WBR0463
| Author | [[PageAuthor::Rim Halaby, M.D. [1], Alison Leibowitz [2] (Reviewed by Alison Leibowitz)]] |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Microbiology |
| Sub Category | SubCategory::Dermatology, SubCategory::General Principles, SubCategory::Infectious Disease |
| Prompt | [[Prompt::A 37-year-old female presents to the physician’s office with a fever of two days duration. Upon further questioning, the patient informs you she went camping on the East Coast a week ago and was bitten by ticks. On physical examination, you note a rash on her left sole and administer her an antibiotic regimen. Which of the following mechanisms of action is most likely associated with the prescribed antibiotic?]] |
| Answer A | AnswerA::A bacteriostatic antibiotic that inhibits the attachment of aminoacyl t-RNA by binding to 30S ribosomal subunit |
| Answer A Explanation | AnswerAExp::See explanation. |
| Answer B | AnswerB::A bacteriostatic antibiotic that inhibits the translocaton during protein synthesis by binding to 50S ribosomal subunit |
| Answer B Explanation | [[AnswerBExp::Macrolides, a bacteriostatic class of antibiotics, inhibit translocaton during protein synthesis by binding to the 23S rRNA of the 50S ribosomal subunit. Macrolides are not typically used to treat rickettsial infections.]] |
| Answer C | AnswerC::A bactericidal antibiotic that inhibits the attachment of aminoacyl t-RNA by binding to 50S ribosomal subunit |
| Answer C Explanation | [[AnswerCExp::Tetracyclines do not act on the 50S ribosome, regardless of whether they are bactericidal or bacteriostatic.]] |
| Answer D | AnswerD::A bactericidal antibiotic that inhibits the translocation during protein synthesis by binding to 50S ribosomal subunit |
| Answer D Explanation | [[AnswerDExp::Macrolides are bacteriostatic and are not typically used to treat rickettsial infections.]] |
| Answer E | AnswerE::A bactericidal antibiotic that activates the attachment of aminoacyl-tRNA by binding to 30S ribosomal subunit |
| Answer E Explanation | AnswerEExp::Mediation of aminoacyl t-RNA attachment is not the mechanism of action for antibiotics. |
| Right Answer | RightAnswer::A |
| Explanation | [[Explanation::The patient most likely presents with Rocky Mountain spotted fever (RMSF), caused by Rickettsia rickettsii and contracted with a tick bite. RMSF frequently manifests with a migrating rash of the the palms and soles, headache, and fever.
Doxycycline is usually administered to patients with rickettsial infections. The mechanism of action of Doxycycline, a tetracycline (baceteriostatic antibiotic, is inhibiting the attachment of aminoacyl-tRNA, by binding to the 30S ribosomal subunit. |
| Approved | Approved::Yes |
| Keyword | WBRKeyword::Rocky Mountain spotted fever, WBRKeyword::RMSF, WBRKeyword::doxycycline, WBRKeyword::tetracycline, WBRKeyword::antibiotic, WBRKeyword::tick, WBRKeyword::mechanism of action, WBRKeyword::rash, WBRKeyword::ribosomal, WBRKeyword::microbiology |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |