Biological potential of an antibacterial substance from Mammaliicoccus sciuri isolated from sheep milk

The growing threat of antibiotic resistance underscores the urgent need to investigate alternative antimicrobial agents, including bacteriocins or bacteriocins like peptides. The purpose of the present work was to isolate and characterize bacteria from sheep milk that produce antibacterial substances. A strain identified as Mammaliicoccus sciuri 1SH was isolated and its extracellular peptides were extracted and partially purified by ethyl acetate. Sodium dodecyl sulphate poly acrylamide gel electrophoresis (SDS-PAGE) analysis revealed a substance with a molecular weight of about 70 kDa. Activity was characterized across varying pH (2.5-8.5) and temperature (25-80 °C) ranges, demonstrating optimal activity between 25-37 °C and pH 6.5-7.4. Enzyme treatment with pepsin and pancreatin significantly reduced the activity, confirming its proteinaceous nature. The antibacterial substance demonstrated antibacterial activity against 26 clinical isolates of Escherichia coli, with minimum inhibitory concentration (MIC) values ranging from 1.125-70 µg/mL and minimum bactericidal concentration (MBC) 6.5-75 µg/mL. Growth kinetic tests demonstrated that growth of Escherichia. coli was suppressed in a dose-dependent way. Mechanistic studies revealed that the peptide induces DNA and protein leakage, indicating membrane disruption as a potential mode of action. Furthermore, the peptide demonstrated significant anti-oxidant activity (IC₅₀: 13.5 μg/mL) and anti-inflammatory properties (IC₅₀: 11 μg/mL). Fourier Transform Infra-Red (FT-IR) analysis identified key functional groups associated with the peptide. This study marks the first characterization and partial purification of a peptide derived from M. sciuri isolated from sheep milk, underscoring its potential as a promising antimicrobial agent with additional functional attributes.