WBR0507

Author	[[PageAuthor::Gonzalo A. Romero, M.D. (Reviewed by Alison Leibowitz)]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Embryology, MainCategory::Microbiology, MainCategory::Pharmacology
Sub Category	SubCategory::Infectious Disease
Prompt	[[Prompt::A 2-year-old girl is brought to the pediatrician because her mother is concerned about her teeth appear abnormally dark. She states that her daughter developed a ring-like rash on her leg after a nature walk, which appeared to be similar to a rash that her 17-year-old son developed following a camping trip. The mother administered her daughter the leftover antibiotics that had been prescribed to her teenage son for his rash. Which of the following mechanisms of action corresponds to the antibiotic most likely provided to the young girl?]]
Answer A	AnswerA::Prevents attachment of aminoacyl-tRNA
Answer A Explanation	AnswerAExp::See overall explanation
Answer B	AnswerB::Inhibits the formation of initiation complex
Answer B Explanation	[[AnswerBExp::This is the mechanism of action of aminoglycosides used for gram negative rod infections.]]
Answer C	AnswerC::Inhibits protein synthesis by binding to the 50S ribosomal subunit
Answer C Explanation	[[AnswerCExp::This is the mechanism of action of macrolides, used to treat atypical pneumonias (Mycoplasma, Chlamydia, Legionella), URiI, STDs, gram-positive cocci (streptococcal infections in patients allergic to penicillin), and Neisseria.]]
Answer D	AnswerD::Inhibits the translocation of the peptidyl-tRNA
Answer D Explanation	[[AnswerDExp::This often corresponds with aminoglycosides use.]]
Answer E	AnswerE::Inhibits protein elongation by blocking peptidyl-transferase
Answer E Explanation	[[AnswerEExp::This is the mechanism of action associated with chloramphenicol.]]
Right Answer	RightAnswer::A
Explanation	[[Explanation::In this scenario a 2-year-old patient presents with discolored teeth. Her mother had previously administered her with an antibiotic treat a rash, which was indicative of Lyme’s disease. Tetracycline, used to treat Lyme disease, is not prescribed to young children due to the high risk of bone and teeth malformation. Tetracycline, specifically doxycycline, inhibits protein synthesis by binding to the 30S ribosomal subunit and preventing the attachment of aminoacyl-tRNA. This image above depicts the "bull's eye" rash associated with Lyme disease Educational Objective: When tetracycline is administered to young children, it is often associated with teeth discoloration (teratogenic) References: First Aid 2013 Microbiology-Pharmacology chapter.]]
Approved	Approved::Yes
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