SCI 251 Exam 4 V2 | SCI 251 Microbiology
with Intervention Skill-Based (ISB)
Experiential Learning | Q&A with
Rationale (SCI251 Exam 4) | Nightingale
College
1. A patient presents with a severe sore throat, high fever, and a distinct ‘strawberry tongue’
appearance. Which pathogen is the most likely cause?
A. Streptococcus pneumoniae
B. Staphylococcus aureus
C. Streptococcus pyogenes
D. Haemophilus influenzae
Correct Answer: C
Rationale: Streptococcus pyogenes is the causative agent of scarlet fever, which follows a
pharyngeal infection. The strawberry tongue and sandpaper-like rash are classic clinical
indicators caused by erythrogenic toxins. These toxins are produced by the bacteria when
they are lysogenized by a specific bacteriophage.
2. Which mechanism of action is primarily used by the influenza virus to enter host
respiratory cells?
A. Neuraminidase cleavage of sialic acid
,B. Endocytosis via protein A
C. Hemagglutinin binding to sialic acid receptors
D. Direct injection of viral RNA via pili
Correct Answer: C
Rationale: Hemagglutinin (HA) is a surface glycoprotein on the influenza virus that
facilitates attachment to sialic acid on host cell membranes. Once attached, the virus enters
the cell through receptor-mediated endocytosis. This process is distinct from the role of
Neuraminidase, which is responsible for the release of new viral particles from the host
cell.
3. A positive Mantoux skin test (PPD) indicates that the individual has been exposed to
Mycobacterium tuberculosis. Which immune response is responsible for this reaction?
A. Type IV Hypersensitivity
B. Type II Hypersensitivity
C. Type III Hypersensitivity
D. Type I Hypersensitivity
Correct Answer: A
Rationale: The PPD test is a classic example of a delayed-type hypersensitivity reaction,
also known as Type IV. It is mediated by T-lymphocytes rather than antibodies and takes
, 48 to 72 hours to manifest after the antigen is injected. A positive result indicates the
presence of memory T cells, signifying prior exposure to the pathogen.
4. Which bacterial species is most commonly associated with the formation of peptic ulcers
and chronic gastritis?
A. Helicobacter pylori
B. Escherichia coli
C. Salmonella enterica
D. Campylobacter jejuni
Correct Answer: A
Rationale: Helicobacter pylori is a gram-negative, spiral-shaped bacterium that inhabits
the acidic environment of the stomach. It produces the enzyme urease, which neutralizes
stomach acid by converting urea into ammonia and carbon dioxide. This localized
neutralization allows the bacteria to survive and damage the protective mucosal lining,
leading to ulceration.
5. Rice-water stools are a pathognomonic sign of an infection caused by which of the
following organisms?
A. Giardia lamblia
B. Shigella dysenteriae
C. Vibrio cholerae
with Intervention Skill-Based (ISB)
Experiential Learning | Q&A with
Rationale (SCI251 Exam 4) | Nightingale
College
1. A patient presents with a severe sore throat, high fever, and a distinct ‘strawberry tongue’
appearance. Which pathogen is the most likely cause?
A. Streptococcus pneumoniae
B. Staphylococcus aureus
C. Streptococcus pyogenes
D. Haemophilus influenzae
Correct Answer: C
Rationale: Streptococcus pyogenes is the causative agent of scarlet fever, which follows a
pharyngeal infection. The strawberry tongue and sandpaper-like rash are classic clinical
indicators caused by erythrogenic toxins. These toxins are produced by the bacteria when
they are lysogenized by a specific bacteriophage.
2. Which mechanism of action is primarily used by the influenza virus to enter host
respiratory cells?
A. Neuraminidase cleavage of sialic acid
,B. Endocytosis via protein A
C. Hemagglutinin binding to sialic acid receptors
D. Direct injection of viral RNA via pili
Correct Answer: C
Rationale: Hemagglutinin (HA) is a surface glycoprotein on the influenza virus that
facilitates attachment to sialic acid on host cell membranes. Once attached, the virus enters
the cell through receptor-mediated endocytosis. This process is distinct from the role of
Neuraminidase, which is responsible for the release of new viral particles from the host
cell.
3. A positive Mantoux skin test (PPD) indicates that the individual has been exposed to
Mycobacterium tuberculosis. Which immune response is responsible for this reaction?
A. Type IV Hypersensitivity
B. Type II Hypersensitivity
C. Type III Hypersensitivity
D. Type I Hypersensitivity
Correct Answer: A
Rationale: The PPD test is a classic example of a delayed-type hypersensitivity reaction,
also known as Type IV. It is mediated by T-lymphocytes rather than antibodies and takes
, 48 to 72 hours to manifest after the antigen is injected. A positive result indicates the
presence of memory T cells, signifying prior exposure to the pathogen.
4. Which bacterial species is most commonly associated with the formation of peptic ulcers
and chronic gastritis?
A. Helicobacter pylori
B. Escherichia coli
C. Salmonella enterica
D. Campylobacter jejuni
Correct Answer: A
Rationale: Helicobacter pylori is a gram-negative, spiral-shaped bacterium that inhabits
the acidic environment of the stomach. It produces the enzyme urease, which neutralizes
stomach acid by converting urea into ammonia and carbon dioxide. This localized
neutralization allows the bacteria to survive and damage the protective mucosal lining,
leading to ulceration.
5. Rice-water stools are a pathognomonic sign of an infection caused by which of the
following organisms?
A. Giardia lamblia
B. Shigella dysenteriae
C. Vibrio cholerae
