Isolation and partial characterization of antimicrobial peptide-enriched fractions from Parabacteroides distasonis

Parabacteroides distasonis is a part of the indigenous human microbiota and plays a significant role in disease etiopathogenesis. This study aimed to evaluate the efficacy of peptides isolated from P. distasonis strains. We focused on the expression, purification, characterization, antimicrobial efficacy through antagonism assays, and in silico studies of antimicrobial peptides produced by 78 P. distasonis strains. Methodology: Seventy-eight P. distasonis strains isolated from broiler (Gallus gallus domesticus) feces were evaluated. Antagonistic activity was assessed using the double-layer diffusion method. The influence of pH, temperature, proteolytic enzymes, and organic solvents on the intracellular peptide fraction (C-50) was analyzed. MIC was determined according to CLSI guidelines with adaptations. The peptide was purified, and its N-terminal amino acid sequence was determined using MALDI-TOF. Sequence identity was confirmed through BLAST-P analysis. Membrane docking was also conducted. Results: Fifty percent of the tested isolates produced antagonistic substances against at least one indicator strain. The C-50 fraction displayed stable antagonistic activity across a wide pH range (5.0-10.0) but was inactivated above 70 °C. MIC and MBC values for P. distasonis ATCC 1295 were 1.81 mg/mL (6.25 AU/mL) and 23.24 mg/mL (160 AU/mL), respectively. Ion-exchange chromatography revealed two peaks of activity. The major active peptide showed 100% identity to segments of histone-like H1 from Bacteroides fragilis. Exploratory molecular docking suggested plausible interactions. These computational findings are preliminary and require experimental validation. This study reports the discovery and partial biochemical characterization of antimicrobial peptides from P. distasonis. The peptides demonstrated extract-level activity and sequence similarity to histone-like proteins. Detailed mechanism of action and safety validation require further investigation.