Antimicrobial effects of Bacillus safensis BS05 cell free supernatant against Campylobacter jejuni and its probiotic evaluation

Campylobacter jejuni (C. jejuni) is a significant foodborne pathogen. The rise of antibiotic-resistant strains has diminished the effectiveness of conventional treatments, highlighting the urgent need for safe and effective alternatives. In this study, a Bacillus safensis (B. safensis) strain (BS05) was isolated from goats and assessed for its probiotic properties and antagonistic activity against C. jejuni. BS05 formed rough colonies on agar, and scanning electron microscopy revealed predominantly short rod-shaped cells. The cell-free culture supernatant (CFS) of BS05 inhibited multiple C. jejuni strains of diverse sequence types. This inhibition was evidenced by reduced optical density (OD₆₀₀) values and MIC-like growth inhibition assays, indicating a dose-dependent antagonistic effect. To explore potential bacteriocin-related compounds, the BS05 genome was analyzed using AntiSMASH 6.0 and BAGEL4. AntiSMASH predicted a total of 12 secondary metabolite gene clusters, while BAGEL4 independently identified 5 putative bacteriocin gene clusters. These clusters may play a role in the observed antibacterial activity. However, further investigations are required to identify the specific compounds responsible. Safety assessment in BALB/c mice demonstrated that oral administration of BS05 caused no detectable histopathological alterations. The cecal mucosa appeared intact, with no visible tissue damage or structural abnormalities observed, comparable to the control group. Collectively, these findings indicate that BS05 CFS shows potential inhibitory activity against C. jejuni. Furthermore, BS05 represents a promising probiotic candidate and a potential source of novel bacteriocins, which may contribute to advancements in poultry health management and antimicrobial development.