Evaluation of residual antibacterial potency in antibiotic production wastewater using a real-time quantitative method

Abstract

a While antibiotic pollution has attracted considerable attention due to its potential in promoting the dissemination of antibiotic resistance genes in the environment, the antibiotic activity of their related substances has been neglected, which may underestimate the environmental impacts of antibiotic wastewater discharge. In this study, a real-time quantitative approach was established to evaluate the residual antibacterial potency of antibiotics and related substances in antibiotic production wastewater (APW) by comparing the growth of a standard bacterial strain (Staphylococcus aureus) in tested water samples with a standard reference substance (e.g. oxytetracycline). Antibiotic equivalent quantity (EQ) was used to express antibacterial potency, which made it possible to assess the contribution of each compound to the antibiotic activity in APW. The real-time quantitative method showed better repeatability (Relative Standard Deviation, RSD 1.08%) compared with the conventional fixed growth time method (RSD 5.62-11.29%). And its quantification limits ranged from 0.20 to 24.00 mg L À1, depending on the antibiotic. We applied the developed method to analyze the residual potency of water samples from four APW treatment systems, and confirmed a significant contribution from antibiotic transformation products to potent antibacterial activity. Specifically, neospiramycin, a major transformation product of spiramycin, was found to contribute 13.15-22.89% of residual potency in spiramycin production wastewater. In addition, some unknown related substances with antimicrobial activity were indicated in the effluent. This developed approach will be effective for the management of antibacterial potency discharge from antibiotic wastewater and other waste streams. Environmental impactAntibiotic pollution from antibiotic production wastewater has caused increasing concern worldwide. Previous studies have focused on the discharge of antibiotics by determining their concentrations. However, some antibiotic related substances in effluents still possess antibacterial activity, which might induce emergence and proliferation of antibiotic resistant bacteria and genes in the environment. Therefore, it is important to investigate residual antibacterial potency in antibiotic production wastewater with high concentrations of antibiotics and related substances. In this study, a real-time quantitative method was developed and applied for the analysis of residual antibacterial potency of antibiotic production wastewater. The results showed that spiramycin production wastewater contained transformation products with high potency. This method made it possible to assess the contribution of each compound and should be a useful tool for environmental risk management for providing the basis for identication of transformation products with antibacterial activity.

Anaerobic treatment of antibiotic production wastewater pretreated with enhanced hydrolysis: Simultaneous reduction of COD and ARGs

“…The antibacterial activities of oxytetracycline and the hydrolyzed solutions were evaluated on a microbiological turbidimetric apparatus (WBS-100, XQWF, Beijing, China). The details of both the UPLC-MS/ MS analysis and antibacterial potency assay were described in SI and carried out according to previous studies (Liu et al, 2012;Zhang et al, 2015).…”

“…Zhang et al analyzed the residual potency of water samples from four APW treatment systems and found that some unknown related substances with antimicrobial activity were indicated in the effluent leaving 9.09e60.26% of wastewater potency unexplained (Zhang et al, 2015). Thus the residual antibacterial potency in the effluent might be contributed by unknown oxytetracycline hydrolysis products, which should be explored in future studies.…”

Establishment of a pretreatment method for tetracycline production wastewater using enhanced hydrolysis

“…The antibacterial activities of tetracycline, its two hydrolysis products (ETC and ATC), and the hydrolyzed solutions were evaluated on a microbiological turbidimetric apparatus (WBS-100, XQWF, Beijing China) according to the procedures designated by United States Pharmacopeia 31 and Zhang [18]. The linear range for the antibacterial activity standard curve of tetracycline was determined to be 0.46-4.6 mg L…”

“…The antibacterial activities (potency) of the two important intermediates, ETC and ATC, were evaluated (Fig. S5) by using a real-time quantitative method developed previously [18]. The antibacterial activities of ETC and ATC were less than one-tenth that of tetracycline.…”

“…The hydrolysis products were identified using high performance liquid chromatography (HPLC) and liquid chromatography-time of flight mass spectrometry (HPLC/TOF/MS) analysis. Since some hydrolysis products of antibiotics may inherit the antibacterial activity of the parent pharmacophores, the antibacterial activities of the hydrolyzed solutions obtained under hydrolysis conditions were assessed using a microbial assay developed previously [18]. Furthermore, an anaerobic inhibition test using simulated tetracycline wastewater and actual tetracycline production water with/without enhanced hydrolysis pretreatment was carried out to verify the effects of the hydrolysis process.…”