title: Application of XCMS Online and toxicity bioassays to the study of transformation products of levofloxacin.
abstract: We studied the nature and antimicrobial activity of ozonolysis transformation products (OTPs) of levofloxacin (LEV), a frequently detected fluoroquinolone antimicrobial in environmental waters. Two bioassays, the Kirby-Bauer test and the broth microdilution assay, were used to measure changes in the antimicrobial activity of solutions at low LEV to O3 molar ratios (2:1, 2:3 and 1:3) compared to solutions without added O3 (LEV:O3 1:0). The Kirby-Bauer test was not sensitive enough to detect significant differences in the growth inhibition zones in samples LEV:O3 2:1 and LEV:O3 1:0; however, the broth microdilution assay showed that bacterial growth inhibition was significantly lower (P<0.001) in the solutions exposed to O3. Loss of antimicrobial activity in LEV:O3 2:1 solutions of (48±16)% was in agreement with the concentration decrease of LEV of (36±3)% in those same samples. A method of identification of OTPs using XCMS Online was applied to LEV:O3 2:1 and 1:0 samples and indicated the presence of an OTP of LEV of formula C18H20O5N3F, which was identified as LEV-N-oxide. The molecular structure of this compound was partially confirmed by tandem mass spectrometry experiments. This study showed that even at sub-optimal ozone doses, OTPs of higher antimicrobial activity than LEV were not formed.
authors.affiliation: Department of Chemistry, Université de Sherbrooke, 2500 boulevard de l'Université, Sherbrooke, QC, Canada J1K 2R1 E-mail: pa.segura@usherbrooke.ca.
authors.forename: Pedro A
authors.initials: PA
authors.lastname: Segura
authors.affiliation: Department of Chemical Engineering, McGill University, 3610 University, Montreal, QC, Canada H3A 0C5.
authors.forename: Karim
authors.initials: K
authors.lastname: Saadi
authors.affiliation: Department of Chemistry, Université de Sherbrooke, 2500 boulevard de l'Université, Sherbrooke, QC, Canada J1K 2R1 E-mail: pa.segura@usherbrooke.ca.
authors.forename: Alexandra
authors.initials: A
authors.lastname: Clair
authors.affiliation: Department of Chemistry, Université de Sherbrooke, 2500 boulevard de l'Université, Sherbrooke, QC, Canada J1K 2R1 E-mail: pa.segura@usherbrooke.ca.
authors.forename: Marc-André
authors.initials: MA
authors.lastname: Lecours
authors.affiliation: Department of Chemical Engineering, McGill University, 3610 University, Montreal, QC, Canada H3A 0C5.
authors.forename: Viviane
authors.initials: V
authors.lastname: Yargeau
mesh_terms: D000890:Anti-Infective Agents; D001681:Biological Assay; D002220:Carbamazepine; D024841:Fluoroquinolones; D064704:Levofloxacin / Q000737:chemistry* / Q000633:toxicity; D008826:Microbial Sensitivity Tests; D015394:Molecular Structure; D010087:Oxides; D010126:Ozone / Q000737:chemistry*; D012984:Software; D014867:Water; D014874:Water Pollutants, Chemical / Q000737:chemistry*
chemical_list: D000890:Anti-Infective Agents; D024841:Fluoroquinolones; D010087:Oxides; D014874:Water Pollutants, Chemical; D014867:Water; D002220:Carbamazepine; D010126:Ozone; D064704:Levofloxacin