View source for WBR0683

 {{WBRQuestion
|QuestionAuthor= {{Rim}} (Reviewed by Will Gibson)
|ExamType=USMLE Step 1
|MainCategory=Microbiology
|SubCategory=General Principles
|MainCategory=Microbiology
|SubCategory=General Principles
|MainCategory=Microbiology
|SubCategory=General Principles
|MainCategory=Microbiology
|MainCategory=Microbiology
|MainCategory=Microbiology
|SubCategory=General Principles
|MainCategory=Microbiology
|SubCategory=General Principles
|MainCategory=Microbiology
|SubCategory=General Principles
|MainCategory=Microbiology
|SubCategory=General Principles
|MainCategory=Microbiology
|MainCategory=Microbiology
|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?
|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.
|AnswerA=S. enterica alternatively expresses 2 flagellar proteins
|AnswerAExp=S. enterica has 2 flagellar variants.
|AnswerB=Intragenic recombination causes pilus antigenic variation in S. enterica
|AnswerBExp=Neisseria gonorrhea undergoes intragenic recombination causes pilus antigenic variation.
|AnswerC=Antigenic drifts and shifts allow continuous antigenic variations in S. enterica
|AnswerCExp=Influenza virus undergoes antigenic drifts and shifts.
|AnswerD=S. enterica undergoes programmed rearrangement
|AnswerDExp=Parasites, such as trypanosomes undergo programmed rearrangement.
|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.
|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
|WBRKeyword=Antigen, Antigenic variation, Salmonella, Salmonella enterica, Flagella, Alternative expression, Microbiology, Gram negative, Immune evasion
|Approved=Yes
}}