Piscidin 4: Genetic expression and comparative immunolocalization in Nile tilapia (Oreochromis niloticus) following challenge using different local bacterial strains

The antimicrobial activity of tilapia piscidin 4 (TP4) was determined in vitro against four bacterial strains, Aeromonas hydrophilla, Pseudomonas fluorescens, Streptococcus iniae and Vibrio anguillarum. Nile tilapia were infected with low and high doses of the tested pathogens; after 3, 6, 24 h and 7 days of the specific TP4 gene expression, tissue immunolocalization was also performed. Histopathological examination revealed septicaemia and necrosis of hemopoietic tissue for all of the tested bacteria. Immunolocalization showed abundance in S. iniae-infected fish tissues. Quantitative RT-PCR analysis revealed that high doses raised mRNA expression levels compared to low doses and expression levels increased in the infected fish, particularly after 24 h, indicating that TP4 exerts potent bactericidal activity against some fish pathogens and plays an essential role in fish immunity. [Display omitted] •Tilapia Piscidin 4 (TP4) could exert potent bactericidal activity against Streptococcus iniae.•TP4 was expressed by injection of A. hydrophilla, P. fluorescens, and V. anguillarum.•Immunostaining was detected in E.G. and goblet cells 6 h S. iniae and V. anguillarum post-infection.•Immunostaining was seen in gills and spleen 24 h P. fluorescens and A. hydrophyla post-infection.•Organs with immunostaining showed mild pathological lesions in comparison to others.