Microbiology Lab Exam 2

Front 1

From your laboratory manual: "Some microbiologists recommend re-incubating organisms producing methyl red-negative results for an additional 2 to 3 days..." Why?

a. To increase test sensitivity

b. To increase test specificity

c. To decrease the chance of false positives

d. To serve as positive controls

e. To provide a negative confirmatory test

Back 1

a. To increase test sensitivity

Front 2

If an organism has a mean growth rate of 4 generations per hour, what is its mean generation time?

a. 240 minutes

b. 20 minutes

c. 25 minutes

d. 15 minutes

e. None of the answers shown are correct

Back 2

d. 15 minutes

Front 3

A colony picked directly from ________ media should never be considered a pure culture.

a. Blood agar

b. Selective media

c. Differential media

d. All-Purpose media

e. Chemically undefined media

Back 3

b. Selective media

Front 4

What type of material is agar?

a. carbohydrates,

b. nucleotides,

c. proteins,

d. lipids,

e. synthetic polymer

Back 4

a. Carbohydrates

Front 5

Which pH indicator is used in Simmon's citrate media?

a. Malachite green

b. Phenol red

c. Methyl red

d. Bromthymol blue

e. Sodium citrate

Back 5

d. Bromthymol blue

Front 6

Which of the following would be most likely to cause false positives on a diagnostic test?

a. low test sensitivity

b. insufficient amount of sample applied

c. low test specificity

d. proteins in test reagent were destroyed

e. answers "a" and "b"

Back 6

c. low test specificity

Front 7

Approximately how many Staphylococcus epidermidis bacteria could fit into a cube that measures 1 millimeter on each side? (assume that each cell is 1 micrometer in diameter)

a. 10^4

b. 10^12

c. 10^9

d. 10^3

e. 10^6

Back 7

c. 10^9

Front 8

Which of the following can be fermented?

a. Lactobacillus spp.

b. Sodium chloride

c. Saccharomyces cerevisiae.

d. CO2

e. glucose

Back 8

e. glucose

Front 9

Suppose a student testing an unknown culture performs the urease test according to the protocol; after the specified incubation, the media has not changed color... Which of the following conclusions would be most proper / justified?

a. This result is sufficient to allow species identification - the unknown must be P. vulgaris

b. No urea hydrolysis occurred in this test; there was zero urease activity

c. No urease activity was observed

d. The bacteria tested does not have a urease gene

e. This result is positive, indicative of urease activity

Back 9

c. No urease activity was observed

Front 10

The properties and function of the enzyme tested in the gelatinase test suggest that it is most likely...?

a. an endoenzyme

b. an exoenzyme

c. a non-catalytic protein

d. B and C

e. A and C

Back 10

b. an exoenzyme

Front 11

Fluid thioglycollate medium contains an indicator, (Blank) , and a reducing agent, (Blank).

a. phenol red, thioglycollate

b. fluid, sodium ions (Na+)

c. resazurin, thioglycollate

d. phenol red, DTT

e. methyl red, resazurin

Back 11

Fluid thioglycollate medium contains an indicator, RESAZURIN, and a reducing agent, THIOGLYCOLLATE.

c. resazurin, thioglycollate

Front 12

Which of the following factors could be rate-limiting with respect to the rate of bacterial population growth?

a. spatial constraints / competition

b. length / size of bacterial genome

c. depletion of substrates / starting materials

d. accumulation of bacterial metabolites / byproducts

e. any of the answers shown

Back 12

e. any of the answers shown

Front 13

At temperatures ABOVE the cardinal temperature of a bacterial species, the rate of cell division (BLANK); at temperatures BELOW that cardinal temperature, the rate of cell division (BLANK).

a. decreases; increases

b. increases, decreases

c. increases; increases

d. decreases; decreases

e. none of the answers shown

Back 13

At temperatures ABOVE the cardinal temperature of a bacterial species, the rate of cell division DECREASES; at temperatures BELOW that cardinal temperature, the rate of cell division DECREASES.

Front 14

In the SIM test media, after a positive test, the H2S indicator was (soluble or insoluble) and (colored or colorless) and (intracellular or extracellular).

a. soluble, colored, intracellular

b. insoluble, colorless, extracellular

c. soluble, colored, extracellular

d. insoluble, colored, intracellular

e. insoluble, colored, extracellular

Back 14

In the SIM test media, after a positive test, the H2S indicator was (INSOLUBLE) and (COLORED) and (EXTRACELLULAR).e. insoluble, colored, extracellular

Front 15

Which set of phenol red carbohydrate fermentation test results shown would be most trusted and reliable?

PR-Base PR-Glucose PR-Lactose PR-Sucrose

a. Positive Positive Negative Negative

b. Negative Negative Negative Negative

c. Negative Positive Negative Positive

d. Negative Negative Positive Negative

e. None of the results shown are reasonable – all seem unreliable, none should be trusted

Back 15

C. PR-Base Negative PR-Glucose Positive PR-Lactose Negative PR-Sucrose Positive

Front 16

Where do the energy-producing steps of the carbohydrate fermentation take place?

a. Inside individual bacterial cells

b. Inside the nucleus / nuclear envelope

c. Outside the bacteria, in the culture media

d. At the sites where macromolecules (polysaccharides) composed of fermentable sugars are located

e. None of the answers shown are reasonable

Back 16

a. Inside individual bacterial cells

Front 17

Addition of 1000 microliters to 9.0 milliliters diluent would be a Blank -fold dilution; addition of 100 microliters sample to 99.9 milliliters diluent is a Blank-fold dilution.

a. 1000; 100

b. 100; 10

c. 10; 100

d. 1000; 10

e. 10; 1000

Back 17

Addition of 1000 microliters to 9.0 milliliters diluent would be a 10 fold dilution; addition of 100 microliters sample to 99.9 milliliters diluent is a 1000 fold dilution.

e. 10; 1000

Front 18

Which of the following is true regarding Selective Media?

a. It is used to aid in isolation of less-abundant or slower-growing species of bacteria

b. Any/all of these answers can be correct

c. It can be produced by adding bacteriostatic agents to all-purpose media

d. It can be produced by excluding certain nutrient sources from chemically-defined media

e. Colonies that appear isolated could have unseen contaminants and should not be considered pure cultures

Back 18

b. Any/all of these answers can be correct

Front 19

What is the fundamental, underlying reason why species of bacteria vary with respect to their abilities to ferment different carbon sources?

a. DNA - fermentation processes are catalyzed by genetically-encoded enzymes

b. None of the answers shown

c. the oxygen requirements of the microbe (i.e., anaerobes vs. aerobes, etc.)

d. variation of the cellular respiration rate and redox potential

e. the abundance of a particular carbohydrate (i.e., ferment lactose if environment is lactose-rich)

Back 19

a. DNA - fermentation processes are catalyzed by genetically-encoded enzymes

Front 20

Suppose you were concerned that a mistake had been made - you suspect that no chemical indicator was included in your “phenol red carbohydrate broth” test media. Which of the following could be a positive control?

a. add phenol red to your sample

b. observe an uninoculated sample (a blank)

c. observe your inoculated sample for additional time

d. inoculate your sample with additional bacteria

e. add acid to your sample - make sure the color changes

Back 20

e. add acid to your sample - make sure the color changes

Front 21

Which type(s) of bacteria could be grown on properly prepared agar deeps?

a. facultative anaerobes

b. obligate aerobes

c. strict anaerobes

d. all of these

e. none of these

Back 21

d. all of these

Front 22

Which trait is most typical of an anaerobic species of bacteria?

a. requires free oxygen

b. not able to survive on the human body

c. insensitive to oxygen levels

d. unable to convert hydrogen peroxide or superoxide radicals to less toxic molecules

e. all of these

Back 22

d. unable to convert hydrogen peroxide or superoxide radicals to less toxic molecules.

Front 23

Which of the following is an indication that molecular oxygen (O2) is present?

a. grey-colored Na-thioglycollate solution

b. growth of strictly aerobic species of bacteria

c. yellow-colored resazurin

d. turbidity in Na-thioglycollate broths

e. gas bubbles in agar deeps

Back 23

b. growth of strictly aerobic species of bacteria

Front 24

What is the selective agent in Mannitol Salt Agar?

a. Mannitol

b. Sodium chloride

c. Phenol red

d. Bile salts

e. Agar

Back 24

b. Sodium chloride

Front 25

This media suppresses the growth of unwanted organisms and encourage the growth of desired microbes.

Back 25

Selective media

Front 26

This allows you to differentiate between two colonies of bacteria growing on the same plate

Back 26

Differential media