BIOL 271 MICROBIOLOGY CASE STUDY
COMPREHENSIVE QUIZ
1. A 24-year-old student presents with a stiff neck, high fever, and a petechial rash. A lumbar
puncture reveals cloudy CSF with high protein, low glucose, and Gram-negative diplococci.
What is the most likely pathogen?
A. Streptococcus pneumoniae
B. Haemophilus influenzae
C. Listeria monocytogenes
D. Neisseria meningitidis
Answer: D
Conceptual Explanation: Neisseria meningitidis is a Gram-negative diplococcus and a
leading cause of bacterial meningitis, often characterized by a petechial rash due to
meningococcemia.
2. A patient presents with a painless, hard-edged ulcer (chancre) on the genitalia. Rapid
Plasma Reagin (RPR) test is positive. Which organism is responsible?
A. Haemophilus ducreyi
B. Neisseria gonorrhoeae
,C. Treponema pallidum
D. Chlamydia trachomatis
Answer: C
Conceptual Explanation: Treponema pallidum causes syphilis; the primary stage is
characterized by a painless chancre and positive serological tests like RPR.
3. An elderly patient on long-term clindamycin therapy develops severe diarrhea and
abdominal pain. A stool toxin assay confirms the presence of Toxin A and Toxin B. What is the
diagnosis?
A. Shigellosis
B. Clostridioides difficile infection
C. Salmonellosis
D. Staphylococcal food poisoning
Answer: B
Conceptual Explanation: C. difficile causes pseudomembranous colitis following antibiotic
use, mediated by the release of enterotoxin A and cytotoxin B.
4. A 5-year-old child presents with a ‘slapped-cheek’ rash on the face and a lacy rash on the
trunk. Which virus is the causative agent?
A. Measles virus
B. Rubella virus
, C. Parvovirus B19
D. Varicella-zoster virus
Answer: C
Conceptual Explanation: Parvovirus B19 causes Erythema Infectiosum, also known as
Fifth Disease, characterized by the classic slapped-cheek appearance.
5. A patient with a history of intravenous drug use presents with jaundice and dark urine. Lab
results show HBsAg and HBeAg positive. Which of the following is true?
A. The patient has a chronic infection with low infectivity.
B. The patient is immune due to previous vaccination.
C. The patient has an acute or chronic infection with high infectivity.
D. The patient has recovered from a past infection.
Answer: C
Conceptual Explanation: HBsAg indicates active infection, and HBeAg indicates high
levels of viral replication and high infectivity.
6. A hiker in Connecticut develops a bull’s-eye rash (erythema migrans) and joint pain. Which
vector is responsible for transmitting the pathogen?
A. Dermacentor variabilis (Dog tick)
B. Xenopsylla cheopis (Rat flea)
C. Amblyomma americanum (Lone star tick)
COMPREHENSIVE QUIZ
1. A 24-year-old student presents with a stiff neck, high fever, and a petechial rash. A lumbar
puncture reveals cloudy CSF with high protein, low glucose, and Gram-negative diplococci.
What is the most likely pathogen?
A. Streptococcus pneumoniae
B. Haemophilus influenzae
C. Listeria monocytogenes
D. Neisseria meningitidis
Answer: D
Conceptual Explanation: Neisseria meningitidis is a Gram-negative diplococcus and a
leading cause of bacterial meningitis, often characterized by a petechial rash due to
meningococcemia.
2. A patient presents with a painless, hard-edged ulcer (chancre) on the genitalia. Rapid
Plasma Reagin (RPR) test is positive. Which organism is responsible?
A. Haemophilus ducreyi
B. Neisseria gonorrhoeae
,C. Treponema pallidum
D. Chlamydia trachomatis
Answer: C
Conceptual Explanation: Treponema pallidum causes syphilis; the primary stage is
characterized by a painless chancre and positive serological tests like RPR.
3. An elderly patient on long-term clindamycin therapy develops severe diarrhea and
abdominal pain. A stool toxin assay confirms the presence of Toxin A and Toxin B. What is the
diagnosis?
A. Shigellosis
B. Clostridioides difficile infection
C. Salmonellosis
D. Staphylococcal food poisoning
Answer: B
Conceptual Explanation: C. difficile causes pseudomembranous colitis following antibiotic
use, mediated by the release of enterotoxin A and cytotoxin B.
4. A 5-year-old child presents with a ‘slapped-cheek’ rash on the face and a lacy rash on the
trunk. Which virus is the causative agent?
A. Measles virus
B. Rubella virus
, C. Parvovirus B19
D. Varicella-zoster virus
Answer: C
Conceptual Explanation: Parvovirus B19 causes Erythema Infectiosum, also known as
Fifth Disease, characterized by the classic slapped-cheek appearance.
5. A patient with a history of intravenous drug use presents with jaundice and dark urine. Lab
results show HBsAg and HBeAg positive. Which of the following is true?
A. The patient has a chronic infection with low infectivity.
B. The patient is immune due to previous vaccination.
C. The patient has an acute or chronic infection with high infectivity.
D. The patient has recovered from a past infection.
Answer: C
Conceptual Explanation: HBsAg indicates active infection, and HBeAg indicates high
levels of viral replication and high infectivity.
6. A hiker in Connecticut develops a bull’s-eye rash (erythema migrans) and joint pain. Which
vector is responsible for transmitting the pathogen?
A. Dermacentor variabilis (Dog tick)
B. Xenopsylla cheopis (Rat flea)
C. Amblyomma americanum (Lone star tick)
