USMLE Step 1 Quiz
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MICROBIOLOGY
Question 1 of 20
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A 50-year-old woman with a history of multiple urinary tract infections is treated with trimethoprim for an uncomplicated cystitis caused by E. coli. The infection persists, and the isolate is found to have acquired a plasmid carrying the dfr gene.
The resistance to trimethoprim in this scenario is mediated by an alteration in which of the following enzymes?
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