Isolation of a spermatozoal immobilization factor from Escherichia coli filtrates.

A low-molecular weight spermatozoal immobilization factor (SIF) has been isolated from Escherichia coli cultures. This factor is stable to heating, freezing, and lyophilization, and immobilizes but does not kill spermatozoa. The concentration of spermatozoa influenced the effectiveness of the SIF in immobilizing spermatozoa, indicating that bacterial infections could have a greater influence on the oligospermic ejaculate than on a normal specimen. SIF is a stable factor and binds to spermatozoa via a reversible mechanism.