WBR0683

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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