Antimicrobial activity in urine: effect on leukocyte count and bacterial culture results

A total of 500 urine specimens collected from non-hospitalized patients were investigated for leukocyte count by microscopy, bacterial recovery by culture, and detection of antimicrobial activity by disc diffusion. Results indicated that 21% of the specimens contained leukocytes > or = 50/cu mm, whereas 14.4% of specimens revealed significant bacterial growth. The use of Staphylococcus aureus ATCC 29737 as a test bacterium detected the antimicrobial activity in 19.2% of the urine specimens, while the use of two clinical isolates of Escherichia coli detected this activity in fewer specimens. Evidence is provided which indicates that bacterial growth inhibitors in urine are mainly due to the intake of antibiotics by patients. These inhibitors confused the interpretation of urine culture results as they were found to play a major role in the occurrence of sterile pyorrhea and in reducing the number of specimens yielding significant bacterial growth.