Biotransformation of macrolide antibiotics using enriched activated sludge culture: Kinetics, transformation routes and ecotoxicological evaluation

Abstract

The biotransformation of three prominent macrolide antibiotics (azithromycin, clarithromycin and erythromycin) by an activated sludge culture, which was adapted to high concentrations of azithromycin (10 mg/L) was investigated. The study included determination of removal kinetics of the parent compounds, identification of their major biotransformation products (TPs) and assessment of ecotoxicological effects of biotransformation. The chemical analyses were performed by ultra-performance liquid chromatography/quadrupole-time-of-flight mass spectrometry, which enabled a tentative identification of TPs formed during the experiments. The ecotoxicological evaluation included two end-points, residual antibiotic activity and toxicity to freshwater algae. The enriched activated sludge culture was capable of degrading all studied macrolide compounds with high removal efficiencies (>99%) of the parent compounds at elevated concentrations (10 mg/L). The elimination of all three macrolide antibiotics was associated with the formation of different TPs, including several novel compounds previously unreported in the literature. Some of the TPs were rather abundant and contributed significantly to the overall mass balance at the end of the biodegradation experiments. Biodegradation of all investigated macrolides was associated with a pronounced reduction of the residual antibiotic activity and algal toxicity, indicating a rather positive ecotoxicological outcome of the biotransformation processes achieved by the enriched sludge culture.

Aerobic biotransformation of the antibiotic ciprofloxacin by Bradyrhizobium sp. isolated from activated sludge

“…The initial activated sludge was unable to degrade macrolide antibiotics at concentration of 1 -10 mg L -1 . After two months of exposure at 10 mg L -1 , the removal efficiency was increased to 99% (Terzic et al, 2018). Accordingly, TrOC-degrading strains have been identified for the removal of previously reported persistent compounds (Moreira et al, 2014;Mulla et al, 2016;Pan et al, 2018;Yu et al, 2007).…”

“…Previous studies have demonstrated that long-term exposure of activated sludge microbiome to TrOCs can alter the microbial community and in some cases selectively enrich specific microbes with enhanced affinity for TrOCs biodegradation (Moreira et al, 2014;Navaratna et al, 2012;Qu & Spain, 2010;Terzic et al, 2018;Zhou et al, 2013). An early example was observed for acesulfame (ACE), a synthetic sweetener.…”

Occurrence and Behavior of Macrolide Antibiotics in Municipal Wastewater Treatment: Possible Importance of Metabolites, Synthesis Byproducts, and Transformation Products

“…It should be pointed out that pure reference standards of these compounds were not available, which prevented obtaining fully quantitative results. Nevertheless, the media from biotransformation experiments described in Terzic et al (2018) 31 were applied as qualitative standards, providing link to structural information, as well as to retention time data for the additional TPs. The overview of the TPs encompassed by this screening is presented in Table 3.…”

“…25 In our earlier study, novel TPs of AZI and roxythromycin (ROX), formed by microbial phosphorylation, were identified in wastewater effluent of a membrane bioreactor, 30 while a recent study on aerobic biodegradation of AZI, CLA and ERY revealed a number of previously unreported, novel TPs and allowed proposing a general transformation pathways scheme for AZI. 31 In addition, non-target analysis of freshwater sediments polluted by pharmaceutical industry effluent indicated the importance of intermediates in AZI synthesis. 32 In order to address the complexity of macrolidederived compounds, we recently developed a novel quantitative analytical method, comprising parent macrolide antibiotics, their major human metabolites and TPs, as well as by-products from AZI synthesis, in wastewater and river water samples.…”

Biodegradation study of methadone by adapted activated sludge: Elimination kinetics, transformation products and ecotoxicological evaluation

“…The cultures AS-1, AS-2 and AS-3 originated from the aeration tank of the Central wastewater treatment plant of the city of Zagreb and were previously enriched on three different amine-moiety containing compounds: azithromycin (10 mg/L), tramadol (20 mg/L) and MTHD (10 mg/L), respectively. The cultures AS-1 and AS-2 were previously proven to be able to degrade macrolide antibiotics (Terzic et al, 2018) and tramadol (unpublished data), respectively. Before being used in M A N U S C R I P T…”