DAO 137:175-183 (2020)  -  DOI: https://doi.org/10.3354/dao03439

ABSTRACT: Flavobacterial infections are among the causes of fish losses in farms with the emergence of antibiotic-resistant isolates. Silver nanoparticles (AgNPs) are known for their potent antimicrobial activity against different types of bacteria. In this study, we evaluated the antibacterial properties of AgNPs (diameter: 23 nm) against Flavobacterium johnsoniae infection in common carp Cyprinus carpio. The assays included both in vitro and in vivo antibacterial tests in addition to evaluation of cell toxicity effects on the fish cell lines. The in vitro results revealed potent inhibitory effects of AgNPs on the growth of F. johnsoniae with a minimum inhibitory concentration of 34 µg ml^-1. Fish cell (epithelioma papulosum cyprini and koi carp fin) viability was 95-100% after exposure to 500 ng ml^-1 (and lower concentrations) of AgNPs. In the exposure experiment, mortality rates decreased from 45% in the infected non-treated group to 30 and 15% in the intraperitoneal injection and immersion-treated groups, respectively. Neither of the treated groups showed any clinical signs or histopathological lesions. The single-dose treatment with AgNPs during early infection with F. johnsoniae aided in minimizing fish losses.

KEY WORDS: Flavobacterium johnsoniae · Silver nanoparticles · AgNPs · Common carp · Antibacterial · Fish diseases