This is the case of an 88-year-old man with fever of 3-day evolution and abdominal pain. The physical examination confirmed the presence of pain in the hypogastrium, no peritoneal irritation. The patient was a carrier of vesical catheter due to a past medical history of benign prostatic hyperplasia. Purple urine bag (Fig. 1). Urine pH was 9.2 with positive nitrites. The urine culture confirmed the growth of Proteus mirabilis and multisensitive Escherichia coli, which is why antibiotic therapy was decided, and symptoms eventually receded. This is a remarkable phenomenon through which intestinal bacteria (sulfatase and phosphatase-producing bacteria) turn the tryptophan of our diet into indoxyl sulfate, that is eventually excreted through urine and transformed into indigo (purple color) and indirubin (red color) that are the two colors capable of staining both the catheter and the urinary bag.

Figure 1

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