Evaluation of the bacterial flora of the prostate using a 16S rRNA gene based polymerase chain reaction

The role of bacteria in the chronic pelvic pain syndrome (nonbacterial prostatitis and prostatodynia) is controversial and difficult to assess because the bacterial flora of the prostate is not well defined. Polymerase chain reaction (PCR) is a highly sensitive molecular method of bacterial detection. It confirms the sterility of tissue with a high level of confidence and detects small numbers of microbial agents that may represent pathogens. We performed PCR to determine bacterial colonization of the prostate in presumably healthy men and in those undergoing simple or radical prostatectomy.

We analyzed 28 prostate samples from 18 organ donors from whom prostate tissue was obtained under sterile surgical conditions at organ withdrawal, 14 sterile surgical prostate specimens from 7 patients undergoing radical prostatectomy for prostate cancer who previously underwent transrectal biopsy and 6 sterile surgical specimens from 2 men who underwent simple prostatectomy for benign prostatic hyperplasia (BPH), including 1 with an indwelling catheter for several weeks. For PCR we used 2 sets of primers to detect bacterial 16S rRNA gene sequences. Normal prostate tissue seeded in vitro with known numbers of Escherichia coli was used to assess the sensitivity of PCR.

Only 3 of the 28 organ donor samples had histological signs of minimal inflammation and all other samples appeared to be normal without evidence of inflammatory reaction. All of these samples were PCR negative. Of several PCR control reactions the mixture of prostate tissue seeded with known numbers of E. coli demonstrated the high sensitivity of the assay, allowing the detection of as few as 6 bacteria in the presence of 25 mg. of prostate tissue. A focal and heterogeneous distribution of inflammation and infection was noted in the 14 radical prostatectomy specimens. In the prostate cancer and BPH groups there was a strong association of inflammation with positive PCR findings. Of 11 samples 3 without but all 9 with inflammation were PCR positive.

PCR is a highly sensitive method for detecting bacteria in the prostate. In our study negative PCR reactions in the prostate tissue of apparently healthy men made the presence of normal bacterial flora in the prostate extremely unlikely. The presence of bacteria and/or inflammation in radical prostatectomy specimens was found to be a localized process. Concordance between inflammation and positive PCR results in simple and radical prostatectomy specimens suggests that bacteria may frequently have a role in histologically inflammatory prostatitis.