MCB 101 Introductory Microbiology Lab
Practice Exam 3 Fall 2013
The MCB101 Final Exam will be given at
8 – 11 AM on Monday, December 16
in rooms 114 & 123 David Kinley Hall
The MCB101 conflict exam will be given at
8 – 11 AM on Friday, December 13
place: 242 Burrill Hall
If you need to take the Conflict Final Exam contact Dr. Chapman by e-mail at:
MCB 101 Introductory Microbiology Lab
Practice Exam 3 Fall 2013
For each question, choose the one BEST answer.
There are 27 multiple choice questions on this practice exam. The actual exam may differ slightly in format but it will be a machine graded test.
1) In Experiment 17: Milk Pasteurization, we used 3M Petrifilm cultures to count the bacteria in the diluted meat samples. What volume of liquid is used to inoculate a 3M Petrifilm culture?
A. 0.1 ml B. 0.3 ml C. 1.0 ml D. 3.0 ml E. 10.0 ml
2) A sewage sample is tested for coliform bacteria by spreading aliquots on standard Petri dish cultures of EMB agar. After incubation the dark purple-green colored coliform colonies are counted. A 0.10 ml aliquot of a 1 x 10-4 dilution of the sample gives 90 coliform colonies. What is the concentration of coliform bacteria in this sample of sewage? (the units are: cells/ml)
A. 9.0 x 10-4 B. 9.0 x 10-2 C. 9.0 x 104 D. 9.0 x 105 E. 9.0 x 106
3) Which one of the following statements about bacteria that cause foodborne illness
is false?
A.Campylobacter jejuni is a Gram negative helical shaped bacteria that can be
transmitted in undercooked poultry and cause fever, headache, muscle pain,
abdominal pain, nausea and diarrhea.
B. Clostridium botulinum is an endospore-forming, Gram positive, rod-shaped, anaerobic
bacteria that produces a neurotoxin that causes double vision, droopy eyelids, trouble
speaking and difficulty breathing. Intoxication can be fatal.
C. Esherichia coli is a Gram negative, rod-shaped bacteria, that ferments lactose
producing acid and gas. Several strains can cause human illness, notably O157:H7.
The normal habitat for E. coli is the mammalian intestinal tract.
D. Salmonella is a genus of Gram negative intestinal bacteria in the same family as
E. coli. Salmonella can be transmitted in undercooked eggs, poultry and meat or in
unpasteurized dairy products. Salmonellosis usually involves diarrhea, stomach pain,
nausea, chills, fever and headache that resolves in a few days but some strains can
cause more serious infections such as typhoid fever.
E. Staphylococcus aureus is a Gram negative rod shaped bacteria that is found primarily
in animal intestines, it is an obligate anaerobe that produces a neurotoxin called botox.
4) On a 3M Petrifilm culture for E. coli/coliforms, such as those we used in
Experiment 17(Pasteurization of Milk), a colony of a fecal coliform appears:
A. red and not associated with a gas bubble.
B. white and not associated with a gas bubble.
C. blue and not associated with a gas bubble.
D. red and associated with a gas bubble.
E. blue and associated with a gas bubble.
5) In experiment 17 we killed E. coli bacteria in milk by heating the milk at:
A. 212oC B. 123oC C. 100oC
D. 63oC E. 37oC
6) What is the term for microorganisms that can grow and cause food spoilage in the
refrigerator?
A. acidophillic B. psychrophillic C. thermophillic
D. mesophillic E. thermoduric
7) What type of microorganism is Penicillium?
A. Fungus B. Bacteria C. Protozoa
D. Archaea E. Virus
8) The food preservative sodium nitrite is:
A. an organic acid.
B. a phenol derivative.
C. a fat soluble antioxidant.
D. an inhibitor of pyruvate-ferrodoxin oxidoreductase.
E. produced as a waste product of microbial fermentation of sugar.
9) Nitrites are added to meat because it gives meat a pink color and inhibits:
A. Pseudomonas aeruginosa B. Bacillus subtilis
C. Clostridium botulinum D. Salmonella typhi
E. Esherichia coli
10) How do propionate and benzoate prevent microbial growth?
A. They attack proteins, prosthetic groups, sugars and nucleic acids in microbes.
B. They inhibit two enzymes; pyruvate-ferrodoxin oxidoreductase and ferrodoxin.
C. They inhibit ripening enzymes that are naturally found in food.
D. They denature protein destroying the cytoplasmic membrane of microbes.
E. They increase the proton concentration of the cytoplasm in microbes.
11) Which one of the following substances is not classified as a disinfectant?
A. alcohol B. bleach C. phenol
D. tetracycline E. hydrogen peroxide
12) An antiseptic is:
A. an antimicrobial substance used to kill microorganisms on an operating table.
B. an antimicrobial substance that is used to kill or inhibit microorganisms on the skin.
C. an antimicrobial substance added to a food or beverage to inhibit spoilage.
D. a drug derived from a natural product that is used fight microorganisms within
a patient's body.
E. a drug that is a completely man-made chemical used to fight microorganisms
within a patient’s body.
13) Which two of the following statements about disinfectants and antiseptics are true?
i. In a diffusion test of an antimicrobial agent, the size of the zone of inhibition is
not affected by the temperature of incubation or the composition of the medium.
ii. Phenol was used as a disinfectant in hospitals for many years.
iii. Chemical disinfectants are more lethal to bacteria at higher concentrations.
iv. In a diffusion test of an antimicrobial agent, a more resistant species of bacteria
will show a larger zone of inhibition.
A. i. and ii. B. i. and iii. C. i. and iv. D. ii. and iii. E. ii. and iv.
14) Which one of the following statements about lactic acid and ethanol fermentations
is false?
A. The predominant sugar found in grape juice is sucrose.
B. Both ethanol and lactic acid can inhibit the growth of undesirable microorganisms
in food products.
C. In a 100% efficient fermentation, lactic acid bacteria can convert 100 grams of sugar
to 100 grams of lactic acid.
D. In ethanol fermentation yeast produce one molecule of CO2 for every molecule of
ethanol they make.
E. Oxygen is needed for fermentation reactions to take place.
15) Yogurt production primarily involves:
A. the fermentation of a sugar to produce lactic acid.
B. hydrolysis of protein to produce short peptides and free amino acids.
C. putrifying bacteria.
D. boiling the milk for 30 minutes.
E. bacteria that grow best in the refrigerator.
16) Which two of the following bacteria are used to make yogurt?
i. Lactobacillus bulgaricus
ii. Pseudomonas aeruginosa
iii. Staphylococcus aureus
iv. Streptococcus thermophilus
A. i. and ii. B. i. and iii. C. i. and iv. D. ii. and iii. E. ii. and iv.
17) Experiment 18b: Yogurt Production
Which two of the following statements about setting up a yogurt culture are true?
i. Boil your milk until it starts to turn brown and then stir in some good yogurt
to inoculate the culture while it's still steaming hot.
ii. The incubation temperature for the yogurt culture is 43-45oC
iii. Before adding yogurt to the skim milk, the milk should be cooled to below 10oC
iv. The production of yogurt is an example of a microbial succession that primarily
involves two species of bacteria.
A. i. and ii. B. i. and iii. C. i. and iv. D. ii. and iii. E. ii. and iv.
18) Which one of the following statements about making cottage cheese is true?
A. Milk curdles when butterfat globules combine to form a large insoluble mass.
B. The incubation temperature for making cheese is higher than that used for yogurt.
C. Lactic acid is made by Lactococcus bacteria as a waste product of aerobic respiration.
D. The whey from cheese tends to have a lower pH than the whey from yogurt.
E. Rennet contains a proteolytic enzyme that cleaves a specific peptide bond in k-casein.
19) You set up a ten-tube Minimum Inhibitory Concentration test where the
concentration of the antibiotic in each tube is a 1/2 dilution of the previous tube.
If the concentration of the antibiotic in tube 1 is 3200 micrograms per ml.
What is the concentration of the antibiotic in tube 6?
A. 3200 mg/ml B. 1600 mg/ml C. 600 mg/ml
D. 100 mg/ml E. 6 mg/ml
20) Redox Reactions Involving Nitrogenous Compounds
Which two of the following chemical changes are oxidation reactions?
i. nitrite is converted to nitrate
ii. ammonia is converted to nitrite
iii. nitrate is converted to elemental nitrogen (N2)
iv. elemental nitrogen (N2) is converted to ammonia
A. i. and ii. B. i. and iii. C. i. and iv. D. ii. and iii. E. ii. and iv.
21) Which one of the following statements about the nitrogen cycle is false?
A. Nitrosococcus bacteria can produce energy by oxidizing ammonia to nitrite.
B. The oxidation of ammonia to nitrate is called denitrification.
C. Some strains of Pseudomonas bacteria can reduce nitrates to nitrogen gas.
D. The enzyme urease breaks down urea to ammonia and CO2.
E. The breakdown of amino acids and other nitrogen-containing organic compounds
to release ammonia is called mineralization.
22) Trommsdorf reagents were used in both Experiment 19b: Denitrification
and in Experiment 19c: Nitrification.
Which one of the following statements about Trommsdorf reagents is false?
A. Trommsdorf reagents produce a dark-blue color when they react with nitrite (NO2-).
B. Trommsdorf reagent II can burn your skin or cause holes to appear in your clothing.
C. For the nitrate reductase test, a color change to blue after the addition of zinc
indicates a NEGATIVE test result (nitrate was not reduced by the bacteria).
D. For the ammonia oxidation test, a color change to blue after addition of zinc
indicates a POSITIVE test. (Bacteria oxidized the ammonia completely to nitrate.)
E. Trommsdorf reagents produce a blue color when they react with ammonium (NH4+).
23) Which one of the following statements about Nitrification is false?
A. Nitrification is also called ammonia oxidation.
B. Nitrification is a two-step process. Nitrosococcus carries out the first step while
Nitrobacter completes the process.
C. Nitrification is an aerobic process.
D. Nitrification requires an energy input, it consumes a lot of ATP and reducing power.
E. Nitrification is the conversion of ammonia to nitrate.
24) Experiment 19: Soil Bacteria and the Nitrogen Cycle
Which one of the following statements about Experiment 19 is false?
A. Denitrification is a form of anaerobic respiration.
B. Mammals excrete excess nitrogen primarily in the form of ammonia.
C. The main carbon source in the ammonia broth used in Experiment 19C is carbonate.
D. The carbon source in nitrate broth (Ex. 19b) is a mixture of organic compounds.
E. The only organisms that can convert elemental nitrogen (N2) to organic forms are
certain prokaryotes.
25) Which one of the following statements about the Kirby-Bauer disc diffusion test
for antibiotic susceptibility is true?
A. If the bacterium is resistant to an antibiotic there is a big clear zone around that disc.
B. If there is any clear zone at all around a given antidiotic disc, even a very small one,
the bacterium is considered to be resistant to that antibiotic.
C. The concentration of the antibiotic on a disc has no effect on the size of any clear
zone that may be seen around that disc.
D. If there is a big clear zone around a given antibiotic disc, that drug might be clinically
useful in treating an infection caused by the bacteria being tested.
E. If the bacterium is susceptible to any of the antibiotics on the discs it won’t grow on
the agar plate at all
26) You perform a MIC test using a new antibiotic, Hexacycline, against an old nemesis,
Bordetella pertussis the bacterium that causes whooping cough.
From the data shown, determine the MIC for Hexacycline against this bacteria.
Antibiotic Concentration (mg/ml): 1000 500 250 125 62.5 31.3 15.6 7.8
Growth?: - - - - + + + +
A. 500 mg/ml B. 250 mg/ml C. 125 mg/ml D. 62.5 mg/ml E. 31.3 mg/ml
27) In regards to the ingredients used to make bacteriological media, which one of the
following substances would be found only in a complex medium?
A. agar B. beef extract C. crystal violet D. phenol red E. glucose
Answer key
1) C 2) E 3) E 4) E 5) D 6) B 7) A 8) D 9) C
10) E 11) D 12) B 13) D 14) E 15) A 16) C 17) E 18) E
19) D 20) A 21) B 22) E 23) D 24) B 25) D 26) C 27) B