Transformation of antibacterial agent roxithromycin in sodium hypochlorite disinfection process of different water matrices

Determination of antibiotics during treatment of hospital wastewater using automated solid-phase extraction followed by UHPLC-MS: occurrence, removal and environmental risks

The extent of removal of pharmaceuticals by African-based wastewater treatment plants (WWTPs) is relatively unknown with various studies observing high concentrations in effluents. This is mainly due to WWTPs still utilising the traditional treatment methods which are known to be less effective. In this study, 15 selected antibiotics (amoxicillin, ampicillin, azithromycin, ciprofloxacin, doxycycline, erythromycin, gentamicin, metronidazole, norfloxacin, ofloxacin, penicillin, sulfamethoxazole, sulfapyridine, tetracycline and trimethoprim) were monitored in wastewater as it goes through sedimentation (primary and secondary), aeration and chlorination stages of a WWTP. Analytical method involved solid-phase extraction followed by liquid chromatographic determination. Removal efficiencies during sedimentation were generally positive with doxycycline achieving 80-95.8%, while negative removal efficiencies were observed for penicillin V (-46.4 to -17.1%) and trimethoprim (-26.2 to -18.9%). The aeration and agitation stage resulted in concentration enhancement for several antibiotics with seven of them ranging between -273 and -15.5%. This stage was responsible for the relatively low overall removal efficiencies in which only 4 antibiotics (doxycycline, tetracycline, ciprofloxacin, and erythromycin) experienced overall removal efficiencies above 50%. The recorded effluent concentrations ranging between 0.0130 and 0.383 ng/mL were translated to low potential for development of antibiotic resistance genes in the receiving environments while ecotoxicity risk was high for only amoxicillin, ampicillin and sulfapyridine. The study has provided an overview of the performance of common wastewater treatment processes in South Africa and hopes that more monitoring and environmental risk data can be made available towards drafting of antibiotic priority lists that cater for Africa.

Transformation of macrolide antibiotics during chlorination process: Kinetics, degradation products, and comprehensive toxicity evaluation

Antibiotics are ubiquitous in wastewater and surface water and their presence is of grave concern. Chlorination, an important disinfection process used in wastewater treatment plants and waterworks, causes antibiotics to be degraded. However, interactions of antibiotics with chlorine result in the generation of multiple transformation products (TPs). TPs may be more toxic than the parent compounds, but their structures, yields and ecotoxicity remain to be ascertained in most cases. This study examined the degradation by chlorine of two typical macrolide (MLs) antibiotics, erythromycin (ERY) and roxithromycin (ROX), and identified the TPs formed as a result of ERY and ROX chlorination. The ecotoxicity of ERY, ROX and their TPs was evaluated using a combination of bioassay and ECOSAR prediction. The degradation of ERY and ROX followed pseudo-first-order kinetic at the molar ratio of FAC to MLs of 10:1, and the degradation kinetic rate depends on pH values. Six TPs of ERY including three chlorinated TPs, and six TPs of ROX including two chlorinated TPs were identified. The tertiary N of the desosamine moiety of ERY and ROX was determined to be the main reactive site. Demethylation and chlorine substitution at the reactive site are the main degradation pathways of ERY and ROX. ECOSAR results showed that the chlorinated byproducts of ERY TP578, TP542 and TP528, and the reduced hydroxylation products of ROX TP851 exhibited higher ecotoxicity than their parent compounds. However, algae growth inhibition assays indicated that the overall ecotoxicity of the chlorinated ERY or ROX mixture was lower than that of ERY or ROX prior to chlorination. This may be attributed to the removal of the parent compound and lower yields of toxic substances. While the yields of the toxic TPs may be low, their accumulation and combined effects of the TPs and other co-occurring pollutants should be examined further.

Bioassay-Guided Interpretation of Antimicrobial Compounds in Kumu, a TCM Preparation From Picrasma quassioides' Stem via UHPLC-Orbitrap-Ion Trap Mass Spectrometry Combined With Fragmentation and Retention Time Calculation

The stem of Picrasma quassioides (PQ) was recorded as a prominent traditional Chinese medicine, Kumu, which was effective for microbial infection, inflammation, fever, and dysentery, etc. At present, Kumu is widely used in China to develop different medicines, even as injection (Kumu zhusheye), for combating infections. However, the chemical basis of its antimicrobial activity has still not been elucidated. To examine the active chemicals, its stem was extracted to perform bioassay-guided purification against Staphylococcus aureus and Escherichia coli. In this study, two types of columns (normal and reverse-phase) were used for speedy bioassay-guided isolation from Kumu, and the active peaks were collected and identified via an UHPLC-Orbitrap-Ion Trap Mass Spectrometer, combined with MS Fragmenter and ChromGenius. For identification, the COCONUT Database (largest database of natural products) and a manually built PQ database were used, in combination with prediction and calculation of mass fragmentation and retention time to better infer their structures, especially for isomers. Moreover, three standards were analyzed under different conditions for developing and validating the MS method. A total of 25 active compounds were identified, including 24 alkaloids and 1 triterpenoid against S. aureus, whereas only β-carboline-1-carboxylic acid and picrasidine S were active against E. coli. Here, the good antimicrobial activity of 18 chemicals was reported for the first time. Furthermore, the spectrum of three abundant β-carbolines was assessed via their IC₅₀ and MBC against various human pathogens. All of them exhibited strong antimicrobial activities with good potential to be developed as antibiotics. This study clearly showed the antimicrobial chemical basis of Kumu, and the results demonstrated that HRMS coupled with MS Fragmenter and ChromGenius was a powerful tool for compound analysis, which can be used for other complex samples. Beta-carbolines reported here are important lead compounds in antibiotic discovery.

Comparative Research of Chemical Profiling in Different Parts of Fissistigma oldhamii by Ultra-High-Performance Liquid Chromatography Coupled with Hybrid Quadrupole-Orbitrap Mass Spectrometry

The roots of Fissistigma oldhamii (FO) are widely used as medicine with the effect of dispelling wind and dampness, promoting blood circulation and relieving pains, and its fruits are considered delicious. However, Hakka people always utilize its above-ground parts as a famous folk medicine, Xiangteng, with significant differences from literatures. Studies of chemical composition showed there were multiple aristolactams that possessed high nephrotoxicity, pending evaluation research about their distribution in FO. In this study, a sensitive, selective, rapid and reliable method was established to comparatively perform qualitative and semi-quantitative analysis of the constituents in roots, stems, leaves, fruits and insect galls, using an Ultra-High-Performance Liquid Chromatography coupled with Hybrid Quadrupole Orbitrap Mass Spectrometry (UPLC-Q-Exactive Orbitrap MS, or Q-Exactive for short). To make more accurate identification and comparison of FO chemicals, all MS data were aligned and screened by XCMS, then their structures were elucidated according to MSn ion fragments between the detected and standards, published ones or these generated by MS fragmenter. A total of 79 compounds were identified, including 33 alkaloids, 29 flavonoids, 11 phenylpropanoids, etc. There were 54 common components in all five parts, while another 25 components were just detected in some parts. Six toxic aristolactams were detected in this experiment, including aristolactam AII, AIIIa, BII, BIII, FI and FII, of which the relative contents in above-ground stems were much higher than roots. Meanwhile, multivariate statistical analysis was performed and showed significant differences both in type and content of the ingredients within all FO parts. The results implied that above-ground FO parts should be carefully valued for oral administration and eating fruits. This study demonstrated that the high-resolution mass spectrometry coupled with multivariate statistical methods was a powerful tool in compound analysis of complicated herbal extracts, and the results provide the basis for its further application, scientific development of quality standard and utilization.

Influence of roxithromycin as antibiotic residue on volatile fatty acids recovery in anaerobic fermentation of waste activated sludge

The removal of antibiotics and resistance genes in wastewater treatment plants has attracted widespread attention, but the potential role of residual antibiotics in the disposal of waste activated sludge (WAS) has not been clearly understood. In this study, the effect of roxithromycin (ROX) on volatile fatty acid (VFA) recovery from WAS anaerobic fermentation was investigated. The experimental results showed that ROX made a positive contribution to the production of VFAs. With the increase of ROX dosages from 0 to 100 mg/kg TSS, the maximum accumulation of VFAs increased from 295 to 610 mg COD/L. Mechanism studies revealed that ROX promoted the solubilization of WAS by facilitating the disruption of extracellular polymeric substances. In addition, ROX enhanced the activity of acetate kinase and inhibited the activities of α-glucosidase and coenzyme F₄₂₀, and showed a stronger inhibitory effect on methane production than the hydrolysis process, thus resulting in an increase in VFA accumulation. These findings provide a new insight for the role of antibiotics in anaerobic fermentation of WAS.

Ultraviolet/peroxydisulfate degradation of ofloxacin in seawater: Kinetics, mechanism and toxicity of products

The ultraviolet/peroxydisulfate (UV/PDS) system was used to degrade ofloxacin (OFL) in fresh water, synthetic marine aquaculture water and synthetic seawater. The comparison of the reaction degradation rate constants proved that the order of reaction rate was the following: synthetic seawater (0.77 min^-1) > synthetic marine aquaculture water (0.74 min^-1) > freshwater (0.30 min^-1). Bromide (Br^-) and bicarbonate (HCO₃^-) promote the degradation of OFL, whereas chloride (Cl^-) inhibits the degradation. The piperazine ring of OFL was the main reactive group, and atoms N1, C6, C7 and N2 were identified as the reaction sites. Based on the intermediate and final products, the possible degradation pathways of OFL in the three kinds of water were proposed. Additionally, during the UV/PDS treatment of synthetic marine aquaculture water containing Cl^- and Br^-, the oxidation products of OFL showed a slight toxicity to Chlorella pyrenoidosa (C. pyrenoidosa) and Priacanthus tayenus (P. tayenus). The maximum growth inhibition rate of the products to C. pyrenoidosa was 9.72%. The products also caused liver cells of P. tayenus to be damaged and reduced the species richness and diversity of intestinal microorganism. Nevertheless, compared with the products degraded by traditional disinfection methods using NaClO, the biological toxicities were much lower. UV/PDS can be used for seawater as a new alternative disinfection method.