The Oxytetracycline and Florfenicol Effect on the Immune System and Oxidative Stress Response of the SHK-1 Cell Line of Salmo salar

The aquaculture industry in Chile, as in the rest of the world, has rapidly grown, becoming a crucial economic sector. However, diseases pose a major threat, causing significant economic losses and environmental impacts. Various antimicrobials, particularly Oxytetracycline and Florfenicol, are used to combat these diseases, which has boosted production and mitigated economic losses. However, excessive antibiotic use has led to pathogen resistance, necessitating higher doses. This overuse can cause side effects in fish, including liver damage and immunosuppression. This study aimed to determine the impact of multiple doses of florfenicol and oxytetracycline on the SHK-11 cell line of Salmo salar by analyzing the expression of genes related to innate immunity and oxidative stress by qRT-PCR in addition to the quantification of immune system proteins via dot blot. The experimental treatments were the following: cells were stimulated with different concentrations of oxytetracycline (0.25, 0.5, and 1.5 &micro:g/mL) and florfenicol (1, 10, and 20 &micro:g/mL) for time kinetics of 0.5, 1, 3, 6, 12, 24, and 48 h. For both cases, controls consisting of cells without antibiotics were included. The expression of the immune system genes was mostly inhibited compared to the control. However, it was observed that TLR-1 and MyD88 present a joint activation pattern at different times and concentrations for both antibiotics. Regarding the expression of CAT and GPx, transcripts were increased in the early stages of stimulation with oxytetracycline and florfenicol, followed by a subsequent decrease in gene expression. This study provides relevant information to understand the effect of antibiotics at the cellular level in one of the most important species for global aquaculture, the Atlantic salmon.