The Effect of Enterococcus faecium-Induced in vitro Infection in Bovine Semen

Bacterial contamination of semen samples represents potential threat to the sperm quality. Enterococcus faecium was identified in our previous study concerning bacteriocenosis of fresh bovine ejaculates. The objectives of this study are focused on the effect of Enterococcus faecium-induced bacteriospermia on sperm motility, mitochondrial membrane potential and reactive oxygen species generation. Bovine semen samples came from breedeng bulls kept in a breeding centre (Slovak Biological Services, a.s., Lužianky, Slovakia). Immediately, samples were subjected to density gradient separation using Percoll PLUS to separate seminal plasma along with seminal bacteriocenosis. An 18-hours culture of E. faecium isolated from bovine semen was diluted to 0.5 McFarland and co-incubated with spermatozoa, while held at 37°C during 4 hours. One-way ANOVA followed by Dunnett’s comparison test were used to express arithmetic mean ± standard error of mean of obtained data. Data obtained using the Computerassisted sperm analysis showed that spermatozoa motility slightly decreased when treated with E. faecium. However, a significant decrease (P<0.01) in mitochondrial membrane potential was recorded after 4 hours treated with E. faecium. After 2 and 4 hours were observed significant increases of ROS levels in the groups with added E. faecium, when compared to control. We may conclude that increased concentrations of Enterococcus faecium may trigger oxidative burst in spermatozoa resulting in decreased mitochondrial membrane potential and thus impaired fertilizing ability of bovine spermatozoa.