WBR0463

Author	[[PageAuthor::Rim Halaby, M.D. [1]]]
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 patient who is previously healthy is brought to the physician’s office for fever since 2 days. Upon further questioning, the patient informs the physician she was camping in the woods in the East coast a week ago and was bitten by ticks. On physical examination, the physician notes a rash on her left buttock. The physician wishes to start her on an antibiotic regimen. What is the most likely mechanism of action of the prescribed antibiotic given to this patient?]]
Answer A	AnswerA::A bacteriostatic antibiotic that inhibits the attachment of aminoacyl t-RNA by binding to 30S ribosomal subunit
Answer A Explanation	AnswerAExp::Doxycyline is the treatment of choice for all rickettsial infections. It is usually considered a baceteriostatic antibiotic, whose mechanism of action is the inhibition of attachment of aminoacyl-tRNA by binding to 30S ribosomal subunit.
Answer B	AnswerB::A bacteriostatic antibiotic that inhibits the translocaton during protein synthesis by binding to 50S ribosomal subunit
Answer B Explanation	AnswerBExp::Macrolides are a bacteriostatic class of antibiotics that inhibit the 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::The exact distinction between bacteriostatic and bactericidal medications can be difficult, especially that many factors play a role in defining the exact action of the antibiotic on the organism, including factors pertaining to the antibiotic itself, such as dosage, or the organism, such as its sensitivity. Tetracyclines, however, 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::Although macrolides can be bactericidal depending on bacterial sensitivity to the antibiotic, their main action is in fact bacteriostatic. Macrolides 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 the attachment of aminoacyl t-RNA and activating the process is not a mechanism of action of any antibiotic. This mechanism is not likely to have antibacterial properties.
Right Answer	RightAnswer::A
Explanation	[[Explanation::The patient presents with Rocky Mountain spotted fever (RMSF) caused by Rickettsia rickettsii. The classic triad for RMSF is fever, rash, and history of camping. The disease is transmitted by a painful tick bite. Symptoms include painful migrating rash that involves the palms and soles, headache, and fever. Doxycycline is the treatment of choice for all rickettsial infections, including Rickettsia rickettsii. Doxycycline is a tetracycline, a baceteriostatic antibiotic, whose mechanism of action is the inhibition of attachment of aminoacyl-tRNA by binding to 30S ribosomal subunit. Educational Objective: Rocky Mountain spotted fever (RMSF) is characterized by an infection caused by Rickettsia rickettsii that is a triad of fever, headache, with a history of tick bite. Doxycyline, a tetracycline that inhibits attachment of aminoacyl-tRNA by binding to 30S ribosomal subunit, is the treatment of choice for all rickettsial infections. Educational Objective: References: ]]
Approved	Approved::No
Keyword	WBRKeyword::Rocky, WBRKeyword::Mountain, WBRKeyword::spotted, WBRKeyword::fever, WBRKeyword::rocky moutain spotted fever, WBRKeyword::RMSF, WBRKeyword::doxycycline, WBRKeyword::tetracycline, WBRKeyword::antibiotic
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