FPGEE Microbiology and Immunology Flashcards

Which type of hypersensitivity reaction is responsible for anaphylaxis?

Answer: Type I (IgE-mediated)

Anaphylaxis is a Type I IgE-mediated hypersensitivity reaction triggered by mast cell degranulation.

Which organism is the most common cause of community-acquired pneumonia (CAP) in the US?

Answer: Streptococcus pneumoniae

Streptococcus pneumoniae (pneumococcus) is the leading bacterial cause of community-acquired pneumonia in adults in the US.

Which antibiotic class inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins (PBPs)?

Answer: Beta-lactams

Beta-lactam antibiotics (penicillins, cephalosporins, carbapenems) inhibit transpeptidation by covalently binding to PBPs.

The Gram stain distinguishes bacteria primarily based on differences in their:

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.

Which vaccine uses live attenuated organisms and is therefore contraindicated in immunocompromised patients?

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.

MRSA (methicillin-resistant Staphylococcus aureus) acquires resistance to beta-lactams primarily through:

Answer: Altered penicillin-binding protein (PBP2a)

MRSA expresses an altered PBP2a (encoded by mecA gene) with low affinity for all beta-lactam antibiotics.