A quadriplegic patient in the spinal cord unit who has a suprapubic bladder catheter has had multiple urinary tract infections in the past. He is presently afebrile and asymptomatic but his physician obtains a culture of urine as a precautionary measure. The urine culture yields > 100 000 colonies of Pseudomonas aeruginosa.  

What is the most appropriate management of this patient?