Bacterial colonization on intraluminal surface of urethral catheter

To determine the relationship between catheter-colonizing bacteria and urinary planktonic bacteria. The significance of catheter-colonizing bacteria for the pathogenesis of urinary tract infection remains unclear, although they are involved in the development of catheter-associated urinary tract infection refractory to antimicrobial chemotherapy.

The subjects were 86 inpatients with urethral catheters. Urinary culture and catheter culture were performed simultaneously. The intraluminal catheter surface was swabbed to prepare a suspension. The suspension and a urine specimen from each patient were quantitatively cultured with the dip slide method and the microorganisms identified.

The catheters had been mainly placed to monitor urine output after urologic surgery, and their median indwelling period was 3.0 days (range 1 to 35). The overall positive rate of catheter culture was significantly greater than that of urine culture (53.5% and 30.2%, respectively, P <0.01), even in patients without a recent antibacterial agent history. The difference was observed at day 2 (60% and 13.3%, catheter versus urine culture, respectively, P = 0.011) and days 3 to 6 (52.4% and 14.3%, respectively, P = 0.010) of the indwelling period, but was indistinguishable at day 14 and thereafter. The percentage of patients who had the same bacterial species isolated from both specimens increased in a time-dependent manner.

The present results revealed considerable differences in the positive rates and bacterial species isolated from urine and catheter cultures, indicating that not all species of bacteria colonizing the intraluminal surface of the urethral catheter are detected as urinary bacteria. These results also suggest that bacterial colonization on the intraluminal catheter surface can precede the emergence of bacteriuria.