Hello Ayesha, i am under the impression that your isolate is not susceptible to the fluoroquinolone it is supposed to degrade. If you expect your isolated strain to degrade a fluoroquinolone, then it means the bacterium is going to use it either as a source of carbon or that of energy; this is bacterial metabolism where the carbon substrate in this case is fluoroquinolone. Our gold standard assay for biodegradation studies is either respirometry (oxygen consumption) or carbon dioxide evolution assay. Please note: Use the term biodegradability for the substrate (fluoroquinolone), it is the potential of the material to be biodegraded. I know there's been a lot of confusion in literature. Please see the attached documents. Cheers!