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{{WBRQuestion
{{WBRQuestion
|QuestionAuthor={{Rim}}
|QuestionAuthor={{Rim}}, {{AJL}} {{Alison}}
|ExamType=USMLE Step 1
|ExamType=USMLE Step 1
|MainCategory=Microbiology
|MainCategory=Microbiology
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|MainCategory=Microbiology
|MainCategory=Microbiology
|SubCategory=Dermatology, General Principles, Infectious Disease
|SubCategory=Dermatology, General Principles, Infectious Disease
|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?
|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?
|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.
|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.


[[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.
|EducationalObjectives=
 
[[Rocky Mountain spotted fever]] ([[RMSF]]), caused by ''[[Rickettsia rickettsii]]'' and contracted with a tick bite manifests with a migrating rash of the the palms and soles, headache, and fever. [[Doxycyline]], a [[tetracycline]], inhibits the attachment of [[aminoacyl-tRNA]] by binding to [[30S ribosomal]] subunit, and is frequently administered to patients with [[rickettsial infections]].
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]].


|AnswerA=A bacteriostatic antibiotic that inhibits the attachment of aminoacyl t-RNA by binding to 30S ribosomal subunit
|AnswerA=A bacteriostatic antibiotic that inhibits the attachment of aminoacyl t-RNA by binding to 30S ribosomal subunit
|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.
|AnswerAExp=See explanation.
|AnswerB=A bacteriostatic antibiotic that inhibits the translocaton during protein synthesis by binding to 50S ribosomal subunit
|AnswerB=A bacteriostatic antibiotic that inhibits the translocaton during protein synthesis by binding to 50S ribosomal subunit
|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.
|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]].
|AnswerC=A bactericidal antibiotic that inhibits the attachment of aminoacyl t-RNA by binding to 50S ribosomal subunit
|AnswerC=A bactericidal antibiotic that inhibits the attachment of aminoacyl t-RNA by binding to 50S ribosomal subunit
|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.
|AnswerCExp=[[Tetracyclines]] do not act on the 50S ribosome, regardless of whether they are bactericidal or bacteriostatic.
|AnswerD=A bactericidal antibiotic that inhibits the translocation during protein synthesis by binding to 50S ribosomal subunit
|AnswerD=A bactericidal antibiotic that inhibits the translocation during protein synthesis by binding to 50S ribosomal subunit
|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.
|AnswerDExp=[[Macrolides]] are bacteriostatic and are not typically used to treat rickettsial infections.
|AnswerE=A bactericidal antibiotic that activates the attachment of aminoacyl-tRNA by binding to 30S ribosomal subunit
|AnswerE=A bactericidal antibiotic that activates the attachment of aminoacyl-tRNA by binding to 30S ribosomal subunit
|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.
|AnswerEExp=Mediation of aminoacyl t-RNA attachment is not the mechanism of action for antibiotics.  
|RightAnswer=A
|RightAnswer=A
|WBRKeyword=Rocky, Mountain, spotted, fever, rocky moutain spotted fever, RMSF, doxycycline, tetracycline, antibiotic
|WBRKeyword=Rocky Mountain spotted fever, RMSF, doxycycline, tetracycline, antibiotic, tick, mechanism of action, rash, ribosomal, microbiology
|Approved=No
|Approved=Yes
}}
}}

Revision as of 15:07, 24 July 2014
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.
Educational Objective: Rocky Mountain spotted fever (RMSF), caused by Rickettsia rickettsii and contracted with a tick bite manifests with a migrating rash of the the palms and soles, headache, and fever. Doxycyline, a tetracycline, inhibits the attachment of aminoacyl-tRNA by binding to 30S ribosomal subunit, and is frequently administered to patients with rickettsial infections.
References: ]]

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::
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