Radiolytic degradation of β-lactam and tetracycline antibiotics in the presence of protein

Abstract

In this study, to explore the influence of protein on antibiotics degradation during ionizing irradiation, the binding interaction between bovine serum albumin (BSA) and the broad spectrum β-lactam and tetractycline antibiotics and its effect on antibiotic degradation were investigated. Static quenching happened between BSA and antibiotics involving penicillin G (PEG), cephalosporin C (CPC), oxytetracycline (OTC) and tetracycline hydrochloride (TTC), indicating the formation of non-fluorescence complexes. The binding capacity followed the order: TTC > CPC > OTC > PEG. As exposed to γ-irradiation, the β-lactam antibiotics showed a higher degradation rate than the tetracyclines. The degradation rate constant (k) of CPC and PEG was 1.4–2.0 times higher than that of OTC and TTC. In presence of BSA, the k values (kBSA) of all the four antibiotics decreased greatly and the degradation rate of CPC and PEG was still higher by 1.2–1.3 times than that of OTC and TTC. No correlation between k/kBSA and the binding affinity was observed. The presence of BSA has little effect on the trend of abatement of antimicrobial activity to S. aureus during γ-irradiation. This suggests that the inhibition of protein to antibiotic degradation was mainly attributed to the competition of protein for the active species such as ·OH radical formed during γ-irradiation, while the binding ability of protein to antibiotics has no obvious effect. The results of this study contributed to develop technical strategies to improve the removal of antibiotics completely in real water matrices.