Aim: Purple urine bag syndrome is a condition in which the urinary catheter bag turns purple. A tryptophan-indigo hypothesis has been proposed as the mechanism of PUBS, in which bacterial decomposition of tryptophan in gut associated with chronic constipation, bacterial overgrowth in the urinary tract and alkaline urine causes production of indigo and discoloration. We considered that further investigation of cases was needed. Methods: We investigated 6 cases exhibiting PUBS (3 males and 3 females). Results: All cases had chronic constipation. Oral ingestion was impossible in one case. PUBS disappeared after antibiotic treatment (3 cases) or spontaneously (one case). Alkaline urine and indicanuria were not found in all cases that showed the disappearance of PUBS. In bacterial culture of urine during the exhibition of PUBS, Enterococcus faecalis was isolated together with Morganella morganii (3 cases) and Pseudomonas aeruginosa (one case). Single infections by Klebsiella pneumoniae or Citrobacter species were also found. After disappearance of PUBS, infected bacterial species changed but no cases showed sterile urine. Urine and blood α-amino-n-butyric acid levels reduced after the disappearance of PUBS whereas tryp-tophan levels did not show related changes. In one case, blood protein concentration increased after the spontaneous disap-pearance of PUBS. Indicanuria and alkalization of urine from urinary catheter bag were more intense than of fresh urine. Conclusions: The present results generally support the Tryptophan-indigo hypothesis'. Furthermore, it was suggested that additional factors associated with the occurrence of PUBS are an environment that facilitates specific bacterial growth in a hospital as well as abnormal metabolism relating to α-amino-n-butyric acid and reduced protein synthesis in patients.
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