CLS CLS Clinical Microbiology and Immunology 2 — Questions and Answers
Question 1: Which antibody class is the FIRST produced during a primary immune response?
- IgA
- IgE
- IgG
- IgM (Correct answer)
Correct answer: IgM
IgM is the first antibody class produced during a primary immune response; its pentameric structure makes it highly effective at agglutination and complement activation.
Question 2: Beta-lactamase-producing organisms are resistant to which antibiotic class?
- Macrolides
- Fluoroquinolones
- Beta-lactams (penicillins/cephalosporins) (Correct answer)
- Aminoglycosides
Correct answer: Beta-lactams (penicillins/cephalosporins)
Beta-lactamase enzymes cleave the beta-lactam ring of penicillins and cephalosporins, inactivating the antibiotic before it can inhibit cell wall synthesis.
Question 3: Which test is used as the CONFIRMATORY test for HIV after a positive 4th-generation ELISA/immunoassay screen?
- HIV viral load (PCR)
- Western blot / HIV-1/2 differentiation immunoassay (Correct answer)
- CD4+ T-cell count
- p24 antigen test
Correct answer: Western blot / HIV-1/2 differentiation immunoassay
An HIV-1/2 differentiation immunoassay (formerly Western blot) confirms HIV infection by detecting antibodies to specific HIV proteins after a reactive screen.
Question 4: The Quellung (capsular swelling) reaction uses type-specific antisera to identify which encapsulated organism?
- Staphylococcus aureus
- Neisseria meningitidis
- Streptococcus pneumoniae (Correct answer)
- Haemophilus influenzae
Correct answer: Streptococcus pneumoniae
The Quellung reaction detects the polysaccharide capsule of Streptococcus pneumoniae; antibody binding causes the capsule to appear swollen and refractile under microscopy.
Question 5: Which type of hypersensitivity reaction is IgE-mediated and involves mast cell degranulation with histamine release?
- Type I (immediate/anaphylactic) (Correct answer)
- Type II (cytotoxic)
- Type III (immune complex)
- Type IV (delayed/cell-mediated)
Correct answer: Type I (immediate/anaphylactic)
Type I hypersensitivity is IgE-mediated; allergen cross-links IgE molecules on mast cells, triggering degranulation and release of histamine and other mediators.
Question 6: Which organism causing chancroid (STI) classically appears in a 'school of fish' or 'railroad track' arrangement on Gram stain?
- Haemophilus ducreyi (Correct answer)
- Listeria monocytogenes
- Corynebacterium diphtheriae
- Neisseria gonorrhoeae
Correct answer: Haemophilus ducreyi
Haemophilus ducreyi, the causative agent of chancroid, appears as small gram-negative coccobacilli arranged in parallel chains resembling a school of fish on Gram stain.
CLS CLS Clinical Microbiology and Immunology 2
Which antibody class is the FIRST produced during a primary immune response?