Exploration of materials suitable for single-chain variable fragment (scFv)-conjugated affinity silk and its novel application in preventing bacterial infections in ornamental fish.

The ornamental fish industry is highly prone to disease outbreaks caused by pathogenic microorganisms and parasites. Affinity silk is a material that contains a fibroin L-chain fused to a single-chain variable fragment (scFv) derived from a mouse monoclonal antibody (mAb). It is an effective affinity material with innovative potential for efficiently preventing infectious diseases in aquarium water. In this study, we explored materials suitable for developing anti-Aeromonas salmonicida affinity silk, associated devices for trapping pathogens in water, and the early detection of pathogens directly from infected fish using this material. Selected spherical materials were coated with affinity silk, and their binding activity was evaluated via an enzyme-linked immunosorbent assay to determine appropriate materials for developing a filtration device and selecting suitable swab materials for fish pathogen detection. As a result, nylon was identified as an effective material. Filtration assays showed that an air-lift aquarium water filter equipped with affinity silk-coated nylon wool captured A. salmonicida with significantly higher efficiency than those equipped with non-coated or silk-coated nylon wool, markedly reducing the bacterial concentration of the water. Pathogen detection assays demonstrated that the minimum concentration of A. salmonicida detected by the affinity silk-coated nylon-flocked swab was 104 CFU/mL. The swab also enabled effective identification of A. salmonicida from the skin, gill, and abdominal fluid of infected fish. These findings establish nylon-based affinity silk as a promising new strategy for diagnosing and preventing infectious diseases in ornamental fish and other species.