Occurrence of fluoroquinolones and fluoroquinolone-resistance genes in the aquatic environment

Effects of clarithromycin exposure on the growth of Microcystis aeruginosa and the production of algal dissolved organic matter

Antibiotics are commonly found in the aquatic environment, which can affect microbial community compositions and activities, and even have potential adverse impacts on human and ecosystem health. The current understanding of the effects of antibiotics on microalgae growth and algal dissolved organic matter (DOM) remains indistinct. To understand the toxic effects of antibiotics on the microalgae, Microcystis aeruginosa was exposed to clarithromycin (CLA) in this study. Cell density determination, chlorophyll content determination, and organic spectrum analysis were conducted to show the effect of CLA exposure on the growth, photosynthetic activity, and organic metabolic processes of Microcystis aeruginosa. The findings revealed that the physiological status of algae could be significantly influenced by CLA exposure in aquatic environments. Specifically, exposure to 1 μg/L CLA stimulated the growth and photosynthetic activity of algal cells. Conversely, CLA above 10 μg/L led to the inhibition of algal cell growth and photosynthesis. Notably, the inhibitory effects intensified with the increasing concentration of CLA. The molecular weight of DOM produced by Microcystis aeruginosa increased when exposed to CLA. Under the exposure of 60 μg/L CLA, a large number of algal cells ruptured and died, and the intracellular organic matter was released into the algal liquid. This resulted in an increase in high molecular weight substances and soluble microbial-like products in the DOM. Exposure to 1 and 10 μg/L CLA stimulated Microcystis aeruginosa to produce more humic acid-like substances, which may be a defense mechanism against CLA. The results were useful for assessing the effects of antibiotic pollution on the stability of the microalgae population and endogenous DOM characteristics in aquatic ecosystems.

Insight into environmental adaptability of antibiotic resistome from surface water to deep sediments in anthropogenic lakes by metagenomics

The escalating antibiotic resistance threatens the long-term global health. Lake sediment is a vital hotpot in transmitting antibiotic resistance genes (ARGs); however, their vertical distribution pattern and driving mechanisms in sediment cores remain unclear. This study first utilized metagenomics to reveal how resistome is distributed from surface water to 45 cm sediments in four representative lakes, central China. Significant vertical variations in ARG profiles were observed (R2 = 0.421, p < 0.001), with significant reductions in numbers, abundance, and Shannon index from the surface water to deep sediment (all p-values < 0.05). ARGs also has interconnections within the vertical profile of the lakes: twelve ARGs persistently exist all sites and depths, and shared ARGs (e.g., vanS and mexF) were assembled by diverse hosts at varying depths. The 0-18 cm sediment had the highest mobility and health risk of ARGs, followed by the 18-45 cm sediment and water. The drivers of ARGs transformed along the profile of lakes: microbial communities and mobile genetic elements (MGEs) dominated in water, whereas environmental variables gradually become the primary through regulating microbial communities and MGEs with increasing sediment depth. Interestingly, the stochastic process governed ARG assembly, while the stochasticity diminished under the mediation of Chloroflexi, Candidatus Bathyarcaeota and oxidation-reduction potential with increasing depth. Overall, we formulated a conceptual framework to elucidate the vertical environmental adaptability of resistome in anthropogenic lakes. This study shed on the resistance risks and their environmental adaptability from sediment cores, which could reinforce the governance of public health issues.

Safety attributes of Pseudomonas sp. P26, an environmental microorganism with potential application in contaminated environments

Currently, the selection of non-pathogenic microorganisms that lack clinically relevant antimicrobial resistance is crucial to bioaugmentation strategies. Pseudomonas sp. P26 (P26) is an environmental bacterium of interest due to its ability to remove aromatic compounds from petroleum, but its safety characteristics are still unknown. The study aimed to: a) determine P26 sensitivity to antimicrobials, b) investigate the presence of quinolone and β-lactam resistance genes, c) determine the presence of virulence factors, and d) evaluate the effect of P26 on the viability of Galleria mellonella (an invertebrate animal model). P26 antimicrobial sensitivity was determined in vitro using the Kirby-Bauer agar diffusion method and the VITEK 2 automated system (BioMerieux®). Polymerase Chain Reaction was employed for the investigation of genes associated with quinolone resistance, extended-spectrum β-lactamases, and carbapenemases. Hemolysin and protease production was determined in human blood agar and skimmed-milk agar, respectively. In the in vivo assay, different doses of P26 were injected into Galleria mellonella larvae and their survival was monitored daily. Control larvae injected with Pseudomonas putida KT2440 (a strain considered as safe) and Pseudomonas aeruginosa PA14 (a pathogenic strain) were included. Pseudomonas sp. P26 was susceptible to most evaluated antimicrobials, except for trimethoprim-sulfamethoxazole. No epidemiologically relevant genes associated with quinolone and β-lactam resistance were identified. Hemolysin and protease production was only evidenced in the virulent strain (PA14). Furthermore, the results obtained in the in vivo experiment demonstrated that inocula less than 108 CFU/mL of P26 and P. putida KT2440 did not significantly affect larval survival, whereas larvae injected with the lowest dose of the pathogenic strain P. aeruginosa PA14 experienced instant mortality. The results suggest that Pseudomonas sp. P26 is a safe strain for its application in environmental bioremediation processes. Additional studies will be conducted to ensure the safety of this bacterium against other organisms.

Removal of enrofloxacin using Eichhornia crassipes in microcosm wetlands

The global consumption of antibiotics leads to their possible occurrence in the environment. In this context, nature-based solutions (NBS) can be used to sustainably manage and restore natural and modified ecosystems. In this work, we studied the efficiency of the NBS free-water surface wetlands (FWSWs) using Eichhornia crassipes in microcosm for enrofloxacin removal. We also explored the behavior of enrofloxacin in the system, its accumulation and distribution in plant tissues, the detoxification mechanisms, and the possible effects on plant growth. Enrofloxacin was initially taken up by E. crassipes (first 100 h). Notably, it accumulated in the sediment at the end of the experimental time. Removal rates above 94% were obtained in systems with sediment and sediment + E. crassipes. In addition, enrofloxacin was found in leaves, petioles, and roots (8.8-23.6 µg, 11-78.3 µg, and 10.2-70.7 µg, respectively). Furthermore, enrofloxacin, the main degradation product (ciprofloxacin), and other degradation products were quantified in the tissues and chlorosis was observed on days 5 and 9. Finally, the degradation products of enrofloxacin were analyzed, and four possible metabolic pathways of enrofloxacin in E. crassipes were described.

A comprehensive review on the application of semiconducting materials in the degradation of effluents and water splitting

In this comprehensive review article, we delve into the critical intersection of environmental science and materials science. The introduction sets the stage by emphasizing the global water shortage crisis and the dire consequences of untreated effluents on ecosystems and human health. As we progress into the second section, we embark on an intricate exploration of piezoelectric and photocatalytic principles, illuminating their significance in wastewater treatment and sustainable energy production. The heart of our review is dedicated to a detailed analysis of the detrimental impacts of effluents on human health, underscoring the urgency of effective treatment methods. We dissected three key materials in the realm of piezo-photocatalysis: ZnO-based materials, BaTiO3-based materials, and bismuth-doped materials. Each material is scrutinized for its unique properties and applications in the removal of pollutants from wastewater, offering a comprehensive understanding of their potential to address this critical issue. Furthermore, our exploration extends to the realm of hydrogen production, where we discuss various types of hydrogen and the role of piezo-photocatalysis in generating clean and sustainable hydrogen. By illuminating the synergistic potential of these advanced materials and technologies, we pave the way for innovative solutions to the pressing challenges of water pollution and renewable energy production. This review article not only serves as a valuable resource for researchers and scholars in the fields of material science and environmental engineering but also underscores the pivotal role of interdisciplinary approaches in addressing complex global issues.

Effect of the molecular weight of DOM on the indirect photodegradation of fluoroquinolone antibiotics

Dissolved organic matter (DOM) is ubiquitous and widespread in natural water and influences the transformation and removal of antibiotics. Nevertheless, the influence of DOM molecular weight (MW) on the indirect photodegradation of antibiotics has rarely been reported. This study attempted to explore the influence of the molecular weight of DOM on the indirect photodegradation of two fluoroquinolone antibiotics (FQs), ofloxacin (OFL) and norfloxacin (NOR), by using UV-vis absorption and fluorescence spectroscopy. The results showed that indirect photodegradation was considered the main photodegradation pathway of FQs in DOM fractions. Triplet-state excited organic matter (3DOM*) and singlet oxygen (1O2) were the main reactive intermediates (RIs) that affected the indirect photodegradation of FQs. The indirect photodegradation rate of FQs was significantly promoted in DOM fractions, especially in the low molecular weight DOM fractions (L-MW DOM, MW < 10 kDa). The results of excitation-emission matrix spectroscopy combined with parallel factor analysis (EEM-PARAFAC) showed that terrestrial humic-like substances had a higher humification degree and fluorophore content in L- MW DOM fractions, which could produce more 3DOM* and 1O2 to promote the indirect photodegradation of FQs. This study provided new insight into the effects of DOM at the molecular weight level on the indirect photodegradation of antibiotics in natural water.

Drivers of Antibiotic Resistance Gene Abundance in an Urban River

In this study, we sought to profile the abundances and drivers of antibiotic resistance genes in an urban river impacted by combined sewage overflow (CSO) events. Water samples were collected weekly during the summer for two years; then, quantitative PCR was applied to determine the abundance of resistance genes associated with tetracycline, quinolones, and β-lactam antibiotics. In addition to sampling a CSO-impacted site near the city center, we also sampled a less urban site ~12 km upstream with no proximal sewage inputs. The tetracycline genes tetO and tetW were rarely found upstream, but were common at the CSO-impacted site, suggesting that the primary source was untreated sewage. In contrast, ampC was detected in all samples indicating a more consistent and diffuse source. The two other genes, qnrA and blaTEM, were present in only 40-50% of samples and showed more nuanced spatiotemporal patterns consistent with upstream agricultural inputs. The results of this study highlight the complex sources of ARGs in urban riverine ecosystems, and that interdisciplinary collaborations across diverse groups of stakeholders are necessary to combat the emerging threat of antibiotic resistance through anthropogenic pollution.

Exploration of an efficient method for removing antibiotics from water and digested sewage sludge using Fe(VI): Kinetics and P phytoavailability and compostability in treated sludge

Potassium ferrate (K₂FeO₄) containing hexavalent iron [Fe(VI)] is an environmentally friendly oxidant, which possesses strong oxidizing power to treat wastewater and sludge. Therefore, the present study investigated degradation of selected antibiotics, namely levofloxacin (LEV), ciprofloxacin (CIP), oxytetracycline (OTC), and azithromycin (AZI), in water and anaerobically digested sewage sludge samples using Fe(VI). The effects of different Fe(VI) concentrations and initial pH values on antibiotic removal efficiency were evaluated. Under the studied conditions, LEV and CIP were almost completely removed from water samples, following second-order kinetics. In addition, over 60% of the four selected antibiotics were removed from sludge samples using 1 g L^-1 Fe(VI). Furthermore, P phytoavailability and compostability of Fe(VI)-treated sludge were evaluated using different extraction reagents and a small composting unit. The extraction efficiency of phytoavailable P using 2% citric acid and neutral ammonium citrate was approximately 40% and 70%, respectively. The mixture of Fe(VI)-treated sludge and rice husk was self-heated in a closed composting reactor through the biodegradation of organic matter derived from the treated sludge. Therefore, Fe(VI)-treated sludge may be used as an organic material containing phytoavailable P for compost.

Inhomogeneous antibiotic distribution in sediment profiles in anthropogenically impacted lakes: Source apportionment, fate drivers, and risk assessment

Antibiotic residues in lake ecosystems have been widely reported; however, the vertical distribution of antibiotics in lake sediment profiles have rarely been examined. This study systematically revealed the vertical distribution pattern, sources, and risks of antibiotics in sediments of four typical agricultural lakes in central China. Nine of 33 target antibiotics were detected with a total concentration range of 39.3-18,250.6 ng/g (dry weight), and the order of average concentration was erythromycin (1447.4 ng/g) > sulfamethoxazole (443.7 ng/g) > oxytetracycline (62.6 ng/g) > enrofloxacin (40.7 ng/g) > others (0.1-2.1 ng/g). The middle-layer sediments (9-27 cm) had significantly higher antibiotic detected number and concentration than those in the top layer (0-9 cm) and bottom layer (27-45 cm) (p < 0.05). Correlation analysis showed that significant relationships existed between antibiotic concentrations and the octanol-water partition coefficients (K_ow) of antibiotics (p < 0.05). Redundancy analysis indicated that Pb, Co, Ni, water content, and organic matter (p < 0.05) jointly affected the distribution of antibiotics in sediment profiles. Risk assessment showed that the highest potential ecological and resistance selection risks of antibiotics occurred in the middle-layer sediments, and oxytetracycline, tetracycline, and enrofloxacin had the most extensive potential risks in the sediment profiles. Additionally, the positive matrix factorization model revealed that human medical wastewater (54.5%) contributed more antibiotic pollution than animal excreta (45.5%) in sediment. This work highlights the inhomogeneous distribution of antibiotics in sediment profiles and provides valuable information for the prevention and control of antibiotic contamination in lakes.

Dissemination of antibiotic resistance genes through fecal sewage treatment facilities to the ecosystem in rural area

Infection of antibiotic-resistant pathogens mostly occurs in rural areas. In this paper, the dissemination of antibiotic resistance genes (ARGs) through fecal sewage treatment facilities to the ecosystem in a typical rural area is investigated. Household three-chamber septic tanks (TCs), household biogas digesters (BDs), wastewater treatment plants (WWTPs), vegetable plots, water ponds, etc. Are taken into account. The relative abundance of ARGs in fecal sewage can be reduced by BDs and WWTPs by 80% and 60%, respectively. While TCs show no reduction ability for ARGs. Fast expectation-maximization microbial source tracking (FEAST) analysis revealed that TCs and BDs contribute a considerable percentage (15-22%) of ARGs to the surface water bodies (water ponds) in the rural area. Most ARGs tend to precipitate in the sediments of water bodies and stop moving downstream. Meanwhile, the immigration of microorganisms is more active than that of ARGs. The results provide scientific basic data for the management of fecal sewage and the controlling of ARGs in rural areas.

Mechanistic insights into surface catalytic oxidation of fluoroquinolone antibiotics on sediment mackinawite

Fluoroquinolone antibiotics (FQs) have been widely detected in the sediments due to vast production and consumption. In this study, the transformation of FQs was investigated in the presence of sediment mackinawite (FeS) under ambient conditions. Moreover, the role of dissolved oxygen was evaluated for the enhanced degradation of FQs induced by FeS. Our results demonstrated that typical FQs (i.e., flumequine, enrofloxacin and ciprofloxacin) could be efficiently adsorbed and degraded by FeS under neutral pH conditions. As indicated by the results of electron paramagnetic resonance analysis (EPR) and free radicals quenching experiments, hydroxyl radical and superoxide radical anions were identified as the dominant reactive species responsible for FQs degradation. Based on the results of product analysis and theoretical calculation, the degradation of FQs mainly occurred at the piperazine ring and quinolone structure. Our results show that FQs could be efficiently removed by FeS, which benefits understanding the transformation of antibiotics in the sediments, and even sheds light on the remediation of organic pollutants contaminated soils.

Cyclodextrin Inclusion Complexes and Their Application in Food Safety Analysis: Recent Developments and Future Prospects

Food safety issues are a major threat to public health and have attracted much attention. Therefore, exploring accurate, efficient, sensitive, and economical detection methods is necessary to ensure consumers' health. In this regard, cyclodextrins (CDs) are promising candidates because they are nontoxic and noncaloric. The main body of CDs is a ring structure with hydrophobic cavity and hydrophilic exterior wall. Due to the above characteristics, CDs can encapsulate small guest molecules into their cavities, enhance their stability, avoid agglomeration and oxidation, and, at the same time, interact through hydrogen bonding and electrostatic interactions. Additionally, they can selectively capture the target molecules to be detected and improve the sensitivity of food detection. This review highlights recent advances in CD inclusion technology in food safety analysis, covering various applications from small molecule and heavy metal sensing to amino acid and microbial sensing. Finally, challenges and prospects for CDs and their derivatives are presented. The current review can provide a reference and guidance for current research on CDs in the food industry and may inspire breakthroughs in this field.

Aquatic Environments as Hotspots of Transferable Low-Level Quinolone Resistance and Their Potential Contribution to High-Level Quinolone Resistance

The disposal of antibiotics in the aquatic environment favors the selection of bacteria exhibiting antibiotic resistance mechanisms. Quinolones are bactericidal antimicrobials extensively used in both human and animal medicine. Some of the quinolone-resistance mechanisms are encoded by different bacterial genes, whereas others are the result of mutations in the enzymes on which those antibiotics act. The worldwide occurrence of quinolone resistance genes in aquatic environments has been widely reported, particularly in areas impacted by urban discharges. The most commonly reported quinolone resistance gene, qnr, encodes for the Qnr proteins that protect DNA gyrase and topoisomerase IV from quinolone activity. It is important to note that low-level resistance usually constitutes the first step in the development of high-level resistance, because bacteria carrying these genes have an adaptive advantage compared to the highly susceptible bacterial population in environments with low concentrations of this antimicrobial group. In addition, these genes can act additively with chromosomal mutations in the sequences of the target proteins of quinolones leading to high-level quinolone resistance. The occurrence of qnr genes in aquatic environments is most probably caused by the release of bacteria carrying these genes through anthropogenic pollution and maintained by the selective activity of antimicrobial residues discharged into these environments. This increase in the levels of quinolone resistance has consequences both in clinical settings and the wider aquatic environment, where there is an increased exposure risk to the general population, representing a significant threat to the efficacy of quinolone-based human and animal therapies. In this review the potential role of aquatic environments as reservoirs of the qnr genes, their activity in reducing the susceptibility to various quinolones, and the possible ways these genes contribute to the acquisition and spread of high-level resistance to quinolones will be discussed.

Low Ciprofloxacin Concentrations Select Multidrug-Resistant Mutants Overproducing Efflux Pumps in Clinical Isolates of Pseudomonas aeruginosa

Low antibiotic concentrations present in natural environments are a severe and often neglected threat to public health. Even if they are present below their MICs, they may select for antibiotic-resistant pathogens. Notably, the minimal subinhibitory concentrations that select resistant bacteria, and define the respective sub-MIC selective windows, differ between antibiotics. The establishment of these selective concentrations is needed for risk-assessment studies regarding the presence of antibiotics in different habitats. Using short-term evolution experiments in a set of 12 Pseudomonas aeruginosa clinical isolates (including high-risk clones with ubiquitous distribution), we have determined that ciprofloxacin sub-MIC selective windows are strain specific and resistome dependent. Nonetheless, in all cases, clinically relevant multidrug-resistant (MDR) mutants emerged upon exposure to low ciprofloxacin concentrations, with these concentrations being below the levels reported in ciprofloxacin-polluted natural habitats where P. aeruginosa can be present. This feature expands the conditions and habitats where clinically relevant quinolone-resistant mutants can emerge. In addition, we established the lowest concentration threshold beyond which P. aeruginosa, regardless of the strain, becomes resistant to ciprofloxacin. Three days of exposure under this sub-MIC "risk concentration" led to the selection of MDR mutants that displayed resistance mechanisms usually ascribed to high selective pressures, i.e., the overproduction of the efflux pumps MexCD-OprJ and MexEF-OprN. From a One-Health viewpoint, these data stress the transcendent role of low drug concentrations, which can be encountered in natural ecosystems, in aggravating the antibiotic resistance problem, especially when it comes to pathogens of environmental origin. IMPORTANCE It has been established that antibiotic concentrations below MICs can select antibiotic-resistant pathogens, a feature of relevance for analyzing the role of nonclinical ecosystems in antibiotic resistance evolution. The range of concentrations where this selection occurs defines the sub-MIC selective window, whose width depends on the antibiotic. Herein, we have determined the ciprofloxacin sub-MIC selective windows of a set of Pseudomonas aeruginosa clinical isolates (including high-risk clones with worldwide distribution) and established the lowest concentration threshold, notably an amount reported to be present in natural ecosystems, beyond which this pathogen acquires resistance. Importantly, our results show that this ciprofloxacin sub-MIC selects for multidrug-resistant mutants overproducing clinically relevant efflux pumps. From a One-Health angle, this information supports that low antimicrobial concentrations, present in natural environments, may have a relevant role in worsening the antibiotic resistance crisis, particularly regarding pathogens with environmental niches, such as P. aeruginosa.

Antimicrobial resistance genes in microbiota associated with sediments and water from the Akaki river in Ethiopia

The spread of antimicrobial-resistant pathogens is a global health concern. Most studies report high levels of antimicrobial resistance genes (ARGs) in the aquatic environment; however, levels associated with sediments are limited. This study aimed to investigate the distribution of ARGs in the sediments and water of the Akaki river in Addis Ababa, Ethiopia. The diversity and abundance of 84 ARGs and 116 clinically important bacteria were evaluated from the sediments and water collected from five sites in the Akaki river. Most of the ARGs were found in the city close to anthropogenic activities. Water samples collected in the middle catchment of the river contained 71-75% of targeted ARGs, with genes encoding aminoglycoside acetyltransferase (aac(6)-Ib-cr), aminoglycoside adenylyl transferase (aadA1), β-lactamase (bla_OXA-10)_, quinolone resistance S (qnrS), macrolide efflux protein A (mefA), and tetracycline resistance (tetA), were detected at all sampling sites. Much fewer ARGs were detected in all sediments, and those near the hospitals had the highest diversity and level. Despite the lower levels and diversity, there were no unique ARGs detected in the sediments that were also not detected in the waters. A wide range of clinically relevant pathogens were also detected in the Akaki river. The findings suggest that the water phase, rather than the sediments in the Akaki river, is a potential conduit for the spread of ARGs and antibiotic-resistant bacteria.

Genome-Based Assessment of Antimicrobial Resistance and Virulence Potential of Isolates of Non-Pullorum/Gallinarum Salmonella Serovars Recovered from Dead Poultry in China

Paratyphoid avian salmonellosis is considered one of the leading causes of poultry death, resulting in significant economic losses to poultry industries worldwide. In China, especially in Shandong province, the leading producer of poultry products, several recurrent outbreaks of avian salmonellosis have been reported during the last decade where the precise causal agent remains unknown. Moreover, the establishment of earlier and more accurate recognition of pathogens is a key factor to prevent the further dissemination of resistant and/or hypervirulent clones. Here, we aim to use whole-genome sequencing combined with in silico toolkits to provide the genomic features of the antimicrobial resistance and virulence potential of 105 regionally representative non-Pullorum/Gallinarum Salmonella isolates recovered from dead poultry between 2008 and 2019 in Shandong, China. Additionally, phenotypic susceptibility to a panel of 15 antibiotics representing 11 classes was assessed by the broth microdilution method. In this study, we identified eight serovars and nine multilocus sequence typing (MLST) types, with Salmonella enterica serovar Enteritidis sequence type 11 (ST11) being the most prevalent (84/105; 80%). Based on their phenotypic antimicrobial resistance, 77.14% of the isolates were defined as multidrug resistant (≥3 antimicrobial classes), with the detection of one S. Enteritidis isolate that was resistant to the 11 classes. The highest rates of resistance were observed against nalidixic acid (97.14%) and ciprofloxacin (91.43%), followed by ampicillin (71.43%), streptomycin (64.77%), and tetracycline (60%). Genomic characterization revealed the presence of 41 resistance genes, with an alarmingly high prevalence of blaTEM-1B (60%), in addition to genomic mutations affecting the DNA gyrase (gyrA) and DNA topoisomerase IV (parC) genes, conferring resistance to quinolones. The prediction of plasmid replicons detected 14 types, with a dominance of IncFIB(S)_1 and IncFII(S)_1 (87.62% for both), while the IncX1 plasmid type was considered the key carrier of antimicrobial resistance determinants. Moreover, we report the detection of critical virulence genes, including cdtB, rck, sodCI, pef, and spv, in addition to the typical determinants for Salmonella pathogenicity island 1 (SPI-1) and SPI-2. Furthermore, phylogenomic analysis revealed the detection of three intra-farm and five inter-farm transmission events. Overall, the detection of Salmonella isolates presenting high antimicrobial resistance and harboring different critical virulence genes is of major concern, which requires the urgent implementation of effective strategies to mitigate non-Pullorum/Gallinarum avian salmonellosis. IMPORTANCE Avian salmonellosis is one of the leading global causes of poultry death, resulting in substantial economic losses in China (constituting 9% of overall financial losses). In Shandong province, a top poultry producer (30% of the overall production in China, with 15% being exported to the world), extensive outbreaks of avian salmonellosis have been reported in the past decade where the causal agents or exact types remain rarely addressed. From approximately 2008 to 2019, over 2,000 Salmonella strains were isolated and identified from dead poultry during routine surveillance of 95 poultry farms covering all 17 cities in Shandong. Approximately 1,500 isolates were confirmed to be of non-Pullorum/Gallinarum Salmonella serovars. There is an urgent need to understand the mechanisms behind the implication of zoonotic Salmonella serovars in systemic infections of poultry. Here, we analyzed populations of clinically relevant isolates of non-Pullorum/Gallinarum Salmonella causing chicken death in China by a whole-genome sequencing approach and determined that antimicrobial-resistant Salmonella Enteritidis remained the major cause in the past decades.

The effect of ultrafiltration process on the fate of antibiotic-related microcontaminants, pathogenic microbes, and toxicity in urban wastewater

Ultrafiltration (UF) was assessed at chemical, microbiological, genetical and toxicological level and in terms of removing specific antibiotic-related microcontaminants from urban wastewater. The UF capacity to remove various antibiotics (clarithromycin, erythromycin, ampicillin, ofloxacin, sulfamethoxazole, trimethoprim, and tetracycline; [A₀] = 100 μg L^-1) was optimised with respect to the feed recirculation rate (25-50%) and feed/transmembrane pressure (1.5-3/1.5-2.4 bar, respectively). Here, we tested the UF capacity to reduce the cultivable bacteria (faecal coliforms, total heterotrophs, Enterococci, Pseudomonas aeruginosa), enteric opportunistic pathogens, including antibiotic-resistant bacteria (ARB) and antibiotic-resistance genes (ARGs) load. Moreover, the toxicity towards Daphnia magna and three plant species was investigated. Upon optimisation of UF, the removal of antibiotics ranged from 19% for trimethoprim to 95% for clarithromycin. The concentration of cultivable faecal coliforms in the permeate was significantly reduced compared to the feed (P < 0.001), whereas all the bacterial species decreased by more than 3 logs. A similar pattern of reduction was observed for the ARGs (P < 0.001) and enteric opportunistic pathogens (~3-4 logs reduction). A nearly complete removal of the antibiotics was obtained by UF followed by granular activated carbon adsorption (contact time: 90 min), demonstrating the positive contribution of such combination to the abatement of chemical microcontaminants.

Synthesis of molecularly imprinted polymers for extraction of fluoroquinolones in environmental, food and biological samples

In recent years, fluoroquinolones have been found present in important water resources and food sources which compromises the food quality and availability, thereby, causing risks to the consumer. Despite the recent advancement in the development of analytical instrumentation for routine monitoring of fluoroquinolones in water, food, and biological samples, sample pre-treatment is still a major bottleneck of the analytical methods. Therefore, fast, selective, sensitive, and cost-effective sample preparation methods prior to instrumental analysis for fluoroquinolones residues in environmental, food and biological samples are increasingly important. Solid-phase extraction using different adsorbents is one of the most widely used pre-concentration/clean-up techniques for analysis of fluoroquinolones. Molecularly imprinted polymers (MIPs) serve as excellent effective adsorbent materials for selective extraction, separation, clean-up and preconcentration of various pollutants in different complex matrices. Therefore, synthesis of MIPs remains crucial for their applications in sample preparation as this offers much-needed selectivity in the extraction of compounds in complex samples. In this study, the progress made in the synthesis of MIPs for fluoroquinolones and their applications in water, food and biological samples were reviewed. The present review discusses the selection of all the elements of molecular imprinting for fluoroquinolones, polymerization processes and molecular recognition mechanisms. In conclusion, the related challenges and gaps are given to offer ideas for future research focussing on MIPs for fluoroquinolones.

Host-guest interactions for extracting antibiotics with a γ-cyclodextrin poly(glycidyl-co-ethylene dimethacrylate) hybrid sorbent

A procedure for the solid-phase extraction of antibiotics (enoxacin, ofloxacin, norfloxacin, ciprofloxacin, and sparfloxacin) in water has been developed. The sorbent used is based on a poly(glycidyl-co-ethylene dimethacrylate) network, whose previously modified surface has been functionalized with γ-cyclodextrin through a click-chemistry reaction. The architecture of the material has been characterized by thermogravimetric analysis, N₂ adsorption-desorption, Raman spectroscopy, confocal microscopy, and scanning electron microscopy, showing good capability to be used as a filler for extraction cartridges. The optimization of the extraction methodology shows good intra-day and inter-day repeatability of the extraction procedure, with coefficients of variation between 2.5 and 5.1% and the possibility of reusing the material at least five times. The detection limits of the method have been established at the μg L^-1 level, confirming the possibility of quantifying trace levels. To end, real groundwater samples have been analyzed and the results are comparable with those obtained with a reference method. The proposed material can be used for assessing the presence of antibiotics in aqueous environments through an extraction procedure taking advantage of the presence of γ-cyclodextrin on its structure.

Enhanced Biosynthesis of Fatty Acids Is Associated with the Acquisition of Ciprofloxacin Resistance in Edwardsiella tarda

Misuse and overuse of antibiotics drive the selection and spread of antibiotic-resistant bacteria. Although genetic mutations have been well defined for different types of antibiotic resistance, ways to revert antibiotic resistance are largely unexplored. Here, we adopted a proteomics approach to investigate the mechanism underlying ciprofloxacin resistance in Edwardsiella tarda, a representative pathogen that infects both economic animal species and human beings. By comparing the protein expression profiles of ciprofloxacin-sensitive and -resistant E. tarda, a total of 233 proteins of differential abundance were identified, where 53 proteins belong to the functional categories of metabolism, featuring a disrupted pyruvate cycle and decreased energy metabolism but increased fatty acid biosynthesis. The altered pyruvate cycle and energy metabolism were confirmed by gene expression and biochemical assays. Furthermore, the role of fatty acid biosynthesis and quinolone resistance were explored. The expression level and enzymatic activity of acetyl coenzyme A (acetyl-CoA) carboxylase, the first step of fatty acid biosynthesis, were increased in ciprofloxacin-resistant E. tarda. Treatment of ciprofloxacin-resistant E. tarda with acetyl-CoA carboxylase and 3-oxoacyl-[acyl carrier protein] synthase II inhibitors, 2-aminooxazole and triclosan, respectively, reduced the expression of fatty acid biosynthesis and promoted quinolone-mediated killing efficacy to antibiotic-resistant bacteria. Similar results were obtained in clinically isolated E. tarda strains. Our study suggests that energy metabolism has been reprogramed in ciprofloxacin-resistant bacteria that favor the biosynthesis of fatty acid, presenting a novel target to tackle antibiotic-resistant bacteria.

IMPORTANCEEdwardsiella tarda is the causative agent of edwardsiellosis, which imposes huge challenges on clinics and aquaculture. Due to the overuse of antibiotics, the emergence and spread of antibiotic-resistant E. tarda threaten human health and animal farming. However, the mechanism of ciprofloxacin resistance in E. tarda is still lacking. Here, iTRAQ (isobaric tags for relative and absolute quantification)-based proteomics was performed to identify a differential proteome between ciprofloxacin-sensitive and -resistant E. tarda. The fluctuated pyruvate cycle and reduced energy metabolism and elevated fatty acid biosynthesis are metabolic signatures of ciprofloxacin resistance. Moreover, inhibition of biosynthesis of fatty acids promotes quinolone-mediated killing efficacy in both lab-evolved and clinically isolated strains. This study reveals that a ciprofloxacin resistance mechanism is mediated by the elevated biosynthesis of fatty acids and the depressed pyruvate metabolism and energy metabolism in E. tarda. These findings provide a novel understanding for the ciprofloxacin resistance mechanism in E. tarda.

Photocatalytic Penicillin Degradation Performance and the Mechanism of the Fragmented TiO2 Modified by CdS Quantum Dots

In this study, a novel method was adopted to construct a CdS-TiO₂ heterostructure to degrade penicillin under sunlight. A potato extract was used during the synthesis process of CdS QDs as a stabilizer and a modifier. The CdS-TiO₂ composite with a heterostructure delivers high photocatalytic degradation efficiency. In detail, 0.6 mg/mL of CdS-TiO₂ can successfully decompose penicillin after 2 h, and 5‰ CdS-TiO₂ shows the optimal degradation efficiency with the degradation rate reaching 88%. Furthermore, the underlying mechanisms of the penicillin decomposition reaction were investigated by the EPR test and trapping experiment. It was found that the high photocatalytic degradation efficiency was attributed to the heterojunction of CdS-TiO₂, which successfully suppresses the recombination of the conduction band of CdS and the valence band of TiO₂. Moreover, it was confirmed that the reaction is the O₂-consuming process, and introducing O₂ can greatly accelerate the generation of a superoxide radical during the photocatalytic degradation process, which eventually improves the degradation of penicillin and shortens the degradation time. Finally, this work provides the possible penicillin degradation pathways, which will inspire the researchers to explore and design novel photocatalysts in the field of wastewater treatment in the future.

Changes in antibiotic resistance of Escherichia coli during the broiler feeding cycle

The purpose of this study was to investigate the drug-resistant phenotypes and genes of Escherichia coli in animal, environmental, and human samples before and after antibiotic use at a large-scale broiler farm to understand the respective effects on E. coli resistance during the broiler feeding cycle. The antibiotic use per broiler house was 143.04 to 183.50 mg/kg, and included tilmicosin, florfenicol, apramycin, and neomycin. All strains isolated on the first day the broilers arrived (T1; day 1) were antibiotic-resistant bacteria. E. coli strains isolated from animal samples were resistant to ampicillin, tetracycline, and sulfamethoxazole (100%), and those isolated from environmental samples were resistant to 5 different drugs (74.07%, 20 of 27). E. coli strains isolated on the last day before the broilers left (T2; day 47) had a higher resistance rate to florfenicol (100%, 36 of 36) than at T1 (P < 0.05). Multidrug resistance increased from T1 (84.21%, 32 of 38) to T2 (97.22%, 35 of 36). Most strains were resistant to 5 classes of antibiotics, and 2 strains were resistant to 6 classes of antibiotics. Among 13 identified drug resistance genes, 11 and 13 were detected at T1 and T2, respectively. NDM-1 was detected in 4 environmental samples and 1 animal sample. In conclusion, the use of antibiotics during breeding increases E. coli resistance to antibacterial drugs. Drug-resistant bacteria in animals and the environment proliferate during the feeding cycle, leading to the widespread distribution of drug resistance genes and an increase in the overall resistance of bacteria.

Prevalence and mechanisms of fluoroquinolone-resistant Escherichia coli among sheltered companion animals

To better understand the prevalence of fluoroquinolone-resistant Escherichia coli among sheltered companion animals, we conducted a screening study of 38 dogs and 78 cats and investigated the resistance mechanisms and characteristics of the isolates. Fluoroquinolone-resistant E. coli was detected in 18 dogs (47.4 %) and 14 cats (17.9 %). The isolates carried one to four mutations in the gyrA, parC and parE genes of the quinolone resistance-determining region, and the number of mutations was proportional to the MIC for ciprofloxacin. For plasmid-mediated quinolone resistance, aac-(6′)-Ib-cr was detected in nine isolates, qnrS in five isolates and qnrB in one isolate. A relationship between the presence of these genes and MIC for ciprofloxacin was not apparent. Statistical analysis indicated that fluoroquinolone-resistant E. coli was widely distributed among sheltered companion animals with various attributes. This may relate to the wide dissemination of fluoroquinolone resistance among humans and other animals in Japan.

Occurrence and risk assessment of fluoroquinolone antibiotics in reclaimed water and receiving groundwater with different replenishment pathways

Artificial recharge to groundwater with reclaimed water is considered a promising method to alleviate groundwater depletion and over-exploitation. However, the occurrence of fluoroquinolone antibiotics (FQs) was ubiquitous in wastewater, surface water, groundwater and even drinking water threating human health and ecology. In this study, the occurrence of six selected FQs in reclaimed water effluent and their removal by tertiary treatment units were investigated. The overall removal efficiencies in average of the tertiary treatment processes in Beijing and Changzhou were ranging from 21.2% to 55.2%. Activated carbon exhibited better performance for FQs removal than ozone and biological treatment such as membrane bioreactor, anaerobic-anoxic-oxic and biofilter. The results of two pilot study showed that the impact of reclaimed water to groundwater quality in terms of FQs concentration by direct injection in GBD was stronger than surface spreading in Changzhou, which might be due to the recharge strategy and the physical and chemical characteristics of sediment and aquifer soil. The hazard quotient (HQ) values of ofloxacin (OFL) in reclaimed water was up to 12.54, indicating the extreme eco-toxicological risk, while enrofloxacin (ENR) exhibited medium risk. After recharge with reclaimed water, the HQ values of OFL and ENR in groundwater ranged from low to medium ecological risk to the environment. Thus, the FQs in reclaimed water need to be paid more attention during their reuse for groundwater recharge, especially by direct injection. It is suggested that FQs should be considered in the priority substances lists in standards and guidelines of reclaimed water reuse for groundwater recharge to ensure the safety of groundwater.

The role of metal contamination in shaping microbial communities in heavily polluted marine sediments

Microorganisms in coastal sediments are fundamental for ecosystem functioning, and regulate processes relevant in global biogeochemical cycles. Still, our understanding of the effects anthropogenic perturbation and pollution can have on microbial communities in marine sediments is limited. We surveyed the microbial diversity, and the occurrence and abundance of metal and antibiotic resistance genes is sediments collected from the Pula Bay (Croatia), one of the most significantly polluted sites along the Croatian coast. With a collection of 14 samples from the bay area, we were able to generate a detailed status quo picture of a site that only recently started a cleaning and remediation process (closing of sewage pipes and reduction of industrial activity). The concentrations of heavy metals in Pula Bay sediments are significantly higher than in pristine sediments from the Adriatic Sea, and in some cases, manifold exceed international sediment quality guidelines. While the sedimentary concentrations of heavy metals did significantly influence the abundance of the tested metal resistance genes, no strong effect of heavy metal pollution on the overall microbial community composition was observed. Like in many other marine sediments, Gammaproteobacteria, Bacteroidota and Desulfobacterota dominated the microbial community composition in most samples, and community assembly was primarily driven by water column depth and nutrient (carbon and nitrogen) availability, regardless of the degree of heavy metal pollution.

Occurrence, distribution, and health risk assessment of quinolone antibiotics in water, sediment, and fish species of Qingshitan reservoir, South China

The residual antibiotics in the environment have lately caused widespread concerns. However, little information is available on the antibiotic bioaccumulation and its health risk in drinking water resources of South China. Therefore, the occurrence, distribution, and health risk of four quinolone antibiotics including ofloxacin (OFX), norfloxacin (NOR), ciprofloxacin (CIP), and enrofloxacin (ENR) in the Qingshitan reservoir using high-performance liquid chromatography were investigated. Results revealed that the concentrations in water, sediment, and edible fish ranged from 3.49–660.13 ng/L, 1.03–722.18 μg/kg, and 6.73–968.66 μg/kg, respectively. The ecological risk assessment via the risk quotient (RQ) method showed that the values in sediment were all greater than 1, posing a high risk to the environment. The health risk index of water samples was at the maximum acceptable level, with OFX at the top while the rest were at the medium risk level. The main edible fish kinds of the reservoir had high dietary safety and the highest contaminations were found in carnivorous feeding habits and demersal habitat fishes with OFX as the highest magnitude. Source identification and correlation analysis using SPSS showed significant relationships between NOR with pH and turbidity (in water), as well as total phosphor (TP) and total organic carbon (TOC) in sediment. NOR was the highest in sediment which mostly sourced from livestock wastewater, croplands irrigation drain water, and stormwater. Correlations between CIP and ENR with TP were significant, while OFX was positively associated with total nitrogen (TN) which mainly originated from urban sewage as well as directly dosed drugs in fish farms. In conclusion, our results are of great significance for ensuring the safety of drinking water and aquatic products in this region.

Evolution of antibiotic resistance at low antibiotic concentrations including selection below the minimal selective concentration

Determining the selective potential of antibiotics at environmental concentrations is critical for designing effective strategies to limit selection for antibiotic resistance. This study determined the minimal selective concentrations (MSCs) for macrolide and fluoroquinolone antibiotics included on the European Commissionʼs Water Framework Directive’s priority hazardous substances Watch List. The macrolides demonstrated positive selection for ermF at concentrations 1–2 orders of magnitude greater (>500 and <750 µg/L) than measured environmental concentrations (MECs). Ciprofloxacin illustrated positive selection for intI1 at concentrations similar to current MECs (>7.8 and <15.6 µg/L). This highlights the need for compound specific assessment of selective potential. In addition, a sub-MSC selective window defined by the minimal increased persistence concentration (MIPC) is described. Differential rates of negative selection (or persistence) were associated with elevated prevalence relative to the no antibiotic control below the MSC. This increased persistence leads to opportunities for further selection over time and risk of human exposure and environmental transmission.

Stanton et al. determine the minimal selective concentrations for macrolide and fluoroquinolone antibiotics and describe a selective window defined by the minimal increased persistence concentration. These assessments and thresholds allow for better assessment of potential selection for antibiotic resistance and the risks of human exposure and environmental transmission.

Functional Identification and Evolutionary Analysis of Two Novel Plasmids Mediating Quinolone Resistance in Proteus vulgaris

Plasmid-mediated quinolone resistance (PMQR) remains one of the main mechanisms of bacterial quinolone resistance and plays an important role in the transmission of antibiotic resistance genes (ARGs). In this study, two novel plasmids, p3M-2A and p3M-2B, which mediate quinolone resistance in Proteus vulgaris strain 3M (P3M) were identified. Of these, only p3M-2B appeared to be a qnrD-carrying plasmid. Both p3M-2A and p3M-2B could be transferred into Escherichia coli, and the latter caused a twofold change in ciprofloxacin resistance, according to the measured minimum inhibitory concentration (MIC). Plasmid curing/complementation and qRT-PCR results showed that p3M-2A can directly regulate the expression of qnrD in p3M-2B under treatment with ciprofloxacin, in which process, ORF1 was found to play an important role. Sequence alignments and phylogenetic analysis revealed the evolutionary relationships of all reported qnrD-carrying plasmids and showed that ORF1–4 in p3M-2B is the most conserved backbone for the normal function of qnrD-carrying plasmids. The identified direct repeats (DR) suggested that, from an evolutionary perspective, p3M-2B may have originated from the 2683-bp qnrD-carrying plasmid and may increase the possibility of plasmid recombination and then of qnrD transfer. To the best of our knowledge, this is the first identification of a novel qnrD-carrying plasmid isolated from a P. vulgaris strain of shrimp origin and a plasmid that plays a regulatory role in qnrD expression. This study also sheds new light on plasmid evolution and on the mechanism of horizontal transfer of ARGs encoded by plasmids.

Involvement of oxidative stress in the sensitivity of two algal species exposed to roxithromycin

Algal species Raphidocelis subcapitata and Chlorella vulgaris are commonly used to test the chemicals with an antibacterial mode of action during marketing authorization process. However, significant differences in the sensitivity toward antibiotic exposure have been reported. The selection of an inappropriate test species would thus underestimate the environmental hazard of target chemicals and pose a potential threat to the ecosystem. Since oxidative stress is a crucial factor determining the inhibition of algal growth, an investigation on oxidative stress and antioxidant defense mechanisms in these two species was performed to explore its roles in species sensitivity. Here, roxithromycin (ROX), a macrolide antibiotic extensively used to treat respiratory, urinary and soft tissue infections, was used for testing. After 7 days exposure to ROX at the low (0.01 mg L^-1) and high (0.09 mg L^-1) concentrations, R. subcapitata was inhibited while the growth of C. vulgaris was stimulated. We investigated the roles of oxidative stress in algae by measuring the oxidative stress biomarkers (MDA), non-enzymatic antioxidants (GSH), and antioxidant enzymes (SOD, CAT, GP, GST). The results suggested that when the growth of algae is inhibited, MDA content as well as activities of oxidative stress enzymes would increase, and thus, activating the antioxidant system. On the contrary, it was inferred that when the growth is stimulated, MDA content and oxidative stress enzymes activities would decrease.

The role of stereochemistry of antibiotic agents in the development of antibiotic resistance in the environment

Antibiotic resistance (ABR) is now recognised as a serious global health and economic threat that is most efficiently managed via a 'one health' approach incorporating environmental risk assessment. Although the environmental dimension of ABR has been largely overlooked, recent studies have underlined the importance of non-clinical settings in the emergence and spread of resistant strains. Despite this, several research gaps remain in regard to the development of a robust and fit-for-purpose environmental risk assessment for ABR drivers such as antibiotics (ABs). Here we explore the role the environment plays in the dissemination of ABR within the context of stereochemistry and its particular form, enantiomerism. Taking chloramphenicol as a proof of principle, we argue that stereoisomerism of ABs impacts on biological properties and the mechanisms of resistance and we discuss more broadly the importance of stereochemistry (enantiomerism in particular) with respect to antimicrobial potency and range of action.

Toxicological effects of ciprofloxacin exposure to Drosophila melanogaster

The abuse of ciprofloxacin (CIP) may cause serious side effects and the mechanisms underlying these effects remain unclear. Here, we determinate the 48 h, 72 h and 96 h LC₅₀ values of CIP to Drosophila melanogaster and demonstrate a series of adverse effects after D. melanogaster was exposed to CIP at a sublethal concentration (3.2 mg mL^-1). Treated individuals showed shorter lifespan, delayed development and many of the treated larvae failed to pupate or hatch. Smaller body size was observed at every life stage when exposed to CIP and the size of pupae, the weight of third-instar larvae exhibited a perfectly dose-response relationship that the larger concentration exposed to, the smaller body size or lighter weight is. Moreover, reduction in fat body cell viability, elevated oxidative stress markers (SOD and CAT) and down-regulation of diap1, ex, two target genes of Yorkie (Yki), was observed in response to CIP exposure. Most importantly, we found two types of black spot in Drosophila and the proportion of larvae with a black spot was positively related to the treatment dose, which is new in the field. This study provides a scientific basis for the potential harm caused by abuse of quinolones with the goal of urging cautious use of antibiotics.

Occurrence, Distribution, and Ecological Risk of Fluoroquinolones in Rivers and Wastewaters

The use of fluoroquinolones for the treatment of infections in humans and animals has increased in Argentina, and they can be found in large amounts in water bodies. The present study investigated the occurrence and associated ecological risk of 5 fluoroquinolones in rivers and farm wastewaters of San Luis, Santa Fe, Córdoba, Entre Ríos, and Buenos Aires provinces of Argentina by high-performance liquid chromatography coupled to fast-scanning fluorescence detection and ultra-high-performance liquid chromatography coupled to triple quadrupole mass spectrometry detection. The maximum concentrations of ciprofloxacin, enrofloxacin, ofloxacin, enoxacin, and difloxacin found in wastewater were 1.14, 11.9, 1.78, 22.1, and 14.2 μg L^-1 , respectively. In the case of river samples, only enrofloxacin was found, at a concentration of 0.97 μg L^-1 . The individual risk of aquatic organisms associated with water pollution due to fluoroquinolones was higher in bacteria, cyanobacteria, algae, plants, and anurans than in crustaceae and fish, with, in some cases, risk quotients >1. The proportion of samples classified as high risk was 87.5% for ofloxacin, 63.5% for enrofloxacin, 57.1% for ciprofloxacin, and 25% for enoxacin. Our results suggest that the prevalence of fluoroquinolones in water could be potentially risky for the aquatic ecosystem, and harmful to biodiversity. Environ Toxicol Chem 2019;38:2305-2313. © 2019 SETAC.

Pseudomonas Diversity Within Urban Freshwaters

Freshwater lakes are home to bacterial communities with 1000s of interdependent species. Numerous high-throughput 16S rRNA gene sequence surveys have provided insight into the microbial taxa found within these waters. Prior surveys of Lake Michigan waters have identified bacterial species common to freshwater lakes as well as species likely introduced from the urban environment. We cultured bacterial isolates from samples taken from the Chicago nearshore waters of Lake Michigan in an effort to look more closely at the genetic diversity of species found there within. The most abundant genus detected was Pseudomonas, whose presence in freshwaters is often attributed to storm water or runoff. Whole genome sequencing was conducted for 15 Lake Michigan Pseudomonas strains, representative of eight species and three isolates that could not be resolved with named species. These genomes were examined specifically for genes encoding functionality which may be advantageous in their urban environment. Antibiotic resistance, amidst other known virulence factors and defense mechanisms, were identified in the genome annotations and verified in the lab. We also tested the Lake Michigan Pseudomonas strains for siderophore production and resistance to the heavy metals mercury and copper. As the study presented here shows, a variety of pseudomonads have inhabited the urban coastal waters of Lake Michigan.

Application of Oxides Electrodes (Ru, Ti, Ir and Sn) for the Electrooxidation of Levofloxacin

Background:

The main sources of antibiotic pollution are industries, hospitals, and urban effluents, as well as wastewater from farms that use antibiotics for veterinary purposes. Fluoroquinolones are very useful as antimicrobial agents and are probably among the most important classes of synthetic antibiotics in veterinary and human medicines worldwide. Despite this relevance, studies on the analysis of fluoroquinolones in wastewaters and alternative processes to degrade these compounds, and their effects on human health and environment are scarce. Here, we prepared different oxide electrodes (Ti/Ru0.3Ti0.7O2, Ti/Ru0.3Sn0.7O2, Ti/Ir0.3Ti0.7O2, and Ti/Ir0.3Sn0.7O2) and used them in the electrochemical oxidation of levofloxacin, an antibiotic belonging to the class of fluoroquinolones.

Methods:

The oxide electrodes with nominal compositions: Ti/Ru0.3Ti0.7O2, Ti/Ru0.3Sn0.7O2, Ti/Ir0.3Ti0.7O2, and Ti/Ir0.3Sn0.7O2 were prepared by the traditional method. Briefly, the precursor solution was dissolved in isopropanol and applied by brushing on both sides of the titanium substrate. The resulting material was thermally decomposed at 400°C for 5 min in a preheated oven, which was followed by cooling. This procedure was repeated until the desired oxide thickness was achieved (2 mm). Using the electrochemical cell, the electrolysis experiments were carried out by applying current densities of 25, 50, and 100 mA cm-2 on the oxide electrodes for 60 min. During this experiment, aliquots were removed at times: 5, 10, 15, 20, 30, 45 and 60 min for quantification. Levofloxacin was quantitatively determined by High-Performance Liquid Chromatography (HPLC).

Results:

The catalytic efficiency of different electrodes is measured as the yield of levofloxacin degradation, which in most cases reaches 50% within 1 h of electrolysis, regardless of the applied current. The electrodes bearing ruthenium afford the same % residual levofloxacin (18%) after 1 h of electrolysis under 100 mA cm-2. The electrodes that contain iridium provide similar results at all the applied currents, being less efficient as compared to the ruthenium-based electrodes. The electrode Ti/Ru0.3Sn0.7O2 presented the highest levofloxacin degradation value (levofloxacin residual is 8% at 50 mA cm-2) and levofloxacin removal rate was calculated considering order 1 kinetics (-lnC/Co=kt), for each of the applied current densities reaching 4.4, 4.9 and 4.5 mg L-1min-1 for the experiments at 25, 50, 100 mA cm-2. Therefore, the Ti/Ru0.3Sn0.7O2 electrode affords the highest yield and the best cost/benefit ratio.

Conclusion:

In this work, electrodes were prepared with different compositions to study the catalytic efficiency in the degradation of levofloxacin, an antibiotic belonging to the class of fluoroquinolones. The mixed oxide electrodes prepared herein have proven to be an efficient alternative to treat effluents contaminated with organic compounds. The electrode containing RuO2 and SnO2 oxidizes levofloxacin the most efficiently, reaching a removal efficiency of 92% (4.9 mg L-1 min-1) under 50 mA cm-2. Hence, the substitution of Ti for Sn generates better degradation efficiency.

Characterization of Quinolone-Resistant Determinants in Tribe Proteeae Isolated from Pet Turtles with High Prevalence of qnrD and Novel gyrB Mutations

Development of antibiotic resistance in bacteria has challenged significantly in both veterinary and human medicine. In this study, we analyzed the potential risk of pet turtles harboring tribe Proteeae as a source of quinolone-resistant determinants, including plasmid-mediated quinolone resistance (PMQR) genes and target gene alterations in the quinolone resistance-determining region (QRDR). Antimicrobial susceptibility of 54 Proteeae isolates against ciprofloxacin, ofloxacin, levofloxacin, and nalidixic acid was examined. The PMQR genes and QRDR alterations were identified using conventional PCR assays and sequencing. Four isolates were resistant to all quinolones tested in this study. Nine isolates showed resistance to nalidixic acid and showed either intermediate resistance or susceptibility to other tested quinolones. All isolates resistant to one or more tested quinolones harbored mutations in gyrB and some also had gyrA and parC mutations. Of 54, 12 Proteeae isolates displayed the novel E466D, N440T, Q411S, and F417L mutations in gyrB. Among the PMQR genes, 41 (76%) isolates harbored the qnrD gene with the highest prevalence, whereas aac(6')Ib-cr, qnrS, qnrA, and qnrB genes were detected in 28 (52%), 9 (17.0%), 7 (13.0%), and 1 (1.9%) study isolates, respectively. The QRDR analysis of selected mutants revealed that increasing quinolone selective pressure led to a predominance of gyrA mutants. All results indicate that a healthy pet turtle can play as a potential reservoir for quinolone-resistant Proteeae, which it might cause public health risk on pet owners.

Prevalence and Antimicrobial Susceptibility of Bacterial Pathogens in Ready-to-Eat Foods Retailed in Osaka Prefecture, Japan

The potential human health risk of Japanese ready-to-eat (RTE) foods was investigated by determining the contamination by foodborne bacterial pathogens, the prevalence of opportunistic and nosocomial pathogens, and the antibiotic susceptibility of the isolates recovered from 96 samples of lightly pickled vegetables, 88 samples of Western-style desserts, and 98 samples of RTE fish and seafood products sold at retail in Osaka, Japan. Staphylococcus aureus, including isolates producing staphylococcal enterotoxin (SE), were isolated from six lightly pickled vegetable products, seven Western-style dessert products, and three RTE fish and seafood products. Of these isolates, one SEC-producing isolate from a cake was identified as community-acquired methicillin-resistant S. aureus, which was multilocus sequence type 8 and staphylococcal cassette chromosome mec type IV. Enterobacteriaceae species, including Escherichia coli, Klebsiella oxytoca, Klebsiella pneumoniae, Proteus mirabilis, Serratia marcescens, Citrobacter freundii-Citrobacter braakii, and/or the Enterobacter cloacae complex, were isolated from 92 (95.8%) of the lightly pickled vegetable products, 39 (44.3%) of the Western-style dessert products, and 74 (75.5%) of the RTE fish and seafood products. On the basis of the antimicrobial susceptibility profiles of the opportunistic and nosocomial Enterobacteriaceae pathogens, the third-generation cephalosporin, fosfomycin, and quinolone resistance determinants were investigated. We detected AmpC products of the CIT group and a qnrB9 product in 5 and 1 C. freundii-C. braakii isolates, respectively, and fosA gene products in 15 E. cloacae complex isolates. Because RTE foods are consumed without a heating process, the spread of bacterial pathogens from contaminated food to human consumers is possible. RTE foods must be handled using hygienic procedures from the processing steps to the table to reduce the prevalence of potentially pathogenic or pathogenic bacteria and to prevent bacterial growth.

Metal-mediated oxidation of fluoroquinolone antibiotics in water: A review on kinetics, transformation products, and toxicity assessment

Fluoroquinolones (FQs) are among the most potent antimicrobial agents, which have seen their increasing use as human and veterinary medicines to control bacterial infections. FQs have been extensively found in surface water and municipal wastewaters, which has raised great concerns due to their negative impacts to humans and ecological health. It is of utmost importance that FQs are treated before their release into the environment. This paper reviews oxidative removal of FQs using reactive oxygen (O₃ and OH), sulfate radicals (SO₄^-), and high-valent transition metal (Mn^VII and Fe^VI) species. The role of metals in enhancing the performance of reactive oxygen and sulfur species is presented. The catalysts can significantly enhance the production of OH and/or SO₄^- radicals. At neutral pH, the second-order rate constants (k, M^-1s^-1) of the reactions between FQs and oxidants follow the order as k(OH)>k(O₃)>k(Fe^VI)>k(Mn^VII). Moieties involved to transform target FQs to oxidized products and participation of the catalysts in the reaction pathways are discussed. Generally, the piperazinyl ring of FQs was found as the preferential attack site by each oxidant. Meanwhile, evaluation of aquatic ecotoxicity of the transformation products of FQs by these treatments is summarized.

Detection of Novel GyrB Mutations Associated with Escherichia coli Clinical Isolates

The following study is investigating the different GyrB mutations associated withEscherichia coliclinical isolates. The study interrogates part of the ATPase binding site (a.a 132-199) as it covers most of the naturally occurring mutations in GyrB. The following results were obtained: for Arg-136 two isolates had mutations, the first is isolate-1 (Ala-136), and the second is isolate-5 (Cys-136). Gly-164 had no changes for all tested isolates. For Thr-165 only isolate-3 had a change to Ser-165. Accuracy of sequence translation was checked by sequencing both CFT073 and MG1655. The current study presents novel mutations in the GyrB24 subdomain of the gyrase enzyme. These new mutations showed normal enzyme activity (no reduction in ATPase functions) indicating that they might be a result of GyrB interaction with ATP analog molecules rather than antibacterial agents such as coumarins. Furthermore, our findings are supporting the idea that mutations in the GyrB24 would require synchronization with the efflux pumps to maintain antibiotic resistance against coumarins.