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NBME 18 Answers

nbme18/Block 2/Question#32 (reveal difficulty score)
Investigator studying vancomycin-resistant ...
Plasmid loss ๐Ÿ” / ๐Ÿ“บ / ๐ŸŒณ / ๐Ÿ“–

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submitted by โˆ—match95(56)
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Transposition of the vanA gene from vancomycin-resistant Enterococcus is how it transfers resistance. They use transposons which are located on plasmids. If you have plasmid loss, you won't have transposons, and resistance will decrease.

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azibird  Why can't this be a point mutation? +6
freenbme23  I don't think that this implies that it can't be point mutation, but rather plasmid loss is more likely. Also, the point mutation Would have to ultimately lead to the plasmid loss. +
thrawn  FA says transposition is responsible for antibiotic resistance and plasmids are for transferring the genes of toxins (though UW says also antibiotic resistance). Make up your minds sheeple +2
mariame  The most common Vancomicin resistant genes, vanA and vanB are found in a transposon. These have been transferred from Enterococcus to a multidrug resistance plasmid in Staph aureus. the super multidrug resistance plasmid now contains resistance genes against lactams, vancomycin, aminoglycosides, trimethoprim, and some desinfectants. +2
an1  @thrawn I recall that too, but I think it said transposition was antibiotic resistance and UW said transposons was for multi drug resistance +
uasid  The plasmid is lost during bacteria replication โ€“ when DNA is being replicated, the plasmid is not always replicated and passed on to subsequent generations, especially if there are several generations of replication. +1

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