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{{WBRQuestion
{{WBRQuestion
|QuestionAuthor={{Rim}}
|QuestionAuthor= {{Rim}} (Reviewed by Will Gibson)
|ExamType=USMLE Step 1
|ExamType=USMLE Step 1
|MainCategory=Microbiology
|MainCategory=Microbiology
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|MainCategory=Microbiology
|MainCategory=Microbiology
|SubCategory=General Principles
|SubCategory=General Principles
|MainCategory=Microbiology
|MainCategory=Microbiology
|MainCategory=Microbiology
|MainCategory=Microbiology
|MainCategory=Microbiology
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|SubCategory=General Principles
|SubCategory=General Principles
|Prompt=Bacterial antigens are responsible for the stimulation of the innate immune system. Nonetheless, several organisms may evade the body's immunity via antigen variation. Which of the following antigenic variations is true about Salmonella enterica species?
|Prompt=Bacterial antigens are responsible for the stimulation of the innate immune system. Nonetheless, several organisms may evade the body's immunity via antigen variation. Which of the following antigenic variations is true about Salmonella enterica species?
|Explanation=Several infectious agents, whether bacteria, parasites, or virus, undergo different processes to achieve antigenic variation. Salmonella is a classic examples of antigenic variation by formation of 2 flagellar variants; where filament proteins FLjB and FliC are alternatively expressed. This process is in fact mediated by DNA inversion event at the level of the chromosome. This is in contrast to other organisms and viruses that achieve antigenic variation by different ways, such as pilus protein recombination in Neisseria, or antigenic drifts and shifts in influenza viruses.
|Explanation=Several infectious agents including bacteria, parasites, or virus, undergo different processes to achieve antigenic variation. Salmonella performs a classic example of antigenic variation by the formation of 2 flagellar variants; where filament proteins FLjB and FliC are alternatively expressed. This process is mediated by DNA inversion event at the level of the chromosome. Other organisms and viruses that achieve antigenic variation through entirely different mechanisms, such as pilus protein recombination in Neisseria, or antigenic drifts and shifts in influenza viruses.
 
Educational Objective:
Salmonella has 2 flagellar variants that are alternatively expressed to allow antigenic variation.
 
Reference:
Bonifield HR, Hughes KT. Flagellar phase variation in salmonella enterica is mediated by a posttranslational control mechanism. J Bacteriol. 2003;185(12):3567-3574.
 
Dai Q, Restrepo BI, Porcella SF, et al. Antigenic variation by Borrelia hermsii occurs through recombination between extragenic repetitive elements on linear plasmids. Mol Microbiol. 2006;60(6):1329-43.
|AnswerA=S. enterica alternatively expresses 2 flagellar proteins
|AnswerA=S. enterica alternatively expresses 2 flagellar proteins
|AnswerAExp=S. enterica has 2 flagellar variants.
|AnswerAExp=S. enterica has 2 flagellar variants.
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|AnswerE=S. enterica undergoes recombination between extragenic repetitive elements on linear plasmids
|AnswerE=S. enterica undergoes recombination between extragenic repetitive elements on linear plasmids
|AnswerEExp=Borrelia hermsii undergoes recombination between extragenic repetitive elements on linear plasmids to cause relapsing fevers.
|AnswerEExp=Borrelia hermsii undergoes recombination between extragenic repetitive elements on linear plasmids to cause relapsing fevers.
|EducationalObjectives=Antigenic variation is an important mechanism of immune evasion. Salmonella alternatively expresses 2 flagellar variants to allow antigenic variation.
|References=Bonifield HR, Hughes KT. Flagellar phase variation in salmonella enterica is mediated by a posttranslational control mechanism. J Bacteriol. 2003;185(12):3567-3574.<br>
Dai Q, Restrepo BI, Porcella SF, et al. Antigenic variation by Borrelia hermsii occurs through recombination between extragenic repetitive elements on linear plasmids. Mol Microbiol. 2006;60(6):1329-43. <br>
First Aid 2015 page 209
|RightAnswer=A
|RightAnswer=A
|WBRKeyword=antigen, antigenic, variation, salmonella, enterica, flagellar, variants, flagella, protein, expressed, expression
|WBRKeyword=Antigen, Antigenic variation, Salmonella, Salmonella enterica, Flagella, Alternative expression, Microbiology, Gram negative, Immune evasion
|Approved=No
|Approved=Yes
}}
}}

Latest revision as of 01:24, 28 October 2020
Author [[PageAuthor::Rim Halaby, M.D. [1] (Reviewed by Will Gibson)]]
Exam Type ExamType::USMLE Step 1
Main Category MainCategory::Microbiology
Sub Category SubCategory::General Principles
Prompt [[Prompt::Bacterial antigens are responsible for the stimulation of the innate immune system. Nonetheless, several organisms may evade the body's immunity via antigen variation. Which of the following antigenic variations is true about Salmonella enterica species?]]
Answer A AnswerA::S. enterica alternatively expresses 2 flagellar proteins
Answer A Explanation AnswerAExp::S. enterica has 2 flagellar variants.
Answer B AnswerB::Intragenic recombination causes pilus antigenic variation in S. enterica
Answer B Explanation AnswerBExp::Neisseria gonorrhea undergoes intragenic recombination causes pilus antigenic variation.
Answer C AnswerC::Antigenic drifts and shifts allow continuous antigenic variations in S. enterica
Answer C Explanation AnswerCExp::Influenza virus undergoes antigenic drifts and shifts.
Answer D AnswerD::S. enterica undergoes programmed rearrangement
Answer D Explanation AnswerDExp::Parasites, such as trypanosomes undergo programmed rearrangement.
Answer E AnswerE::S. enterica undergoes recombination between extragenic repetitive elements on linear plasmids
Answer E Explanation AnswerEExp::Borrelia hermsii undergoes recombination between extragenic repetitive elements on linear plasmids to cause relapsing fevers.
Right Answer RightAnswer::A
Explanation [[Explanation::Several infectious agents including bacteria, parasites, or virus, undergo different processes to achieve antigenic variation. Salmonella performs a classic example of antigenic variation by the formation of 2 flagellar variants; where filament proteins FLjB and FliC are alternatively expressed. This process is mediated by DNA inversion event at the level of the chromosome. Other organisms and viruses that achieve antigenic variation through entirely different mechanisms, such as pilus protein recombination in Neisseria, or antigenic drifts and shifts in influenza viruses.

Educational Objective: Antigenic variation is an important mechanism of immune evasion. Salmonella alternatively expresses 2 flagellar variants to allow antigenic variation.
References: Bonifield HR, Hughes KT. Flagellar phase variation in salmonella enterica is mediated by a posttranslational control mechanism. J Bacteriol. 2003;185(12):3567-3574.
Dai Q, Restrepo BI, Porcella SF, et al. Antigenic variation by Borrelia hermsii occurs through recombination between extragenic repetitive elements on linear plasmids. Mol Microbiol. 2006;60(6):1329-43.
First Aid 2015 page 209]]

Approved Approved::Yes
Keyword WBRKeyword::Antigen, WBRKeyword::Antigenic variation, WBRKeyword::Salmonella, WBRKeyword::Salmonella enterica, WBRKeyword::Flagella, WBRKeyword::Alternative expression, WBRKeyword::Microbiology, WBRKeyword::Gram negative, WBRKeyword::Immune evasion
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