Soluble products of Escherichia coli induce mitochondrial dysfunction-related sperm membrane lipid peroxidation which is prevented by lactobacilli.

Unidentified soluble factors secreted by E. coli, a frequently isolated microorganism in genitourinary infections, have been reported to inhibit mitochondrial membrane potential (ΔΨm), motility and vitality of human spermatozoa. Here we explore the mechanisms involved in the adverse impact of E. coli on sperm motility, focusing mainly on sperm mitochondrial function and possible membrane damage induced by mitochondrial-generated reactive oxygen species (ROS). Furthermore, as lactobacilli, which dominate the vaginal ecosystem of healthy women, have been shown to exert anti-oxidant protective effects on spermatozoa, we also evaluated whether soluble products from these microorganisms could protect spermatozoa against the effects of E. coli. We assessed motility (by computer-aided semen analysis), ΔΨm (with JC-1 dye by flow cytometry), mitochondrial ROS generation (with MitoSOX red dye by flow cytometry) and membrane lipid-peroxidation (with the fluorophore BODIPY C11 by flow cytometry) of sperm suspensions exposed to E. coli in the presence and in the absence of a combination of 3 selected strains of lactobacilli (L. brevis, L. salivarius, L. plantarum). A Transwell system was used to avoid direct contact between spermatozoa and microorganisms. Soluble products of E. coli induced ΔΨm loss, mitochondrial generation of ROS and membrane lipid-peroxidation, resulting in motility loss. Soluble factors of lactobacilli prevented membrane lipid-peroxidation of E. coli-exposed spermatozoa, thus preserving their motility. In conclusion, sperm motility loss by soluble products of E. coli reflects a mitochondrial dysfunction-related membrane lipid-peroxidation. Lactobacilli could protect spermatozoa in the presence of vaginal disorders, by preventing ROS-induced membrane damage.

Effect of vaginal probiotic lactobacilli on in vitro-induced sperm lipid peroxidation and its impact on sperm motility and viability.

A combination of three selected strains of lactobacilli (Lactobacillus brevis [CD2], L. salivarius [FV2], and L. plantarum [FV9]), whose effectiveness in treating bacterial vaginosis in the form of vaginal tablets has been reported recently, prevented sperm lipid peroxidation that was induced in vitro by a ferrous ion promoter, thus preserving sperm motility and viability. This finding suggests the potential of vaginal probiotic lactobacilli for protecting human spermatozoa from radical oxygen species in the presence of vaginal disorders, thereby improving the fertilization potential of the female host.