Detection and identification of bacterial DNA in semen.

Objective: To detect and identify bacteria in semen by sequencing polymerase chain reaction (PCR)-amplified ribosomal RNA gene regions (rDNAs).

Design: Bacterial rDNAs were detected by PCR amplification of semen DNA. Conditions were adjusted to detect only abundant organisms, no fewer than 20,000 bacteria/mL of semen.

Setting: Clinical andrology laboratory and academic research laboratories.

Patient(s): Men undergoing fertility evaluation (n = 29) or vasectomy (n = 5).

Intervention(s): None. MAIN OUTCOME MEAURE(S): Frequency of bacterial rDNA-positive specimens, relationship of rDNAs to bacteria in GenBank, and correlation with semen cells.

Result(s): Twenty-five (56%) of the specimens from 22 (65%) of the men were positive. A total of 141 bacterial rDNA sequences were compared with GenBank data for identification. The largest group matched gram-positive anaerobic cocci (Peptoniphilis, Anaerococcus, Finegoldia, Peptostreptococcus spp.) in 13 specimens, followed by Corynebacterium spp. in 10 specimens, Staphylococcus, Lactobacillus, and Streptococcus spp. in 7 specimens each, Pseudomonas spp. in 4 specimens, and Haemophilus and Acinetobacter spp. in 2 specimens each. The rDNA-positive specimens averaged 59 +/- 13 million sperm/mL, 46 +/- 5% of which were motile, not statistically different from the rDNA-negative specimens (77 +/- 16 million/mL, 47 +/- 5% motile). Normal sperm forms were lower in the rDNA-positive (10 +/- 1.1%) than in the rDNA-negative specimens (22 +/- 2%), and lymphocytes/monocytes were fivefold lower in the rDNA-positive specimens (0.4 +/- 0.2 million/mL) than in the negative specimens (1.9 +/- 0.7 million/mL).

Conclusion(s): Abundant bacteria in semen are not commensal, arise from infection in the male genitourinary tract, may influence fertility, and may reflect an inadequate cellular immune response.