Bailey & Scott Diagnostic Microbiology 15th
Edition Test Bank
SECTION I: BASIC MEDICAL MICROBIOLOGY
1. Which of the following best defines a bacterial species according to modern
taxonomic principles?
A. A group of strains that share identical phenotypic characteristics
B. A collection of bacterial strains that share many common physiologic and
genetic features
C. Any organism capable of causing disease in humans
D. A population of bacteria that grows on selective media
B. A collection of bacterial strains that share many common physiologic
and genetic features
Rationale: A bacterial species is defined as a collection of strains that
share many common physiologic and genetic features. This definition
acknowledges both phenotypic and genotypic similarity, reflecting the polyphasic
approach to taxonomy. Option A is too restrictive because phenotypic
characteristics alone can be misleading due to phenotypic plasticity. Option C
describes pathogens, not species. Option D describes growth characteristics, not
taxonomic classification.
2. The most specific and exclusive taxon used in the classification of
microorganisms is:
A. Family
B. Order
C. Species
D. Genus
C. Species
Rationale: The taxonomic hierarchy from most inclusive to most specific
is: Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species. Species is the
,most specific and exclusive taxon. A species represents a collection of strains
sharing many common features. Family and order are more inclusive categories.
Genus is more specific than family but less specific than species.
3. Pieces of DNA that move from one genetic element to another and contain
genes for movement as well as genes for other features are called:
A. Transposons
B. Insertion sequences
C. Plasmids
D. Chromatoids
A. Transposons
Rationale: Transposons are mobile genetic elements that contain genes
for their own movement (transposase) as well as additional genes such as
antibiotic resistance genes. Insertion sequences (option B) only code for
movement and do not carry additional genes. Plasmids are extrachromosomal
circular DNA molecules that replicate independently but do not inherently encode
movement. Chromatoids are not a recognized term in bacterial genetics.
4. A bacterium that has been moved from one genus (Pseudomonas) to another
genus (Burkholderia) would be correctly noted as:
A. Pseudomonas (Burkholderia)
B. Burkholderia (Pseudomonas)
C. Burkholderia only
D. Pseudomonas only
B. Burkholderia (Pseudomonas)
Rationale: When an organism is reclassified from one genus to another,
the new genus name is written first, followed by the old genus name in
parentheses. This convention indicates the reclassification while preserving
historical context. The correct notation is Burkholderia (Pseudomonas), indicating
,that the organism was formerly classified as Pseudomonas but is now placed in
the genus Burkholderia.
5. Which of the following statements best describes the difference between
Gram-positive and Gram-negative bacterial cell walls?
A. Gram-positive bacteria have an outer membrane; Gram-negative bacteria do
not
B. Gram-positive bacteria have a thick peptidoglycan layer; Gram-negative
bacteria have a thin peptidoglycan layer and an outer membrane
C. Gram-positive bacteria lack peptidoglycan entirely
D. Gram-negative bacteria have teichoic acids in their cell walls
B. Gram-positive bacteria have a thick peptidoglycan layer; Gram-
negative bacteria have a thin peptidoglycan layer and an outer membrane
Rationale: The critical difference is that Gram-positive bacteria possess a
thick peptidoglycan layer (20–80 nm) that retains the crystal violet-iodine
complex during decolorization. Gram-negative bacteria have a thin peptidoglycan
layer (2–7 nm) and an outer membrane containing lipopolysaccharide (LPS),
which is dissolved by the decolorizer, allowing the crystal violet to wash out.
Teichoic acids are found in Gram-positive cell walls, not Gram-negative.
6. Miniature chromosomes composed of several genes in double-stranded,
closed, circular structures are called:
A. Transposons
B. Plasmids
C. Insertion sequences
D. Bacteriophages
B. Plasmids
Rationale: Plasmids are extrachromosomal, double-stranded, closed-
circular DNA molecules that replicate independently of the bacterial
chromosome. They can carry genes for antibiotic resistance, virulence factors, and
, metabolic capabilities. Transposons are mobile genetic elements that can move
within the genome. Insertion sequences are the simplest transposable elements.
Bacteriophages are viruses that infect bacteria.
7. Which of the following is NOT a mechanism of horizontal gene transfer in
bacteria?
A. Transformation
B. Transduction
C. Conjugation
D. Binary fission
D. Binary fission
Rationale: Binary fission is a form of asexual reproduction in which a
bacterial cell divides into two identical daughter cells. It is NOT a mechanism of
horizontal gene transfer. The three main mechanisms of horizontal gene transfer
are transformation (uptake of naked DNA from the environment), transduction
(transfer of DNA via bacteriophages), and conjugation (direct cell-to-cell transfer
of DNA via a sex pilus).
8. The transfer of genetic material from one bacterium to another via a
bacteriophage is called:
A. Transformation
B. Transduction
C. Conjugation
D. Recombination
B. Transduction
Rationale: Transduction is the transfer of bacterial DNA from one
bacterium to another by a bacteriophage (bacterial virus). During the viral
replication cycle, the phage may accidentally package bacterial DNA instead of
viral DNA and inject it into a new host cell. Transformation involves uptake of free
Edition Test Bank
SECTION I: BASIC MEDICAL MICROBIOLOGY
1. Which of the following best defines a bacterial species according to modern
taxonomic principles?
A. A group of strains that share identical phenotypic characteristics
B. A collection of bacterial strains that share many common physiologic and
genetic features
C. Any organism capable of causing disease in humans
D. A population of bacteria that grows on selective media
B. A collection of bacterial strains that share many common physiologic
and genetic features
Rationale: A bacterial species is defined as a collection of strains that
share many common physiologic and genetic features. This definition
acknowledges both phenotypic and genotypic similarity, reflecting the polyphasic
approach to taxonomy. Option A is too restrictive because phenotypic
characteristics alone can be misleading due to phenotypic plasticity. Option C
describes pathogens, not species. Option D describes growth characteristics, not
taxonomic classification.
2. The most specific and exclusive taxon used in the classification of
microorganisms is:
A. Family
B. Order
C. Species
D. Genus
C. Species
Rationale: The taxonomic hierarchy from most inclusive to most specific
is: Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species. Species is the
,most specific and exclusive taxon. A species represents a collection of strains
sharing many common features. Family and order are more inclusive categories.
Genus is more specific than family but less specific than species.
3. Pieces of DNA that move from one genetic element to another and contain
genes for movement as well as genes for other features are called:
A. Transposons
B. Insertion sequences
C. Plasmids
D. Chromatoids
A. Transposons
Rationale: Transposons are mobile genetic elements that contain genes
for their own movement (transposase) as well as additional genes such as
antibiotic resistance genes. Insertion sequences (option B) only code for
movement and do not carry additional genes. Plasmids are extrachromosomal
circular DNA molecules that replicate independently but do not inherently encode
movement. Chromatoids are not a recognized term in bacterial genetics.
4. A bacterium that has been moved from one genus (Pseudomonas) to another
genus (Burkholderia) would be correctly noted as:
A. Pseudomonas (Burkholderia)
B. Burkholderia (Pseudomonas)
C. Burkholderia only
D. Pseudomonas only
B. Burkholderia (Pseudomonas)
Rationale: When an organism is reclassified from one genus to another,
the new genus name is written first, followed by the old genus name in
parentheses. This convention indicates the reclassification while preserving
historical context. The correct notation is Burkholderia (Pseudomonas), indicating
,that the organism was formerly classified as Pseudomonas but is now placed in
the genus Burkholderia.
5. Which of the following statements best describes the difference between
Gram-positive and Gram-negative bacterial cell walls?
A. Gram-positive bacteria have an outer membrane; Gram-negative bacteria do
not
B. Gram-positive bacteria have a thick peptidoglycan layer; Gram-negative
bacteria have a thin peptidoglycan layer and an outer membrane
C. Gram-positive bacteria lack peptidoglycan entirely
D. Gram-negative bacteria have teichoic acids in their cell walls
B. Gram-positive bacteria have a thick peptidoglycan layer; Gram-
negative bacteria have a thin peptidoglycan layer and an outer membrane
Rationale: The critical difference is that Gram-positive bacteria possess a
thick peptidoglycan layer (20–80 nm) that retains the crystal violet-iodine
complex during decolorization. Gram-negative bacteria have a thin peptidoglycan
layer (2–7 nm) and an outer membrane containing lipopolysaccharide (LPS),
which is dissolved by the decolorizer, allowing the crystal violet to wash out.
Teichoic acids are found in Gram-positive cell walls, not Gram-negative.
6. Miniature chromosomes composed of several genes in double-stranded,
closed, circular structures are called:
A. Transposons
B. Plasmids
C. Insertion sequences
D. Bacteriophages
B. Plasmids
Rationale: Plasmids are extrachromosomal, double-stranded, closed-
circular DNA molecules that replicate independently of the bacterial
chromosome. They can carry genes for antibiotic resistance, virulence factors, and
, metabolic capabilities. Transposons are mobile genetic elements that can move
within the genome. Insertion sequences are the simplest transposable elements.
Bacteriophages are viruses that infect bacteria.
7. Which of the following is NOT a mechanism of horizontal gene transfer in
bacteria?
A. Transformation
B. Transduction
C. Conjugation
D. Binary fission
D. Binary fission
Rationale: Binary fission is a form of asexual reproduction in which a
bacterial cell divides into two identical daughter cells. It is NOT a mechanism of
horizontal gene transfer. The three main mechanisms of horizontal gene transfer
are transformation (uptake of naked DNA from the environment), transduction
(transfer of DNA via bacteriophages), and conjugation (direct cell-to-cell transfer
of DNA via a sex pilus).
8. The transfer of genetic material from one bacterium to another via a
bacteriophage is called:
A. Transformation
B. Transduction
C. Conjugation
D. Recombination
B. Transduction
Rationale: Transduction is the transfer of bacterial DNA from one
bacterium to another by a bacteriophage (bacterial virus). During the viral
replication cycle, the phage may accidentally package bacterial DNA instead of
viral DNA and inject it into a new host cell. Transformation involves uptake of free
