Question 1

Which of the following best explains why attenuated vaccines generally provide longer-lasting immunity than inactivated vaccines?

Accepted Answer

Attenuated vaccines replicate in the host, providing continuous antigenic stimulation and activating both humoral and cell-mediated immunity.

Question 2

A patient receives a vaccine composed of purified capsular polysaccharide from Haemophilus influenzae type b linked to a protein carrier. What type of vaccine is this?

Accepted Answer

Conjugated vaccine

Question 3

Which of the following best describes the mechanism by which sulfa drugs selectively inhibit bacterial growth?

Accepted Answer

They act as competitive inhibitors of the enzyme that converts PABA to folic acid, a pathway absent in humans.

Question 4

A laboratory test detects the presence of antibodies against HIV in a patient's serum using a Western blot. Which step is essential for confirming the specificity of the detected antibodies?

Accepted Answer

Separation of viral proteins by electrophoresis, followed by transfer to a membrane and probing with patient serum.

Question 5

Which of the following statements about the blood–brain barrier is correct?

Accepted Answer

It is composed of tight junctions between endothelial cells, restricting passage of most substances except for small, lipid-soluble molecules like chloramphenicol.

Question 6

A patient with type O+ blood receives a transfusion of type A+ blood. Which immunological reaction is most likely to occur?

Accepted Answer

The patient's anti-A antibodies will bind to the transfused A+ red blood cells, leading to complement-mediated hemolysis.

Question 7

Which of the following best explains why the oral (Sabin) polio vaccine can, in rare cases, cause polio, while the injected (Salk) vaccine does not?

Accepted Answer

The Sabin vaccine contains live attenuated virus, which can rarely revert to a neurovirulent form and cause disease.

Question 8

A patient is diagnosed with a delayed-type hypersensitivity reaction after a tuberculin skin test. Which immune cells are primarily responsible for this reaction, and why is there a delay?

Accepted Answer

CD4+ T helper cells, because they recruit macrophages and other immune cells over 24–48 hours.

Question 9

Which of the following best describes the mechanism of action of aminoglycoside antibiotics?

Accepted Answer

They bind to the 30S subunit of bacterial ribosomes, causing misreading of mRNA and inhibiting protein synthesis.

Question 10

A patient with a history of multiple antibiotic treatments develops a Clostridioides difficile infection. Which term best describes this phenomenon?

Accepted Answer

Superinfection

Question 11

Which of the following is the most common mechanism by which bacteria develop resistance to penicillin?

Accepted Answer

Production of beta-lactamase enzymes that hydrolyze the beta-lactam ring

Question 12

A patient is given a direct ELISA test for a suspected viral infection. What is being detected in this test?

Accepted Answer

Viral antigens present in the patient's sample

Question 13

Which of the following best explains why antibiotics that inhibit peptidoglycan synthesis are effective against bacteria but not mammalian cells?

Accepted Answer

Bacteria have peptidoglycan in their cell walls, while mammalian cells lack peptidoglycan.

Question 14

A patient with HIV is found to have a CD4+ T cell count of 300/μl. According to CDC criteria, does this count alone confirm a diagnosis of AIDS?

Accepted Answer

No, because a CD4+ T cell count below 200/μl is required for an AIDS diagnosis.

Question 15

Which of the following is the most common mode of HIV transmission worldwide?

Accepted Answer

Heterosexual contact

Question 16

A patient is diagnosed with meningitis caused by Listeria monocytogenes after consuming refrigerated deli meats. What property of Listeria allows it to cause disease in this context?

Accepted Answer

It is a psychrotroph, able to grow at low temperatures found in refrigerators.

Question 17

Which of the following best describes the function of an adjuvant in a vaccine formulation?

Accepted Answer

It enhances the immune response to the antigen by stimulating innate immunity.

Question 18

A patient with a history of allergies undergoes desensitization therapy. Which antibody type is the main target for blocking to reduce allergic symptoms?

Accepted Answer

IgE

Question 19

Which of the following best explains why erythromycin is more effective against gram-positive bacteria than gram-negative bacteria, despite both having similar ribosomal targets?

Accepted Answer

Erythromycin cannot penetrate the outer membrane of gram-negative bacteria.

Question 20

A patient is diagnosed with a fungal infection and prescribed amphotericin B. What is the primary target of this drug in fungal cells?

Accepted Answer

Ergosterol in the cell membrane

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