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{{WBRQuestion
{{WBRQuestion
|QuestionAuthor=Gerald
|QuestionAuthor=Gerald Chi (Reviewed by {{YD}})
|ExamType=USMLE Step 1
|ExamType=USMLE Step 1
|MainCategory=Microbiology
|MainCategory=Microbiology
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|MainCategory=Microbiology
|MainCategory=Microbiology
|SubCategory=Gastrointestinal
|SubCategory=Gastrointestinal
|MainCategory=Microbiology
|MainCategory=Microbiology
|MainCategory=Microbiology
|MainCategory=Microbiology
|MainCategory=Microbiology
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|MainCategory=Microbiology
|MainCategory=Microbiology
|SubCategory=Gastrointestinal
|SubCategory=Gastrointestinal
|Prompt=A 28-year-old male presents to the clinic with abdominal cramps, general malaise, fever, and diarrhea 6 hours after consuming ground beef. Few leukocytes are found in his fecal specimen. Growth of colorless colonies on sorbitol-MacConkey agar is noted. The pathogen produces toxins which contains an enzymatic subunit that interferes with protein synthesis. Which of the following antibiotics has a similar mechanism regarding to the toxin's action on translation?
|Prompt=A 28-year-old man presents to the clinic with abdominal cramps, general malaise, fever, and diarrhea 6 hours after consuming ground beef. Few leukocytes are found in his fecal specimen. Growth of colorless colonies on sorbitol-MacConkey agar is noted. The pathogen produces toxins which contain enzymatic subunits that interfere with protein synthesis. Which of the following antibiotics has a similar mechanism regarding to the toxin's action on translation?
|Explanation=E. coli O157:H7 is negative for invasiveness (Sereny test), adheres through the E. coli common pilus (ECP), and does not produce heat-stable or heat-labile toxins. In addition, E. coli O157:H7 is usually sorbitol negative, whereas most of all E. coli with human origin ferment sorbitol. Among the virulence factors, Shiga-like toxins (SLTs) are iron-regulated toxins that catalytically cleaves N-glycoside bond of adenine in 28S rRNA of the 60S ribosome unit to prevent aminoacyl tRNA binding, thereby inhibiting protein synthesis.
|Explanation=''E. coli'' O157:H7 (EHEC) is negative for invasiveness (Sereny test), adheres through the ''E. coli'' common pilus (ECP), and does not produce either heat-stable or heat-labile toxins. In addition, ''E. coli'' O157:H7 is usually sorbitol-negative, whereas other ''E. coli'' ferment sorbitol. Among the virulence factors, Shiga-like toxin (SLT-1) is an iron-regulated toxin that catalytically inactivates 60S ribosomal subunits of eukaryotic cells. It cleaves N-glycoside bond of adenine in 28S rRNA of the 60S ribosome unit to prevent EF-1-dependent aminoacyl tRNA binding, thereby inhibiting protein synthesis. This mechanism of action is similar to tetracyclines, which also inhibit protein synthesis by blocking the entry and binding of aminoacyl transfer RNA.
 
|AnswerA=Linezolid
|AnswerA=Linezolid.
 
|AnswerAExp=Linezolid and aminoglycosides block the formation of initiation complex, thereby inhibiting protein synthesis.
|AnswerAExp=Linezolid and aminoglycosides block the formation of initiation complex, thereby inhibiting protein synthesis.


|AnswerB=Tetracycline.
|AnswerB=Tetracycline
 
|AnswerBExp=Tetracycline blocks the entry and binding of aminoacyl transfer RNA, thereby inhibiting protein synthesis.
|AnswerBExp=Correct. Tetracycline blocks the entry and binding of aminoacyl transfer RNA, thereby inhibiting protein synthesis.
|AnswerC=Quinupristin/dalfopristin
 
|AnswerC=Quinupristin/dalfopristin.
 
|AnswerCExp=Quinupristin/dalfopristin and other streptogramins block peptidyl transferase which forms peptide bonds between adjacent amino acids using tRNAs during the translation process.
|AnswerCExp=Quinupristin/dalfopristin and other streptogramins block peptidyl transferase which forms peptide bonds between adjacent amino acids using tRNAs during the translation process.
 
|AnswerD=Clindamycin
|AnswerD=Clindamycin.
 
|AnswerDExp=Clindamycin and macrolides block translocation by binding to the 50S rRNA of the large bacterial ribosome subunit.
|AnswerDExp=Clindamycin and macrolides block translocation by binding to the 50S rRNA of the large bacterial ribosome subunit.
 
|AnswerE=Chloramphenicol
|AnswerE=Chloramphenicol.
 
|AnswerEExp=Chloramphenicol blocks peptidyl transferase which forms peptide bonds between adjacent amino acids using tRNAs during the translation process.
|AnswerEExp=Chloramphenicol blocks peptidyl transferase which forms peptide bonds between adjacent amino acids using tRNAs during the translation process.
|EducationalObjectives=Among the virulence factors of ''E. coli'' O157:H7, Shiga-like toxin (SLTs) is an iron-regulated toxin that catalytically cleaves N-glycoside bond of adenine in 28S rRNA of the 60S ribosome unit to prevent aminoacyl tRNA binding, thereby inhibiting protein synthesis. This mechanism of action is similar to tetracyclines, which also inhibit protein synthesis by blocking the entry and binding of aminoacyl transfer RNA.
|References=First Aid 2015 page 138.
|RightAnswer=B
|RightAnswer=B
|WBRKeyword=Protein synthesis
|WBRKeyword=Protein synthesis, Shiga-like toxin, Tetracycline, Gastroenteritis
|Approved=No
|Approved=Yes
}}
}}

Revision as of 01:50, 17 August 2015

 
Author [[PageAuthor::Gerald Chi (Reviewed by Yazan Daaboul, M.D.)]]
Exam Type ExamType::USMLE Step 1
Main Category MainCategory::Microbiology
Sub Category SubCategory::Gastrointestinal
Prompt [[Prompt::A 28-year-old man presents to the clinic with abdominal cramps, general malaise, fever, and diarrhea 6 hours after consuming ground beef. Few leukocytes are found in his fecal specimen. Growth of colorless colonies on sorbitol-MacConkey agar is noted. The pathogen produces toxins which contain enzymatic subunits that interfere with protein synthesis. Which of the following antibiotics has a similar mechanism regarding to the toxin's action on translation?]]
Answer A AnswerA::Linezolid
Answer A Explanation AnswerAExp::Linezolid and aminoglycosides block the formation of initiation complex, thereby inhibiting protein synthesis.
Answer B AnswerB::Tetracycline
Answer B Explanation AnswerBExp::Tetracycline blocks the entry and binding of aminoacyl transfer RNA, thereby inhibiting protein synthesis.
Answer C AnswerC::Quinupristin/dalfopristin
Answer C Explanation AnswerCExp::Quinupristin/dalfopristin and other streptogramins block peptidyl transferase which forms peptide bonds between adjacent amino acids using tRNAs during the translation process.
Answer D AnswerD::Clindamycin
Answer D Explanation AnswerDExp::Clindamycin and macrolides block translocation by binding to the 50S rRNA of the large bacterial ribosome subunit.
Answer E AnswerE::Chloramphenicol
Answer E Explanation AnswerEExp::Chloramphenicol blocks peptidyl transferase which forms peptide bonds between adjacent amino acids using tRNAs during the translation process.
Right Answer RightAnswer::B
Explanation [[Explanation::E. coli O157:H7 (EHEC) is negative for invasiveness (Sereny test), adheres through the E. coli common pilus (ECP), and does not produce either heat-stable or heat-labile toxins. In addition, E. coli O157:H7 is usually sorbitol-negative, whereas other E. coli ferment sorbitol. Among the virulence factors, Shiga-like toxin (SLT-1) is an iron-regulated toxin that catalytically inactivates 60S ribosomal subunits of eukaryotic cells. It cleaves N-glycoside bond of adenine in 28S rRNA of the 60S ribosome unit to prevent EF-1-dependent aminoacyl tRNA binding, thereby inhibiting protein synthesis. This mechanism of action is similar to tetracyclines, which also inhibit protein synthesis by blocking the entry and binding of aminoacyl transfer RNA.

Educational Objective: Among the virulence factors of E. coli O157:H7, Shiga-like toxin (SLTs) is an iron-regulated toxin that catalytically cleaves N-glycoside bond of adenine in 28S rRNA of the 60S ribosome unit to prevent aminoacyl tRNA binding, thereby inhibiting protein synthesis. This mechanism of action is similar to tetracyclines, which also inhibit protein synthesis by blocking the entry and binding of aminoacyl transfer RNA.
References: First Aid 2015 page 138.]]

Approved Approved::Yes
Keyword WBRKeyword::Protein synthesis, WBRKeyword::Shiga-like toxin, WBRKeyword::Tetracycline, WBRKeyword::Gastroenteritis
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