FPGEE FPGEE Microbiology and Immunology 1 — Questions and Answers
Question 1: Which type of hypersensitivity reaction is responsible for anaphylaxis?
- Type I (IgE-mediated) (Correct answer)
- Type II (cytotoxic)
- Type III (immune complex)
- Type IV (delayed)
Correct answer: Type I (IgE-mediated)
Anaphylaxis is a Type I IgE-mediated hypersensitivity reaction triggered by mast cell degranulation.
Question 2: Which organism is the most common cause of community-acquired pneumonia (CAP) in the US?
- Haemophilus influenzae
- Streptococcus pneumoniae (Correct answer)
- Klebsiella pneumoniae
- Legionella pneumophila
Correct answer: Streptococcus pneumoniae
Streptococcus pneumoniae (pneumococcus) is the leading bacterial cause of community-acquired pneumonia in adults in the US.
Question 3: Which antibiotic class inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins (PBPs)?
- Fluoroquinolones
- Macrolides
- Beta-lactams (Correct answer)
- Aminoglycosides
Correct answer: Beta-lactams
Beta-lactam antibiotics (penicillins, cephalosporins, carbapenems) inhibit transpeptidation by covalently binding to PBPs.
Question 4: The Gram stain distinguishes bacteria primarily based on differences in their:
- Ribosome size
- Cell wall composition (Correct answer)
- Plasma membrane lipids
- Capsule thickness
Correct answer: Cell wall composition
Gram-positive bacteria retain crystal violet due to their thick peptidoglycan layer, while gram-negative bacteria have a thin peptidoglycan and outer membrane.
Question 5: Which vaccine uses live attenuated organisms and is therefore contraindicated in immunocompromised patients?
- Hepatitis B vaccine
- MMR vaccine (Correct answer)
- Pneumococcal polysaccharide vaccine (PPSV23)
- Inactivated influenza vaccine
Correct answer: MMR vaccine
The MMR (measles-mumps-rubella) vaccine contains live attenuated viruses and must be avoided in immunocompromised individuals due to risk of vaccine-strain infection.
Question 6: MRSA (methicillin-resistant Staphylococcus aureus) acquires resistance to beta-lactams primarily through:
- Production of beta-lactamase
- Altered penicillin-binding protein (PBP2a) (Correct answer)
- Efflux pump upregulation
- Reduced outer membrane permeability
Correct answer: Altered penicillin-binding protein (PBP2a)
MRSA expresses an altered PBP2a (encoded by mecA gene) with low affinity for all beta-lactam antibiotics.
FPGEE FPGEE Microbiology and Immunology 1
Which type of hypersensitivity reaction is responsible for anaphylaxis?