,BIOD 171 Module 5 Exam | Essential Microbiology
| Portage Learning | Q & A | 2026 Edition
1. Which of the following best describes the concept of universal precautions in a microbiology
laboratory?
A) Wearing gloves only when handling known pathogenic samples
B) Treating all human blood and certain body fluids as infectious, regardless of the perceived status of
the source individual
C) Using antibiotics to prevent infection from any accidental exposure
D) Sterilizing all equipment after each use to prevent contamination
Correct Answer: Treating all human blood and certain body fluids as infectious, regardless of the
perceived status of the source individual
Rationale: Universal precautions are an infection control approach that treats all human blood and
certain body fluids as potentially infectious, regardless of the source. This minimizes the risk of exposure
to bloodborne pathogens and is critical for laboratory and clinical safety, applying to all samples
whether known or unknown.
2. What is the primary reason a researcher must determine motility before determining Gram status
when using the same liquid sample?
A) Motility requires a larger sample volume than Gram staining
B) Gram staining requires heat fixation, which would kill the organism and prevent motility observation
C) Motility status influences which Gram stain procedure to use
D) The Gram stain reagents would permanently alter the organism's motility
Correct Answer: Gram staining requires heat fixation, which would kill the organism and prevent motility
observation
Rationale: Motility requires a wet mount of living cells, while Gram staining requires heat fixing the
sample. Heat fixation kills the organism, making any observations regarding motility impossible.
Therefore, motility must be assessed first on the live sample.
,3. A facultative anaerobe is a microorganism capable of growth under which conditions?
A) Only in the presence of oxygen
B) Only in the absence of oxygen
C) In both the presence and absence of oxygen
D) Only in environments with very low oxygen concentrations
Correct Answer: In both the presence and absence of oxygen
Rationale: A facultative anaerobe can grow under both aerobic (with oxygen) and anaerobic (without
oxygen) conditions. This flexibility allows it to thrive in a variety of environments, making it distinct from
obligate aerobes or obligate anaerobes.
4. As Streptococcus is catalase negative, what would happen in the presence of peroxides?
A) It would thrive because peroxides provide an energy source
B) It would die because it cannot break down peroxides
C) It would form endospores to protect itself
D) It would become catalase positive through mutation
Correct Answer: It would die because it cannot break down peroxides
Rationale: Streptococcus is catalase negative, meaning it cannot break down peroxides. Left unchecked,
peroxides would damage its cellular integrity, causing lysis or cell death. Catalase-positive organisms can
detoxify peroxides, but Streptococcus lacks this enzyme.
5. Which agar plate is most appropriate for culturing and identifying a suspected Streptococcus sample
based on its hemolytic properties?
A) MacConkey agar
B) Eosin Methylene Blue (EMB) agar
C) Blood agar plate (BAP)
, D) Mannitol salt agar
Correct Answer: Blood agar plate (BAP)
Rationale: Blood agar is a non-selective yet differential medium used to identify and classify
Streptococcus based on its hemolytic properties (alpha, beta, or gamma hemolysis). This is the quickest
way to differentiate streptococcal species.
6. Left untreated, streptococcal pharyngitis (strep throat) can progress to which condition, and what
type of hemolytic activity does it display?
A) Strep septicemia; gamma hemolysis
B) Rheumatic fever; beta hemolysis
C) Strep pharyngitis; alpha hemolysis
D) Scarlet fever; alpha hemolysis
Correct Answer: Rheumatic fever; beta hemolysis
Rationale: Strep throat can lead to rheumatic fever in approximately 3% of untreated cases, presenting
2-3 weeks post-infection. Streptococcus pyogenes, the causative agent, displays beta-hemolytic activity.
7. Which of the following statements is true regarding the Lancefield classification system?
A) It is used to subdivide alpha-hemolytic streptococci
B) It is used to subdivide beta-hemolytic streptococci
C) It is used to subdivide gamma-hemolytic streptococci
D) It is based on the organism's hemolytic pattern
Correct Answer: It is used to subdivide beta-hemolytic streptococci
Rationale: Lancefield grouping is based on the carbohydrate composition of cell wall antigens and is
primarily used to classify beta-hemolytic streptococci, not alpha- or gamma-hemolytic strains. All strep
under Lancefield groupings are catalase negative and beta-hemolytic.
| Portage Learning | Q & A | 2026 Edition
1. Which of the following best describes the concept of universal precautions in a microbiology
laboratory?
A) Wearing gloves only when handling known pathogenic samples
B) Treating all human blood and certain body fluids as infectious, regardless of the perceived status of
the source individual
C) Using antibiotics to prevent infection from any accidental exposure
D) Sterilizing all equipment after each use to prevent contamination
Correct Answer: Treating all human blood and certain body fluids as infectious, regardless of the
perceived status of the source individual
Rationale: Universal precautions are an infection control approach that treats all human blood and
certain body fluids as potentially infectious, regardless of the source. This minimizes the risk of exposure
to bloodborne pathogens and is critical for laboratory and clinical safety, applying to all samples
whether known or unknown.
2. What is the primary reason a researcher must determine motility before determining Gram status
when using the same liquid sample?
A) Motility requires a larger sample volume than Gram staining
B) Gram staining requires heat fixation, which would kill the organism and prevent motility observation
C) Motility status influences which Gram stain procedure to use
D) The Gram stain reagents would permanently alter the organism's motility
Correct Answer: Gram staining requires heat fixation, which would kill the organism and prevent motility
observation
Rationale: Motility requires a wet mount of living cells, while Gram staining requires heat fixing the
sample. Heat fixation kills the organism, making any observations regarding motility impossible.
Therefore, motility must be assessed first on the live sample.
,3. A facultative anaerobe is a microorganism capable of growth under which conditions?
A) Only in the presence of oxygen
B) Only in the absence of oxygen
C) In both the presence and absence of oxygen
D) Only in environments with very low oxygen concentrations
Correct Answer: In both the presence and absence of oxygen
Rationale: A facultative anaerobe can grow under both aerobic (with oxygen) and anaerobic (without
oxygen) conditions. This flexibility allows it to thrive in a variety of environments, making it distinct from
obligate aerobes or obligate anaerobes.
4. As Streptococcus is catalase negative, what would happen in the presence of peroxides?
A) It would thrive because peroxides provide an energy source
B) It would die because it cannot break down peroxides
C) It would form endospores to protect itself
D) It would become catalase positive through mutation
Correct Answer: It would die because it cannot break down peroxides
Rationale: Streptococcus is catalase negative, meaning it cannot break down peroxides. Left unchecked,
peroxides would damage its cellular integrity, causing lysis or cell death. Catalase-positive organisms can
detoxify peroxides, but Streptococcus lacks this enzyme.
5. Which agar plate is most appropriate for culturing and identifying a suspected Streptococcus sample
based on its hemolytic properties?
A) MacConkey agar
B) Eosin Methylene Blue (EMB) agar
C) Blood agar plate (BAP)
, D) Mannitol salt agar
Correct Answer: Blood agar plate (BAP)
Rationale: Blood agar is a non-selective yet differential medium used to identify and classify
Streptococcus based on its hemolytic properties (alpha, beta, or gamma hemolysis). This is the quickest
way to differentiate streptococcal species.
6. Left untreated, streptococcal pharyngitis (strep throat) can progress to which condition, and what
type of hemolytic activity does it display?
A) Strep septicemia; gamma hemolysis
B) Rheumatic fever; beta hemolysis
C) Strep pharyngitis; alpha hemolysis
D) Scarlet fever; alpha hemolysis
Correct Answer: Rheumatic fever; beta hemolysis
Rationale: Strep throat can lead to rheumatic fever in approximately 3% of untreated cases, presenting
2-3 weeks post-infection. Streptococcus pyogenes, the causative agent, displays beta-hemolytic activity.
7. Which of the following statements is true regarding the Lancefield classification system?
A) It is used to subdivide alpha-hemolytic streptococci
B) It is used to subdivide beta-hemolytic streptococci
C) It is used to subdivide gamma-hemolytic streptococci
D) It is based on the organism's hemolytic pattern
Correct Answer: It is used to subdivide beta-hemolytic streptococci
Rationale: Lancefield grouping is based on the carbohydrate composition of cell wall antigens and is
primarily used to classify beta-hemolytic streptococci, not alpha- or gamma-hemolytic strains. All strep
under Lancefield groupings are catalase negative and beta-hemolytic.
