PAP248-286 is a proteolytic cleavage product of the human prostatic acid phosphatase (PAP) and is found in seminal fluid. The fibrillar form of this peptide enhances viral infections and was therefore called Semen-derived Enhancer of Virus Infection (SEVI). Like many described antimicrobial peptides, PAP248-286 is small and positively charged. Hence, we wanted to test PAP248-286 and SEVI for antibacterial activity.

Therefore, a radial diffusion assay and survival assays were performed. Since PAP248-286 is found in seminal fluid, the vaginal milieu was mimicked for our experiments. The peptide was tested against all ESKAPE pathogens as well as pathogenic bacteria of the female genital tract, like Streptococcus agalactiae or Listeria monocytogenes. Transmission electron microscopy (TEM) and membrane permeabilization assays were used to investigate putative mechanisms of action.

The survival of Pseudomonas aeruginosa, S. agalactiae and L. monocytogenes was significantly reduced after SEVI treatment. In radial diffusion assays, further activity against Klebsiella pneumoniae, Escherichia coli and Acinetobacter baumannii was detected. The antimicrobial activity of SEVI increased with lower pH. By TEM analysis, no effect of PAP248-286 or SEVI on the membrane of P. aeruginosa or S. agalactiae was visible, which was further substantiated by membrane permeabilization assays. Interestingly, TEM together with energy-dispersive X-ray (EDX) spectroscopy analysis showed that P. aeruginosa formed polyphosphate bodies after treatment with PAP248-286.

This study uncovers SEVI's substantial antibacterial potential against vaginal tract pathogens, suggesting a physiological role in the human body.