Isolation of a spermatozoal immobilization factor from Staphylococcus aureus filtrates
Staphylococcus aureus isolated from the cervix of an infertile woman was found to cause complete immobilization of human spermatozoa in vitro. Only the cell culture and cell-free supernatant showed immobilization activity, indicating that the sperm immobilization factor might be released extracellularly by the organism because no activity was observed with the washed cells. Heat treatment of the supernatant at 60 °C for 10 min waived its immobilizing activity, indicating that the active component may be a protein. The bioactive molecule from the supernatant was purified to homogeneity by ammonium sulfate precipitation, gel permeation chromatography, and ion exchange chromatography. Sperm immobilization factor (SIF) was found to be an ~20 kDa protein. SIF at a concentration of 10 µg/mL was required to cause 100% immobilization of human spermatozoa after 30 min of incubation at 37 °C, whereas a concentration of 150 µg/mL caused immediate immobilization, and a concentration of 200 µg/mL resulted in instant loss of viability of human spermatozoa, observed by eosin–nigrosin staining. Scanning electron microscopy showed that the treatment of human spermatozoa with SIF caused multiple defects in the head, midpiece, neck, and tail region of human spermatozoa.