Oral administration of Bacillus subtilis spores expressing Staphylococcus aureus IsdB induces mucosal immune responses in mice.

Abstract

Purpose: Bacillus subtilis spores, known for their durability and well-developed genetic manipulation tools, show promise for oral vaccine delivery. Staphylococcus aureus is a major global health concern due to multidrug resistance and lack of a vaccine. This study explored the potential of B. subtilis spores engineered to express IsdB, a key S. aureus iron acquisition protein, on their surface and evaluated the immunogenic effect of recombinant spores through oral administration in mice.

Method: B. subtilis spores were engineered to display a key S. aureus protein, IsdB, fused with spore coat protein, CotB, and confirmed by PCR. Western blotting, sporeELISA, and immunofluorescence microscopy verified the surface expression of IsdB. The engineered BsHT2377 spores were orally administered to Swiss mice at two different doses, and antibody levels in both serum and feces were measured using ELISA.

Result: PCR confirmed the targeted integration of the isdB gene into B. subtilis, generating the strain BsHT2377. Western blotting, sporeELISA, and immunofluorescence microscopy validated IsdB surface display on BsHT2377 spores. Oral administration triggered a gut-localised immune response in mice, with significantly elevated fecal IgA but no substantial increase in serum IgG.

Conclusion: This study engineered a novel B. subtilis strain, BsHT2377, that displays the S. aureus IsdB protein on its spore surface. Oral administration in mice significantly increased fecal IgA, indicating a mucosal immune response. These findings highlight the potential of B. subtilis spores as oral vaccine carriers and offer insights to support the optimization of future vaccine designs.