John Wiley & Sons, Ltd.

Antibacterial activity of soil‐bound antimicrobials oxytetracycline and ofloxacin

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Soil contamination of antimicrobials has become an increasing concern due to the potential risks to the soil microbial ecosystem and human health. This study investigated sorption and desorption behaviors of oxytetracycline (OTC) and ofloxacin (OFL) in three typical soils (A, B and C), and evaluated the antibacterial activity of soil‐adsorbed compounds to a pure sensitive strain Escherichia coli ATCC 25922. The results showed different sorption and desorption behaviors of oxytetracycline and ofloxacin in the three soils, which are mainly influenced by soil organic matter content and cation exchange capacity (CEC) as well as pH value, and that complexation and cation‐exchange reactions are the main sorption mechanisms. Strong adsorption was found in the soil B with high organic matter content and in soil C with high CEC, while enhanced desorption was observed in soil A with low organic matter content. The results also demonstrated that soil‐bound antimicrobials retained antibacterial activity toward E. coli. Opposite patterns of antibacterial activity were found for the two antimicrobials in the three soils: A > B > C for OFL; and C > B > A for OTC. This suggests that soil‐bound antimicrobials could still exert selective pressure on soil bacteria although less effective in comparison to the dissolved forms. Environ Toxicol Chem © 2014 SETAC

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