Antibiotics Induce Metabolic and Physiological Responses in Daphnia magna

Antibiotics represent a unique and diverse group of drugs, which are known to exert deleterious effects on non-target species and contribute to the phenomenon of antimicrobial resistance. With central inclusion on the EU Surface Water Watch List, and reported known affects in multiple model organisms, the importance of the sufficient monitoring of antibiotics in the aquatic environment has been highlighted. Most studies report the impact of individual antibiotics following exposure for a single generation in animals. In this study, we assessed the impact of four antibiotics with different modes of action (amoxicillin, trimethoprim, erythromycin, and sulfamethoxazole) and their mixture on the sentinel species Daphnia magna over three generations, via biochemical markers and a targeted metabolomic analysis of central metabolic pathways. No mortality was observed at 50 mg/L of each selected antibiotic and their composite mixture. Thus, a working concentration of 1 mg/L was chosen to progress this study. Results indicated that enzyme activity was particularly sensitive to exposure to amoxicillin and the mixture, whereas trimethoprim and the mixture induced the most metabolic changes in glycolysis and the TCA cycle. Additionally, the quaternary mixture had a stronger impact on the first generation of daphnids, altering the activity of β-galactosidase, glutathione S-transferase, and acid and alkaline phosphatase, suggesting that Daphnia can adapt to stress caused by antibiotics.