Solar-mediated degradation of linezolid and tedizolid under simulated environmental conditions: Kinetics, transformation and toxicity

Linezolid (LIN) and Tedizolid (TED) are representatives of oxazolidinone antibiotics of last resort with a strong efficacy against gram-positive bacteria. This study focused on their solar-mediated degradation to understand better their fate in aquatic environment, for the realistic concentrations in the range of 1 μg/L. Results showed that both antibiotics (ABs) are degradable by simulated sunlight (1 kW/m²), with half-lives of 32 and 93 h in ultrapure water, for LIN and TED, respectively. LIN showed similar photolytic behaviour in pure solution and in surface water, whereas sunlight enhanced the degradation of LIN in pure solutions, but not in surface water. Structure elucidation by liquid chromatography coupled to high resolution mass spectrometry provided information about seven transformation products for LIN and five for TED. The morpholinyl-ring was identified as the target site for most transformation reactions of LIN. TED was prone to oxidation and cleavage of the oxazolidinone ring. Results of a growth inhibition test on Bacillus subtilis exposed to UV light showed antibacterial efficacy of transformation products of LIN and no significant efficacy of degradation products of TED for the concentration range of 100 μg/L-10 mg/L of parent compounds. Photolytically treated solutions of the ABs maintained their inhibitory effect on the bioluminescence of Aliivibrio fischeri.