Excessive use of enrofloxacin leads to growth inhibition of juvenile giant freshwater prawn Macrobrachium rosenbergii

Dynamic impacts of short-term bath administration of enrofloxacin on juvenile black seabream Acanthopagrus schlegelii

Dynamic impacts of short-term enrofloxacin (ENR) exposure on juvenile marine fish are not well understood, and the underlying mechanisms remain unclear. We therefore investigated the accumulation and elimination of ENR in the liver of juvenile black seabream Acanthopagrus schlegelii. Meanwhile, the dynamic alterations of biochemical parameters and liver transcriptomes after short-term bath immersion and withdrawal treatment were explored. The results indicated that the contents of ENR in the liver were significantly increased after bath administration for 24 h, and then quickly declined to very low concentrations along with the decontamination time increasing. Judging from the changes in biochemical indicators and liver transcriptomic alterations, 0.5 and 1 mg/L ENR exposure for 24 h triggered oxidative stress, impairment of immune system, as well as aberrant lipid metabolism via differential molecular pathways. Interestingly, biochemical and transcriptome analysis as well as integrated biomarker response (IBR) values showed that more significant changes appeared in 1 mg/L ENR group at decontamination periods, which indicated that the impact of high dose ENR on juvenile A. schlegelii may persist even after depuration for 7 days. These results revealed that the risk of short-term bath of 1 mg/L ENR should not be overlooked even after depuration period. Therefore, attention should be paid to the dosage control when administering the drug to juvenile A. schlegelii, and the restoration of physiological disturbance may be an important factor in formulating a reasonable treatment plan.

Fluoroquinolone antibiotics in the aquatic environment: environmental distribution, the research status and eco-toxicity

The increasing presence of fluoroquinolone (FQ) antibiotics in aquatic environments is a growing concern due to their widespread use, negatively impacting aquatic organisms. This paper provides an overview of the environmental distribution, sources, fate, and both single and mixed toxicity of FQ antibiotics in aquatic environments. It also examines the accumulation of FQ antibiotics in aquatic organisms and their transfer into the human body through the food chain. The study identifies critical factors such as metabolism characteristics, physiochemical characteristics, light, temperature, dissolved oxygen, and environmental compatibility that influence the presence of FQ antibiotics in aquatic environments. Mixed pollutants of FQ antibiotics pose significant risks to the ecological environment. Additionally, the paper critically discusses advanced treatment technologies designed to remove FQ antibiotics from wastewater, focusing on advanced oxidation processes (AOPs) and electrochemical advanced oxidation processes (EAOPs). The discussion also includes the benefits and limitations of these technologies in degrading FQ antibiotics in wastewater treatment plants. The paper concludes by proposing new approaches for regulating and controlling FQ antibiotics to aid in the development of ecological protection measures.

A Review on Fluoroquinolones' Toxicity to Freshwater Organisms and a Risk Assessment

Fluoroquinolones (FQs) have achieved significant success in both human and veterinary medicine. However, regulatory authorities have recommended limiting their use, firstly because they can have disabling side effects; secondly, because of the need to limit the spread of antibiotic resistance. This review addresses another concerning consequence of the excessive use of FQs: the freshwater environments contamination and the impact on non-target organisms. Here, an overview of the highest concentrations found in Europe, Asia, and the USA is provided, the sensitivity of various taxa is presented through a comparison of the lowest EC50s from about a hundred acute toxicity tests, and primary mechanisms of FQ toxicity are described. A risk assessment is conducted based on the estimation of the Predicted No Effect Concentration (PNEC). This is calculated traditionally and, in a more contemporary manner, by constructing a normalized Species Sensitivity Distribution curve. The lowest individual HC5 (6.52 µg L-1) was obtained for levofloxacin, followed by ciprofloxacin (7.51 µg L-1), sarafloxacin and clinafloxacin (12.23 µg L-1), and ofloxacin (17.12 µg L-1). By comparing the calculated PNEC with detected concentrations, it is evident that the risk cannot be denied: the potential impact of FQs on freshwater ecosystems is a further reason to minimize their use.

Characterization and removal mechanism of fluoroquinolone-bioremediation by fungus Cladosporium cladosporioides 11 isolated from aquacultural sediments

Antibiotics have been widely detected in aquatic environments, and fungal biotransformation receives considerable attention for antibiotic bioremediation. Here, a fungus designated Cladosporium cladosporioides 11 (CC11) with effective capacity to biotransform fluoroquinolones was isolated from aquaculture pond sediments. Enrofloxacin (ENR), ciprofloxacin (CIP) and ofloxacin (OFL) were considerably abated by CC11, and the antibacterial activities of the fluoroquinolones reduced significantly after CC11 treatment. Transcriptome analysis showed the removal of ENR, CIP and OFL by CC11 is a process of enzymatic degradation and biosorption which consists well with ligninolytic enzyme activities and sorption experiments under the same conditions. Additionally, CC11 significantly removed ENR in zebrafish culture water and reduced the residue of ENR in zebrafish. All these results evidenced the potential of CC11 as a novel environmentally friendly process for the removal of fluoroquinolones from aqueous systems and reduce fluoroquinolone residues in aquatic organisms.

Cefotaxime Exposure-Caused Oxidative Stress, Intestinal Damage and Gut Microbial Disruption in Artemia sinica

Cefotaxime (CTX) is an easily detectable antibiotic pollutant in the water environment, but little is known about its toxic effects on aquatic invertebrates, especially on the intestine. Here, we determined the oxidative stress conditions of A. sinica under CTX exposure with five concentrations (0, 0.001, 0.01, 0.1 and 1 mg/L) for 14 days. After that, we focused on changes in intestinal tissue morphology and gut microbiota in A. sinica caused by CTX exposure at 0.01 mg/L. We found malondialdehyde (MDA) was elevated in CTX treatment groups, suggesting the obvious antibiotic-induced oxidative stress. We also found CTX exposure at 0.01 mg/L decreased the villus height and muscularis thickness in gut tissue. The 16S rRNA gene analysis indicated that CTX exposure reshaped the gut microbiota diversity and community composition. Proteobacteria, Actinobacteriota and Bacteroidota were the most widely represented phyla in A. sinica gut. The exposure to CTX led to the absence of Verrucomicrobia in dominant phyla and an increase in Bacteroidota abundance. At the genus level, eleven genera with an abundance greater than 0.1% exhibited statistically significant differences among groups. Furthermore, changes in gut microbiota composition were accompanied by modifications in gut microbiota functions, with an up-regulation in amino acid and drug metabolism functions and a down-regulation in xenobiotic biodegradation and lipid metabolism-related functions under CTX exposure. Overall, our study enhances our understanding of the intestinal damage and microbiota disorder caused by the cefotaxime pollutant in aquatic invertebrates, which would provide guidance for healthy aquaculture.

The effects of enrofloxacin exposure on responses to oxidative stress, intestinal structure and intestinal microbiome community of largemouth bass (Micropterus salmoides)

Antibiotic residues in the aquaculture environments may lead to antibiotic resistance, and potentially exert adverse effects on health of the non-target organisms and humans. In order to evaluate the effect of enrofloxacin of environmental concentrations on largemouth bass (Micropterus salmoides). Two hundred and seventy largemouth basses (with an average weight of 7.88 ± 0.60 g) were randomly divided into three groups, and separately exposed to 0, 1, 100 μg/L enrofloxacin (Control, ENR1, ENR100) for 30 days to detect the effect of enrofloxacin on the growth performance, oxidative stress, intestinal microbiota structure, inflammatory response and structure of the intestine. The results showed that ENR significantly reduced the final body weight (FBW) and weight gain rate (WGR), and increased feed conversion ratio (FCR) (P < 0.05). The histopathological analysis revealed that the villus width and muscular thickness of anterior intestine were significantly decreased with the increasing of enrofloxacin concentration. The activity of SOD was significantly increased at enrofloxacin stress, while CAT and POD activity were significantly decreased compared to control group (P < 0.05). The activities of lysozyme (LZM), alkaline phosphatase (AKP) and peroxidase (POD) in ENR1 was higher than that of control and ENR100 groups. Enrofloxacin treatment up-regulated the expression IL-1β and TNF-α, and down-regulated IL-10, and decreasing the expression level ZO-1, claudin-1, and occludin. Furthermore, the enrofloxacin treatment significantly decreased the intestinal bacterial diversity (P < 0.05). Exposure to 100 μg/L enrofloxacin obviously increased the relative abundance of Bacteroidota, Myxococcota, and Zixibacteria of fish gut, and reduced Firmicutes; 1 μg/L enrofloxacin considerably increased Bacteroidota, Myxococcota, and Actinobacteria, and reduced Firmicutes. The relative abundance of DTB120 and Elusimicrobiota was positively correlated with the occludin and claudin-1 gene. Taken together, exposure to enrofloxacin inhibited the growth of largemouth bass, influenced intestinal health, and induced dysbiosis of the intestinal microbiota.

Disruption of sex steroid hormones biosynthesis by short-term enrofloxacin antibiotic exposure in Carassius auratus var. Pengze

BACKGROUND

It has been reported that antibiotic enrofloxacin can impair reproductive function of mammals, induces multi-generational oscillatory effects on reproduction of Caenorhabditis elegans, and disturbes endocrine system in grass carp.

OBJECTIVES

This study aims to explore the effect of short-term enrofloxacin exposure on sex steroid hormones biosynthesis in Carassius auratus var. Pengze through assessing the contents of growth hormone (GH), thyroid hormone 4 (T4), estradiol (E2) and testosterone (T) in plasma, and investigating sex steroid hormones biosynthesis based on targeted metabonomics analysis, and determining expression level of some important genes, gonadotropin-releasing hormone (gnrh), gonadotropin hormone 1-β (gth1-β), gonadotropin hormone 2-β (gth2-β) and cyp19a1a in hypothalamus-pituitary-ovary axis (HPOA).

RESULTS

We found that short-term exposure of enrofloxacin disordered contents of E2 and T in plasma of fish determined by ELISA detection, T content elevation and E2 content decline, which was confirmed by the following data from targeted metabonomics analysis of plasma. The metabonomic results showed that both T and its upstream intermediate products during the process of sex steroid hormones biosynthesis in fish were increased significantly, but E2 content was decreased markedly. At the exposure 24 h of enrofloxacin, expression of gnrh in hypothalamus, gth1-β and gth2-β in pituitary were promoted. Meanwhile GH and T4 contents in plasma, two inducers of sex steroid hormones synthesis, were augmented, which indicated that sex steroid hormones biosynthesis was improved. However cyp19a1a expression in ovary was repressed, and content of estriol (E3) was upregulated. These data suggested that enrofloxacin promoted sex steroid hormones biosynthesis and conversion of E2 to estriol (E3), but inhibited the conversion of T to E2. Finally, content of E2 was declined sharply.

DISCUSSION

Animal specific antibacterial enrofloxacin is widely detectable in aquatic ecosystem, exposure of the agent can induce adverse effects on plants and animals. This study firstly evidenced induction of disruption of sex steroid hormones by enrofloxacin in fish, which indicates enrofloxacin is an endocrine disruption compound that can induce endocrine disruption of animals, including fish.

Enrofloxacin (ENR) exposure induces lipotoxicity by promoting mitochondrial fragmentation via dephosphorylation of DRP1 at S627 site

Enrofloxacin (ENR) is a kind of widespread hazardous pollutant on aquatic ecosystems and causes toxic effects, such as disorders of metabolism, on aquatic animals. However, its potential mechanisms at an environmental concentration on metabolic disorders of aquatic organisms remain unclear. Herin, we found that hepatic lipotoxicity was induced by ENR exposure, which led to ENR accumulation, oxidative stress, mitochondrial fragmentation, and fatty acid transfer blockage from lipid droplets into fragmented mitochondria. ENR-induced lipotoxicity and mitochondrial β-oxidation down-regulation were mediated by reactive oxygen species (ROS). Moreover, dynamin-like protein 1 (DRP1) mediated ENR-induced mitochondrial fragmentation and changes of lipid metabolism. Mechanistically, ENR induced increment of DRP1 mitochondrial localization via dephosphorylating DRP1 at S627 and promoted its interaction with mitochondrial fission factor (MFF), leading to mitochondria fragmentation. For the first time, our study provides an innovative mechanistic link between hepatic lipotoxicity and mitochondrial fragmentation under ENR exposure, and thus identifies previously unknown mechanisms for the direct relationship between environmental ENR concentration and lipotoxicity in aquatic animals. Our study provides innovative insights for toxicological mechanisms and environmental risk assessments of antibiotics in aquatic environment.

The Research Status, Potential Hazards and Toxicological Mechanisms of Fluoroquinolone Antibiotics in the Environment

Fluoroquinolone antibiotics are widely used in human and veterinary medicine and are ubiquitous in the environment worldwide. This paper recapitulates the occurrence, fate, and ecotoxicity of fluoroquinolone antibiotics in various environmental media. The toxicity effect is reviewed based on in vitro and in vivo experiments referring to many organisms, such as microorganisms, cells, higher plants, and land and aquatic animals. Furthermore, a comparison of the various toxicology mechanisms of fluoroquinolone antibiotic residues on environmental organisms is made. This study identifies gaps in the investigation of the toxic effects of fluoroquinolone antibiotics and mixtures of multiple fluoroquinolone antibiotics on target and nontarget organisms. The study of the process of natural transformation toward drug-resistant bacteria is also recognized as a knowledge gap. This review also details the combined toxicity effect of fluoroquinolone antibiotics and other chemicals on organisms and the adsorption capacity in various environmental matrices, and the scarcity of data on the ecological toxicology evaluation system of fluoroquinolone antibiotics is identified. The present study entails a critical review of the literature providing guidelines for the government to control the discharge of pollutants into the environment and formulate policy coordination. Future study work should focus on developing a standardized research methodology for fluoroquinolone antibiotics to guide enterprises in the design and production of drugs with high environmental biocompatibility.

Transcriptomic analysis of lipid metabolism in zebrafish offspring of parental long-term exposure to bisphenol A

Bisphenol A (BPA) is one of the most common environmental endocrine disruptor chemicals (EDCs) and exhibits reproductive, cardiovascular, immune, and neurodevelopmental toxic effects. The development of the offspring was examined in the present investigation to determine the cross-generational effects of long-term exposure of parental zebrafish to environmental concentrations of BPA (15 and 225 µg/L). Parents were exposed to BPA for 120 days, and their offspring were evaluated at 7 days after fertilization in BPA-free water. The offspring exhibited higher mortality, deformity, and heart rates, and showed significant fat accumulation in abdominal region. RNA-Seq data showed that more lipid metabolism-related KEGG pathways, such as the PPAR signaling pathway, adipocytokine signaling pathway, and ether lipid metabolism pathway were enriched in the 225 µg/L BPA-treated offspring compared to 15 µg/L BPA-treated offspring, indicating greater effects of high dose BPA on offspring lipid metabolism. Lipid metabolism-related genes implied that BPA is responsible for disrupting lipid metabolic processes in the offspring through increased lipid production, abnormal transport, and disruption of lipid catabolism. The present study will be helpful for further evaluation of the reproductive toxicity of environmental BPA to organisms and the subsequent parent-mediated intergenerational toxicity.

Effects of Florfenicol on Intestinal Histology, Apoptosis and Gut Microbiota of Chinese Mitten Crab (Eriocheir sinensis)

Excessive use of antibiotics in aquaculture causes residues in aquatic animal products and harms human health. However, knowledge of florfenicol (FF) toxicology on gut health and microbiota and their resulting relationships in economic freshwater crustaceans is scarce. Here, we first investigated the influence of FF on the intestinal health of Chinese mitten crabs, and then explored the role of bacterial community in FF-induced intestinal antioxidation system and intestinal homeostasis dysbiosis. A total of 120 male crabs (48.5 ± 4.5 g) were experimentally treated in four different concentrations of FF (0, 0.5, 5 and 50 μg/L) for 14 days. Responses of antioxidant defenses and changes of gut microbiota were assessed in the intestine. Results revealed that FF exposure induced significant histological morphology variation. FF exposure also enhanced immune and apoptosis characteristics in the intestine after 7 days. Moreover, antioxidant enzyme catalase activities showed a similar pattern. The intestinal microbiota community was analyzed based on full-length 16S rRNA sequencing. Only the high concentration group showed a marked decrease in microbial diversity and change in its composition after 14 days of exposure. Relative abundance of beneficial genera increased on day 14. These findings illustrate that exposure to FF could cause intestinal dysfunction and gut microbiota dysbiosis in Chinese mitten crabs, which provides new insights into the relationship between gut health and gut microbiota in invertebrates following exposure to persistent antibiotics pollutants.

Ecotoxicological effect of enrofloxacin on Spirulina platensis and the corresponding detoxification mechanism

Enrofloxacin is a widely used antibiotic targeting DNA gyrase and has become the commonly detected micropollutant in aquatic environments. Thus, the potential toxicity of enrofloxacin to Spirulina platensis which is a kind of prokaryote similar to Gram-negative bacteria has been hypothesized. However, little is known about the toxicity and degradation mechanism of enrofloxacin during the growth process of Spirulina platensis. Herein, the biomass accumulation of Spirulina platensis was stimulated to 115% of the control group by 0.1 mg L^-1 enrofloxacin (10th day), which could be removed probably through the metabolism. Further increasing the enrofloxacin level to 5.0 mg L^-1 almost inhibited the growth and remediation ability of Spirulina platensis for 35 days. Environmental stress also caused the variations of photosynthetic pigments (chlorophyll a and carotenoids) and primary biocomponents (proteins, lipids, and carbohydrates), reflecting the adaptation of Spirulina platensis for handling the negative effects of enrofloxacin. The detoxification mechanism was studied by identifying the degradation products of enrofloxacin, suggesting the occurrence of dealkylation and oxidation reactions primarily at the piperazine group. The decreased antimicrobial activity was confirmed by the reduced binding affinity of degradation products with enzymes. The obtained results could help us understand the role of enrofloxacin in the growth of Spirulina platensis, thus providing great support for employing Spirulina platensis in risk assessment and hazard reduction.

Virome Analysis of Normal and Growth Retardation Disease-Affected Macrobrachium rosenbergii

The giant freshwater prawn, Macrobrachium rosenbergii, is an important aquaculture species in China. Growth retardation disease (GRD) is a common contagious disease in M. rosenbergii, resulting in slow growth and precocious puberty in prawns, and has caused growing economic losses in the M. rosenbergii industry. To investigate the viral diversity of M. rosenbergii and identify potentially high-risk viruses linked to GRD, virome analysis of the GRD-affected and normal M. rosenbergii was carried out using next-generation sequencing (NGS). A total of 327 contigs (>500 bp) were related to viral sequences belonging to 23 families/orders and a group of unclassified viruses. The majority of the viral contigs in M. rosenbergii belonged to the order Picornavirales, with the Solinviviridae family being the most abundant in both the diseased and normal groups. Furthermore, 16 RNA viral sequences with nearly complete genomes were characterized and phylogenetically analyzed, belonging to the families Solinviviridae, Flaviviridae, Polycipiviridae, Marnaviridae, and Dicistroviridae as well as three new clades of the order Picornavirales. Notably, the cross-species transmission of a picorna-like virus was observed between M. rosenbergii and plants. The "core virome" seemed to be present in the diseased and normal prawns. Still, a clear difference in viral abundance was observed between the two groups. These results showed that the broad diversity of viruses is present in M. rosenbergii and that the association between viruses and disease of M. rosenbergii needs to be further investigated. IMPORTANCE Growth retardation disease (GRD) has seriously affected the development and economic growth of the M. rosenbergii aquaculture industry. Our virome analysis showed that diverse viral sequences were present in M. rosenbergii, significantly expanding our knowledge of viral diversity in M. rosenbergii. Some differences in viral composition were noted between the diseased and normal prawns, indicating that some viruses become more abundant in occurrences or outbreaks of diseases. In the future, more research will be needed to determine which viruses pose a risk for M. rosenbergii. Our study provides important baseline information contributing to disease surveillance and risk assessment in M. rosenbergii aquaculture.

Long-term BPA exposure leads to bone malformation and abnormal expression of MAPK/Wnt/FoxO signaling pathway genes in zebrafish offspring

Bisphenol A (BPA) is one of the world's most widely used plasticizer, and its hazardous impacts have been well studied. However, few studies focused on the effects of parental long-term BPA exposure on the bone development of offspring. In the present study, the bone development of offspring was studied following long-term exposure of parental zebrafish to environmentally relevant 15 and 225 µg/L BPA. The results showed that BPA increased the mortality and deformity rate of offspring and caused craniofacial deformities characterized by changes in various cartilage angles and lengths. The alizarin red and calcein staining showed that BPA could delay bone mineralization and reduce bone mass accumulation. The results of acridine orange staining indicated that BPA induced apoptosis of the skull. The degree of harm of BPA presented a dose-dependent pattern. The results of the comparative transcriptome showed that there were 380 different expression genes (DEGs) in the 15 µg/L BPA group, and 645 DEGs in the 225 µg/L BPA group. MAPK/Wnt/FoxO signaling pathway-related genes were significantly down-regulated in the BPA-exposed groups. The present study demonstrates that long-term parental BPA exposure would severely affect cartilage development and bone mineralization of fish offspring, and MAPK/Wnt/FoxO signaling pathways may be involved in this process.

Cytotoxicity and apoptosis induced by enrofloxacin in loach fin cells in vitro

The cytotoxic effect and cell death were studied in loach fin cells in vitro after enrofloxacin (ENR) exposure. The semi-lethal concentration of ENR for loach cells was calculated as 1296.2 ± 3.11 mol/L (about 512.5 mg/L). Loss of cell viability, increase in vacuoles, disappearance of microvilli, and apoptotic bodies were evident in cells exposed to 400, 800, and 1200 μmol/L ENR. Besides, dose-dependent inhibitory effects on SOD, CAT, Na⁺-K⁺-ATPase, and Ca²⁺-ATPase activities were also observed in loach cells exposed to ENR. Quantitative gene expression results showed that ENR induced caspase-3- and caspase-8-mediated apoptosis as well as caspase-activated DNase in loach cells. The findings also indicated a role of JNK pathway in ENR-induced apoptosis in loach cells. Transcriptome sequencing results showed 10,016 differentially expressed genes in ENR vs. control groups, which were all enriched in "Molecular Function" process in GO term. Furthermore, 6763 genes were enriched in 291 KEEG pathways, with most of them belonging to immune and material metabolic pathways. The large number of transcriptome data and pathways determined in this study provide a database foundation for the toxicity analysis of ENR in loach cells, which must be thoroughly examined to further investigate the cytotoxic mechanism of antibiotics in fish cells.

A Novel Disease (Water Bubble Disease) of the Giant Freshwater Prawn Macrobrachium rosenbergii Caused by Citrobacter freundii: Antibiotic Treatment and Effects on the Antioxidant Enzyme Activity and Immune Responses

The giant freshwater prawn, Macrobrachium rosenbergii, is an important and economical aquaculture species widely farmed in tropical and subtropical areas of the world. A new disease, "water bubble disease (WBD)", has emerged and resulted in a large loss of M. rosenbergii cultured in China. A water bubble with a diameter of about 7 mm under the carapace represents the main clinical sign of diseased prawns. In the present study, Citrobacter freundii was isolated and identified from the water bubble. The optimum temperature, pH, and salinity of the C. freundii were 32 °C, 6, and 1%, respectively. A challenging experiment showed that C. freundii caused the same typical signs of WBD in prawns. Median lethal dose of the C. freundii to prawn was 104.94 CFU/g. According to the antibiogram tests of C. freundii, florfenicol and ofloxacin were selected to evaluate their therapeutic effects against C. freundii in prawn. After the challenge with C. freundii, 86.67% and 72.22% survival of protective effects against C. freundii were evaluated in the oral florfenicol pellets and oral ofloxacin pellets feding prawns, respectively, whereas the mortality of prawns without fed antibiotics was 93%. After antibiotic treatment and C. freundii infection, the activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione S-transferase (GST), malondialdehyde (MDA), acid phosphatase (ACP), alkaline phosphatase (ALP), and lysozyme (LZM) in the hemolymph and hepatopancreas of the prawns and the immune-related gene expression levels of Cu/Zn-SOD, CAT, GPx, GST, LZM, ACP, anti-lipopolysaccharide factor, crustin, cyclophilin A, and C-type lectin in hepatopancreas were all significantly changed, indicating that innate immune responses were induced by C. freundii. These results can be beneficial for the prevention and control of C. freundii in prawns.

Exposure to enrofloxacin and depuration: Endocrine disrupting effect in juvenile grass carp (Ctenopharyngodon idella)

This study aimed to determine the effects of Enrofloxacin (ENR) exposure and depuration on the disruption of thyroid function and growth of juvenile grass carp (Ctenopharyngodon idella) as well as to assess the risk of ENR exposure to human health. Juvenile grass carp were treated with ENR solutions at different concentration gradients for 21 days and then depurated for 14 days. The results indicated ENR accumulation in the juvenile grass carp muscles, which persisted after depuration. In addition, exposure to ENR could alter growth by regulating the expression of genes associated with growth hormone/insulin-like growth factor (GH)/IGF) axis and the hypothalamic-pituitary-thyroid (HPT) axis. During ENR exposure, no significant changes in growth hormone levels were observed; however, a significant increase in the growth hormone level was noted. GH/IGF axis-related genes were upregulated after ENR exposure, and their expression levels remained high after depuration. Notably, a significant increase in the serum triiodothyronine (T3) and thyroxine (T4) levels coincided with the upregulation of HPT axis-related genes in both exposure and depuration treatments, and their expression levels remained high after depuration. Therefore, juvenile grass carp exposure to ENR induces physiological stress through HPT and GH/IGF axes that cannot be recovered after depuration. ENR accumulates in the muscles of juvenile grass carp and may pose a threat to human health. Therefore, exposure of juvenile grass carp to ENR results in impaired thyroid function and impaired growth. In addition, consumption of ENR-exposed fish poses human health risks.

Enrofloxacin—The Ruthless Killer of Eukaryotic Cells or the Last Hope in the Fight against Bacterial Infections?

Enrofloxacin is a compound that originates from a group of fluoroquinolones that is widely used in veterinary medicine as an antibacterial agent (this antibiotic is not approved for use as a drug in humans). It reveals strong antibiotic activity against both Gram-positive and Gram-negative bacteria, mainly due to the inhibition of bacterial gyrase and topoisomerase IV enzymatic actions. The high efficacy of this molecule has been demonstrated in the treatment of various animals on farms and other locations. However, the use of enrofloxacin causes severe adverse effects, including skeletal, reproductive, immune, and digestive disorders. In this review article, we present in detail and discuss the advantageous and disadvantageous properties of enrofloxacin, showing the benefits and risks of the use of this compound in veterinary medicine. Animal health and the environmental effects of this stable antibiotic (with half-life as long as 3–9 years in various natural environments) are analyzed, as are the interesting properties of this molecule that are expressed when present in complexes with metals. Recommendations for further research on enrofloxacin are also proposed.

Toxicity induced by ciprofloxacin and enrofloxacin: oxidative stress and metabolism

Ciprofloxacin (CIP) (human use) and enrofloxacin (ENR) (veterinary use) are synthetic anti-infectious medications that belong to the second generation of fluoroquinolones. They have a wide antimicrobial spectrum and strong bactericidal effects at very low concentrations via enzymatic inhibition of DNA gyrase and topoisomerase IV, which are required for DNA replication. They also have high bioavailability, rapid absorption with favorable pharmacokinetics and excellent tissue penetration, including cerebral spinal fluid. These features have made them the most applied antibiotics in both human and veterinary medicine. ENR is marketed exclusively for animal medicine and has been widely used as a therapeutic veterinary antibiotic, resulting in its residue in edible tissues and aquatic environments, as well as the development of resistance and toxicity. Estimation of the risks to humans due to antimicrobial resistance produced by CIP and ENR is important and of great interest. Moreover, in rare cases due to their overdose and/or prolonged administration, the development of CIP and ENR toxicity may occur. The toxicity of these fluoroquinolones antimicrobials is mainly related to reactive oxygen species (ROS) and oxidative stress (OS) generation, besides metabolism-related toxicity. Therefore, CIP is restricted in pregnant and lactating women, pediatrics and elderly similarly ENR do in the veterinary field. This review manuscript aims to identify the toxicity induced by ROS and OS as a common sequel of CIP and ENR. Furthermore, their metabolism and the role of metabolizing enzymes were reported.

Novel electrochemical sensor modified with molecularly imprinted polymers for determination of enrofloxacin in marine environment

Molecularly imprinted polymers were synthesized by gel-sol method with multi-walled carbon nanotubes as support and enrofloxacin as a template and further modified on the surface of glassy carbon electrode to construct a molecularly imprinted electrochemical sensor. The performance of the imprinted electrochemical sensor was thoroughly investigated by using cyclic voltammetry and differential pulse voltammetry. The influence of imprinted polymers amount, electrolyte pH, and incubation time on the sensor performance was investigated for the detection of enrofloxacin. Under the optimal experimental conditions in a three-electrode system with the modified electrode as the working electrode the differential pulse voltammetry response current of the sensor had a good linear relationship at 0.2 V (vs. saturated calomel reference electrode) with the enrofloxacin concentration within 2.8 pM-28 μM and the limit of detection of the method was 0.9 pM. The competitive interference experiment showed that the imprinted electrochemical sensor could selectively recognize enrofloxacin. The method was applied to analyze spiked natural seawater, fish, and shrimp samples. The recovery was 96.4%-102%, and RSD was less than 4.3% (n = 3), indicating that the proposed imprinted electrochemical sensor was suitable for the determination of trace enrofloxacin in marine environment samples.

Occurrence of antibiotics and antibiotic resistance genes in cultured prawns from rice-prawn co-culture and prawn monoculture systems in China

Antibiotics and antibiotic resistance genes (ARGs) in the aquatic environment have raised great concerns, as the deleterious effects of residual antibiotics and the emergence of ARGs are challenges to aquaculture. This study analyzed feed, water, sediment and prawns' tissues from six culture ponds (integrated culture: rice-prawn pond; monoculture: prawn pond) in Tianjin, Northeast China. Eighteen types of antibiotics were detected in all ponds, which conferring to four classes of antibiotics including sulfonamides, tetracyclines, fluoroquinolones, macrolides. The mean log bioaccumulation factor (BAF) values for five antibiotics were analyzed in the hepatopancreas, muscle, and plasma, and we found the maximum Log BAF (1.45) for enrofloxacin in prawn plasma. Correlation analysis of antibiotic concentrations between the plasma and the other two tissues indicated that enrofloxacin, norfloxacin, and erythromycin levels in the hepatopancreas and muscle can be predicted by their plasma concentrations. We also conducted a hazard quotient analysis and found that the risk to human health of eating antibiotic-exposed prawns from the two types of aquaculture method was relatively low. Compared with monoculture, rice-prawn co-culture could significantly decrease the abundance of ARGs; additionally, significant correlations were detected among ARGs, antibiotics, and non-antibiotic environmental factors (e.g., total nitrogen, total ammonia nitrogen, and chemical oxygen demand) in prawn. The present study indicated that the rice-prawn co-culture system is more effective than monoculture for mitigating the bioaccumulation of antibiotics and the occurrence of ARGs in prawn.

Multi-generational effects of enrofloxacin on lifespan and reproduction of Caenorhabditis elegans with SKN-1-mediated antioxidant responses and lipid metabolism disturbances

Antibiotics are ubiquitous environmental pollutants and they can provoke multi-generational impacts due to their pseudo-persistence. However, their multi-generational effects and potential mechanisms remained poorly studied. Presently, effects of enrofloxacin (ENR) were studied on Caenorhabditis elegans with a continuous exposure over 9 generations (from F1 to F9) at an environmentally realistic level. Regarding reproduction, ENR showed stimulation in F1 (1.18-fold of the control) and F2 (1.08), inhibition in F3 (0.70), stimulation in F4 (1.86), F5 (3.18) and F6 (1.53), inhibition in F7 (0.73) and F8 (0.69) and stimulation again in F9 (1.89). That is to say, ENR provoked multi-generational oscillatory effects on the reproduction. Such oscillation was also observed in effects on lifespan with much less magnitudes than those on reproduction. Biochemical assays were performed in F1, F3, F4 and F9 which represented the oscillation over generations. Results showed more antioxidants (e.g., superoxide dismutase and glutathione), mild oxidative stress (e.g., reactive oxygen species) and less oxidative damage (i.e., protein carbonyl) underlying the generation-dependent stimulation. Moreover, ENR provoked multi-generational oscillation on the enzymes that regulate the lipogenesis (e.g., fatty acid synthase and acetyl-CoA carboxylase) and lipolysis (e.g., acyl-CoA synthetase), with similarities to the effects on the oxidative stress and damage. Further analysis on SKN-1 and its activating PMK-1 and GSK-3 demonstrated their involvement in regulating both antioxidant detoxification and lipid metabolism.

Characteristics of tylosin and enrofloxacin degradation in swine manure digested by black soldier fly (Hermetia illucens L.) larvae

Black soldier fly, Hermetia illucens L. (Diptera: Stratiomyidae) larvae (BSF larvae or BSFL) offer an environmental-friendly method for degrading antibiotics, such as tylosin (TYL) and enrofloxacin (EF), in swine manure. This study examined the impact of temperature on this process, role of associated microbes, dynamics of resistant genes, and a description of the microbial community associated with the BSF larval gut, how microbes isolated from the BSF larval gut as inoculants impact the process as well as enhance antibiotic digestion, and finally a quantification of antibiotics in BSF larvae fed manure with TYL or EF. Antibiotic degradation in manure was optimized at 28 °C with at least 10% greater than 23 °C and 37 °C. More than 40% reduction in TYL and EF concentrations in the manure occurred when BSF larval gut associated microbes were present. Furthermore, DNA extracted from the gut of non-sterile BSF larvae fed manure with TYL or EF indicated at least two 2^-△△Ct fold increase in antibiotic resistance genes for TYL and EF. We identified 250, 4, and 16 unique operational taxa for larvae fed control manure and manure with either TYL or EF. Intestinal microbes isolated from non-sterile larvae fed manure with TYL or EF, were identified, cultured, and examined for their ability to degrade TYL and EF in Luria-Bertani (LB) medium. Three strains (two strains of Enterococcus faecalis and one strain of Proteus mirabilis) resulted in at least 50% TYL or EF degradation within 96 h. Sterile BSF larvae inoculated with P. mirabilis recovered >60% of the degradation ability exhibited by non-sterile larvae. Finally, no TYL residuals were found in 14-d-old larvae, prepupae, or pupae of BSF immatures fed manure containing these antibiotics. While ∼65 μg/g and ∼20 μg/g of EF were found in larval contents and pupal exoskeleton, respectively.

Influence of chemical speciation on enrofloxacin degradation by UV irradiation: Kinetics, mechanism and disinfection by-products formation

Fluoroquinolones (FQs) were frequently detected in aqueous environment. The UV irradiation have been reported as an efficient method for FQs degradation. This study investigated the influence of chemical speciation on enrofloxacin (ENR) photolysis process by UV irradiation. The results showed that chemical speciation of ENR significantly affected the photodegradation kinetics, and the highest degradation rate was observed in the zwitterion form. Presence of natural organic matter (NOM) and inorganic anions had different degrees of influences on ENR photodegradation for three chemical speciation of ENR. The contribution of ¹O₂ on ENR degradation in neutral and alkalinity condition was significantly higher than that in acidic condition. The cation and zwitterion of ENR was beneficial to the formation of trichloromethane (TCM) and haloacetonitrile (HAN) during the chlorination alone. Compared with the chlorination of ENR, the UV pretreatment respectively caused 4.06-fold and 3.14-fold decrease in TCM formation at acidic and neutral reaction condition during subsequent chlorination. Also the decrease in HAN formation at neutral and alkalinity condition was found after UV treatment followed by chlorination. The UV pretreatment caused higher yield of HAN in the subsequent chlorination at acidic condition than that at neutral and alkalinity condition. Through the UV pretreatment at neutral condition, the generated concentration of halonitromethane (HNM) reached the maximum value during the subsequent chlorination. Potential toxic risk analysis showed the toxicity decreased in zwitterion form of ENR, while toxicity increased in cationic and anionic form after UV irradiation pretreatment.

Acute BPA exposure-induced oxidative stress, depressed immune genes expression and damage of hepatopancreas in red swamp crayfish Procambarus clarkii

Bisphenol A is a typical endocrine disrupting chemicals (EDCs) and produce various toxic effects on animals due to its potential endocrine disruption, oxidative damage effect, mutagenic effect and hypomethylation. To study its effect on the immune system of crustaceans, the Procambarus clarkii were utilized to detect the immune related indicators after 225 μg/L BPA exposure for 1 week. Hepatopancreatic histology and ultrastructure analysis showed that the brush border disappeared, the lumen increased, and the connection between the hepatic tubules fade away in BPA treated group. BPA could significantly increase the level of ROS, inhibit the activities of antioxidant-related enzymes (SOD, POD, and CAT), and thereby cause the oxidative stress. The enzyme activities of AKP, ACP and lysozyme in hepatopancreas after BPA exposure were also depressed even after Aeromonas hydrophila infections. The relative expression profiles of immune-related genes after BPA exposure and bacterial infection showed suppressed trends of most selected genes. Under A. hydrophila infections, the cumulative mortality of 225 μg/L BPA-treated crayfish was significantly higher than other groups. All these results indicated that BPA exposure had adverse effects on the immune ability of P. clarkii. The present study will provide an important foundation for further understanding the effects of EDCs on crustacean immune functions.

Chronic exposure to dietary antibiotics affects intestinal health and antibiotic resistance gene abundance in oriental river prawn (Macrobrachium nipponense), and provokes human health risk

Antibiotics are employed worldwide to treat diseases of humans and other animals, but most antibiotics and their secondary metabolites are discharged into the aquatic environment, and these pollutants are emerging as a severe threat to human health. However, the systematic effects of dietary antibiotics on intestinal health in crustaceans and the associated risk to human health have not been thoroughly investigated, especially the effects on growth, immune responses, intestinal health, and the abundance of antibiotic residues and antibiotic resistance genes (ARGs). In the present work, two typical antibiotics (sulfamethoxazole and oxytetracycline) were administered orally to juvenile oriental river prawn (Macrobrachium nipponense) for eight weeks to mimic long-term use of antibiotics at legal aquaculture doses. The results indicate that dietary exposure to antibiotics significantly inhibited the growth performance of prawns, suppressed immunological parameters, and caused higher mortality in prawns challenged with Aeromonas hydrophila. Furthermore, prawns fed a diet containing antibiotics displayed a decrease in the number of intestinal goblet cells and lower digestive enzyme activity, as well as impaired intestine antioxidant ability and immune responses. Additionally, redundancy analysis revealed that different dominant bacterial phyla were responsible for increased ARG abundance in the prawn intestinal tract between control and antibiotic diet groups. The health risks posed by antibiotic residues in prawn muscle were also evaluated. Our findings demonstrate the risk posed by long-term use of dietary antibiotics in prawns, and suggest that antibiotics should be administered more carefully during aquaculture.

Investigation of growth retardation in Macrobrachium rosenbergii based on genetic/epigenetic variation and molt performance

Giant freshwater prawn, Macrobrachium rosenbergii is an important freshwater aquaculture species worldwide, and China contributes the most to its global production. However, in recent years in China, many prawns have shown serious growth retardation, which is referred to as "iron prawn." To explore the mechanism behind this phenomenon, we compared the difference between these "iron prawns" and normal prawns in three aspects-changes in genetic diversity, DNA methylation, and transcriptomes-as well as comparing differences in their molt performance. The results are as follows: first, compared with normal prawns, "iron prawns" showed no significant decrease in genetic diversity, but they did show obvious genetic differentiation, and different DNA methylation levels were observed. The genetic and epigenetic variations that existed between "iron prawn" and normal prawn indicated the influence of germplasm on growth performance. Second, transcriptome analysis revealed 1813 differentially expressed genes (DEGs) between the "iron prawn" and normal prawn, and the DEGs mainly enriched the glucose metabolism- and immune-related pathways, such as in glycolysis/gluconeogenesis metabolism, insulin secretion, glucagon signaling pathway, antigen processing and presentation, as well as in complement and coagulation cascades. Enrichment analysis indicated the importance of the glucose level and pathogen attacks to growth performance in the "iron prawn." Finally, a comparison of the molt performance showed that the length of the molt cycle in the "iron prawn" was comparable to normal prawns with the same size, but the specific growth was much lower in the "iron prawn." This result suggested that lower body weight gain per molt cycle should be responsible for growth retardation in the "iron prawn," but not in the longer molt cycle. The results in this study provided fundamental information about the mechanism behind growth retardation in M. rosenbergii.