hypochlorites except : a)release
hypochlorous acid in solution; b)cause denaturation of enzymes; c) found in
iodophors;
d) disrupts proteins by breaking disulfide bonds; e) found in
common household bleach.
19.___A__ Dry heat: a) is less efficient at killing microbes than moist heat of the same
temperature; b) cannot sterilize; c) includes tyndallization; d) is used in devices
called autoclaves; e) will sterilize at 121 C for 15 minutes.
20.__B___Generally, the more concentrated an agent is the better it kills
microorganisms. An exception to this “rule” is (are): a) halogens; b) alcohols;
c) phenolics; d) aldehydes; e) hydrogen peroxide.
21.___C__ All of the following are methods of disinfection or sterilization except:
a)gamma radiation; b) dry air oven; c) lyophilization; d) triclosan; e)ethanol.
22.___A__Suppose you develop a novel germicidal agent. To determine its relative
effectiveness, the killing power of your novel agent would be compared to the killing
ability of this substance: a) phenol; b) ethanol; c) triclosan; d) chorhexidine;
e) hydrogen peroxide.
23.___D__In a job interview, you are asked if you can operate a chemiclave. In order
to provide a convincing affirmative answer, you should know that a chemiclave
involves the use of this substance: a) gamma rays; b) surfactants; c) HEPA filters;
d) gluteraldehyde; e) ethanol.
24.___B__An antiseptic agent is known to kill bacteria by inserting into the bacterial
cell membrane, creating channels in the membrane, which causes things to enter
and leave the cell that shouldn’t. Based upon this information you should know that
the agent belongs to this class of antimicrobial compounds: a) aldehydes;
b) surfactants; c) halogens; d) heavy metals; e) bisphenols.
25.__B___Suppose you are hired to manage a water treatment facility. You goal is use
a disinfection process that eliminates the production of trihalomethanes
(carcinogens) in the treated water. To meet this goal, you could adopt the use of
which of the following disinfectant choices: a) chlorine; b) chloramine; UV radiation;
C) UV radiation and chlorine; D) chloramines.
26.___B__You own a company that develops products designed for disinfection of
substances and you use a lot of cellulose acetate and diatomaceous earth in
producing your product. The line of work that your company is most likely involved
in is: a) production of gas autoclaves; b) production of water filtration devices;
c) production of gamma irradiators for the food industry; d) production of
ultrasonic baths (sonicators); e) production of chemiclaves.
27.__D___ When they are dissolved in water, all chlorine disinfectants produce this
powerful antibacterial chemical: a) chloramines; b) hypochlorite;
d) trihalomethanes; d) hypochlorous acid; e)hydrogen peroxide
28. (4 points each). Agree or disagree with the following statements. In either case,
fully defend your position
A. Oxygen is toxic to obligate anaerobes.
Agree-Oxygen produces toxic byproducts such as superoxide anions, OH
radicals, and peroxides. Aerobic bacteria typically have enzymes such as
catalase and superoxide dismutase which protect them from these toxins but
obligate anaerobes lack these enzymes.
B. The observation that an organism grown at 37 C in an incubator has more
growth than if it were grown at 37 C in a Gas Pak provided compelling
evidence that the organism in a facultative anaerobe.
Agree- An obligate anaerobe wouldn’t grow in the incubator, an obligate
aerobe wouldn’t grow in the Gas Pak, but a facultative would grow in both
(but would give less growth in the GAS Pack than the incubator. This is
because Aerobic respiration and anaerobic respiration both produce ATP but
aerobic respiration produces more ATP-supporting greater growth.
C. The characteristic “fishy” smell is the result of bacterial decomposition of fish
proteins
Agree-Bacterial decomposition of fish protein produces TMAO (but this
doesn’t smell). However, TMAO is used as a terminal electron acceptor by
facultative anaerobes producing reduced TMAO (which does have the fishy
smell).
D. The method of choice for killing microbes in the food industry is heating.
Disagree-There is no real method of choice for killing microbes in all foods.
Heating works good for some foods (meats) but other foods or beverages do
not handle heat well. Other methods are used in these cases including
preservatives, salting, irradiation, and filtration. The method used depends
on the food product. By the way-pasteurization is a form of heating.
29. (10 points) Referring to type bacteria, type of chlorophyll, number of
photosystems involved, substrates used, and type of end products produced,
describe the difference between oxygenic and anoxygenic photosynthesis.
Oxygenic-Cyanobacteria; chlorophyll a & B; 2 photosystems (I and II);
substrates are ADP, NADPH,CO2 and H20, products are carbohydrate, ATP,
NADPH2 and O2.
Anoxygenic –Purple and green bacteria; bacteriachlorophyll; I photosystem (I
for green, II for purple); substrates (green- ADP, NADPH,CO2 and H2)(purple- ADP,CO2); products (green carbohydrate, ATP, NADPH2 and S2)purple (carbohydrate, ATP).
30. (10 points) Why does life depends on a functioning nitrogen cycle? Discuss four
different aspects of the nitrogen cycle that are the result of bacterial metabolic
processes. In each case, describe specifically how the metabolic process contributes
to the functioning of the nitrogen cycle.
Life depends on producer plants. Plants need nitrogen in the form of NH4+ to
make proteins and cannot use N2 for this process. Therefore we need a cycle
to convert N2NH4+N2.
4 metabolic sequences make up the nitrogen cycle and all involve bacterial
metabolism:
A. Nitrogen fixation (requires the enzyme nitrogenase to break the triple bond of N2energy expensive) -N2 to ammonia (plant nutrients) Reduction. Nitorgenase- 02
sensitive (leghaemoglobin and heterocycts)
Rhizobium. Symbiotic. Some
Cyanobacteria.
B. Ammonification-Many bacteria produce ammonia (important plant nutrient) as
they decompose tissue containing protein and urea. (deamination of amino acids.)
C. Nitrification-Ammonia can be oxidized by chemoautotrophs into nitrite (NO2-) by
Nitrosomonas. Nitrobacter can oxidized nitrite (NO2-) into nitrate (NO3-both of these
are toxic to plants). Important step in sewage treatment because these compounds
neutralize ammonia which is toxic to aquatic organisms.
D. Denitrification-Nitrate and nitrite-->NO--->N2O--->N2 (requires the enzyme
nitrate reductase) can be used as terminal electron acceptors in anaerobic respiration.
Usually a different species carries out each reduction. Some species of Bacillus and
Pseudomonas can reduce nitrate to ammonia.
31. (10 points) Hydrogen peroxide and chlorhexidine come the closest to having all
of the characteristics of being an ideal antimicrobial agent. Distinguish between
these 2 compounds using the following criteria: 1) mode of action, 2)
applications,
3) advantages, 4) disadvantages and 5) an example (if possible)
of a commercial product containing the agent.
H2O21. Generates oxygen which then produces bacteria killing toxic oxygen
byproducts.
2. Low concentration (3%)for disinfecting cuts/scrapes; high
concentrations (35%)used to sterilize medical instruments
(endoscopes)
3. Stable
4. Low concentrations can be broken down by bacterial peroxidases
5. Peroxide based contact lens cleaners.
Chlorhexidines-note this is a bisphenol not a chlorine compound that
produces hypochlorous acid
1. Denatures proteins and disrupts cell membranes
2. Surgical scrubbing, preparation of skin for surgery, neonatal wash
(replaced hexachlorophene)
3. Destroys both gram (+) and (-)
4. Not sporocidal
5. Some acne medications