Features of the Semen Microbial Contamination and Its Interactive Influence on SIRT1 Expression and the Development...

In recent years, there has been growing interest in the male reproductive tract microbial contamination and its potential impact on semen quality and the effectiveness of reproductive biotechnologies.

The aim of this study was to evaluate the microbial profile of bull semen, determine the antibiotic resistance of isolated bacterial strains, and assess their effect on the expression of SIRT1 as a key protein involved in the cellular response to oxidative stress.

Semen samples collected during routine cryopreservation procedures were analyzed. Microorganisms were identified, their susceptibility to 10 selected antibiotics was tested, and SIRT1 protein levels were measured at three time points (T0, T24, and T48). Microbial presence was detected in 8 out of 13 semen samples, most commonly Escherichia coli, Streptococcus sp., and Pseudomonas aeruginosa. Significant resistance to antibiotics commonly used in semen extenders, such as penicillin, lincomycin, streptomycin, and tetracyclines, was observed.

The highest levels of resistance were found in E. coli and Streptococcus sp. strains. A statistically significant decrease in SIRT1 concentration was also observed in bacterially contaminated samples-from an initial value of 7.09 ng/mL ± 0.53 (T0) to 2.71 ng/mL ± 0.96 after 48 h of incubation (T48). This decline was notably greater than in uncontaminated samples, suggesting an effect of oxidative stress triggered by the presence of pathogens.

The results of this study indicate a strong association between microbial contamination of semen, oxidative stress, and decreased SIRT1 expression. The growing resistance of bacteria to commonly used antibiotics was also confirmed, posing a challenge to the effectiveness of current sanitary protocols in artificial insemination. SIRT1 may serve as a sensitive biomarker of semen quality and infection presence, providing added value in bull fertility diagnostics.