The Toxicological Study Of Different Adsorbed Levofloxacin On Escherichia Coli

In recent years, antibiotics as contaminants exist in the environment, increasingly attract wide attention. Antibiotics pollute the water environment, the soil and sediments in the environment. Antibiotics in the soil may affect the survival and reproduction, metabolism, the number of organisms, changing the biomass, community structure and biodiversity, thus antibiotics affect biogeochemical processes and self-purification capacity of the soil elements. To determine the influnce of adsorbed antibiotics by different minerals on soil microorganisms, the study contrasted the different influence of antibiotic (levofloxacin as the representative, LEV for short) to the number of microorganisms (Escherichia coli as a representative, E.coli for short) in the presence of two minerals (commonly selected secondary minerals-goethite and montmorillonite) and explored a common approach to counting the live bacteria in experiments. The main conclusions are as follows:1) This article used a method for the determination of the live cells of E.coli ——MTT colorimetric method, explored the toxicology of LEV to E.coli, and determined the following experimental conditions ultimately. The results showed that MTT colorimetric method had good repeatability, simple operation, so it was suitable for counting live bacteria in batch experiment.2) This article studied the effect of LEV on E.coli in the presence of goethite. Experimental results showed:When containing 10% LB medium, under neutral condition, the adsorption of LEV on goethite reached the equilibrium in the first 4 h, and was fitted to the Freundlich isotherm. Goethite could promote the growth of E.coli in certain extent, when E.coli was added into the systems after reaching equilibrium, and the LEV adsorbed by goethite significantly attenuated killing effect on E.coli.3) This article studied the effect of LEV on E.coli in the presence of montmorillonite. Experimental results showed:When containing 10% LB medium, under neutral condition, the adsorption of LEV on montmorillonite reached equilibrium in the first 2 h, and was fitted to the Freundlich isotherm. Montmorillonite could not kill or inhibit bacteria, when E.coli was added into the systems after reaching adsorption equilibrium. The LEV adsorbed by montmorillonite attenuated killing effect of E.coli, but still had a role in killing E.coli.4)This article compared the adsorption mechanisms of goethite and montmorillonite, and analyzed LEV molecular structure. Experimental results showed:Levofloxacin likely forms an complex on the goethite surface through the keto group and the carboxylate group. Adsorption of levofloxacin on montmorillonite was mainly due to electrostatic attraction and interlayer cation exchange. When antibiotics was in soil minerals, the adsorbed antibiotics decreased the toxicity to microorganisms. However, antibiotics which has low concentration may promote the growth of microorganisms, or the emergence of antibiotic resisrance genes for a long time, because the efficacy of antibiotics can not be completely eliminated. Thus, they may cause potential harm to humanity and even the entire ecosystem.