"Something really bizarre" in a foley bag

The correct diagnosis is Purple Urine Bags Syndrome

This syndrome results from infection or sympomatic bacteriuria, but its very name sounds like a jest. It affects a considerable number of persons, for many of whom discoloration of the plastic is more intense than that of the urine. It is the subject of numerous reports, of which a small subset are cited here,^1-13 yet it remains unfamiliar to most clinicians.

Beautifully Worked-Out Chemistry
Although descriptions of the staining of bags and urine go back to 1978,^1-3 the effect of indigo is barely alluded to in a review of abnormal urine color a decade later.⁴ Early speculation about mechanism was replaced by detailed chemical analysis in ² sentinel papers by Dealler and associates.^5,6 These showed that tryptophan(Drug information on tryptophan) is metabolized in the intestine to indole, which then ascends the portal vein and is conjugated in the liver to indoxyl sulfate, a species of indican. Indoxyl sulfate is excreted, considerably concentrated, into the urine. There, high concentrations of viable bacteria, if they possess the requisite sulfatase/phosphatase enzyme, can cleave the molecule. Following further chemical reactions, indigo (the familiar dark blue that is synthesized by the plant of the same name and, in the industrial era, in factories) can form, along with a violet pigment called indirubin. The latter in particular has an affinity for plastic and is incorporated into the tubing and bag. This combination of blue and violet stains the bag purple.

Case Discussion
Bacteriology, Epidemiology, and the Bowel
Providencia stuartii is the bacterium most commonly isolated from persons with purple urine bags, followed by Klebsiella pneumoniae and Enterobacter agglomerans. Ingenious studies have looked at the formation of blue bacterial colonies on conventional agar plates in a variety of conditions, including the addition of the filtered urine of affected persons. Careful microbiologic work has shown that the requisite enzymes are most common and most abundant in these species; however, other investigators find a several-log higher mean urinary bacterial count the most strongly predictive factor, rather than the presence of one particular organism.

Providencia stuartii, formerly classified asa Proteus species, is unfamiliar, yet it has proved to be a formidable and often multiply antibiotic-resistant cause of infection and persistent colonization, particularly in urethral catheter systems in nursing home settings.⁷ So although some cases of purple urine bags syndrome have been successfully managed with a change of the catheter and the bag, thus removing a principal reservoir, many others have necessitated systemic antibiotic therapy.^8-11 Surely for an organism that is often multiply resistant, one would prefer the earliest possible warning, regardless of which management decisions are ultimately made and the fact that Providencia stuartii has a color indicator, even a poorly sensitive one, sometimes provides just that.

Some readers will recall an indican test for malabsorption. Although this is no longer used because of insufficient sensitivity and specificity, there is actually a connection with the syndrome in question: the constipation that is a usual part of the setting of purple urine bags syndrome results in increased bacterial metabolism of tryptophan in the intestines of patients so affected, compared with persons who have normal intestinal transit time; hence, there is more substrate from which indoxyl sulfate can be derived. One could speculate on whether the use of l-tryptophan as a dietary or "nutraceutical" supplement, a use that fell sharply in the wake of its association with the eosinophilia-myalgia syndrome, would have led to additional cases of purple urine bags syndrome because of enhancement of urinary concentration of indoxyl sulfate. However, persons who are free of the requisite bacteriuria should have been immune regardless of the concentration of this chemical in the bladder urine.