A model of catheter-associated urinary tract infection initiated by bacterial contamination of the catheter tip.

OBJECTIVE: To examine the microbial colonization of urinary catheters that have been used by patients, to model catheter colonization in vitro and thus provide information about the way bacteria gain access to the bladder during catheterization.

MATERIALS AND METHODS: Microbial growth patterns from patients' indwelling catheters and from catheters used in an in vitro model of the catheterized urinary tract were compared. Catheters were cut into short segments, microorganisms from the inside and outside of each segment of the catheters were removed by sonication, and viable bacteria counted. DNA was extracted from selected patient catheter isolates and the DNA fragment of 16S ribosomal RNA was amplified by polymerase chain reaction and confirmed by DNA sequencing. The DNA sequences from the isolates obtained from different catheter sections and from urine in the same patient were compared.

RESULTS: After 1 day of catheterization there was significant bacterial growth on the outside of all the segments of patient catheters; there was significant growth on the inside of all segments by 4 days. Higher viable counts and a wider spectrum of genera were found on the outside than on the inside of these catheters. The same strains of bacteria, as determined by >or=98% similarity of the 16S ribosomal DNA sequence, were found on the outside and inside of catheters and in the urine. In the in vitro model, when the distal urethra was inoculated before inserting the catheter, the viable counts after incubation were variable along the outside of the catheter and the inside counts were uniformly high. By contrast, there was a different pattern after inoculating the inside of the distal end of the catheter, leading to an ascending biofilm on the inside. A smaller inoculum delayed but did not prevent infection in the model.

CONCLUSION: The present results are consistent with the hypothesis that contamination of the tip of the catheter while it is being inserted is a possible means by which bacteria gain access to the bladder.