Long-term catheter-associated bacteriuria: species at low concentration

Polymicrobial bacteriuria in patients with long-term (greater than or equal to 30 days) indwelling urethral catheters is common and is associated with potentially serious acute and long-term complications. The dynamics of organisms at low concentration (less than 10(5) cfu/mL) in this setting has not been well-characterized; however, in patients with short-term catheters organisms initially present at low concentration (less than 10(5) cfu/mL) usually grow to high concentration (greater than or equal to 10(5) cfu/mL). At the time of catheter replacement for 7 long-term catheterized patients who were not receiving antibiotics, we identified all species at greater than or equal to 10(2) cfu/mL in fresh urine aspirated from the old indwelling catheter and the new sterile replacement catheter and then determined which of these species were present at high concentration two weeks later. A total of thirty-seven species, nineteen at high and eighteen at low concentration were detected in either the old or the new catheters. Eighteen of the nineteen initially detected at high concentration but only one of the eighteen initially detected at low concentration (p less than 0.001) were present at high concentration two weeks later. In patients with long-term indwelling urethral catheters, the number and multiplicity of species causing bacteriuria at low concentration rival that of species at high concentration; however, species at low concentration usually do not grow to high concentration in the presence of other species at high concentration.