USMLE Step 1
Antibiotic Resistance Drill

Select a module to begin.

💊 Mechanisms → Antibiotics

Match mechanisms to the specific antibiotic classes they disable.

🦠 Mechanisms → Organisms

Identify the key bugs associated with each resistance mechanism.

📝 High Yield Notes

Connect clinical vignettes, gene names, and definitions to mechanisms.

🔀 Master Mix

All 60 questions shuffled together for maximum retention.

Module

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USMLE Step 1 Reference

[Interactive Diagram: Bacterial Cell Envelope Resistance Mechanisms]
(Click points to zoom: Porins, PBP, Ribosomes, DNA Gyrase)

Men are resistance to PBP: Methicillin resistance (MRSA) is due to altered PBP (mecA gene).
Vanc "Lacks" efficacy: Vancomycin resistance involves changing D-Ala to D-Lac.
Pseudomonas is the "Pump & Pore" King: Suspect combination of Efflux Pumps and Porin Mutations.
Aminoglycosides get "Modified": Enzymes add chemical groups (acetyl, phosphate, adenyl) to the drug itself.
The "Efflux" Rule: Low intracellular concentration despite high permeability = Efflux Pumps.

Mechanism	Antibiotics Affected	Key Organisms	Notes / Genes
Altered Porins	Carbapenems, Aminoglycosides	P. aeruginosa, Enterobacteriaceae	Prevents entry into periplasm (Gram-negatives only).
Efflux Pumps	Tetracyclines, Macrolides, Quinolones	Pseudomonas, E. coli, Staph	Energy-dependent (proton motive force). Active transport out.
Increased Folate	Sulfonamides, Trimethoprim	Gram-negatives	Overproduction of PABA to outcompete drug.
Altered PBP	Methicillin, Cephalosporins	MRSA, S. pneumo	mecA gene encodes PBP2a. Low affinity for beta-lactams.
Beta-lactamase	Penicillins, Aminopenicillins	S. aureus (non-MRSA), H. flu, Klebsiella	Hydrolyzes beta-lactam ring. Treat w/ Clavulanic acid.
Altered Peptidoglycan	Vancomycin	VRE, VRSA	D-Ala-D-Ala becomes D-Ala-D-Lac.
Ribosomal Methylation	Macrolides, Clindamycin	Bacteroides, Gram-positives	erm gene. Methylates 23S rRNA of 50S subunit.
Modifying Enzymes	Aminoglycosides	Pseudomonas, Enterobacter	Transferases add Acetyl/Phosphate/Adenyl groups.
DNA Gyrase Mutation	Fluoroquinolones	Gonorrhea, Salmonella, Campylobacter	gyrA gene mutation alters binding site.