Control of Staphylococcus aureus infection by biosurfactant derived from Bacillus rugosus HH2: Strain isolation, structural characterization, and mechanistic insights.

Novel antimicrobials are urgently needed to combat methicillin-resistant Staphylococcus aureus (MRSA) infections. This study explores the potential of biosurfactants derived from Bacillus rugosus HH2 as a novel antibacterial agent against MRSA. The biosurfactant, identified as surfactin, demonstrated surface-active properties, reducing surface tension to 37.63 mN/m and lowering contact angles in a concentration-dependent manner. It remained stable across a wide range of pH (4-10), temperatures (30-80 °C), and salinity levels (3-18 %). The biosurfactant inhibited the growth of both methicillin-sensitive S. aureus and MRSA, with minimum inhibitory concentrations ranging from 128 to 256 μg/mL. Additionally, it showed anti-biofilm activity, preventing biofilm formation and dispersing established biofilms. Field-emission scanning electron microscopy revealed that the biosurfactant disrupted bacterial cell membranes, leading to leakage. Furthermore, it reduced the production of virulence factors in S. aureus, including hemolysin and lipase. Transcriptomic analysis indicated downregulation of genes associated with quorum sensing and cell adhesion in MRSA. Molecular docking studies showed strong interactions between surfactin and key MRSA proteins, underscoring its potential to overcome antibiotic resistance. Biocompatibility was confirmed through in vitro cytotoxicity and in vivo phytotoxicity tests. In summary, this study presents surfactin as a promising novel antibacterial agent against MRSA, providing insights into its mechanisms of action.