Question 1

You have isolated a bacterium from a contaminated river but you are unable to culture it in the laboratory. Which method could you use to identify the organism?

Accepted Answer

A)   Gram staining
B)   Biochemical testing
C)   MALDI-TOF mass spectrometry
D)   Nucleic acid amplification tests
E)   Antibiograms D

Question 2

A DNA similarity of 75% between two organisms

Accepted Answer

A)   suggests the organisms are closely related at the species level.
B)   suggests the organisms are not closely related at all.
C)   suggests the organisms may or may not be related.
D)   means the GC content in both organisms is 45%.
E)   means the GC content in one organism is 75% and 25% in the other. A

Question 3

Based on DNA hybridization, humans and chimpanzees are the same species.

Accepted Answer

A) True 
 B)False  True

Question 4

Size and shape may allow one to differentiate between a bacterium, fungus, and protozoan.

Accepted Answer

A) True 
 B)False

Question 5

When DNA probes are used to identify bacterial DNA similarities by hybridization, the probe DNA is heated and the template DNA is treated to separate the two strands. Why would the probe DNA be heated?

Accepted Answer

A)   This is the only way to properly label the probe DNA.
B)   The probe may contain parts that are double-stranded. Heating it up breaks the hydrogen bonds holding the strands together, creating single-stranded sequences that hybridize with their complementary targets.
C)   Heating it up activates the tag on the probe DNA before it hybridizes to the bacterial template DNA.
D)   DNA hybridization can only take place at high temperatures, so all the DNA must be heated up prior to hybridization.
E)   The probe may contain many parts that are single-stranded. Heating it up creates hydrogen bonds that hold the probe tightly to its complementary target sequences.

Question 6

All known species of bacteria are described in Bergey's Manual of Systematic Bacteriology.

Accepted Answer

A) True 
 B)False

Question 7

If the GC content of two organisms is 45% in both,

Accepted Answer

A)   they are definitely related.
B)   they are definitely not related.
C)   they may or may not be related.
D)   the AT content is 65%.
E)   they are definitely related AND the AT content is 65%.

Question 8

In the 1930s Kluyver and van Niel proposed a classification scheme based on

Accepted Answer

A)   Gram reactions.
B)   biochemical relationships.
C)   DNA sequences.
D)   presumed evolutionary relationships.
E)   cell wall.

Question 9

Phage typing

Accepted Answer

A)   is useful for determining eukaryotic cell types.
B)   is used to extract DNA from cells.
C)   is used to distinguish bacterial strains.
D)   is dependent on the type of eukaryotic cell.
E)   is used to distinguish bacterial strains AND is dependent on the type of eukaryotic cell.

Question 10

Strain differences are helpful in

Accepted Answer

A)   understanding replica plating.
B)   carrying out electrophoresis.
C)   performing transformation in the laboratory.
D)   initiating transduction in E. coli.
E)   tracing the source of outbreaks of disease.

Question 11

DNA probes have been very useful in

Accepted Answer

A)   coding the DNA of organisms grown in vivo.
B)   identifying organisms in pure culture.
C)   detecting toxins.
D)   diagnosing diseases of protozoa.
E)   sequencing rRNA genes.

Question 12

Horizontal DNA transfer may make it more difficult to construct phylogenetic trees.

Accepted Answer

A) True 
 B)False

Question 13

Wisconsin state health authorities alerted the CDC about an E. coli O157:H7 outbreak. Soon thereafter, officials from two other states reported that they also had cases of illness associated with this pathogen. Within days, the CDC determined that the E. coli strains from all three states were the same, and the likely source of the outbreak was a particular brand of pre-packaged fresh spinach. The CDC then issued a press release advising people not to eat bagged fresh spinach. 
-E. coli is a Gram-negative bacillus that is found as intestinal normal microbiota. Which of the following would not be useful for an initial step in identifying E. coli O157:H7 strains in a stool sample?

Accepted Answer

A)   Gram staining, because E. coli strains will appear identical using this approach.
B)   Serology, because E. coli strains all express the same antigens.
C)   Growth on selective media, because all strains of E. coli will have the same metabolic capabilities.
D)   RFLPs, because E. coli strains will be identical at the genome level. 
E)   These methods can all be used to differentiate between E. coli strains.

Question 14

Wisconsin state health authorities alerted the CDC about an E. coli O157:H7 outbreak. Soon thereafter, officials from two other states reported that they also had cases of illness associated with this pathogen. Within days, the CDC determined that the E. coli strains from all three states were the same, and the likely source of the outbreak was a particular brand of pre-packaged fresh spinach. The CDC then issued a press release advising people not to eat bagged fresh spinach. 
-If you were the lab technician trying to identify the causative organism of this foodborne outbreak, would you inoculate several biochemical tests at the same time, or would you inoculate each test after getting the results from the previous test?

Accepted Answer

A)   I would inoculate each test after obtaining results from the last one because the tests are very quick and give instant results, and doing one test at a time will avoid confusion in the results.
B)   I would inoculate several tests simultaneously, because most biochemical tests require at least 18 hours of incubation, so inoculating several tests simultaneously saves time and also aids in conclusive identification.
C)   I would inoculate each test after obtaining results from the last one because the tests are extremely expensive so the fewer tests I can do, the less money I have to invest in the identification process.
D)   I would inoculate several tests simultaneously, because these tests can only be analyzed using specialized equipment, so I need to have the tests ready at the same time. 
E)   I would inoculate each test after obtaining results from the last one because these tests are very time consuming and difficult to set up, so it would be more practical to take this approach.

Question 15

From most general to most specific, which is the correct order?

Accepted Answer

A)   Phylum, class, kingdom, order, family, genus, species
B)   Kingdom, phylum, class, order, family, genus, species
C)   Kingdom, phylum, family, class, order, genus, species
D)   Kingdom, order, family, genus, phylum, class, species
E)   Genus, species, class, order, phylum, kingdom, family

Question 16

If the GC content of two organisms is 60%, the

Accepted Answer

A)   organisms are most likely related.
B)   organisms are definitely not related.
C)   organisms will have identical RFLP profiles.
D)   organisms are probably both pathogens.
E)   AT content is 60%.

Question 17

Various strains of E. coli

Accepted Answer

A)   may cause disease.
B)   may be harmless.
C)   are all exactly the same.
D)   are all very different from one another.
E)   may cause disease AND may be harmless.

Question 18

In 1908 Orla-Jensen suggested that bacteria be grouped according to their

Accepted Answer

A)   arrangement.
B)   morphology.
C)   physiology.
D)   Gram stain.
E)   flagella.

Question 19

In 1970 Stanier proposed that classification be based on

Accepted Answer

A)   evolution.
B)   Gram stain.
C)   physiology.
D)   DNA sequence.
E)   flagella.

Question 20

Serratia marcescens are red when incubated at 37°C.

Accepted Answer

A) True 
 B)False

Exam 10: Identifying and Classifying Microorganisms

You have isolated a bacterium from a contaminated river but you are unable to culture it in the laboratory. Which method could you use to identify the organism?

A DNA similarity of 75% between two organisms

Based on DNA hybridization, humans and chimpanzees are the same species.

Size and shape may allow one to differentiate between a bacterium, fungus, and protozoan.

When DNA probes are used to identify bacterial DNA similarities by hybridization, the probe DNA is heated and the template DNA is treated to separate the two strands. Why would the probe DNA be heated?

All known species of bacteria are described in Bergey's Manual of Systematic Bacteriology.

If the GC content of two organisms is 45% in both,

In the 1930s Kluyver and van Niel proposed a classification scheme based on

Phage typing

Strain differences are helpful in

DNA probes have been very useful in

Horizontal DNA transfer may make it more difficult to construct phylogenetic trees.

From most general to most specific, which is the correct order?

If the GC content of two organisms is 60%, the

Various strains of E. coli

In 1908 Orla-Jensen suggested that bacteria be grouped according to their

In 1970 Stanier proposed that classification be based on

Serratia marcescens are red when incubated at 37°C.