Comparison of techniques for the selection of bacteria-free sperm preparations.

The authors compared the three most commonly used sperm preparation techniques--swim-up, fall-down, and Percoll gradient--for their ability to recover highly motile sperm and minimize bacterial contamination. Eleven human semen samples collected by masturbation were used and run in parallel with the three methods. A semiquantitative bacterial analysis was performed in all samples and results expressed in colony-forming units per milliliter (CFU/ml). The Percoll gradient technique resulted in an average sperm concentration of 5.81 +/- 4.4 X 10(6) ml, and the average bacterial concentration dropped from 8.66 +/- 12.96 X 10(3) CFU/ml in semen to 0.01 +/- 0.03 X 10(3) CFU/ml. The bacterial count was not significantly different when the raw semen was compared with the swim-up or the fall-down preparations. The authors conclude that the Percoll gradient method yields an adequate sperm concentration, with high motility and improved morphology, while eliminating bacterial contamination.