Change in hydrophilicity of penicillins during advanced oxidation by radiolytically generated OH compromises the elimination of selective pressure on bacterial strains

• Published in: The Science of the total environment 2016-05, Vol.551-552, p.393-403
• Main Authors: Szabó, László, Tóth, Tünde, Engelhardt, Tekla, Rácz, Gergely, Mohácsi-Farkas, Csilla, Takács, Erzsébet, Wojnárovits, László
• Format: Article
• Language: English
• Subjects: Advanced oxidation; Anti-Bacterial Agents - chemistry; Anti-Bacterial Agents - toxicity; Antibiotic resistance; Bacteria; Bacterial susceptibility; Bacterial toxicity; Gram-Negative Bacteria - drug effects; Hydrophobic and Hydrophilic Interactions; Hydroxyl radical; Hydroxyl Radical - chemistry; Microbial Sensitivity Tests; Oxidation-Reduction; Penicillin; Penicillins - chemistry; Penicillins - toxicity
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2016.02.002

Advanced oxidation processes are promising technologies for removal of antibiotic residues from wastewater in terms of their high efficacy. However, recent studies have reported the remaining antibacterial activity of the products at early-stages of treatment. The present study investigates the effect of such products of model β-lactams (amoxicillin, ampicillin, cloxacillin) on bacteria introducing structure-based, and biological approaches involving Gram-positive and Gram-negative bacterial strains. Chemical analysis revealed the destruction of the β-lactam pharmacophore in competition with the reaction at the aromatic ring. Multisite attack occurs on the penicillin skeleton producing OH-substituted products. The enhanced hydrophilicity confers higher diffusion rate through the porin channels of Gram-negative bacteria and through the hydrophilic cell wall of Gram-positive species. Accordingly, an increase in acute toxicity of treated samples was observed at the beginning of the treatment. The same tendency was observed for target-specific antimicrobial activity investigated with antibiotic susceptibility testing (agar-diffusion, bacterial growth). Prolonged treatments yielded products, e.g. polyhydroxylated phenolic compounds, being also deleterious for bacteria. Therefore, the advanced oxidation process should be judiciously optimized. [Display omitted] •OH can demolish the β-lactam system that determines the antibacterial activity.•Products form with polar groups at early stages of the treatment.•The enhanced hydrophilicity implies an increase in biological activity.•The underlying reason resides in a higher diffusion rate into the bacterial cell.•Prolonged treatment is also deleterious due to some forming toxic agents.