Most antibiotics are metabolized incompletely by patients after administration and enter the municipal sewage with the patients' excretion. Therefore, studies on the biodegradability of some clinically important drugs can be taken as a very first step of an environmental risk assessment. The present study reports the biodegradation of CIP by Lactobacillus gesseri, Enterobacter sp., Bacillus sp., Bacillus subtilius and Micrococcus luteus which were isolated as CIP resistance, non pathogenic

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... ria. The presence of antibioticresistant bacteria was identified using the 16s rRNA sequencing. A 0.5ml of overnight starved bacterial suspensions was introduced into medium containing CIP at 5 ppm. Triplicate samples were incubated at 28 0 C with shaking at 100ppm. A 0.5 ml of subsamples was removed at 2 days interval for a period of 14 days. Samples were subjected to High Performance Liquid Chromatography (HPLC) analysis. Fourier Transform Infrared Spectroscopy (FTIR) analyses were carried out for each sample at the end of the 14 days to find structures of by-products. Complete degradation of CIP by L. gasserri was detected at the end of 14 days of incubation with average degradation rate of 0.182 ±0.15µg /day. Descending degradation rates were followed by Enterobacter sp. (0.75 ±0.03 d -1 ) and Bacillus sp. (0.41±0.02d -1 ) at 8 and 6 days respectively. However, clear cut degradation of CIP was not detected for B.subtilis and Micrococcus luteus respectively. Further, FTIR spectrum revealed that incubation of L. gesseri, Enterobacter sp. and Bacillus sp., changed the piperazine ring and quinolone part in the CIP structure while degradation occurred.