Study On The Toxic Effects Of ?-lactam Antibiotics On Three Tested Organisms

Antibiotics,as a magic drug in the 20th century,have saved tens of millions of infected people.But at the same time,they have rapidly become emerging pollutant in the decades after its widely use.In this study,three?-lactam antibiotics,amoxicillin,aztreonam and cefoperazone were selected to test their toxic effects on three model organisms,in order to fully understand the environmental toxicity of?-lactam antibiotics.The study of the toxicity of?-lactam antibiotics to Vibrio Qinghai sp.-Q67 showed that amoxicillin,cefoperazone and aztreonam had no significant toxic effect when the exposure time was 15 minutes;when the exposure time was prolonged to 24 hours,EC₅₀of amoxicillin,cefoperazone and aztreonam were 18.67,14.41 and 132.71 mg/L,respectively.Therefore,the chronic toxicity effects of three?-lactam antibiotics were cefoperazone>amoxicillin>aztreonam.According to the toxicity unit,addition index and mixture toxicity index method,it was found that the type of combined toxicity of multiple?-lactam antibiotics to Vibrio Qinghai sp.-Q67 was additive or synergistic.The survival and reproduction ability of Daphnia magna were affected by antibiotics.The effect was not only related to the antibiotics concentration,but also to the exposure time.The results showed that the 48h-LC₅₀ of amoxicillin,cefoperazone and aztreonam were 122.328,138.915 and 27.293 mg/L respectively.And at 14 days of exposure,the effects of antibiotics on reproduction of Daphnia magna were investigated,the results showed that the 14d-EC₅₀ values of chronic toxicity were 57.796,85.049 and17.949 mg/L,respectively.The toxic effects of three?-lactam antibiotics on Daphnia magna were aztreonam>amoxicillin>cefoperazone.In addition,the toxic effects of?-lactam antibiotics on Daphnia magna were additive or synergistic.The results showed that the minimum inhibitory concentration of amoxicillin,cefoperazone and aztreonam on Shewanella absorbance were 4.00,0.50,and 1.00?g/m L,and the minimum bactericidal concentration values were 32.00,1.00,and 2.00?g/m L,respectively.Three antibiotics have different degrees of antibacterial effect on Shewanella,of which cefoperazone has the best antibacterial effect.Determination of the combined of binary antibiotics by chessboard microdilution,the results showed that the fractional inhibitory concentration index of amoxicillin/cefoperazone,amoxicillin/aztreonam,and aztreonam/cefoperazone were 0.75,0.16,and 0.16,respectively.Amoxicillin/cefoperazone showed additive effect on bacteriostatic,the other mixtures showed synergistic effect.The combined toxic effect of the three antibiotics by equal proportion mixing was synergistic.