Aquaculture practices and potential human health risks: current knowledge and future priorities

An understated danger: Antimicrobial resistance in aquaculture and pet fish in Switzerland, a retrospective study from 2000 to 2017

Aquaculture is a rapidly growing field of food production. However, morbidity and mortality are higher in aquaculture species than in domestic animals. Bacterial diseases are a leading cause of farmed fish morbidity and are often treated with antimicrobials. Since most Swiss fish farms release effluents directly into surface water without treatment and since aquaculture fish are consumed by humans, antimicrobial resistance (AMR) and multi-resistance in aquaculture fish are important for environmental and public health. In this study, AMR tests for 14 antimicrobials were performed on 1,448 isolates from 1,134 diagnostic laboratory submissions from farmed and ornamental fish submissions for the period from 2000 to 2017. Amoxicillin, gentamycin and norfloxacin had the lowest proportion of resistant samples. However, AMR was highly variable over time. Resistance proportions were higher in: (a) ornamental fish compared with farmed fish, (b) fish from recirculation systems compared with those from other farming systems and (c) isolates originating from skin compared with those originating from inner organs. Multiple resistances were common. The results of this study provide useful data for Swiss fish veterinarians and some interesting hypotheses about risk factors for AMR in aquaculture and pet fish in Switzerland. However, further research is needed to define risk factors.

Occurrence, spatiotemporal variation, and ecological risk of antibiotics in the water of the semi-enclosed urbanized Jiaozhou Bay in eastern China

The occurrence, temporal variation, and spatial variation of antibiotics in coastal bays and estuaries worldwide are not well documented or understood. Fifteen target antibiotics within the five classes of β-lactams, amphenicols, macrolides, fluoroquinolones, and sulfonamides were measured during the summer and winter in the water of Jiaozhou Bay in China, which is a semi-enclosed urbanized bay. Fourteen antibiotics (excluding tylosin) were detected, thus demonstrating the widespread occurrence of their residues in the bay. The total antibiotic concentration ranged from 71.8 ng L^-1 to 840 ng L^-1 for the estuarine water, which was significantly higher than that for the bay water (38.7-181 ng L^-1). The antibiotic classes in the bay water were dominated by fluoroquinolones and β-lactams, which accounted for nearly 90% of the total antibiotic concentration. In addition, amoxicillin contamination was the most prominent among the 14 detected antibiotics as it accounted for ~44% of the total antibiotic concentration. The concentrations of amoxicillin, leucomycin, enrofloxacin, and sulfamonomethoxine in the bay water were usually higher than those reported for coastal bays and estuaries worldwide. The average total antibiotic concentration in the bay water was 84.7 ng L^-1 during the summer, which was significantly lower than that during the winter (129.0 ng L^-1). This was mainly due to high dilution by runoff during the summer. The florfenicol concentration in the bay water was significantly higher during the summer than in winter due to its higher usage in aquaculture during the summer. Spatially, the total antibiotic concentration (both summer and winter) was higher in the water along the eastern coast of the bay, where the population and hospital densities are high. However, the sum of the veterinary antibiotic concentrations was higher in the northeastern aquaculture area of the bay during the summer. A risk assessment revealed that amoxicillin and enrofloxacin could pose high risks (risk quotient of > 1) to algae in the bay. The synergic effects of pharmaceutical mixtures and the bioaccumulation of antibiotics through the food web should be considered in future studies.

Abdelhamid F, El-Mleeh A, Elmahallawy EK, Elsayed MM. Investigation of the Prevalence, Virulence Genes, and Antibiogram of Motile Aeromonads Isolated from Nile Tilapia Fish Farms in Egypt and Assessment of their Water Quality

The aquaculture industry is a fast-growing sector in Egypt; however, the progress of this industry is impeded by many challenges such as poor water quality and associated bacterial infections. Among others, Motile Aeromonas Septicemia (MAS), caused by aeromonads, is among the most important bacterial diseases affecting aquaculture due to its zoonotic potential. In the present work, motile aeromonads were isolated from water samples (n= 8) and Nile tilapia (n= 240) in four fish farms (farms I, II, III, and IV) in Kafr El-Sheikh province during the period March to August 2017. This step was followed by investigation of the prevalence and phenotypic, molecular, and histopathological characterization of aeromonads. In addition, antimicrobial susceptibility and virulence gene detection were analyzed. Interestingly, physicochemical water analysis revealed different ranges in relation to the fish farms and seasons. More importantly, Aeromonas isolates were phenotypically identified in 33.3% and 12.5% from fish and water samples, respectively. The highest prevalence of motile aeromonads (46.7%) was recorded from farm IV, and only 12.5% of water samples were positive for them. Out of 80 isolates, 65 (81.25%) were molecularly identified at the genus level using gyrase B (gyrB). The prevalence of the virulence genes detected in the isolated motile aeromonads was aerolysin (aer), 52.2%; elastase (ahp), 26.25%; hemolysin (hyl), 35%; and lipase (lip), 3.75%. The antibiogram profile revealed that the highest resistance of aeromonads isolates (80%) was recorded to chloramphenicol, kanamycin, and azithromycin. Meanwhile, lower resistance levels of 40%, 30%, and 20% were found for streptomycin, cefotaxime, and amoxicillin, respectively. The multiple antibiotic resistance (MAR) index values ranged between 0.27 and 0.82 of motile aeromonads isolates. Furthermore, the histopathological examinations of naturally diseased tilapia revealed widespread hepatocellular necrosis with diffuse, numerous rod-shaped bacteria in liver with melanomacrophages and lymphocytic depletion with edema and hemosiderosis in the spleen. Our findings provide an updated epidemiological baseline for future reference and highlight the likely role of the adverse impact of water quality in the outbreaks of motile aeromonads with special reference to virulence genes and antibiotic resistant traits.

A Hundred Years of Bacteriophages: Can Phages Replace Antibiotics in Agriculture and Aquaculture?

Agriculture, together with aquaculture, supplies most of the foodstuffs required by the world human population to survive. Hence, bacterial diseases affecting either agricultural crops, fish, or shellfish not only cause large economic losses to producers but can even create food shortages, resulting in malnutrition, or even famine, in vulnerable populations. Years of antibiotic use in the prevention and the treatment of these infections have greatly contributed to the emergence and the proliferation of multidrug-resistant bacteria. This review addresses the urgent need for alternative strategies for the use of antibiotics, focusing on the use of bacteriophages (phages) as biocontrol agents. Phages are viruses that specifically infect bacteria; they are highly host-specific and represent an environmentally-friendly alternative to antibiotics to control and kill pathogenic bacteria. The information evaluated here highlights the effectiveness of phages in the control of numerous major pathogens that affect both agriculture and aquaculture, with special emphasis on scientific and technological aspects still requiring further development to establish phagotherapy as a real universal alternative to antibiotic treatment.

Toward Sustainable Environmental Quality: Priority Research Questions for Asia

Environmental and human health challenges are pronounced in Asia, an exceptionally diverse and complex region where influences of global megatrends are extensive and numerous stresses to environmental quality exist. Identifying priorities necessary to engage grand challenges can be facilitated through horizon scanning exercises, and to this end we identified and examined 23 priority research questions needed to advance toward more sustainable environmental quality in Asia, as part of the Global Horizon Scanning Project. Advances in environmental toxicology, environmental chemistry, biological monitoring, and risk-assessment methodologies are necessary to address the adverse impacts of environmental stressors on ecosystem services and biodiversity, with Asia being home to numerous biodiversity hotspots. Intersections of the food-energy-water nexus are profound in Asia; innovative and aggressive technologies are necessary to provide clean water, ensure food safety, and stimulate energy efficiency, while improving ecological integrity and addressing legacy and emerging threats to public health and the environment, particularly with increased aquaculture production. Asia is the largest chemical-producing continent globally. Accordingly, sustainable and green chemistry and engineering present decided opportunities to stimulate innovation and realize a number of the United Nations Sustainable Development Goals. Engaging the priority research questions identified herein will require transdisciplinary coordination through existing and nontraditional partnerships within and among countries and sectors. Answering these questions will not be easy but is necessary to achieve more sustainable environmental quality in Asia. Environ Toxicol Chem 2020;39:1485-1505. © 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Social Acceptance of Aquaculture in Andalusian Atlantic Coast (Spain): An Emerging Economy Sector

Aquaculture is an important source of food. This document analyses its acceptance by consumers from the perspective of social carrying capacity. This concept determines the point at which its development begins to be excessive, and poses difficulties to its geographical area. In this context, our work is innovative, since, although Spain is the leading aquaculture producer in the European Union, not much research on this aspect has been developed. With this objective, we carried out 579 personal interviews with consumers from the Andalusian Atlantic coast (Spain), to determine an index of acceptance for this food and its industry. After applying a principal component analysis, we stratified the samples following Dalenius-Hodges method. According to our surveys, there is a high level of acceptance, which would place aquaculture far from its saturation point, the level at which this sector generates relevant problems for society in terms of economy or environment. Respondents also recommended its further development. Women and low-income consumers were the groups with the greatest reticence about this sector. We consider that general acceptance would be improved by implementing informative campaigns, especially for these groups, that would extend consumers’ knowledge and improve their perception of this kind of food.

A review of emerging organic contaminants (EOCs), antibiotic resistant bacteria (ARB), and antibiotic resistance genes (ARGs) in the environment: Increasing removal with wetlands and reducing environmental impacts

Emerging organic contaminants (EOCs) include a diverse group of chemical compounds, such as pharmaceuticals and personal care products (PPCPs), pesticides, hormones, surfactants, flame retardants and plasticizers. Many of these compounds are not significantly removed in conventional wastewater treatment plants and are discharged to the environment, presenting an increasing threat to both humans and natural ecosystems. Recently, antibiotics have received considerable attention due to growing microbial antibiotic-resistance in the environment. Constructed wetlands (CWs) have proven effective in removing many EOCs, including different antibiotics, before discharge of treated wastewater into the environment. Wastewater treatment systems that couple conventional treatment plants with constructed and natural wetlands offer a strategy to remove EOCs and reduce antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) far more efficiently than conventional treatment alone. This review presents as overview of the current knowledge on the efficiency of different wetland systems in reducing EOCs and antibiotic resistance.

Investigation of the Correlation between the Use of Antibiotics in Aquaculture Systems and Their Detection in Aquatic Environments: A Case Study of the Nera River Aquafarms in Italy

Antimicrobial resistance (AMR) arises mostly because of the use and abuse of antibiotics in both the human and veterinary sectors. Furthermore, antibiotic residues can be discharged into the environment, promoting the spread of AMR as well as becoming a potential ecotoxicological risk. Aquaculture is one such source of environmental pollution. In the present work, we evaluated the correlation between antibiotic consumption in 11 selected aquafarms located along the Nera River, and the detection of their residues in surface water and sediment samples gathered monthly from the same stream. Antibiotic consumption was calculated using the ESVAC defined daily doses for animals (DDDvet) method, and a chemical analysis was conducted using a multiclass method. Therefore, the ecological risk of antibiotics being detected in surface waters was established based on the risk quotient (RQ). A strong positive correlation was identified between the concentrations detected in surface waters and the consumption of flumequine (r = 72%, p-value = 0.0085) and florfenicol (r = 83%, p-value = 0.0008). The RQ, however, was low for all the detected antibiotics in surface waters. Therefore, we proved that the antibiotics used in aquaculture can reach the near aquatic environment, but, in this work, they did not represent a toxicological risk to the surrounding ecosystem.

Propagation of antibiotic resistance genes in an industrial recirculating aquaculture system located at northern China

The increasing prevalence and spread of antibiotic resistance genes (ARGs) in intensive aquaculture environments are of great concern to food safety and public health. However, the level of ARGs and their potential propagation factors in an industrial recirculating aquaculture system (RAS) have not previously been comprehensive explored. In this study, the levels of 14 different ARG markers and 2 kinds of mobile genetic elements (MGEs) were investigated in a RAS (including water, fish, feces, pellet feed meal, and biofilm samples) located northern China. qnrA, qnrB, qnrS, qepA, aac(6')-Ib, and floR were dominant ARGs, which average concentration levels were presented at 4.51-7.74 copies/L and 5.36-13.07 copies/g, respectively, suggesting that ARGs were prevalent in RAS with no recorded history of antibiotic use. Elevated level of ARGs was found in water of RAS even after the final UV treatment compared with its influent. In RAS, Proteobacteria, Verrucomicrobia, Bacteroidetes, and Planctomycetes were the predominant phyla. Notably, elevated levels of potential opportunistic pathogens were observed along with abundant ARGs suggesting an increasing risk of capturing ARGs and MGEs for human pathogens. This study has revealed for the first time that reared fish, their feces, pellet feed meal as the introduction sources and the selection roles of treatment units co-driven the ARG profile, and the co-selection of water environmental factors and their consequently induced bacterial community shifts formed by their influence are the determining drivers for the ARG propagation in RAS.

Efficacy of a Modified Health Assessment Utilized on Two Genetically Distinct Stocks of Rainbow Trout

The Rainbow Trout Oncorhynchus mykiss is a salmonid fish that is maintained in aquaculture facilities and used as a source of protein around the world. Veterinarians need accurate, efficient tools and straightforward assessments to evaluate the health status of fish, like Rainbow Trout, that are cultivated on farms. In this study, two genetically distinct broodstock lines of Rainbow Trout originally obtained from two different U.S. states but propagated at Rushing Waters Trout Farm (Palmyra, Wisconsin) were evaluated. Groups originating from both states (State A: n = 20; State B: n = 20) were surveyed with a modified health assessment in a prospective, randomized, single-blind study. The adapted health assessment included external and internal gross evaluations, skin scrapes, gill clips, intestinal scrapes, and calculated indices, including condition factor and the hepatosomatic index. Generally, there were few significant differences in health assessment values between State A and State B fish. When this information was presented to the producer, it was discovered that perceived differences between groups were due to management errors in calculated growth rates. The results of this study add validity to the use of standardized health assessments for evaluating fish within aquaculture.

The Effect of Acute Erythromycin Exposure on the Swimming Ability of Zebrafish (Danio rerio) and Medaka (Oryzias latipes)

Erythromycin is a widely used antibiotic, and erythromycin contamination may pose a threat to aquatic organisms. However, little is known about the adverse effects of erythromycin on swimming ability. To quantify erythromycin-induced damage to fish swimming ability, Oryzias latipes and Danio rerio were acutely exposed to erythromycin. The swimming ability of the experimental fish was measured after exposure to varying doses of erythromycin (2 µg/L, 20 µg/L, 200 µg/L, and 2 mg/L) for 96 h. Burst speed (U_burst) and critical swimming speed (U_crit) of experimental fish significantly decreased. In addition, gene expression analysis of O. latipes and D. rerio under erythromycin treatment (2 mg/L) showed that the expression of genes related to energy metabolism in the muscle was significantly reduced in both species of fish. However, the gene expression pattern in the head of the two species was differentially impacted; D. rerio showed endocrine disruption, while phototransduction was impacted in O. latipes. The results of our study may be used as a reference to control erythromycin pollution in natural rivers.

Distribution, combined pollution and risk assessment of antibiotics in typical marine aquaculture farms surrounding the Yellow Sea, North China

This study focused on the distribution, combined pollution, potential source and risk assessment of 17 antibiotics in an aquaculture ecosystem surrounding the Yellow sea, North China. Antibiotics were detected in various matrices (seawater, sediment/biofilm, organism and feed) in different aquaculture modes (greenhouse and outdoor aquaculture) during the wet and dry seasons in coastal areas of Shandong province. The innovation points of the study were as follows: (1) To the best of our knowledge, this study was one of the few to investigate the occurrence and distribution of antibiotics in mariculture environments along the Yellow Sea coast; (2) Biofilms, a focus of the study, might act as a sink for antibiotics in the aquaculture ecosystem; and (3) The correlation of heavy metals and antibiotic concentrations was proved, which could correspondingly be used as an indicator for antibiotic concentrations in the studied area. The levels of antibiotics in water were observed to be relatively low, at the ng/L level. Trimethoprim was the most prevalent antibiotic, and was detected in all water samples. Oxytetracycline was detected at high concentrations in biofilms (up to 1478.29 ng/g). Moreover, biofilms exhibited a higher antibiotic accumulation capacity compared to sediments. Concentrations of oxytetracycline and doxycycline were high in feed, while other antibiotics were almost undetected. Tetracycline was widely detected and the concentration of enrofloxacin was highest in organisms. Correlation analysis demonstrated that environmental parameters and other coexisting contaminants (e.g. heavy metals) significantly affected antibiotic concentrations. In addition, the concentration of Zn was significantly correlated with the total antibiotic concentration and was proportional to several antibiotics in water and sediment (biofilm) samples (p < 0.01). High Mn concentrations were closely related to total and individual (e.g. sulfadiazine, sulfamethazine and enrofloxacin) antibiotic levels, which may result in the combined contamination of the environment. Antibiotics in estuaries and groundwater generally originated from aquaculture wastewater and untreated/treated domestic sewage. Most of the detected antibiotics posed no risk to the environment. Ciprofloxacin and enrofloxacin found in water may present high ecological and resistance risks, while the two antibiotics observed to accumulate in fish may pose a considerable risk to human health through diet consumption. All antibiotics detected in seafood were lower than the respective maximum residue limits. This study can act as a reference for the government for the determination of antibiotic discharge standards in aquaculture wastewater and the establishment of a standardized antibiotic monitoring and management system.

Assessment of long-term effects from cage culture practices on heavy metal accumulation in sediment and fish

Fish cage farming has been generally banned in some regions since there is growing concern about adverse environmental issue caused by cage culture practices. This paper presents the long-term effects of past cage culture activities on heavy metal accumulation in sediment and fish in one historical cage culture lake (Changshou reservoir, Chongqing, China). Although cages were removed for over one decade in this studied lake, the average concentrations of heavy metals in sediments were still above 2 times higher than their background values, posing a moderate ecological risk. Higher levels of heavy metals appeared in demersal fish who is more susceptible to heavy metals exposure in sediment. Fish consumption would not lead to a significant health risk of most heavy metals. Hg levels in catfish posed a health risk to vulnerable group (children) and specific group (fishermen), whereas the presence of Se decreased Hg toxicity to a safety level. Therefore, it can be speculated that the cage culture activities could influence the heavy metal accumulation in sediment in the long term, however, consumption of current farmed fish in one lake used to carry out cage-culture is safe for local residents.

Prevalence and distribution analysis of antibiotic resistance genes in a large-scale aquaculture environment

This study examined the profiles of antibiotic resistance genes (ARGs) in water and sediments from one large-scale freshwater pond farming system. A qPCR array was used to quantify ARGs (16S, Tetx, Tetw, TetG, Intll, and Sull) and microbial community structure was analyzed by 16S rRNA gene sequencing. A large number of ARGs (2 8 8) were detected. The ARG richness of the sediments was significantly higher than that of water and an average of 15 more genes were detected (p < 0.01). Sediment samples showed significantly higher taxonomic diversity and higher abundance of Gammaproteobacteria, Betaproteobacteria, and Flavobacteria. A significant correlation was observed between antibiotic resistance genes and breeding periods. The taxonomic diversity of the samples in ponds was significantly higher than that in ditch samples (p < 0.05), suggesting that pond farming systems could act as a local reservoir to spread ARGs into aquatic environments of rural communities.

Evolution and distribution of resistance genes and bacterial community in water and biofilm of a simulated fish-duck integrated pond with stress

Integrated fish-duck pond is a common circular farming model in South China, besides, it is also hot-spot for the co-selection of antibiotic resistance genes (ARGs). The aim of this study was to investigate the effects of duck manure, As and cefotaxime on the bacterial community, and the evolution and distribution of ARGs and metal(loid) resistance genes (MRGs) in water and biofilm. Five groups of fish tanks included a control and four test groups. The experimental period lasted for 100 days. Six ARGs (CIT, DHA, EBC, FOX, MOX, TEM), two MRGs (arsB, arsC), and two integron genes (intI1, intI2) were tracked and detected in water and biofilm. The results showed that duck manure brought ARGs and MRGs into fish tanks. Stress factors (cefotaxime, As) increased the relative abundance of resistance genes, and this was positively correlated with stress concentrations. The biofilm was visible significantly at the end of stage 3, and the total relative abundance of resistance genes in biofilm was higher than water from stage 5 onwards. Evolution of AmpC β-lactamase resistance genes was more obvious than MRGs, especially for MOX, which increased by 3 orders of magnitude. The abundance of Flavobacterium was higher in biofilm than in water. Moreover, correlation analysis showed that both arsB and MOX were significantly correlated with intI1 (p < 0.05), which suggested a potentially dissemination risk of resistance genes. This study provides a reference for health risk assessment in integrated aquaculture environment contaminated with duck manure, antibiotics and metalloids.

Short-term spatiotemporal biomarker changes in oysters transplanted to an anthropized estuary in Southern Brazil

Estuarine ecosystems are increasingly being affected by pollution caused by anthropogenic activities. In this study, Crassostrea gasar oysters were transplanted and maintained for seven days at three sites (S1, S2, and S3) in the Laguna Estuarine System (LES)-situated in southern Brazil-that has been exposed to multiple anthropic stresses. On the basis of the concentrations of metal and organic pollutants in oysters, we identified marked spatial variations in pollutant levels, with S3 showing the highest concentration of Ag, Fe, Ni, Zn, and total polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and linear alkylbenzenes (LABs), followed by S2 and S1. Along with the concentrations of pollutants, a set of biomarkers was analyzed. Oysters maintained at S3 showed enhanced protective defenses in gills, as observed by the increased levels of superoxide dismutase (SOD-like) and heat shock protein 90 (HSP90-like) transcripts and catalase (CAT) activity, concomitant with reduced lipid peroxidation (MDA) levels. Decreased antioxidant activities together with increased MDA levels are indicative of the digestive gland being more susceptible to pollutant-induced oxidative damage. Oysters transplanted into LES showed lower levels of cytochrome P450 transcripts (CYP356A1-like and CYP2AU1), and decreased glutathione S-transferase (GST) enzyme activity, suggesting lower biotransformation capacity. By integrating information regarding the concentration of metal and organic pollutants with that of molecular as well as biochemical biomarkers, our study provides novel insights into pollutant exposure and the potential biological impacts of such exposure on estuarine organisms in southern Brazil.

Determinants influencing antibiotic use in Singapore's small-scale aquaculture sectors: A qualitative study

Singapore’s Antimicrobial Resistance (AMR) national strategic action plan includes inappropriate use of antimicrobials in food-producing animals as a specific priority. Although the use of antibiotics and other drugs are monitored by regulatory bodies, food fish farmers are allowed to buy and administer antimicrobials without a veterinary prescription. We conducted a qualitative study of Singaporean food fish farmers to understand patterns and determinants of antibiotic use, their knowledge of antibiotic resistance, as well as perceptions of on-farm infection prevention and control measures. During the interview, participants were asked about their farming processes, farm infrastructure, antibiotic use and any disease prevention measures. Thematic analysis of participants’ interviews showed that antibiotic for growth promotion and infection prevention was uncommon among local food fish farmers. The following three main themes influenced participants’ decisions to use antibiotics in their practice: 1) individual factors, 2) local regulatory factors as well as 3) market-related factors. Individual factors included their personal experience and knowledge both with antibiotics as well as with alternate options. In terms of local regulatory factors, we found that regular oversight was a strong deterrent in antibiotic use. Last, at the market level, the relatively high price of antibiotics in Singapore coupled with stiff competition was a strong disincentive for participants to use antibiotics in their farming practice. These factors were also influential in their relationships with local regulatory bodies as well as their counterparts. Although industries differ significantly across countries, lessons learnt from Singapore’s food fish farming demonstrate the importance of an environment where multi-dimensional factors come together to discourage the irrational use of antibiotics in food animal production. In addition, our results allow greater insight into food fish farmers’ perspectives on infection control and form a basis from which further research work can be undertaken.

Purification and Characterization of an Antibacterial Substance from Aerococcus urinaeequi Strain HS36

A bacterial strain inhibiting the growth of Vibrio anguillarum, the causative agent of vibriosis, was isolated from fish intestines. The isolated strain HS36 was identified as Aerococcus urinaeequi based on the characteristics of the genus according to Bergey's Manual of Systematic Bacteriology and by 16S rRNA sequencing. The growth rate and antibacterial activity of strain HS36 in shaking culture were higher than those in static culture, while the optimal pH and temperature for antibacterial activity were 7.0 and 30°C, respectively. The active antibacterial substance was purified from a culture broth of A. urinaeequi HS36 by Sephadex G-75 gel chromatography, Sephadex G-25 gel chromatography, and reverse-phase high-performance liquid chromatography. Its molecular weight, as estimated by Tricine SDS-polyacrylamide gel electrophoresis, was approximately 1,000 Da. The antibacterial substance produced by strain HS36 was stable after incubation for 1 h at 100°C. Although its antibacterial activity was optimal at pH 6-8, activity was retained at a pH range from 2 to 11. The purified antibacterial substance was inactivated by proteinase K, papain, and β-amylase treatment. The newly purified antibacterial substance, classified as a class II bacteriocin, inhibited the growth of Klebsiella pneumoniae, Salmonella enterica, and Vibrio alginolyticus.

Desorption kinetics of tetracyclines in soils assessed by diffusive gradients in thin films

Tetracyclines (TCs) are frequently detected in agricultural soils worldwide, causing a potential threat to crops and human health. In this study, diffusive gradients in thin films technique (DGT) was used to measure the distribution and exchange rates of three TCs (tetracycline (TC), oxytetracycline (OTC) and chlortetracycline (CTC)) between the solid phase and solution in five farmland soils. The relationship between the accumulated masses with time suggested that TCs consumption in soil solution by DGT would induce the supply from the soil solid phase. The distribution coefficient for the labile antibiotics (K_dl), response time (T_c) and desorption/adsorption rates (k_b and k_f) between dissolved and sorbed TCs were derived from the dynamic model of DIFS (DGT induced fluxes in soils). The K_dl showed similar sizes of labile solid phase pools for TC and OTC while larger pool sizes were observed for CTC in the soils. Although the concentrations of CTC were lowest in soil solution, the potential hazard caused by continuous release from soil particles could not be ignored. The long response time (>30 min in most cases) suggested that the resupply of TCs from soil solids was limited by their desorption rates (1.26-121 × 10^-6 s^-1). The soils in finer texture, with higher clay and silt contents (<50 μm) showed a greater potential for TCs release.

Biodegradation and metabolic fate of thiamphenicol via Chlorella sp. UTEX1602 and L38

Thiamphenicol (TAP) is a typical medicament in animal husbandry and aquaculture for treating diverse infections. In this work, thiamphenicol biodegradation performance via microalgae was tested. The cultivation results showed that TAP could be biodegraded via the target algae. Chlorella sp. L38 presented strong adaptive ability to high concentration TAP. Biodegradation, biosorption and bioaccumulation were the dominant metabolic fates. Biodegradation contributed around 97% of the total removal efficiency at the TAP concentration of 46.2 mg·L^-1. The removal of TAP by Chlorella L38 and UTEX1602 agreed with the kinetic range of zero-order reaction, and the shortest half-lives were 3.2 d and 5.0 d. Based on the identification of metabolites, the metabolic pathway of TAP by microalgae was proposed, including chlorination, chlorine substitution, dehydration and hydroxylation. Therefore, biological treatment via microalgae has the potential for TAP purification.

Aeration-assisted sulfite activation with ferrous for enhanced chloramphenicol degradation

In this study, an Fe(Ⅱ)/S(IV) system was designed for the degradation of chloramphenicol (CAP). The pseudo-first-order rate constants for CAP degradation under typical conditions with and without air purging were investigated. The greatly enhanced rate of 0.0099 min^-1 with air purging compared with 0.0006 min^-1 with no air purging indicated that aeration was significant to the degradation of CAP in Fe(Ⅱ)/S(Ⅳ) system. Radical scavenging experiments revealed that SO₄^- was the primary oxidant generated from the activation of S(IV) with Fe(II), accounting for around 70% of degradation under weak acidic and neutral conditions. Increasing Fe(II) and S(IV) doses promoted the degradation of CAP, whereas the overdose of them led to a decreased degradation rate by scavenging radicals. Owing to the participation of oxygen in the formation of ferric sulfite complex and SO₅^-, the increase of dissolved oxygen improved the removal efficiency of CAP. The removal efficiency of CAP was also found to be pH dependent, decreasing from acid condition (initial pH = 4) to basic condition (initial pH = 8). The presence of coexisting anions and water matrix was found inhibiting CAP degradation in Fe(Ⅱ)/S(Ⅳ) system. This work provides an understanding on the working mechanism and possible applications of Fe(Ⅱ)/S(Ⅳ) system in organic compound degradation in wastewater.

Current trends of antimicrobials used in food animals and aquaculture

Human population has been increasing rapidly, which ultimately increases human consumption, especially, animal protein requirements. Therefore, demands of animal protein consumption are increasing worldwide at an extraordinary rate. In order to meet the protein demand, intensive animal and aquaculture farming are considered. Like livestock farming (poultry, pigs, sheep, livestock, horses, rabbits, etc.), aquaculture farming (fish, crustaceans, mollusks, etc.) is also becoming the globe's emergent protein production sector. More than 580 aquaculture species are farmed worldwide. Current food animal and aquaculture farming are coupled with standard usage of antimicrobials. The antimicrobial drugs are major solutions for the management of contagious illnesses in food animals and aquaculture. In animal husbandry, antimicrobials are widely utilized for animal therapy, prophylaxis, or as growth promoters. Imprudent usage of these antimicrobials in food animals and aquaculture is a major contributing factor in the spread of antimicrobial resistance. The widespread use of veterinary medicines is considered to signify a frightening population health threat. It not only results in the disclosure and escalation of resistant microbes but also causes other individual, animal, and ecological deterioration. The contribution of resistant microbes from various sources seems to be the major base of resistance in the environment. However, strict policies and regulations for antimicrobial usage in food animals and aquaculture must be made and applied. It is important to prevent their negative effects in humans, food animals, aquaculture, and the environment.

The discrepant mobility of antibiotic resistant genes: Evidence from their spatial distribution in sewage sludge flocs

The present study stratified excess activated sludge from six municipal wastewater treatment plants into four extracellular fractions including supernatant, slime, slightly-bond extracellular polymeric substances (LB-EPS) and tightly-bond EPS (TB-EPS) and one intracellular fraction (pellet) according to their different degrees of tight binding to sludge microbial aggregates and determined the abundance of seven antibiotic resistance genes (ARGs) (sul-I, sul-II, tet-C, tet-X, blaTEM, mefA and cat) and one mobile genetic elements (MGEs) (IntI-1) in each fraction. Extracellular ARGs were found to make up 0.1% - 74.2% of total ARGs, while the ratio of extracellular DNA to total DNA was only 1.2% - 4.2%, implying that EPS was a major ARG reservoir in sewage sludge. The genes of sul-I, tet-C and mefA have the highest mobility owing to a large proportion ranging from 0.5% to 32.7% in the fractions of LB-EPS, slime and supernatant, which indicates an increased risk of mediating the transfer of ARGs to environment. Comparatively, the proportion of blaTEM in the TB-EPS of sludge accounted for 0.3%-34.9% and caused limited-mobility. Sul-II, tet-X and cat and IntI-1, made up approximately 82.6% - 99.6% proportion in the cells, and were thus less mobile. This study proposes that ARGs and MGEs can have different mobilities. Those located in the outermost layers of sludge have a higher mobility potential of propagation into the natural environment during wastewater treatment and sludge utilization, leading to an increased risk of transferability.

Characterization of Mechanisms Lowering Susceptibility to Flumequine among Bacteria Isolated from Chilean Salmonid Farms

Despite their great importance for human therapy, quinolones are still used in Chilean salmon farming, with flumequine and oxolinic acid currently approved for use in this industry. The aim of this study was to improve our knowledge of the mechanisms conferring low susceptibility or resistance to quinolones among bacteria recovered from Chilean salmon farms. Sixty-five isolates exhibiting resistance, reduced susceptibility, or susceptibility to flumequine recovered from salmon farms were identified by their 16S rRNA genes, detecting a high predominance of species belonging to the Pseudomonas genus (52%). The minimum inhibitory concentrations (MIC) of flumequine in the absence and presence of the efflux pump inhibitor (EPI) Phe-Arg-β-naphthylamide and resistance patterns of isolates were determined by a microdilution broth and disk diffusion assays, respectively, observing MIC values ranging from 0.25 to >64 µg/mL and a high level of multi-resistance (96%), mostly showing resistance to florfenicol and oxytetracycline. Furthermore, mechanisms conferring low susceptibility to quinolones mediated by efflux pump activity, quinolone target mutations, or horizontally acquired resistance genes (qepA, oqxA, aac(6′)-lb-cr, qnr) were investigated. Among isolates exhibiting resistance to flumequine (≥16 µg/mL), the occurrence of chromosomal mutations in target protein GyrA appears to be unusual (three out of 15), contrasting with the high incidence of mutations in GyrB (14 out of 17). Bacterial isolates showing resistance or reduced susceptibility to quinolones mediated by efflux pumps appear to be highly prevalent (49 isolates, 75%), thus suggesting a major role of intrinsic resistance mediated by active efflux.

Antibiotic resistance and microbiota in the gut of Chinese four major freshwater carp from retail markets

Fish-associated antibiotic resistance genes (ARGs) have attracted increasing attention due to their potential risks to human beings via the food chain. However, data are scarce regarding the antibiotic resistance in fish themselves. Herein, the antibiotic resistance genes (ARGs) were assessed in the gut of four major Chinese freshwater carp (i.e., silver carp, grass carp, bighead carp, and crucian carp) from food retail markets. Results show that the abundances of target ARGs (e.g., tetA, tetO, tetQ, tetW, sulI, sulII, and bla_TEM-1) and class 1 integrase (intI1) were in the range 9.4 × 10^-6 - 1.6 × 10^-1 and 6.7 × 10^-5 - 5.2 × 10^-2 gene copies per 16S rRNA gene, respectively. The sulI, sulII, and tetQ strongly correlated with silver and mercury resistance genes (e.g., silE and merR). The microbial taxa of fish gut could be partly separated among retail markets based on the PCA analysis. About 15.0% of the OTUs in fish gut were shared and 74.5% of the shared OTUs were identified as Acidobacteria, Bacteroidetes, Chloroflexi, Cyanobacteria, Firmicutes, and Proteobacteria. These phyla may constitute the core microbiota in the guts of the four Chinese freshwater carp. The possible ARG hosts were revealed based on the network analysis, and the presence of pathogen-associated resistant genera in fish gut highlights the need to fully understand their potential human health risks.

Effects of microplastics on distribution of antibiotic resistance genes in recirculating aquaculture system

Microplastics and antibiotic resistance genes (ARGs) are two kinds of emerging contaminants with frequent detection in coastal regions. However, rare information on co-occurrence of microplastics and ARGs in coastal recirculating aquaculture system (RAS) is available. This study performed field sampling and laboratory analysis to investigate the distribution of microplastics and ARGs in a typical RAS farm. The results showed that microplastics were detected in all water samples with the abundances ranging from 58 to 72 items/m³. Absolute abundances of total 10 ARGs in water samples ranged from 3.24 × 10⁵ to 7.83 × 10⁵ copies/mL while those on microplastic samples were in the range of 1.59 × 10⁹-1.83 × 10⁹ copies/g. Microbial communities of microplastics and water showed significant difference at both phylum and genus levels. Microbial community diversity of microplastics was higher than that of water. ARGs including tetG, qnrS, sul1, sul2, and ermF possessed relatively more active relationships with bacterial community in water and on microplastics of the RAS farm. The results suggested that microplastics might be an important reservoir of ARGs in RAS farms. The findings of this study will provide useful information on pollution control and environmental management for both microplastics and ARGs in coastal aquaculture systems.

Characterization of a Novel Conjugative Plasmid in Edwardsiella piscicida Strain MS-18-199

Edwardsiella piscicida is a pathogenic bacterium responsible for significant losses in important wild and cultured fish species. E. piscicida strain MS-18-199 recovered from a diseased hybrid catfish from East Mississippi and showed resistance to florfenicol, chloramphenicol, oxytetracycline, doxycycline, erythromycin, tetracycline, azitromycin, spectinomycin, sulfonamide, and bacitracin. To explore the mechanisms of resistance in E. piscicida strain MS-18-199, genomic DNA was extracted and subjected to whole genome sequencing (WGS) using a combination of long (Oxford Nanopore) and short (Illumina) reads. The genome of strain MS-18-199 revealed a novel plasmid named pEPMS-18199. The 117,448 bp plasmid contains several antimicrobial resistance (AMR) elements/genes, including florfenicol efflux pump (floR), tetracycline efflux pump (tetA), tetracycline repressor protein (tetR), sulfonamide resistance (sul2), aminoglycoside O-phosphotransferase aph(6)-Id (strB), and aminoglycoside O-phosphotransferase aph(3)-Ib (strA). Two genes, arsA and arsD, that encode protein components related to transport/resistance to arsenic were also found in pEPMS-18199. In addition, pEPMS-18199 carried twelve conjugative transfer genes (tra), eight transposases and insertion elements, two plasmid stability proteins, two replication proteins, and three partitioning proteins (par system). Results from mobilization and stability experiments revealed that pEPMS-18199 is highly stable in the host cell and could be transferred to Escherichia coli and Edwardsiella ictaluri by conjugation. To our knowledge, this is the first detection of a multidrug resistance (MDR) conjugative plasmid in E. piscicida in the United States. Careful tracking of this plasmid in the aquaculture system is warranted. Knowledge regarding the molecular mechanisms of AMR in aquaculture is important for antimicrobial stewardship.

Heavy metal content in farmed rainbow trout in relation to aquaculture area and feed pellets

Fish contamination by heavy metals, even at low levels, has an adverse effect on human health. Mercury (Hg), cadmium (Cd), and lead (Pb) are the most common heavy metals that contaminate sea foods. Rainbow trout is a fish species which is widely cultured in fresh water regions, e.g. in Yasuj, southwest of Iran. Heavy metal contamination was measured in three different culture areas (A, B, and C), with three different feed pellets used in Yasuj farms (I, II, and III). The sampling was conducted during February-April 2018 and the metals were measured using cold vapour atomic absorption with a Perkin Elmer 4100. The mean values of Hg, Cd, and Pb levels in the muscular tissue of the samples were 0.022, 0.105, and 1.07 mg/kg, respectively. Concentrations of Hg and Cd in edible tissues of rainbow trout were lower than the permitted values set by the WHO, the FDA, and the EC. The samples fed on mixture pellets III showed a significantly higher Hg content and a lower concentration of Cd in the muscle tissue compared to those given feed mixtures I and II (P < 0.05). Pearson correlation tests revealed significant correlations between the Cd and Pb concentrations and the weight of the fish samples (r = –0.519, r = –0.580). The lowest Cd concentration (0.076 mg/kg–1) was found in site A located close to the spring and not polluted by sewage from urban or rural areas. The study showed a correlation between the concentration of heavy metals in the fish samples and their weight, the degree of pollution, and the feeding mixture used in the farms.

Deep Dehalogenation of Florfenicol Using Crystalline CoP Nanosheet Arrays on a Ti Plate via Direct Cathodic Reduction and Atomic H

Efficient elimination of antibacterial activity of halogenated antibiotics by dehalogenation pretreatment is desired for a biochemical treatment process. In this study, crystalline cobalt phosphide nanosheet arrays on a Ti plate (C-CoP/Ti) are fabricated by a simple electrodeposition and phosphorization process. The crystalline structure greatly promotes atomic hydrogen (H*) generation. Moreover, the nanosheet arrays can provide abundant active sites and accelerate electron transfer and mass transport. As a result, the dehalogenation rate of florfenicol (FLO, an emerging organic pollutant) on C-CoP/Ti is 11.1, 2.97, and 13.6 times higher than that on amorphous CoP/Ti, Pd/Ti, and bare Ti, respectively. The C-CoP/Ti electrode achieves 97.4% dehalogenation of FLO (20 mg L^-1) within 30 min at -1.2 V (vs Ag/AgCl). Nearly 100% of Cl and 20% of F are broken away within 120 min, showing the highest electrocatalytic defluorination efficiency reported so far. Both experimental results and theoretical calculations reveal that the dehalogenation of FLO on C-CoP/Ti is synergistically accomplished via direct reduction of electron transfer and indirect reduction of H*. This study develops a highly efficient non-noble metal electrode material for dehalogenation of halogenated organic compounds.

A global spatial analysis reveals where marine aquaculture can benefit nature and people

Aquaculture of bivalve shellfish and seaweed represents a global opportunity to simultaneously advance coastal ecosystem recovery and provide substantive benefits to humanity. To identify marine ecoregions with the greatest potential for development of shellfish and seaweed aquaculture to meet this opportunity, we conducted a global spatial analysis using key environmental (e.g., nutrient pollution status), socioeconomic (e.g., governance quality), and human health factors (e.g., wastewater treatment prevalence). We identify a substantial opportunity for strategic sector development, with the highest opportunity marine ecoregions for shellfish aquaculture centered on Oceania, North America, and portions of Asia, and the highest opportunity for seaweed aquaculture distributed throughout Europe, Asia, Oceania, and North and South America. This study provides insights into specific areas where governments, international development organizations, and investors should prioritize new efforts to drive changes in public policy, capacity-building, and business planning to realize the ecosystem and societal benefits of shellfish and seaweed aquaculture.

A new potential therapeutic remedy against Aeromonas hydrophila infection in rainbow trout (Oncorhynchus mykiss) using tetra, Cotinus coggygria

Different antibiotic-based drugs are being used for the treatment of Aeromonas hydrophila infection in rainbow trout, and several studies emphasize the use of medicinal plants as immunostimulants for prophylactic measure against Aeromoniasis disease. However, therapeutic effects of aqueous methanolic extracts of tetra (Cotinus coggygria) against A. hydrophila in rainbow trout were not investigated. Four different concentrations of tetra extract (0 [control], 4, 8 and 12 mg/100 µl) and also two different positive control groups (florfenicol and doxycycline antibiotics) were administered orally using feeding needles to individual rainbow trout, Oncorhynchus mykiss of all experimental groups twice a day after intramuscular inoculation of A. hydrophila. The study period was for 10 days. On 0th, 3rd, 7th and 10th day, blood and tissues were collected from the fish and changes in humoral immune responses, haematology and immune-related gene expressions were determined. In the study, superoxide radical production was decreased generally in all experimental groups except in 12 mg tetra and florfenicol treatments compared to control (p < .05). Lysozyme activity was generally decreased (p < .05), or no differences were observed in all experimental groups compared to the control. Myeloperoxidase activity was significantly increased in florfenicol-treated fish group on 7th day (p < .05). Generally, myeloperoxidase activity showed an increase in almost all tetra-treated groups. Haematological parameters increased but were not significantly high enough in treatments. Almost all immune-related gene expressions were significantly enhanced on 3rd and 10th day of the study. Survival rate of 53.33% was found in control group. There were no significant differences in survival between control and 4 mg tetra-treated group (p > .05). All the other groups' survival rate was significantly increased compared to control. The highest survival rate was found in florfenicol group (80%). In 12 mg tetra-, doxycycline- and 8 mg tetra-treated groups, survival rate was recorded as 74.44%, 70% and 70%, respectively. Our results suggest that tetra methanolic extract is an effective therapeutic remedy against A. hydrophila infection in rainbow trout at the dose of 24 mg/32.34 g body weight/day.

Occurrence and dietary exposure of organochlorine pesticides in common carp obtained from integrated production systems

The aim of this study was to determine the level of the organochlorine pesticides (OCPs) in meat, liver and skin of common carp. Fish were collected in spring and in autumn from fishpond that receives purified water from slaughterhouse. OCPs, including α-HCH, β-HCH, δ-HCH, lindane, heptachlor, aldrin, heptachlor epoxide, trans-chlordane, cis-chlordane, endosulfan I, DDE, dieldrin, endrin, DDD, endosulfan II, dichlorodiphenyltrichloroethane (DDT), endosulfan sulphate, methoxychlor, and endrin ketone, were determined by using a gas chromatography-mass spectrometry method. OCPs were present at low concentrations and only aldrin was detected in all examined tissues. The estimated daily intake for OCPs via common carp from integrated system of production was at the lower level compared with the acceptable daily intake recommended by different organisations, showing no significant risk on consumers.

Occurrences, levels and risk assessment studies of emerging pollutants (pharmaceuticals, perfluoroalkyl and endocrine disrupting compounds) in fish samples from Kalk Bay harbour, South Africa

A comprehensive analysis of 15 target chemical compounds (pharmaceuticals and personal care product, perfluoroalkyl compounds and industrial chemicals) were carried out to determine their concentrations in selected commercially exploited, wild caught small and medium sized pelagic fish species and their organs (Thyrsites atun (snoek), Sarda orientalis (bonito), Pachymetopon blochii (panga) and Pterogymnus laniarius (hottentot)) obtained from Kalk Bay harbour, Cape Town. Solid phase extraction (SPE) method based on Oasis HLB cartridges were used to concentrate and clean-up the samples. Liquid chromatography-mass spectrometry analysis of these chemical compounds revealed the simultaneous presence of at least 12 compounds in different parts of the selected fish species in nanogram-per-gram dry weight (ng/g dw) concentrations. The results revealed that perfluorodecanoic acid, perfluorononanoic acid and perfluoroheptanoic acid were the most predominant among the perfluorinated compounds and ranged between: (20.13-179.2 ng/g), (21.22-114.0 ng/g) and (40.06-138.3 ng/g). Also, diclofenac had the highest concentration in these edible fish species out of all the pharmaceuticals detected (range: 551.8-1812 ng/g). The risk assessment values were above 0.5 and 1.0 for acute and chronic risk respectively which shows that these chemicals have a high health risk to the pelagic fish, aquatic organisms and to humans who consume them. Therefore, there is an urgent need for a precautionary approach and the adequate regulation of the use and disposal of synthetic chemicals that persist in aquatic/marine environment in this province and other parts of South Africa, to prevent impacts on the sustainability of our marine environment, livelihood and lives.

Efflux proteins MacAB confer resistance to arsenite and penicillin/macrolide-type antibiotics in Agrobacterium tumefaciens 5A

Antibiotic and arsenic (As) contaminations are worldwide public health problems. Previously, the bacterial ABC-type efflux protein MacAB reportedly conferred resistance to macrolide-type antibiotics but not to other metal(loid)s. In this study, the roles of MacAB for the co-resistance of different antibiotics and several metal(loid)s were analyzed in Agrobacterium tumefaciens 5A, a strain resistant to arsenite [As(III)] and several types of antibiotics. The macA and macB genes were cotranscribed, and macB was deleted in A. tumefaciens 5A and heterologously expressed in Escherichia coli AW3110 and E. coli S17-1. Compared to the wild-type strain 5A, the macB deletion strain reduced bacterial resistance levels to several macrolide-type and penicillin-type antibiotics but not to cephalosporin-type antibiotics. In addition, the macB deletion strain showed lower resistance to As(III) but not to arsenate [As(V)], antimonite [Sb(III)] and cadmium chloride [Cd(II)]. The mutant strain 5A-ΔmacB cells accumulated more As(III) than the cells of the wild-type. Furthermore, heterologous expression of MacAB in E. coli S17-1 showed that MacAB was essential for resistance to macrolide, several penicillin-type antibiotics and As(III) but not to As(V). Heterologous expression of MacAB in E. coli AW3110 reduced the cellular accumulation of As(III) but not of As(V), indicating that MacAB is responsible for the efflux of As(III). These results demonstrated that, in addition to macrolide-type antibiotics, MacAB also conferred resistance to penicillin-type antibiotics and As(III) by extruding them out of cells. This finding contributes to a better understanding of the bacterial resistance mechanisms of antibiotics and metal(loid)s.

Bioaccumulation and human health implications of essential and toxic metals in freshwater products of Northeast China

Bioaccumulation and human health risks of essential and toxic metals in ten species of freshwater products from Northeast China were investigated in this study. The concentrations (mg/kg wet weight) of target metals in aquatic products were: Fe (4.6-165.4), Zn (4.1-33.4), Mn (0.28-80.0), Cu (0.24-15.8), Cr (0.074-0.80), As (0.0068-0.72), Hg (0.016-0.58), Ni (0.019-0.58), Pb (0.017-0.27) and Cd (0.0004-0.058). There was no significant regional difference of target metal levels in fish samples between Liaoning province and Inner Mongolia Autonomous Region according to matched sample t-test. Every daily intakes (EDI) of target metals from freshwater products were far below their corresponding limits. However, health risk assessment of individual metal in freshwater products showed methyl mercury (MeHg) and Mn could pose potential noncarcinogenic risk to human, and inorganic arsenic (iAs) would cause potential carcinogenic risk to consumers at the level of 1 in 100,000. Furthermore, freshwater product species-specific bioaccumulation characteristics for different metals are quite different. The total hazard quotients of target metals in different aquatic product species demonstrated that co-exposure of target metals by consumption of these six species (C. auratus, E. sinensis, C. erythropterus, C. carpio, M. anguillicaudatus and O. cantor) from Northeast China could cause potential noncarcinogenic risk to human, and the pollution of toxic metals in E. sinensis and C. auratus were most serious among all investigated aquatic species.

Oxytetracycline accumulation in the macroalgae Ulva: Potential risks for IMTA systems

Oxytetracycline (OTC) is one of the most used antibiotics in aquaculture. With the development of Integrated Multitrophic Aquaculture (IMTA) systems in order to mitigate some aquacultures' adverse effects, attention needs to be shifted to other co-cultured species that can also accumulate such pharmaceuticals and pose a risk to human consumption. Therefore, the present work evaluated the exposure of the seaweed Ulva to OTC at two realistic concentrations (0.040 and 0.120 mg L^-1). Oxytetracycline degradation rates in seawater were dependent on the initial concentration but were not influenced by the presence of Ulva. The macroalgae presented good assimilation rates of OTC, with internal concentrations reaching 40.9934 ng g^-1 WW for the lowest concentration tested and 108.6787 ng g^-1 WW for the highest, with a steep decrease after 48 and 24 h, respectively. Nonetheless, concentrations were still half of the Maximum Residue Limit set for fish (100 μg kg^-1) 48 h after C2 treatment. The highest dosage tested stimulated growth 96 h after the beginning of the trial, although some signs of decay could also be found in Ulva's fronds.

Bacteria-assisted removal of fluoroquinolones from wheat rhizospheres in an agricultural soil

Extensive fluoroquinolone antibiotics use results in their widespread occurrence in various environments including soil, which threatens the soil ecology and public health. The fate of fluoroquinolones in agricultural soil and the efficacy of enhanced degradation in the presence of an agricultural crops and antibiotic degrading bacteria could be better understood. The current study examined ciprofloxacin (CIP), enrofloxacin (ENR), and levofloxacin (LEV) biodegradation in a Maury Silt Loam soil in greenhouse conditions by bacterial-assisted removal of individual and mixed antibiotics in wheat rhizospheres. Fluoroquinolones were added at rates of 5, 50, and 100 mg kg^-1. Three bacterial isolates were applied at 10⁶ CFU g^-1 soil individually and in consortium. Antibiotics appeared in wheat tissue, with more accumulation in roots than shoots. Low recoveries (<50%) of CIP, ENR, and LEV were observed at all levels and treatments in a bacteria and wheat-free control compared to the initial concentrations applied Contaminated soil with wheat had greater antibiotic recovery than the wheat-free control. Antibiotic recovery with bacterial inoculum was less than that of the indigenous bacteria. The least antibiotic recovery occurred with wheat and bacterial inoculum together. At concentrations of 5 and 50 mg kg^-1, but not at 100 mg kg^-1, CIP, ENR, and LEV were below detection limits in soil after 30 days through the combination of wheat and bacteria compared to the control. This synergistic removal of the fluoroquinolone antibiotics is proposed to be due to enhanced antibiotic bioavailability, which suggests it as an environment-friendly approach to biodegradation.

Graphene oxide as a tool for antibiotic-resistant gene removal: a review

Environmental pollutants, including antibiotics (ATBs), have become an increasingly common health hazard in the last several decades. Overdose and abuse of ATBs led to the emergence of antibiotic-resistant genes (ARGs), which represent a serious health threat. Moreover, water bodies and reservoirs are places where a wide range of bacterial species with ARGs originate, owing to the strong selective pressure from presence of ATB residues. In this regard, graphene oxide (GO) has been utilised in several fields including remediation of the environment. In this review, we present a brief overview of resistant genes of frequently used ATBs, their occurrence in the environment and their behaviour. Further, we discussed the factors influencing the binding of nucleic acids and the response of ARGs to GO, including the presence of salts in the water environment or water pH, because of intrinsic properties of GO of not only binding to nucleic acids but also catalysing their decomposition. This would be helpful in designing new types of water treatment facilities.

Degradation of sulfadimethoxine by permanganate in aquatic environment: Influence factors, intermediate products and theoretical study

The excess sulfadimethoxine (SDM) in the environment could lead to antibiotic resistance by microorganisms and may do harm to many aquatic organisms. In this work, the removal of SDM by potassium permanganate (KMnO₄) was comprehensively studied. The influence of various factors, including the pH, oxidant doses, and temperature, on SDM removal were investigated. The optimal reaction conditions were determined to be pH 5.0, T = 25 °C and [KMnO₄]₀ = 200 μmol L^-1. Anions (Cl^-, SO₄^2-, HCO₃^2-, and NO₃^-) and cations (K⁺, Ca²⁺, Mg²⁺, and NH₄⁺) had no significant influence on the removal of SDM. However, H₂PO₄^- improved the efficiency of SDM removal by KMnO₄. Humic acid (0-10 mg L^-1) promoted the removal of SDM, which was attributed to the generation of in situ MnO₂. Meanwhile, the degradation of SDM in various water matrices was studied, and the removal order was ultrapure water > Jiuxiang river water ≈ synthetic water > secondary clarifier effluent. According to ten intermediate products identified and a frontier electron densities (FED) calculation, several pathways were proposed that involve the oxidation of amidogen, the cleavage of CS and SN bonds, and an oligomerization reaction. The predicted toxicity assessment indicated that most of the degradation products were not harmful to aquatic organisms except SDM dimers (connection by HNNH), suggesting that byproducts, such as dimers, formed during the oxidation of SDM and other sulfonamides should be taken into consideration. In sum, KMnO₄ has the potential to remove SDM from the aquatic environment.

Tissue residue depletion kinetics and withdrawal time estimation of doxycycline in grass carp, Ctenopharyngodon idella, following multiple oral administrations

This study aimed to determine the plasma and tissue residue depletion kinetics of doxycycline (DC) in grass carp (Ctenopharyngodon idella) after daily oral administrations at 20 mg/kg for 3 days, and to calculate the corresponding withdrawal times. Following drug administrations, samples of plasma, liver, kidney, gill and muscle + skin were collected at predetermined time points (0.25, 0.5, 1, 3, 5, 7, 14, 21, 28, 35, 42, 49 and 56 days) and analyzed for concentrations of DC using a LC-MS/MS method. The results showed that liver had the highest concentrations and the slowest depletion compared to other tissues, with detectable DC up to 49 days (58.9 ± 12.8 μg/kg). The WT 1.4 software and "reschem" package were used to calculate withdrawal times, and the results were similar. The results suggest a withdrawal time of 41 days for Europe and China and 50 days for Japan is needed for DC in grass carp after 3 daily oral administrations at 20 mg/kg. Overall, this study improves our understanding of the tissue residue depletion kinetics of DC in fish, and the results may help regulatory agencies to determine proper withdrawal periods based on different regulatory standards in different countries to ensure safety of aquatic food products.

Pesticides and antibiotics in permanent rice, alternating rice-shrimp and permanent shrimp systems of the coastal Mekong Delta, Vietnam

BACKGROUND

Salinity intrusion into coastal regions is an increasing threat to agricultural production of salt sensitive crops like paddy rice. In the coastal Mekong Delta, farmers respond by shifting to more salinity tolerant agricultural production systems such as alternating rice-shrimp and permanent shrimp. While shrimps are sensitive to pesticide residues used on rice, the use of antibiotics in shrimp farming can cause contamination in rice crops. These patterns of cross-contamination are not well documented empirically in the rapidly changing agricultural landscape.

OBJECTIVE AND METHODS

Our objective was to understand changing pollution patterns induced by shifts in agricultural land use system. We addressed this by i) documenting pesticide and antibiotic use in three different agriculture land use systems (permanent rice, alternating rice-shrimp and permanent shrimp), and by ii) determining residues of pesticides and antibiotics in top soil layers of these three land use systems. Samples were taken in Sóc Trăng and Bến Tre province in the Mekong Delta, Vietnam. Chemical analyses comprised 12 of the most commonly used pesticides in rice paddies and six common antibiotics used in shrimp production.

RESULTS

Results showed that residues of pesticides were present in all agricultural land use systems, including shrimp aquaculture. Active ingredients were mostly fungicides with a maximum concentration of 67 μg kg^-1 found for isoprothiolane in permanent rice systems, followed by alternating rice-shrimp and permanent shrimp systems. Furthermore, antibiotics were present ubiquitously, with fluoroquinolones accumulating to larger amounts than sulfonamides and diaminopyrimidines. All concentrations were below critical lethal threshold values.

CONCLUSION

Overall, farmers were most conscious of agrochemical use in alternating rice-shrimp systems to prevent harm to shrimps, which was reflected in overall lower concentrations of agrochemicals when compared to rice systems. Thus, alternating rice-shrimp systems present a low risk option in terms of food safety, which may bring additional benefits to this so far rather low-input system in brackish water transition zone.