Difficulties in quantitating the contribution of urethral bacteria to prostatic fluid and seminal fluid cultures.

A greater than 10-fold increase in the concentration of a bacterium in expressed prostatic secretions or seminal fluid compared to the first voided urine specimen generally is considered as evidence of prostatic infection. To test the validity of this criterion serial culture studies using expressed prostatic secretions and/or seminal fluid were done in 6 men with no clinical evidence of genitourinary infection. In each case during the study period prostatic infection by at least 2 different bacteria that commonly colonize the urethra was suggested by the culture results. Concurrent expressed prostatic secretions or seminal fluid cultures suggesting prostatic infection by the same organism occurred in only 1 of 14 culture studies. These observations suggest that expressed prostatic secretions and seminal fluid are more susceptible to contamination by urethral bacteria than urine and that this phenomenon, rather than infection of the prostate, was the cause of culture results suggesting prostatic infection.