ANIMAL HEALTH

A Novel Oral Strategy Using Probiotic Spores Offers Protection Against Vibrio Infection in Farmed Fish

Naples, Italy, 16 May 2025 | A ground-breaking new strategy could significantly reduce the reliance on antibiotics in the fight against vibriosis

Medaka fish | Wikipedia

Researchers at the University of Naples Federico II in Italy have successfully combined probiotics with a non-recombinant oral vaccine to combat vibriosis, one of the most damaging diseases in aquaculture.

The findings, published in Microbial Cell Factories, present an innovative solution: the use of probiotic spores from Bacillus megaterium as a delivery system for antigens targeting Vibrio harveyi, a common pathogen in farmed fish.

Currently, vibriosis is typically treated with antibiotics. However, increasing antibiotic resistance and the negative impact on the animal’s microbiota have cast doubt on this approach. Injectable vaccines, though effective, are often impractical for large-scale aquaculture due to high costs and potential effects on fish growth. Oral vaccines, while easier to administer, often suffer from poor immune efficacy.

In response, the team selected probiotic strains capable of adsorbing antigens without the need for genetic modification. The bacillus megaterium MV30 strain proved most effective at binding proteins to its surface. Two antigens from Vibrio harveyi were chosen: Hsp33 (a heat stock protein) and a fragment of OmpK (an outer membrane protein) both involved in the fish’s immune response.

Efficacy trials were conducted on Oryzias latipes (medaka fish) larvae, treated via immersion with spores loaded with the antigens. After exposure to a virulent strain of Vibrio harveyi, survival rates exceeded 80% in fish trated with antigen-bound spores, compared to just 40% in control groups. Neither the spores alone nor the antigens on their own offered the same level of protection.

“Oral immunization using spores with adsorbed antigens induced a significant protective effect. This approach avoids biosecurity concerns as it dosen’t involve modified organisms,” the researchers noted.

These findings pave the way for trials under real aquaculture conditions. At a time when the industry is urgently seeking sustainable and effective responses to bacterial diseases, this combination of probiotics and non-recombinant oral vaccination offers a promising new direction.

Reference:

Marina De Stefano, Giovanni Di Gregorio Barletta, Simona Morgera, Ylenia De Luca, Chiara Belaeff, Karen Power, Loredana Baccigalupi, Gionata De Vico, Ivan Conte, Ezio Ricca, Anella Saggese. Probiotic spore-based antigen delivery: a novel oral vaccine strategy against Vibrio infections in aquaculture. Microbial Cell Factories. https://doi.org/10.1186/s12934-025-02725-w