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

The influence of antimicrobial agents approved as veterinary drugs in Japan on the growth of green algae, Selenastrum capricornutum and Chlorella vulgaris, was studied in accordance with the OECD guidelines for testing chemicals. Among the agents tested, growth inhibitory activity was very varied, i.e. erythromycin showed the strongest activity (EC50 50% effective concentration, =0.037 mg/l), sulfa drugs had activity to some extent (EC(50)s of sulfamethoxazole, sulfadiazine, and sulfadimethoxine were 1.5, 2.2, and 2.3 mg/l, respectively), but arnpicillin and cefazolin did not inhibit growth (EC(50)s > 1000mg/1). We also investigated synergistic effect of combining sulfa drugs with trimethoprim or pyrimethamine, which are cormnonly used as a combined drug. By adding trimethoprim, the growth inhibitory activity of sulfamethoxazole and sulfadiazine was significantly enhanced. Growth inhibition by sulfa drugs was reduced by the addition of folic acid, indicating that they inhibit folate synthesis in green algae. (C) 2004 Elsevier Ltd. All rights reserved.