MS-2596

A 28-year-old woman visits her doctor complaining of increased dysuria and polyuria. Her urine dipstick test reveals the following results:

Leukocytes ++
Protein ++
Erythrocytes +
Nitrites +

The doctor prescribes trimethoprim for an uncomplicated urinary tract infection and advises the patient to come back if her symptoms worsen.

What is the mechanism of action of the prescribed antibiotic?