Evaluation of antimicrobial agents for veterinary use in the ecotoxicity test using microalgae

Area of Science:

• Environmental Science
• Ecotoxicology
• Microbiology

Background:

• Antimicrobial agents are widely used in veterinary medicine.
• The environmental impact of these drugs on non-target organisms, such as algae, requires investigation.
• Green algae are primary producers in aquatic ecosystems and sensitive indicators of water quality.

Purpose of the Study:

• To assess the ecotoxicity of veterinary antimicrobial drugs on green algae species.
• To determine the growth inhibitory effects and effective concentrations (EC50) of various antimicrobials.
• To investigate potential synergistic effects and mechanisms of action.

Main Methods:

• Standardized OECD guidelines for chemical testing were followed.
• Growth inhibition assays were performed on Selenastrum capricornutum and Chlorella vulgaris.
• Combinations of sulfa drugs with trimethoprim or pyrimethamine, and the effect of folic acid, were evaluated.

Main Results:

• Erythromycin exhibited the strongest growth inhibition (EC50 = 0.037 mg/l).
• Sulfa drugs (sulfamethoxazole, sulfadiazine, sulfadimethoxine) showed moderate activity (EC50s 1.5–2.3 mg/l).
• Ampicillin and cefazolin did not inhibit growth (EC50s > 1000 mg/l); trimethoprim enhanced sulfa drug activity.

Conclusions:

• Veterinary antimicrobials pose varying risks to green algae, with erythromycin being the most potent inhibitor.
• Sulfa drugs inhibit folate synthesis in green algae, and their activity can be potentiated by trimethoprim.
• The findings highlight the need for environmental risk assessment of veterinary drugs to protect aquatic ecosystems.