,BIO 2100 EXAM 4 - Original Practice Study Guide
BIO 2100 Exam 4 | Microbiology | 2026 Update |100%
Correct – Galen College
1. A patient has a painful skin abscess that yields gram-positive cocci in clusters. Which organism is most
likely?
A) Bordetella pertussis
B) Streptococcus pyogenes
C) Neisseria gonorrhoeae
D) Staphylococcus aureus
Correct Answer: Staphylococcus aureus
Rationale: Staphylococcus aureus commonly causes purulent skin and soft-tissue infections and appears as gram-
positive cocci in clusters. Streptococci more often form chains, while the other organisms primarily cause urogenital or
respiratory disease. This distinction is useful for prioritizing microbiologic interpretation and avoiding distractors that
describe a different organism, transmission route, mechanism, or diagnostic principle.
2. A rapidly spreading erythematous skin infection is accompanied by fever and sharply advancing
margins. Which bacterial pathogen is a common cause of erysipelas?
A) Escherichia coli
B) Clostridioides difficile
C) Treponema pallidum
D) Streptococcus pyogenes
Correct Answer: Streptococcus pyogenes
Rationale: Group A Streptococcus can cause erysipelas and cellulitis by invading superficial tissues. Its virulence factors
include adhesins, enzymes, and immune-evasion mechanisms that promote spread. This distinction is useful for
prioritizing microbiologic interpretation and avoiding distractors that describe a different organism, transmission route,
mechanism, or diagnostic principle.
3. A person develops severe pain, tissue destruction, gas production, and systemic toxicity after a
contaminated crush injury. Which organism is most strongly associated with gas gangrene?
A) Clostridium perfringens
B) Corynebacterium diphtheriae
C) Mycoplasma pneumoniae
D) Chlamydia trachomatis
Correct Answer: Clostridium perfringens
Rationale: Clostridium perfringens is an anaerobic spore-forming bacterium whose toxins can cause myonecrosis and
gas gangrene after traumatic inoculation into poorly oxygenated tissue. This distinction is useful for prioritizing
microbiologic interpretation and avoiding distractors that describe a different organism, transmission route, mechanism,
or diagnostic principle.
4. Which feature is most characteristic of cutaneous anthrax?
A) Honey-colored crusts around the mouth
B) Grouped painful vesicles on an erythematous base
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, BIO 2100 EXAM 4 - Original Practice Study Guide
C) A painless black eschar with surrounding edema
D) Diffuse pruritic scaling between toes
Correct Answer: A painless black eschar with surrounding edema
Rationale: Cutaneous anthrax classically forms a painless papule that progresses to a vesicle and then a black eschar
with marked edema. The pattern differs from herpes, impetigo, and dermatophyte infection. This distinction is useful for
prioritizing microbiologic interpretation and avoiding distractors that describe a different organism, transmission route,
mechanism, or diagnostic principle.
5. A child develops honey-colored crusted lesions around the nose and mouth. Which diagnosis is most
likely?
A) Tinea corporis
B) Impetigo
C) Herpes zoster
D) Trachoma
Correct Answer: Impetigo
Rationale: Impetigo is a superficial bacterial skin infection commonly caused by Staphylococcus aureus or
Streptococcus pyogenes. Honey-colored crusting is a classic feature. This distinction is useful for prioritizing
microbiologic interpretation and avoiding distractors that describe a different organism, transmission route, mechanism,
or diagnostic principle.
6. A patient has grouped painful vesicles that recur at the same lip location. Which pathogen best fits this
pattern?
A) Human papillomavirus
B) Herpes simplex virus type 1
C) Parvovirus B19
D) Adenovirus
Correct Answer: Herpes simplex virus type 1
Rationale: HSV-1 establishes latency in sensory ganglia and can reactivate, producing recurrent painful vesicular lesions
near the mouth. This distinction is useful for prioritizing microbiologic interpretation and avoiding distractors that describe
a different organism, transmission route, mechanism, or diagnostic principle.
7. A dermatomal painful vesicular eruption occurs in an older adult. Which mechanism explains the
illness?
A) Reactivation of latent varicella-zoster virus in sensory ganglia
B) Primary infection with Epstein-Barr virus
C) Transformation by human papillomavirus
D) Acute adenovirus bacteremia
Correct Answer: Reactivation of latent varicella-zoster virus in sensory ganglia
Rationale: Herpes zoster results from reactivation of latent varicella-zoster virus in dorsal root or cranial nerve ganglia,
producing a unilateral dermatomal eruption. This distinction is useful for prioritizing microbiologic interpretation and
avoiding distractors that describe a different organism, transmission route, mechanism, or diagnostic principle.
8. A child has fever, oral ulcers, and vesicular lesions on the hands and feet. Which viral disease is most
consistent?
Page 3
BIO 2100 Exam 4 | Microbiology | 2026 Update |100%
Correct – Galen College
1. A patient has a painful skin abscess that yields gram-positive cocci in clusters. Which organism is most
likely?
A) Bordetella pertussis
B) Streptococcus pyogenes
C) Neisseria gonorrhoeae
D) Staphylococcus aureus
Correct Answer: Staphylococcus aureus
Rationale: Staphylococcus aureus commonly causes purulent skin and soft-tissue infections and appears as gram-
positive cocci in clusters. Streptococci more often form chains, while the other organisms primarily cause urogenital or
respiratory disease. This distinction is useful for prioritizing microbiologic interpretation and avoiding distractors that
describe a different organism, transmission route, mechanism, or diagnostic principle.
2. A rapidly spreading erythematous skin infection is accompanied by fever and sharply advancing
margins. Which bacterial pathogen is a common cause of erysipelas?
A) Escherichia coli
B) Clostridioides difficile
C) Treponema pallidum
D) Streptococcus pyogenes
Correct Answer: Streptococcus pyogenes
Rationale: Group A Streptococcus can cause erysipelas and cellulitis by invading superficial tissues. Its virulence factors
include adhesins, enzymes, and immune-evasion mechanisms that promote spread. This distinction is useful for
prioritizing microbiologic interpretation and avoiding distractors that describe a different organism, transmission route,
mechanism, or diagnostic principle.
3. A person develops severe pain, tissue destruction, gas production, and systemic toxicity after a
contaminated crush injury. Which organism is most strongly associated with gas gangrene?
A) Clostridium perfringens
B) Corynebacterium diphtheriae
C) Mycoplasma pneumoniae
D) Chlamydia trachomatis
Correct Answer: Clostridium perfringens
Rationale: Clostridium perfringens is an anaerobic spore-forming bacterium whose toxins can cause myonecrosis and
gas gangrene after traumatic inoculation into poorly oxygenated tissue. This distinction is useful for prioritizing
microbiologic interpretation and avoiding distractors that describe a different organism, transmission route, mechanism,
or diagnostic principle.
4. Which feature is most characteristic of cutaneous anthrax?
A) Honey-colored crusts around the mouth
B) Grouped painful vesicles on an erythematous base
Page 2
, BIO 2100 EXAM 4 - Original Practice Study Guide
C) A painless black eschar with surrounding edema
D) Diffuse pruritic scaling between toes
Correct Answer: A painless black eschar with surrounding edema
Rationale: Cutaneous anthrax classically forms a painless papule that progresses to a vesicle and then a black eschar
with marked edema. The pattern differs from herpes, impetigo, and dermatophyte infection. This distinction is useful for
prioritizing microbiologic interpretation and avoiding distractors that describe a different organism, transmission route,
mechanism, or diagnostic principle.
5. A child develops honey-colored crusted lesions around the nose and mouth. Which diagnosis is most
likely?
A) Tinea corporis
B) Impetigo
C) Herpes zoster
D) Trachoma
Correct Answer: Impetigo
Rationale: Impetigo is a superficial bacterial skin infection commonly caused by Staphylococcus aureus or
Streptococcus pyogenes. Honey-colored crusting is a classic feature. This distinction is useful for prioritizing
microbiologic interpretation and avoiding distractors that describe a different organism, transmission route, mechanism,
or diagnostic principle.
6. A patient has grouped painful vesicles that recur at the same lip location. Which pathogen best fits this
pattern?
A) Human papillomavirus
B) Herpes simplex virus type 1
C) Parvovirus B19
D) Adenovirus
Correct Answer: Herpes simplex virus type 1
Rationale: HSV-1 establishes latency in sensory ganglia and can reactivate, producing recurrent painful vesicular lesions
near the mouth. This distinction is useful for prioritizing microbiologic interpretation and avoiding distractors that describe
a different organism, transmission route, mechanism, or diagnostic principle.
7. A dermatomal painful vesicular eruption occurs in an older adult. Which mechanism explains the
illness?
A) Reactivation of latent varicella-zoster virus in sensory ganglia
B) Primary infection with Epstein-Barr virus
C) Transformation by human papillomavirus
D) Acute adenovirus bacteremia
Correct Answer: Reactivation of latent varicella-zoster virus in sensory ganglia
Rationale: Herpes zoster results from reactivation of latent varicella-zoster virus in dorsal root or cranial nerve ganglia,
producing a unilateral dermatomal eruption. This distinction is useful for prioritizing microbiologic interpretation and
avoiding distractors that describe a different organism, transmission route, mechanism, or diagnostic principle.
8. A child has fever, oral ulcers, and vesicular lesions on the hands and feet. Which viral disease is most
consistent?
Page 3
