Bacterial contamination of bovine ejaculates intended for artificial insemination may be reflected in a significant economic loss due to unsuccessful fertilization as well as health issues of the recipients. The Staphylococcus genus represents a large part of bacteriocenosis of bovine ejaculates. Therefore, this study aims to get a closer look on the effects of Staphylococcus-induced bacteriospermia under in vitro conditions on bovine sperm quality. Prior to inducing bacteriospermia, spermatozoa were separated from each ejaculate using Percoll® Plus gradient medium in order to limit the effects only to the selected bacterial species. Seven Staphylococcus species previously isolated from bovine semen were used for our experiments at a turbidity of 0.5 McFarland (equivalent to 1.5 × 108 colony-forming units per mL). The contaminated semen samples were incubated at 37 °C and at times of 0, 2, and 4 h, motility, mitochondrial membrane potential, reactive oxygen species (ROS) generation, sperm DNA fragmentation, and magnesium (Mg) and calcium (Ca) extracellular concentration were analyzed and compared with the control group (uncontaminated). The results showed no significant changes at the initial measurement. However, significant adverse effects were observed after 2 h and 4 h of incubation. Most notably, the presence of S. aureus, S. warneri, S. kloosii, and S. cohnii caused a significantly increased ROS production, leading to sperm DNA fragmentation, changes in the mitochondrial membrane potential, and a decreased sperm motility. Furthermore, the presence of Staphylococcus species led to lower extracellular concentrations of Mg and Ca. In conclusion, the overgrowth of Staphylococcus bacteria in bovine semen may contribute to oxidative stress resulting in sperm DNA fragmentation, altered mitochondrial membrane potential, and diminished sperm motility.
Keywords: DNA fragmentation; Staphylococcus; bacteria; bacterial contamination; bull sperm; oxidative stress; sperm quality.