Abstract This study focused on the isolation and comprehensive evaluation of a postbiotic synthesized by E. coli Nissle 1917. The research specifically investigated its diverse biological activities, including its potential antibacterial, bacteriostatic, bactericidal effects, and its antioxidant capacity. The primary objective was to determine the postbiotic’s efficacy in reducing semen bacterial load and mitigating oxidative stress, enhancing the quality and structural integrity. The results indicated that E. coli Nissle 1917 postbiotic exhibited significant antibacterial activity against K. pneumoniae , S. epidermidis , and S. aureus . The bacteriostatic effect was observed against K. pneumoniae (900 µg/mL), E. coli (1800 µg/mL), P. aeruginosa (1500 µg/mL), S. aureus (1200 µg/mL), S. epidermidis (900 µg/mL), and B. subtilis (1500 µg/mL). The bactericidal effect was most pronounced against K. pneumoniae and S. epidermidis , which were the most sensitive, with a minimum bactericidal concentration (MBC) of 1000 µg/mL, followed by S. aureus (1400 µg/mL), P. aeruginosa and B. subtilis (1650 µg/mL). The main components of the postbiotic are docosanoic acid, 1,2,3-propanetriyl ester (0.90%), stearic acid, 3-(octadecyloxy)propyl ester (1.24%), 1-methyl-2-pyrrolidineethanol (1.49%), 4(3 H)-pyrimidinone / 1 H-imidazole-4,5-dihydro-2-methyl (0.96% / 0.87%), 10-octadecenoic acid methyl ester and similar C18 fatty acid methyl esters (3.74%), cyclohexanol, 1R-4-acetamido-2,3-cis-epoxy (3.34%), 2-myristynoyl-glycinamide (1.85%), 1-monolinoleoylglycerol trimethylsilyl ether (1.81%), and glycine, N-3,5,7,12-tetrakis(trimethylsiloxy)cholan-24-yl derivative (0.82%). Supplementation with 1000–2000 µg/mL postbiotic significantly improved sperm motility (25.7%, and 29.5%), viability (26.8%, and 34%), membrane integrity (22.2%, and 27.1%), and kinematic parameters compared to the control group ( p < 0.01, respectively). Postbiotic addition also increased the percentage of live sperm with intact acrosome and reduced the percentages of live and dead sperm with detached acrosome. Postbiotic addition (250, 500, 1000 and 2000 µg/mL) significantly improved total antioxidant capacity (35.6, 36.9, 52 and 63%), reduced oxidative stress markers such as malondialdehyde (6.1, 8.7, 19.5 and 22.9%), and nitric oxide (20, 28.2, 36.4 and 38.9%, respectively) and decreased the percentage of apoptotic sperm (26, 46.5, 48.9 and 51.2%) in post-thawed semen compared to control group ( p < 0.01). Postbiotic supplementation preserved sperm ultrastructure and enhanced pregnancy rates as well as reduced the bacterial load in post-thawed semen ( p < 0.05). In summary, the E. coli Nissle 1917 postbiotic acts as a crucial protective agent. By exerting antimicrobial, anti-apoptotic, and antioxidant activities, it effectively regulates the semen’s antioxidant status and maintains the quality of cryopreserved buffalo sperm.
Darwish et al. (2026) studied this question.