Genome-guided antimicrobial potential of Bacillus stercoris from coastal sand with activity against multidrug-resistant bacteria, including MRSA.

Coastal beach environments harbor diverse bacterial communities, yet their antimicrobial potential remains largely unexplored. This study evaluates the antimicrobial potential of a bacterial isolate 2AT10 from Brazilian beach sand through in vitro, in silico, and ex vivo assays. Isolate 2AT10, a rod-shaped Gram-positive bacterium, exhibited broad-spectrum antimicrobial activity, with its culture supernatants showing greater efficacy against Gram-positive bacteria, including multidrug-resistant strains such as methicillin-resistant Staphylococcus aureus (MRSA). Antimicrobial activity from two differently processed supernatants decreased after heat treatment, enzymatic digestion, and pH changes, suggesting similar proteolytic profiles. Fourier-transform infrared spectroscopy (FTIR) revealed peaks corresponding to C = O and NO₂ groups, indicating the presence of amide functional groups. Importantly, the supernatants did not cause irritation in the ex vivo chorioallantoic membrane assay. Genomic analysis identified isolate 2AT10 as Bacillus stercoris, harboring genes encoding subtilosin A, bacilysin, bacillibactin, bacillaene and lactococcin-like bacteriocins, all associated with antimicrobial activity. A mutation in the sboA gene, involved in subtilosin A biosynthesis and previously linked to in vitro hemolytic activity and enhanced activity against Gram-positive bacteria, was also detected. Molecular docking and dynamics analyses suggested a possible interaction between lactococcin-like bacteriocin and a membrane component of the S. aureus phosphotransferase system transporter, possibly increasing membrane permeability.