Sulfamethoxazole (SMX) Alters Immune and Apoptotic Endpoints in Developing Zebrafish (Danio rerio)

Sulfamethoxazole (SMX) is a broad-range bacteriostatic antibiotic widely used in animal and fish farming and is also employed in human medicine. These antibiotics can ultimately end up in the aquatic ecosystem and affect non-target organisms such as fish. To discern the effect of SMX on developing zebrafish embryos and larvae, we investigated a broad range of sub-lethal toxicity endpoints. Higher concentrations of SMX affected survivability, caused hatch delay, and induced malformations including edema of the yolk sac, pericardial effusion, bent tail, and curved spine in developing embryos. Lower levels of SMX provoked an inflammatory response in larvae at seven days post fertilization (dpf), as noted by up-regulation of interferon (ifn-gamma) and interleukin 1 beta (il-1 beta). SMX also increased the expression of genes related to apoptosis, including BCL2-Associated Agonist of Cell Death (bad) and BCL2 Associated X, Apoptosis Regulator (bax) at 50 mu g/L and decreased caspase 3 (casp3) expression in a dose-dependent manner. SMX induced hyperactivity in larval fish at 500 and 2500 mu g/L based upon the light/dark preference test. Collectively, this study revealed that exposure to SMX can disrupt the immune system by altering host defense mechanisms as well as transcripts related to apoptosis. These data improve understanding of antibiotic chemical toxicity in aquatic organisms and serves as a baseline for in-depth environmental risk assessment of SMX and antibiotics.

Automated summary

The broad-range bacteriostatic antibiotic sulfamethoxazole (SMX) has been found to have sub-lethal toxicity effects on developing zebrafish embryos and larvae, including decreased survivability, delayed hatch, and induced malformations. It also triggers an inflammatory response and alters the expression of genes related to apoptosis. These findings contribute to the understanding of antibiotic toxicity in aquatic organisms and provide a foundation for environmental risk assessment of SMX and other antibiotics.