Prevalence, geographic distribution and phenotypic differences of Piscirickettsia salmonis EM-90-like isolates

Assessment of Single-Dose Pharmacokinetics of Oxolinic Acid in Rainbow Trout and Determination of In Vitro Antibacterial Activity Against Pathogenic Bacteria From Diseased Fish

In response to the heightened risk of bacterial diseases in fish farms caused by increased demand for fish consumption and subsequent overcrowding, researchers are currently investigating the efficacy and residue management of oxolinic acid (OA) as a treatment for bacterial infections in fish. This research is crucial for gaining a comprehensive understanding of the pharmacokinetics of OA. The present study investigates pharmacokinetics of OA in juvenile rainbow trout. The fish were given a 12 mg kg-1 dose of OA through their feed, and tissue samples were collected of the liver, kidney, gill, intestine, muscle, and plasma for analysis using LC-MS/MS. The highest concentrations of the drug were found in the gill (4096.55 μg kg-1) and intestine (11592.98 μg kg-1), with significant absorption also seen in the liver (0.36 L/h) and gill (0.07 L/h) (p < 0.05). The liver (0.21 L/h) and kidney (0.03 L/h) were found to be the most efficient (p < 0.05) at eliminating the drug. The study also confirmed the drug antimicrobial effectiveness against several bacterial pathogens, including Shewanella xiamenensis (0.25 μg mL-1), Lactococcus garvieae (1 μg mL-1), and Chryseobacterium aquaticum (4 μg mL-1). The study concludes significant variations among different fish tissues, with higher concentrations and longer half-lives observed in the kidney and intestine. The lowest MIC value recorded against major bacterial pathogens demonstrated its therapeutic potential in aquaculture. It also emphasizes the importance of understanding OA pharmacokinetics to optimize antimicrobial therapy in aquaculture.

Pharmacokinetic Data Show That Oxolinic Acid and Flumequine Are Absorbed and Excreted Rapidly From Plasma and Tissues of Lumpfish

This study examined the uptake, tissue distribution and elimination of the antibacterial agents oxolinic acid and flumequine in lumpfish (Cyclopterus lumpus L.) by use of LC-MS/MS following a single oral administration of 25 mg/kg fish given in feed. Lumpfish are increasingly used as cleaner fish for removal of sea lice on commercially farmed salmon. The production of lumpfish is successful, but there are challenges with bacterial infections and the number of antibacterial treatments has increased in recent years. As the lumpfish is a novel species to farming, there is a need for pharmacokinetic data and establishment of protocols for efficient antibacterial treatment. The current study describes the pharmacokinetic properties of oxolinic acid and flumequine in lumpfish. Absorption of oxolinic acid was moderate and was characterized by a calculated peak plasma concentration (C_max) of 2.12 μg/ml after 10.3 h (T_max) and an elimination half-life (t_1/2β) of 21 h. Area under curve (AUC) and AUC from 0 to 24 h (AUC_0−24h) were calculated to be 60.9 and 34.0 h μg/ml, respectively. For flumequine, plasma C_max was found to be 2.77 μg/ml after 7.7 h (T_max) with t_1/2β of 22 h. The area under the curve (AUC) and AUC from 0 to 24 h (AUC₀₋₂₄) were calculated as 104.3 and 50.3 h μg/ml, respectively. Corresponding C_max values in muscle, liver, and head-kidney for oxolinic acid were 4.01, 3.04, and, 4.68 μg/g, respectively and T_max of 11.1, 9.2, and 10.0 h, respectively. For flumequine, C_max values of 4.16, 4.01, and 7.48 μg/g were obtained in muscle, liver, and head kidney, respectively, with corresponding T_max values of 10.2, 10.3, and 6.0 h. Antimicrobial susceptibility values as determined by minimum inhibitory concentration (MIC) analyses against 28 isolates of Aeromonas salmonicida isolated from diseased lumpfish ranged from 0.06 to 15 μg/ml for oxolinic acid and 0.024 to 6.25 μg/ml for flumequine. Bimodal distributions in susceptibility to both oxolinic acid and flumequine were observed. The combination of pharmacokinetic properties and MIC data make possible calculation of efficient treatment doses, which are needed to improve the welfare of lumpfish and minimize development of antibiotic resistant bacteria.

Adsorption of Quinolone Antibiotics to Goethite under Seawater Conditions: Application of a Surface Complexation Model

The assessment of antibiotics mobility under seawater conditions has been rarely studied, as an accurate description of such multicomponent systems is quite challenging. In this study, the adsorption of a widely used quinolone antibiotic in aquaculture, Oxolinic acid (OA), to a synthetic goethite (α-FeOOH) was examined in the presence of major (e.g., Mg²⁺, SO₄^2-) and trace (e.g., Cu²⁺) ions naturally occurring in seawater. The OA adsorption can be successfully predicted using a charge distribution multisite complexation model (CD-MUSIC) coupled with the three plane model (TPM). This modeling approach allowed a quantification of the competitive and synergetic effects of different ions in seawater over a large range of environmentally relevant conditions. In addition, the transport of OA in flow-through columns can be well predicted through coupling hydrodynamic parameters and surface complexation constants obtained under seawater conditions. These results may have strong implications for assessment and prediction of the fate of quinolones in sediment-seawater interface systems.

Current Status of the Use of Antibiotics and the Antimicrobial Resistance in the Chilean Salmon Farms

The Chilean salmon industry has undergone a rapid development making the country the world's second largest producer of farmed salmon, but this growth has been accompanied by an intensive use of antibiotics. This overuse has become so significant that Chilean salmon aquaculture currently has one of the highest rates of antibiotic consumption per ton of harvested fish in the world. This review has focused on discussing use of antibiotics and current status of scientific knowledge regarding to incidence of antimicrobial resistance and associated genes in the Chilean salmonid farms. Over recent years there has been a consistent increase in the amount of antimicrobials used by Chilean salmonid farms, from 143.2 tons in 2010 to 382.5 tons in 2016. During 2016, Chilean companies utilized approximately 0.53 kg of antibiotics per ton of harvested salmon, 363.4 tons (95%) were used in marine farms, and 19.1 tons (5%) in freshwater farms dedicated to smolt production. Florfenicol and oxytetracycline were by far the most frequently used antibiotics during 2016 (82.5 and 16.8%, respectively), mainly being used to treat Piscirickettsia salmonis, currently considered the main bacterial threat to this industry. However, the increasing development of this industry in Chile, as well as the intensive use of antimicrobials, has not been accompanied by the necessary scientific research needed to understand the impact of the intensive use of antibiotics in this industry. Over the last two decades several studies assessing antimicrobial resistance and the resistome in the freshwater and marine environment impacted by salmon farming have been conducted, but information on the ecological and environmental consequences of antibiotic use in fish farming is still scarce. In addition, studies reporting the antimicrobial susceptibility of bacterial pathogens, mainly P. salmonis, have been developed, but a high number of these studies were aimed at setting their epidemiological cut-off values. In conclusion, further studies are urgently required, mainly focused on understanding the evolution and epidemiology of resistance genes in Chilean salmonid farming, and to investigate the feasibility of a link between these genes among bacteria from salmonid farms and human and fish pathogens.

Current Status of the Use of Antibiotics and the Antimicrobial Resistance in the Chilean Salmon Farms

The Chilean salmon industry has undergone a rapid development making the country the world's second largest producer of farmed salmon, but this growth has been accompanied by an intensive use of antibiotics. This overuse has become so significant that Chilean salmon aquaculture currently has one of the highest rates of antibiotic consumption per ton of harvested fish in the world. This review has focused on discussing use of antibiotics and current status of scientific knowledge regarding to incidence of antimicrobial resistance and associated genes in the Chilean salmonid farms. Over recent years there has been a consistent increase in the amount of antimicrobials used by Chilean salmonid farms, from 143.2 tons in 2010 to 382.5 tons in 2016. During 2016, Chilean companies utilized approximately 0.53 kg of antibiotics per ton of harvested salmon, 363.4 tons (95%) were used in marine farms, and 19.1 tons (5%) in freshwater farms dedicated to smolt production. Florfenicol and oxytetracycline were by far the most frequently used antibiotics during 2016 (82.5 and 16.8%, respectively), mainly being used to treat Piscirickettsia salmonis, currently considered the main bacterial threat to this industry. However, the increasing development of this industry in Chile, as well as the intensive use of antimicrobials, has not been accompanied by the necessary scientific research needed to understand the impact of the intensive use of antibiotics in this industry. Over the last two decades several studies assessing antimicrobial resistance and the resistome in the freshwater and marine environment impacted by salmon farming have been conducted, but information on the ecological and environmental consequences of antibiotic use in fish farming is still scarce. In addition, studies reporting the antimicrobial susceptibility of bacterial pathogens, mainly P. salmonis, have been developed, but a high number of these studies were aimed at setting their epidemiological cut-off values. In conclusion, further studies are urgently required, mainly focused on understanding the evolution and epidemiology of resistance genes in Chilean salmonid farming, and to investigate the feasibility of a link between these genes among bacteria from salmonid farms and human and fish pathogens.

Oxolinic Acid Binding at Goethite and Akaganéite Surfaces: Experimental Study and Modeling

Oxolinic acid (OA) is a widely used quinolone antibiotic in aquaculture. In this study, its interactions with synthetic goethite (α-FeOOH) and akaganéite (β-FeOOH) particle surfaces were monitored to understand the potential fate of OA in marine sediments where these phases occur. Batch sorption experiments, liquid chromatography (LC) analyses of supernatants, attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy and multisite complexation (MUSIC) modeling were used to monitor OA binding at these particle surfaces. Both LC and ATR-FTIR showed that adsorption did not degrade OA, and that OA adsorption was largely unaffected by NaCl concentrations (10-1000 mM). This was explained further by ATR-FTIR suggesting the formation of metal-bonded complexes at circumneutral to low pHc = -log [H(+)] and with a strongly hydrogen-bonded complex at high pHc. The stronger OA binding to akaganéite can be explained both by the higher isoelectric point/point-of-zero charge (9.6-10) of this mineral than of goethite (9.1-9.4), and an additional OA surface complexation mechanism at the (010) plane. Geminal sites (≡Fe(OH2)2(+)) at this plane could be especially reactive for metal-bonded complexes, as they facilitate a mononuclear six-membered chelate complex via the displacement of two hydroxo/aquo groups at the equatorial plane of a single Fe octahedron. Collectively, these findings revealed that Fe-oxyhydroxides may strongly contribute to the fate and transport of OA-type antibacterial agents in marine sediments and waters.

Degradation of oxolinic acid and flumequine in aquaculture pond waters and sediments

Oxolinic acid (OA) and flumequine (FLU) are two of the quinolone antibiotics (QAs) that are widely used in aquaculture. The purpose of this study was to understand the fates of OA and FLU in waters and sediment slurries from aquaculture ponds in a laboratory experiment. Waters and sediments were sampled from an eel (Anguilla japonica) pond and a shrimp (Penaeus vannamei) pond. The effects of light, microbial activities, and temperature on the degradation of these two QAs were elucidated. Results indicated that light plays a major role in the degradation of OA and FLU in waters and sediment slurries. Under illuminated and non-sterile conditions, the half-lives (t(1/2)) of OA were 2.3-4.8 and 9.5-15.0 days in the waters and sediment slurries, respectively. For FLU, under the same conditions, t(1/2) values were 1.9-2.3 and 3.6-6.4 days, respectively. Photodegradation of OA and FLU was much faster in water than in sediment slurry. In both environments, degradation became very slow or would plateau after only minimal change in the dark. Besides the effect of light, biodegradation had very minor effects on the degradation of the two QAs in the sediment slurries. The only independent biodegradation was found when OA was placed in shrimp pond sediment slurry, but at a much lower rate (t(1/2) of 98.7 days) than in light. Biodegradation of FLU was also found in the eel pond sediment slurry but only through an additional connection with light. Also, re-addition enhanced the degradation of OA in shrimp pond sediment slurry, but slowed the degradation of FLU in the eel pond sediment slurry in the dark. The temperature experiment in this study showed no significant effects on degradation of the two QAs in either pond waters or sediment slurries.

A preliminary investigation on the occurrence and distribution of antibiotics in the Yellow River and its tributaries, China

This study investigated the residues of antibiotics present in the Yellow River and its tributaries. Ofloxacin, norfloxacin, roxithromycin, erythromycin, and sulfamethoxazole, were found in the river with mean concentrations from 25 to 152 ng/L, and in certain tributaries from 44 to 240 ng/L. The other four analytes were all below the limits of quantification. The results indicated that the detected antibiotics in the middle and lower Yellow River were primarily from its tributaries and ambient wastewater discharge. The concentrations of the antibiotics detected in the river were greater than that in other rivers in Europe. The antibiotics in the river and its tributaries at ng/L concentrations found in this study are unlikely to induce lethal toxicity to aquatic organism but could cause chronic ecological effects.

The bryophyte Fontinalis antipyretica Hedw. bioaccumulates oxytetracycline, flumequine and oxolinic acid in the freshwater environment

In recent years, the fate of pharmacological substances in the aquatic environment have been more and more studied. Oxolinic acid (OA), flumequine (FLU) and oxytetracycline (OTC) are commonly used antibacterial agents. A large amount of these drugs is released into water directly by dissolved fraction and indirectly in urine and feces. Monitoring these compounds in the freshwater environment is difficult because of the lack of suitable indicators. The aim of this work was to evaluate the OA, FLU and OTC bioaccumulation abilities of Fontinalis antipyretica Hedw., known for heavy metal bioaccumulation. The experiment described was decomposed for two times: a 10-days accumulation period during which bryophytes were in contact with antibiotics and a 15-days post-exposure period during which bryophytes were in water with no antibiotic. This experiment showed that this bryophyte strongly accumulates OA, FLU and OTC in freshwater. Bioaccumulation factors (ratio of concentrations in bryophyte and water) ranged between 75 and 450. Moreover, OA, FLU and OTC persisted in the bryophyte for a long time with clearance between 0.19 and 3.04 ng/g/day. Mean residence times ranged between 18 and 59 days. Accumulation and decontamination mechanism models were proposed.

A single-dose pharmacokinetic study of oxolinic acid and vetoquinol, an oxolinic acid ester, in cod, Gadus morhua L., held in sea water at 8 degrees C and in vitro antibacterial activity of oxolinic acid against Vibrio anguillarum strains isolated from diseased cod

The pharmacokinetic properties of the antibacterial agent oxolinic acid and vetoquinol, the carbitol ester of oxolinic acid, were studied after intravenous (i.v.) and oral (p.o.) administration to 100-150 g cod, Gadus morhua L., held in sea water at 8 degrees C. Following i.v. injection, the plasma drug concentration-time profile showed two distinct phases. The distribution half-life (t1/2alpha) was estimated at 1.3 h, the elimination half-life (t1/2beta) as 84 h and the total body clearance (Cl(T)) as 0.047 L kg(-1) h(-1). The volume of distribution at steady state, Vd(ss) was calculated to be 5.5 L kg(-1), indicating good tissue penetration of oxolinic acid in cod. Following p.o. administration of oxolinic acid or vetoquinol, the peak plasma concentrations (C(max)) of oxolinic acid and the time to peak plasma concentrations (T(max) were estimated to be 1.2 and 2.5 microg mL(-1) and 24 and 12 h, respectively. The bioavailabilities of oxolinic acid following p.o. administration of oxolinic acid and vetoquinol were calculated to be 55 and 72%, respectively. The in vitro minimum inhibitory concentration (MIC) values of oxolinic acid against three strains of Vibrio anguillarum isolated from diseased cod were 0.016 microg mL(-1) (HI-610), 0.250 microg mL(-1) (HI-618) and 0.250 microg mL(-1) (HI-A21). Based on a MIC value of 0.016 microg mmL(-1) a single p.o. administration of 25 mg kg(-1) of oxolinic acid maintains plasma levels in excess of 0.064 microg mL(-1), corresponding to four times the MIC-value, for approximately 12 days. The analogous value for a single p.o. dose of 25 mg kg(-1) of oxolinic acid administered as vetoquinol was 13 days.