WGU D311
Microbiology
OA EXAM
Actual Questions with Verified Answers
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What You Will Get:
➢85 OA Exam Questions w/ Answers
➢ OA Definitions,
➢ Concept Reviews
➢ Study Guide
➢ Expert Rationales included.
Take and pass the OA :)
, D311 Microbiology OA Exam
Preview Pages Below
Get the Complete PDF After Purchase
"If you require further clarification or in need of any
study resources, feel free to Message me."
Preview sample - complete PDF available after purchase
,Table of Contents
D311 Microbiology OA Exam ............................................................ 2
D311 OA Definitions, Concept Reviews & Study Guide ................. 40
D311 Microbiology OA Exam
1. Which type of organism would be most likely to grow on food stored in a
refrigerator or freezer?
A. Thermophile
B. Mesophile
C. Psychrophile
D. Acidophile
Correct Answer: C. Psychrophile
Expert Rationale: Psychrophiles (cold-loving organisms) thrive at temperatures of
0–15°C, with optimal growth around 10°C. They produce cold-adapted enzymes
with high catalytic efficiency at low temperatures. Common psychrotrophic
pathogens include Listeria monocytogenes and Yersinia enterocolitica, which can
proliferate in refrigerated foods and cause foodborne illness if contaminated
products are consumed without adequate heating.
,2. Staphylococcus epidermidis is a member of the human resident microbiota
and considered part of the human innate immune system. S. epidermidis uses
our dead skin cells as a source of nutrients. What type of relationship between
S. epidermidis and humans is described above?
A. Mutualism
B. Parasitism
C. Commensalism
D. Competition
Correct Answer: C. Commensalism
Expert Rationale: Commensalism is a symbiotic relationship in which one
organism benefits while the other is neither harmed nor benefited.
Staphylococcus epidermidis colonizes human skin, obtaining nutrients from dead
keratinocytes and sebaceous secretions without causing disease in
immunocompetent hosts. In fact, it contributes to innate immunity by producing
antimicrobial peptides that inhibit pathogen colonization.
3. Why is the production of lactic acid by the resident microbe Lactobacillus
important to human health?
A. It enhances viral replication in the gut
B. It inhibits the growth of pathogenic microbes
C. It degrades the intestinal mucosal barrier
D. It neutralizes stomach acid completely
Correct Answer: B. It inhibits the growth of pathogenic microbes
Expert Rationale: Lactobacillus species ferment carbohydrates to produce lactic
acid, lowering the pH of the vaginal canal and gastrointestinal tract. This acidic
environment inhibits colonization by pathogenic bacteria and yeast by disrupting
their metabolic enzymes and membrane integrity. Additionally, Lactobacillus
,A. The cell has a capsule
B. The cell has flagella
C. The cell is gram-positive
D. The cell produces endospores
Correct Answer: A. The cell has a capsule
Expert Rationale: India ink is a negative staining technique where the acidic,
opaque dye is repelled by the negatively charged bacterial surface. The capsule,
being non-ionic and hydrophilic, excludes the ink particles, creating a
characteristic clear halo around the cell against a dark background. This is clinically
used to identify Cryptococcus neoformans in cerebrospinal fluid.
16. How do basic stains work?
A. The negatively charged stain is attracted to the positively charged portion of the
cell
B. The positively charged stain is attracted to the negatively charged portion of the
cell
C. The stain penetrates the capsule and stains the nucleus exclusively
D. The stain binds to lipopolysaccharide in the outer membrane
Correct Answer: B. The positively charged stain is attracted to the negatively
charged portion of the cell
Expert Rationale: Basic stains (e.g., methylene blue, crystal violet, safranin) carry a
positive charge on their chromophore and are electrostatically attracted to
negatively charged bacterial components—primarily nucleic acids (phosphate
backbone) and acidic proteins. This ionic interaction ensures uniform coloration of
the cell for visualization under light microscopy.
,A. Antibody production by plasma cells
B. Mucous secretions trapping and removing microbes from the respiratory tract
C. T-cell mediated cytotoxicity
D. Memory B cell activation upon re-exposure
Correct Answer: B. Mucous secretions trapping and removing microbes from the
respiratory tract
Expert Rationale: Innate physical (mechanical) defenses are nonspecific barriers
that prevent pathogen entry or remove them without antigen-specific recognition.
Mucous secretions in the respiratory, gastrointestinal, and genitourinary tracts
physically trap microbes, while peristalsis, coughing, sneezing, and urine flow
mechanically expel them. Antibody production, T-cell cytotoxicity, and memory
responses are adaptive immune functions requiring antigen-specific recognition.
35. Which vaccine type would be effective against an organism that can produce
a capsule?
A. Live attenuated vaccine
B. Inactivated vaccine
C. Toxoid vaccine
D. Conjugate vaccine
Correct Answer: D. Conjugate vaccine
Expert Rationale: Conjugate vaccines link capsular polysaccharides (T-
independent antigens that poorly stimulate infant immune systems) to protein
carriers such as tetanus toxoid or diphtheria toxoid. This conjugation converts the
response to T-dependent, eliciting robust IgG production, memory B-cell
formation, and efficacy in children under 2 years. Examples include Hib, PCV13
(pneumococcal), and MenACWY vaccines.
,Correct Answer: B. Clostridium perfringens
Expert Rationale: Clostridium perfringens (formerly C. welchii) is an anaerobic,
spore-forming gram-positive rod that causes gas gangrene (myonecrosis) through
rapid tissue destruction, gas production, and hemolysis. The alpha-toxin
(lecithinase/phospholipase C) destroys cell membranes and erythrocytes.
Traumatic wounds with compromised blood supply create anaerobic conditions
ideal for spore germination. Surgical debridement, hyperbaric oxygen, and
antibiotics (penicillin + clindamycin) are essential.
72. Which gram-positive, spore-forming bacterium causes muscle stiffness and
spasms?
A. Clostridium botulinum
B. Clostridium perfringens
C. Clostridium tetani
D. Bacillus cereus
Correct Answer: C. Clostridium tetani
Expert Rationale: Clostridium tetani produces tetanospasmin, a neurotoxin that
blocks inhibitory neurotransmitter release (glycine and GABA) from spinal
interneurons. This results in unopposed motor neuron activity, causing
characteristic muscle rigidity, lockjaw (trismus), opisthotonus, and severe spasms.
The toxin travels retroaxonally to the CNS. Tetanus is prevented by the DTaP/Tdap
toxoid vaccine; treatment requires tetanus immune globulin, wound care, muscle
relaxants, and ventilatory support.
73. When are narrow-spectrum antibiotics used?
A. When the infection is polymicrobial and the causative agent is unknown
B. When the target bacteria has been identified
, D311 OA Definitions, Concept Reviews & Study Guide
Differentiate Prokaryotic and Eukaryotic Cells
Prokaryotic Cells No true nucleus ( nucleoid region )
Differentiate Prokaryotic and Eukaryotic Cells
Prokaryotic Cells Organelles No membrane - bound organelles Ribosomes Smaller
( 70S )
Differentiate Prokaryotic and Eukaryotic Cells
Prokaryotic Cells Cell Wall Present ( contains peptidoglycan in bacteria )
Differentiate Prokaryotic and Eukaryotic Cells
Eukaryotic Cells Membrane - bound organelles present
Differentiate Prokaryotic and Eukaryotic Cells
Eukaryotic Cells True nucleus enclosed in a membrane
Differentiate Prokaryotic and Eukaryotic Cells
Cell Wall May or may not be present , composition varies
Prokaryotic Cells Examples
Bacteria , Archaea
Eukaryotic Cells Examples
Animals plants , fungi , protists
,Living : Livestock ( sheep , goats , cattle ) . Nonliving : Soil contaminated by animal
waste .
Influenza Reservoir
Living : Humans , birds , pigs ( avian and swine influenza ) .
SARS ( Severe Acute Respiratory Syndrome ) and MERS ( Middle East Respiratory
Syndrome ) Reservoir
Living : Bats ( primary reservoir ) ; camels ( intermediate host for MERS ) .
Giardiasis ( Giardia lamblia ) Reservoir
Living : Humans , wild animals ( e.g. , beavers ) . Nonliving : Contaminated water .
Human Granulocytic Anaplasmosis ( HGA ) ( Anaplasma phagocytophilum )
Reservoir
Living : Small mammals ( e.g. , mice , deer ) . Arthropod vector : Ticks ( Ixodes
scapularis ) .
Epidemic Typhus ( Rickettsia prowazekii ) Reservoir
Living : Humans ( primary reservoir ) . Arthropod vector : Body lice .
Lyme Disease ( Borrelia burgdorferi ) Reservoir :
Living : Small mammals ( e.g. , white - footed mice ) , deer . Arthropod vector :
Ticks ( Ixodes scapularis ) .
Relapsing Fever ( Borrelia species ) Reservoir
Living : Rodents . Arthropod vector : Ticks or lice .
Toxoplasmosis ( Toxoplasma gondii ) Reservoir :
Definitive host : Cats ( where the parasite undergoes sexual reproduction ) .
Intermediate hosts : Humans , livestock .
, Acid - Fast Stain Identifies which bacteria
genera Mycobacterium and Nocardia
Hyaluronidase S Degrades hyaluronic acid in
Staphylococcus aureus
DNAse
DNAse produced by
Staphylococcus aureus
Example of Phospholipase C from
Bacillus anthracis
Collagenase is also in
Clostridium perfringens
Endotoxin Source
Gram - negative bacteria
Exotoxin Source
Gram - positive ( primarily ) and gram - negative bacteria
Endotoxin Effect on host
General systemic symptoms of inflammation and fever
Exotoxin Effect on host
Specific damage to cells dependent upon receptor- mediated targeting of cells and
specific mechanisms of action
Examples of general types of exotoxins
Microbiology
OA EXAM
Actual Questions with Verified Answers
Pass the Exam with Confidence
What You Will Get:
➢85 OA Exam Questions w/ Answers
➢ OA Definitions,
➢ Concept Reviews
➢ Study Guide
➢ Expert Rationales included.
Take and pass the OA :)
, D311 Microbiology OA Exam
Preview Pages Below
Get the Complete PDF After Purchase
"If you require further clarification or in need of any
study resources, feel free to Message me."
Preview sample - complete PDF available after purchase
,Table of Contents
D311 Microbiology OA Exam ............................................................ 2
D311 OA Definitions, Concept Reviews & Study Guide ................. 40
D311 Microbiology OA Exam
1. Which type of organism would be most likely to grow on food stored in a
refrigerator or freezer?
A. Thermophile
B. Mesophile
C. Psychrophile
D. Acidophile
Correct Answer: C. Psychrophile
Expert Rationale: Psychrophiles (cold-loving organisms) thrive at temperatures of
0–15°C, with optimal growth around 10°C. They produce cold-adapted enzymes
with high catalytic efficiency at low temperatures. Common psychrotrophic
pathogens include Listeria monocytogenes and Yersinia enterocolitica, which can
proliferate in refrigerated foods and cause foodborne illness if contaminated
products are consumed without adequate heating.
,2. Staphylococcus epidermidis is a member of the human resident microbiota
and considered part of the human innate immune system. S. epidermidis uses
our dead skin cells as a source of nutrients. What type of relationship between
S. epidermidis and humans is described above?
A. Mutualism
B. Parasitism
C. Commensalism
D. Competition
Correct Answer: C. Commensalism
Expert Rationale: Commensalism is a symbiotic relationship in which one
organism benefits while the other is neither harmed nor benefited.
Staphylococcus epidermidis colonizes human skin, obtaining nutrients from dead
keratinocytes and sebaceous secretions without causing disease in
immunocompetent hosts. In fact, it contributes to innate immunity by producing
antimicrobial peptides that inhibit pathogen colonization.
3. Why is the production of lactic acid by the resident microbe Lactobacillus
important to human health?
A. It enhances viral replication in the gut
B. It inhibits the growth of pathogenic microbes
C. It degrades the intestinal mucosal barrier
D. It neutralizes stomach acid completely
Correct Answer: B. It inhibits the growth of pathogenic microbes
Expert Rationale: Lactobacillus species ferment carbohydrates to produce lactic
acid, lowering the pH of the vaginal canal and gastrointestinal tract. This acidic
environment inhibits colonization by pathogenic bacteria and yeast by disrupting
their metabolic enzymes and membrane integrity. Additionally, Lactobacillus
,A. The cell has a capsule
B. The cell has flagella
C. The cell is gram-positive
D. The cell produces endospores
Correct Answer: A. The cell has a capsule
Expert Rationale: India ink is a negative staining technique where the acidic,
opaque dye is repelled by the negatively charged bacterial surface. The capsule,
being non-ionic and hydrophilic, excludes the ink particles, creating a
characteristic clear halo around the cell against a dark background. This is clinically
used to identify Cryptococcus neoformans in cerebrospinal fluid.
16. How do basic stains work?
A. The negatively charged stain is attracted to the positively charged portion of the
cell
B. The positively charged stain is attracted to the negatively charged portion of the
cell
C. The stain penetrates the capsule and stains the nucleus exclusively
D. The stain binds to lipopolysaccharide in the outer membrane
Correct Answer: B. The positively charged stain is attracted to the negatively
charged portion of the cell
Expert Rationale: Basic stains (e.g., methylene blue, crystal violet, safranin) carry a
positive charge on their chromophore and are electrostatically attracted to
negatively charged bacterial components—primarily nucleic acids (phosphate
backbone) and acidic proteins. This ionic interaction ensures uniform coloration of
the cell for visualization under light microscopy.
,A. Antibody production by plasma cells
B. Mucous secretions trapping and removing microbes from the respiratory tract
C. T-cell mediated cytotoxicity
D. Memory B cell activation upon re-exposure
Correct Answer: B. Mucous secretions trapping and removing microbes from the
respiratory tract
Expert Rationale: Innate physical (mechanical) defenses are nonspecific barriers
that prevent pathogen entry or remove them without antigen-specific recognition.
Mucous secretions in the respiratory, gastrointestinal, and genitourinary tracts
physically trap microbes, while peristalsis, coughing, sneezing, and urine flow
mechanically expel them. Antibody production, T-cell cytotoxicity, and memory
responses are adaptive immune functions requiring antigen-specific recognition.
35. Which vaccine type would be effective against an organism that can produce
a capsule?
A. Live attenuated vaccine
B. Inactivated vaccine
C. Toxoid vaccine
D. Conjugate vaccine
Correct Answer: D. Conjugate vaccine
Expert Rationale: Conjugate vaccines link capsular polysaccharides (T-
independent antigens that poorly stimulate infant immune systems) to protein
carriers such as tetanus toxoid or diphtheria toxoid. This conjugation converts the
response to T-dependent, eliciting robust IgG production, memory B-cell
formation, and efficacy in children under 2 years. Examples include Hib, PCV13
(pneumococcal), and MenACWY vaccines.
,Correct Answer: B. Clostridium perfringens
Expert Rationale: Clostridium perfringens (formerly C. welchii) is an anaerobic,
spore-forming gram-positive rod that causes gas gangrene (myonecrosis) through
rapid tissue destruction, gas production, and hemolysis. The alpha-toxin
(lecithinase/phospholipase C) destroys cell membranes and erythrocytes.
Traumatic wounds with compromised blood supply create anaerobic conditions
ideal for spore germination. Surgical debridement, hyperbaric oxygen, and
antibiotics (penicillin + clindamycin) are essential.
72. Which gram-positive, spore-forming bacterium causes muscle stiffness and
spasms?
A. Clostridium botulinum
B. Clostridium perfringens
C. Clostridium tetani
D. Bacillus cereus
Correct Answer: C. Clostridium tetani
Expert Rationale: Clostridium tetani produces tetanospasmin, a neurotoxin that
blocks inhibitory neurotransmitter release (glycine and GABA) from spinal
interneurons. This results in unopposed motor neuron activity, causing
characteristic muscle rigidity, lockjaw (trismus), opisthotonus, and severe spasms.
The toxin travels retroaxonally to the CNS. Tetanus is prevented by the DTaP/Tdap
toxoid vaccine; treatment requires tetanus immune globulin, wound care, muscle
relaxants, and ventilatory support.
73. When are narrow-spectrum antibiotics used?
A. When the infection is polymicrobial and the causative agent is unknown
B. When the target bacteria has been identified
, D311 OA Definitions, Concept Reviews & Study Guide
Differentiate Prokaryotic and Eukaryotic Cells
Prokaryotic Cells No true nucleus ( nucleoid region )
Differentiate Prokaryotic and Eukaryotic Cells
Prokaryotic Cells Organelles No membrane - bound organelles Ribosomes Smaller
( 70S )
Differentiate Prokaryotic and Eukaryotic Cells
Prokaryotic Cells Cell Wall Present ( contains peptidoglycan in bacteria )
Differentiate Prokaryotic and Eukaryotic Cells
Eukaryotic Cells Membrane - bound organelles present
Differentiate Prokaryotic and Eukaryotic Cells
Eukaryotic Cells True nucleus enclosed in a membrane
Differentiate Prokaryotic and Eukaryotic Cells
Cell Wall May or may not be present , composition varies
Prokaryotic Cells Examples
Bacteria , Archaea
Eukaryotic Cells Examples
Animals plants , fungi , protists
,Living : Livestock ( sheep , goats , cattle ) . Nonliving : Soil contaminated by animal
waste .
Influenza Reservoir
Living : Humans , birds , pigs ( avian and swine influenza ) .
SARS ( Severe Acute Respiratory Syndrome ) and MERS ( Middle East Respiratory
Syndrome ) Reservoir
Living : Bats ( primary reservoir ) ; camels ( intermediate host for MERS ) .
Giardiasis ( Giardia lamblia ) Reservoir
Living : Humans , wild animals ( e.g. , beavers ) . Nonliving : Contaminated water .
Human Granulocytic Anaplasmosis ( HGA ) ( Anaplasma phagocytophilum )
Reservoir
Living : Small mammals ( e.g. , mice , deer ) . Arthropod vector : Ticks ( Ixodes
scapularis ) .
Epidemic Typhus ( Rickettsia prowazekii ) Reservoir
Living : Humans ( primary reservoir ) . Arthropod vector : Body lice .
Lyme Disease ( Borrelia burgdorferi ) Reservoir :
Living : Small mammals ( e.g. , white - footed mice ) , deer . Arthropod vector :
Ticks ( Ixodes scapularis ) .
Relapsing Fever ( Borrelia species ) Reservoir
Living : Rodents . Arthropod vector : Ticks or lice .
Toxoplasmosis ( Toxoplasma gondii ) Reservoir :
Definitive host : Cats ( where the parasite undergoes sexual reproduction ) .
Intermediate hosts : Humans , livestock .
, Acid - Fast Stain Identifies which bacteria
genera Mycobacterium and Nocardia
Hyaluronidase S Degrades hyaluronic acid in
Staphylococcus aureus
DNAse
DNAse produced by
Staphylococcus aureus
Example of Phospholipase C from
Bacillus anthracis
Collagenase is also in
Clostridium perfringens
Endotoxin Source
Gram - negative bacteria
Exotoxin Source
Gram - positive ( primarily ) and gram - negative bacteria
Endotoxin Effect on host
General systemic symptoms of inflammation and fever
Exotoxin Effect on host
Specific damage to cells dependent upon receptor- mediated targeting of cells and
specific mechanisms of action
Examples of general types of exotoxins
