Fertilizing potential of ejaculated human spermatozoa during in vitro semen bacterial infection

Objective To assess the in vitro effect of three bacterial isolates ( Escherichia coli , serotype O75:HNT, Staphylococcus haemolyticus , and Bacteroides ureolyticus ) and/or leukocytes on sperm motility, subcellular changes in sperm plasma membranes, and sperm fertilizing potential. Design An in vitro model of semen bacterial infection. Setting Basic research laboratory. Patient(s) Healthy normozoospermic volunteers and healthy blood donors. Intervention(s) None. Main Outcome Measure(s) Sperm plasma membrane stability was evaluated with a LIVE/DEAD Sperm Viability Kit and with the merocyanine 540 (M540) test both performed using flow cytometry. An oxiSelect TBARS Assay Kit was used for quantitative measurement of malondialdehyde content. Functional ability of spermatozoa was assessed by hypo-osmotic swelling (HOS) test and sperm penetration assay (SPA). Result(s) The incubation of sperm with bacteria and/or leukocytes was associated with the reduction of their fertilizing potential demonstrated in both the HOS test and SPA, and this effect can be considered as a natural consequence of diminished motility and sperm membrane injury of lipid bilayers. Bacteroides ureolyticus demonstrated the most significant detrimental effect on sperm structure and function. Conclusion(s) Sperm motility and lipid sperm membrane status might be the earliest and the most sensitive indicators of sperm damage with negative consequences for male factor fertility, which can be attributed to both bacteria and leukocytes action.