Temperature-dependent in vitro antimicrobial activity of four 4-quinolones and oxytetracycline against bacteria pathogenic to fish

Valorization of sesame seed coat waste: phenolic composition, antibacterial efficacy, and nanoemulsion encapsulation for food preservation

The study highlighted the potential of sesame seed coat (SSC), typically discarded during sesame paste processing, as a valuable resource for valorization through extracting bioactive compounds. It examined the phenolic composition and antioxidant activity of SSC, and evaluated its antibacterial properties against foodborne pathogens such as Listeria monocytogenes, Escherichia coli O157:H7, and Salmonella Typhimurium. Additionally, SSC underwent nanoemulsion coating, analyzed using dynamic light scattering and scanning electron microscopy, to enhance its application as a natural preservative. The research specifically focused on incorporating SSC nanoemulsion into milk to determine its effectiveness as a preservative. SSC demonstrated considerable antioxidant activity and phenolic content, with catechin identified as the predominant polyphenol. GC-MS analysis revealed seven major compounds, led by oleic acid. Notably, SSC effectively inhibited L. monocytogenes in broth at 100 mg/ml. The application of SSC and its nanoemulsion resulted in changes to bacterial morphology and a significant reduction in bacterial counts in milk, highlighting its potential as an effective natural antibacterial agent. The findings of this study highlight the potential use of SSC as a valuable by-product in the food industry, with significant implications for food preservation.

Pharmacokinetics, withdrawal period and risk assessment of enrofloxacin in the northern snakehead (Channa argus) following bath administration

Enrofloxacin (ENR) is widely used in aquaculture practice, but little is known about its pharmacokinetic, withdrawal period and dietary risk in fish via bath administration. The purpose of this study was to provide data support for the use of ENR bath therapy in the northern snakehead (Channa argus). The pilot study was carried out to evaluate the therapy concentrations of ENR in northern snakehead with immersion concentrations ranged from 5 to 40 mg/L for 6 h. Based on results of the pilot study, an ENR immersion concentration of 20 mg/L was used for the formal experiment. At this dose, the peak concentrations of ENR in plasma, muscle plus skin, liver and kidney were 4.85, 4.55, 3.87 and 7.42 μg/mL (or g), respectively. According to the AUC0-∞ values, the distribution of ENR in northern snakehead followed the order of kidney > plasma > liver > muscle + skin. The elimination of ENR in northern snakehead was very slow, the half-lives (T1/2λz ) were up to 90.31, 85.5, 104.56 and 120.9 h in plasma, muscle plus skin, liver and kidney, respectively. Ciprofloxacin (CIP) was not detected in any samples in the pilot study and was only occasionally detected in muscle plus skin and liver samples in formal experiment. Based on the calculated PK/PD index AUC/MIC and Cmax /MIC, the current bath treatment regimen will have a good therapeutic effect on infections caused by bacteria with MIC below 0.6 μg/mL. The dietary risk assessment suggested that there was a dietary risk (Hazard Quotients > 10%) until day 6 after bath treatment. It is mandatory for ENR to maintain a withdrawal period of at least 450°C-day in northern snakehead after bath treatment ceased.

Date (Phoenix dactylifera L.) seed oil is an agro-industrial waste with biopreservative effects and antimicrobial activity

Antimicrobial resistant (AMR) infections are a leading health threat globally. Previous literature has underscored the farm-to-fork continuum as a potential focal point for the emergence and spread of AMR. In the present study, date (Phoenix dactylifera L.) seed oil was investigated for its chemical composition and antimicrobial activity against common foodborne pathogens including Escherichia coli O157:H7, Salmonella enteritidis, Salmonella typhimurium, Listeria monocytogenes, and Staphylococcus aureus in vitro, and in ultra-high-temperature (UHT) milk as a food model at storage temperatures of 37 °C (24 h) and 10 °C (7 days). GC-MS analysis of the seed oil revealed 20 compounds, with octadecane (52.2-55.4%) as the major constituent, and the fatty acid analysis revealed 17 fatty acids, with oleic acid (42.3-43.1%) as the main constituent, followed by lauric acid (19.8-20.3%). The antimicrobial activity of date seed oil was determined using the microdilution method. A significant inhibition against gram-negative bacteria was noted in microbiological media and UHT milk, with a log reduction ranging from 4.3 to 6.7 (at 37 °C/24 h) and 5.7 to 7.2 (at 10 °C/7 days), respectively, at oil concentrations ranging between 10 and 15 µl/ml. The oil showed a similar significant inhibitory effect against St. aureus in the microbiological media (2.0-6.0 log reduction), whereas the inhibitory effect against L. monocytogenes was not statistically significant, with a maximum log reduction of 0.64 achieved at a concentration of 10 µl/ml. AFM imaging of the bacteria showed that oil treatment led to morphological changes in the bacteria including the formation of distorted shapes, surface blebs, indentations, stiffness, and swelling. Present findings suggest that date seed oil can be a promising by-product with potential antimicrobial activity and a food preservative.

Plasma and muscle tissue disposition of enrofloxacin in Nile tilapia (Oreochromis niloticus) after intravascular, intraperitoneal, and oral administrations

The aim of the study was to investigate the plasma and muscle pharmacokinetic of enrofloxacin (ENR) and its active metabolite ciprofloxacin (CIP) in Nile tilapia (Oreochromis niloticus) following single intravascular (IV), intraperitoneal (IP), or oral (PO) administration at 30 ± 1 °C. In this study, 234 healthy Nile tilapia (120-150 g) were used. The fish received a single IV, IP, or PO treatment of ENR at a dose of 10 mg/kg. The plasma and muscle tissue concentrations of ENR and CIP were measured using high-performance liquid chromatography with fluorescence detection and were evaluated using non-compartmental analysis. The elimination half-life, volume of distribution at steady state, and total body clearance of ENR were 21.7 h, 2.69 L/kg, and 0.09 L/h/kg, respectively. The peak plasma concentrations of ENR after IP or PO administration were 6.11 and 4.21 µg/mL at 0.25 and 2 h, respectively. The bioavailability of ENR for IP or PO routes was 78% and 86%, respectively. AUC_{(0-120)muscle}/AUC_{(0-120)plasma} ratios following the IV, IP, or PO administrations were 1.43, 1.49, and 1.07, respectively. CIP was detected after all routes, but the AUC_0-last ratios of CIP to ENR were <1.0% for plasma and muscle. ENR was detected up to 120 h following the IV, IP, or PO administrations. The long residence time of ENR after single IV, IP, or PO administration ensured the plasma concentration was ≥1 × MIC for bacteria with threshold MIC values of 0.92, 0.72, and 0.80 μg/mL over the whole 120 h observed. However, further studies are necessary to determine the optimum pharmacokinetic/pharmacodynamics data of ENR for the treatment of infections caused by susceptible bacteria in tilapia.

Pharmacokinetics and Tissue Residue Profiles of Enrofloxacin in Crucian Carp (Carassius auratus gibelio) Following Single and Multiple Oral Administration

The pharmacokinetics, tissue distribution, and elimination of enrofloxacin (ENR) and its metabolite ciprofloxacin (CIP) were investigated to the crucian carp (Carassius auratus gibelio) after single (20 mg/kg b. w.) and multiple oral administration (20 mg/kg b.w. one time daily for 5 days) at 28°C. The concentrations of ENR and CIP in the plasma and tested tissues (muscle/skin, liver, and kidney) were detected simultaneously by high-performance liquid chromatography (HPLC), and the pharmacokinetic data were analyzed with a non-compartmental model using WinNonLin 6.1 PK software (Pharsight Corporation, Mountain View, CA, USA). The pharmacokinetic characteristics of ENR in crucian carp exhibited slow absorption, wide tissue distribution, and long elimination half-life. In the single-dose group, the peak concentrations (Cmax) of ENR in the plasma, muscle/skin, liver, and kidney were 8.93 μg/mL, 13.9 μg/g, 31.2 μg/g, and 27.3 μg/g, respectively, observed at 3 h, 6 h, 1 h, and 3 h after dosing. The elimination half-lives (T1/2λz ) of ENR in plasma, muscle/skin, liver, and kidney were calculated to be 67.4, 82.8, 94.4, and 114 h, respectively. In the multiple-dose group, the Cmax of ENR in the plasma, muscle/skin, liver, and kidney were 18.4 μg/mL, 26.8 μg/g, 82.8 μg/g, and 74.5 μg/g, respectively, achieved at 3 h, 6 h, 1 h, and 1 h after the last dose. The T1/2λz of ENR in the plasma, muscle/skin, liver, and kidney were calculated to be 76.4 h, 91.5 h, 114 h, and 148 h, respectively. During the multiple-dose administration, significant accumulations of ENR and CIP were observed in the plasma and tissues of crucian carp, possibly due to their long elimination half-lives. In both dose groups, the AUC0-∞ for both ENR and CIP followed the order of liver > kidney > muscle/skin > plasma. The finding suggested that the liver may play an important role in the metabolism of ENR. According to the calculated PK/PD indices of Cmax/minimum inhibitory concentrations (MIC) and AUC24h/MIC, the multiple-dose regimen would be highly effective against pathogenic bacteria with a MIC value of ≤ 1.84 μg/ml. Depletion studies indicated that a withdrawal period of at least 29 or 32 days was necessary to guarantee food security after single or multiple oral gavage administration at 28°C.

EVALUATION OF LOCALIZED INFLAMMATORY REACTIONS SECONDARY TO INTRAMUSCULAR INJECTIONS OF ENROFLOXACIN IN STRIPED BASS (MORONE SAXATILIS)

Enrofloxacin is a fluoroquinolone widely used in animals including fish. Intramuscular (IM) injection of enrofloxacin is a feasible and efficacious option for drug delivery. In many species IM injection has been associated with injection site reactions and increases in serum muscle enzymes. Injection site reactions have not been well characterized in fish. Three groups of striped bass (Morone saxatilis) received an IM injection of enrofloxacin 2.27% in the right epaxial musculature 24, 48, or 96 hr prior to evaluation. Mean dose was 7.69 mg/ kg (6.14-9.69 mg/kg). The 24- and 48-hr groups received an injection of equal-volume 0.9% saline in the left epaxial musculature. A corresponding noninjected tissue sample was designated in the left epaxial musculature from each fish of the 96-hr group. Fish were euthanized and injection sites and noninjection control sites were evaluated grossly and histologically. Grades 1-4 were assigned to samples, with grade 1 corresponding to normal tissue and grades 2, 3, and 4 corresponding to mild, moderate, and severe inflammation and/or necrosis respectively. Externally, all control and injection sites appeared visually unremarkable. On cut surface, epaxial muscle of the enrofloxacin-injected tissue appeared moderately to severely hemorrhagic compared to saline and noninjected tissue, which was normal or mildly hemorrhagic. Histologically, eight of eight noninjected tissues were grade 1. For saline-injected tissues, 14 of 16 tissues were grade 2 and 2 samples were grade 3 when 24- and 48-hr groups were combined. For enrofloxacin-injected tissues, 8 of the 8 24-hr samples were grade 3 and 16 of the 16 48- and 96-hr samples were grade 4. These data show that IM injection of enrofloxacin 2.27% is associated with severe hemorrhage, necrosis, and inflammation in striped bass, and may negatively affect animal welfare.

Pharmacokinetics and tissue residues of enrofloxacin in the largemouth bass (Micropterus salmoides) after oral administration

The study was carried out to evaluate the pharmacokinetic disposition of enrofloxacin (ENF) with a single dose of 20 mg/kg after oral administration in largemouth bass (Micropterus salmoides) at 28°C. The concentrations of ENF and of its metabolite ciprofloxacin (CIP) in plasma, liver, and muscle plus skin in natural proportions were determined using HPLC. The concentration-time data for ENF in plasma were best described by a two-compartment open model. After oral administration, the maximum ENF concentration (C_max ) of 10.99 μg/ml was obtained at 0.60 hr. The absorption half-life (T_1/2Ka ) of ENF was calculated to be 0.07 hr whereas the elimination half-life (T_1/2β ) of the drug was 90.79 hr. The estimates of area under the plasma concentration-time curve (AUC) and apparent volume of distribution (Vd/F) were 1,185.73 μg hr/ml and 2.21 L/kg, respectively. ENF residues were slowly depleted from the liver and muscle plus skin of largemouth bass with the T_1/2β of 124.73 and 115.14 hr, respectively. Very low levels of ciprofloxacin were detected in the plasma and tissues. A withdrawal time of 24 days was necessary to ensure that the residues of ENF + CIP in muscle plus skin were less than the maximal residue limit (MRL) of 100 μg/kg established by the European Union.

Enrofloxacin Pharmacokinetics and Sampling Techniques in California Sea Hares (Aplysia californica)

This pharmacokinetic study was designed to determine the pharmacokinetics of enrofloxacin at 5 mg/kg when given to sea hares in their hemolymph. Enrofloxacin is a commonly used antimicrobial in veterinary medicine and potentially could be used to treat sea hares exposed to susceptible bacterial species. We individually identified 8 juvenile Aplysia californica and group housed them in an open seawater flow system at 14 to 18 °C; 2 served as untreated controls. The remaining 6 animals were injected into the hemocoel with 0.030 mL of 22.7 mg/mL enrofloxacin (average dose, 5 to 6 mg/kg). At each time point, 300 μL hemolymph was collected from the pedal hemolymph sinus and HPLC-analyzed for enrofloxacin and ciprofloxacin levels. Enrofloxacin was detected in all dosed animals, at an average peak concentration of 3 μg/mL in hemolymph, and remained in the body for 20.3 h with an average clearance of 0.19 μg × h/mL. No ciprofloxacin was detected in any Aplysia in this study. Hemocoel injection appears to be an effective way to administer enrofloxacin to Aplysia and reach clinically relevant concentrations. Enrofloxacin reached therapeutic target concentrations in A. californica when dosed according to the regimen described in the current report.

Pharmacokinetic/pharmacodynamic relationship of enrofloxacin against Aeromonas hydrophila in crucian carp (Carassius auratus gibelio)

The pharmacokinetic (PK) properties of enrofloxacin (ENR) and its metabolite ciprofloxacin (CIP) were investigated in crucian carp following oral administration at different dose levels (5, 10, 20, 40 mg/kg body weight). The disposition kinetics of ENR was found to be linear over the dose range studied. Serum half-lives ranged from 64.56 to 72.68 hr. The in vitro and ex vivo activities of ENR in serum against a pathogenic strain of Aeromonas hydrophila were determined. In vitro and ex vivo bactericidal activity of ENR was concentration dependent. Dosing of 10 mg/kg resulted in an AUC/minimum inhibitory concentration (MIC) ratio of 368.92 hr and a C_max /MIC ratio of 7.23, respectively, against A. hydrophila 147 (MIC = 0.48 μg/ml), indicating a likely high level of effectiveness in clinical infections caused by A. hydrophila with MIC value ≤ 0.48 μg/ml. Modeling of ex vivo growth inhibition data to the sigmoid Emax equation provided the values of AUC_24 hr /MIC required to produce bacteriostasis, bactericidal activity, and elimination of bacteria, these values were 21.70, 53.01, and 125.21 hr, respectively. These findings in conjunction with MIC₉₀ data suggested that ENR at the dose of 7.81 mg/kg predicted a positive clinical outcome and minimize the risk of emergence of resistance.

Pharmacokinetics of enrofloxacin after oral, intramuscular and bath administration in crucian carp (Carassius auratus gibelio)

The pharmacokinetics of enrofloxacin (ENR) was studied in crucian carp (Carassius auratus gibelio) after single administration by intramuscular (IM) injection and oral gavage (PO) at a dose of 10 mg/kg body weight and by 5 mg/L bath for 5 hr at 25°C. The plasma concentrations of ENR and ciprofloxacin (CIP) were determined by HPLC. Pharmacokinetic parameters were calculated based on mean ENR or CIP concentrations using WinNonlin 6.1 software. After IM, PO and bath administration, the maximum plasma concentration (C_max ) of 2.29, 3.24 and 0.36 μg/ml was obtained at 4.08, 0.68 and 0 hr, respectively; the elimination half-life (T_1/2β ) was 80.95, 62.17 and 61.15 hr, respectively; the area under the concentration-time curve (AUC) values were 223.46, 162.72 and 14.91 μg hr/ml, respectively. CIP, an active metabolite of enrofloxacin, was detected and measured after all methods of drug administration except bath. It is possible and practical to obtain therapeutic blood concentrations of enrofloxacin in the crucian carp using IM, PO and bath immersion administration.

Antibacterial activity of poly-l-arginine under different conditions

BACKGROUND AND OBJECTIVES

Arginine-rich peptides are an important class of antimicrobial peptides (AMPs) that exert their antibacterial activity via a lytic mechanism. Although the antibacterial activity of arginine-rich peptides has been already evaluated, no reports have so far been evaluated the influence of reaction conditions on their antimicrobial potential. The aim of the present study was to investigate the influence of pH, temperature, and glycine on antibacterial activity of poly-l-arginine (PLA) with a molecular weight of 5-15 kDa against Escherichia coli O157:H7 and Staphylococcus aureus.

MATERIALS AND METHODS

The percentage of growth inhibition of PLA against both bacteria was analyzed at various pH, temperatures and sub-inhibitory concentrations of glycine by two-fold broth microdilution method.

RESULTS

The results showed that PLA had antibacterial activity against E. coli O157:H7 and S. aureus and the inhibitory effect increased with increasing PLA concentration. The antimicrobial activity of PLA against both microorganisms was higher in basic media than under acidic or neutral conditions. At 1/2 times the MIC, heat treatment intensified the toxicity of PLA against E. coli O157:H7 whereas the susceptibility to PLA seems to be temperature independent for S. aureus. The MICs of glycine against E. coli O157:H7 and S. aureus were 12.5 and 25 mg ml^-1, respectively. The antibacterial activity of PLA against both microorganisms increased, as indicated by the increasing growth inhibition percentage of this peptide with increasing glycine concentration.

CONCLUSION

The antibacterial activity of PLA against S. aureus and E. coli O157:H7 depends on pH and glycine concentration.

Ceftiofur pharmacokinetics in Nile tilapia Oreochromis niloticus after intracardiac and intramuscular administrations

Ceftiofur is a broad-spectrum third generation cephalosporin, which acts by inhibiting bacterial cell wall synthesis. It is active against Gram-positive and Gram-negative bacteria such as Aeromonas hydrophila and β-lactamase-producing strains, which are common pathogens in freshwater fish. Ceftiofur pharmacokinetics in Nile tilapia Oreochromis niloticus were studied following single intracardiac (i.c.) or intramuscular (i.m.) administration of ceftiofur sodium (NAXCEL®) in a dose of 5 mg ceftiofur kg-1 body weight. After i.c. injection, ceftiofur plasma concentrations decreased biexponentially, suggesting a 2-compartmental open model. Distribution and elimination half-lives (t0.5(α) and t0.5(β)) were 0.61 ± 0.22 and 0.14 ± 0.03 h mean ±SD, respectively. Elimination constant (Kel) and total body clearances (Cltot) were 3.22 ± 0.48 h-1 and 1.64 ± 0.47 l h-1 kg-1, respectively. Volume of distribution (Vss) and areas under curves (AUC) were 0.12 ± 0.03 l kg-1 and 24.18 ± 8.81 µg ml-1 h, respectively. Following i.m. injection of ceftiofur, plasma concentrations were best described by a 1-compartment open model with a first order absorption; bioavailability was quite high (96.85 ± 23.74%). Plasma maximum concentration (Cmax) was 12.32 ± 6.53 µg ml-1; achieved at time of maximum concentration (Tmax) of 0.74 ± 0.04 h. Absorption and elimination half-lives (t0.5ab and t0.5β) were 0.49 ± 0.06 and 0.53 ± 0.03 h, respectively. In conclusion, i.m. injection of ceftiofur sodium produced extremely high bioavailability with high plasma concentrations that persisted up to 6 h post injection, which may make ceftiofur a useful alternative antibiotic for treatment of brood stock or important ornamental fishes.

Temperature effects on the antimicrobial efficacy of condensed smoke and lauric arginate against Listeria and Salmonella

Condensed smoke or liquid smoke (LS) and lauric arginate (LAE) are antimicrobials used in food preservation. They have demonstrated abilities to reduce or inhibit pathogenic and spoilage organisms. Few studies, however, have reported on the effectiveness of LS or LAE over the range of temperatures typically encountered in food marketing channels. Therefore, the effects of temperature on the antimicrobial properties of two commercial LS fractions, an LS derived from pecan shells, and LAE against two common foodborne pathogens, Listeria and Salmonella, were investigated. The MICs of the three LS samples and LAE were measured at 4, 10, and 37°C for Listeria monocytogenes strains 2045 (Scott A, serotype 4b) and 10403S (serotype 1/2a) and two strains of Listeria innocua, a well-established surrogate, and at 10, 25, and 37°C for Salmonella enterica serovar Typhimurium and Salmonella enterica serovar Heidelberg. The MICs for LS against Listeria ranged from 3 to 48% (vol/vol), with higher MICs seen with lower temperatures. The MICs for LS on Salmonella ranged from 3 to 24%. Values for LAE ranged between 0.004 and 0.07% for both pathogens, and like LS, higher MICs were always associated with lower incubation temperatures. Understanding how storage temperature affects the efficacy of antimicrobials is an important factor that can contribute to lowering the hurdles of use levels and costs of antimicrobials and ultimately improve food safety for the consumer.

Effect of biofilm formation on antimicrobial tolerance of Flavobacterium psychrophilum

Treatment of bacterial fish diseases can be complicated by resistant bacterial biofilms harbouring pathogenic bacteria and causing recurrent exposure of fish to infections. In this study, the effect of biofilm formation on antimicrobial tolerance was examined using three bacterial isolates of the fish pathogen Flavobacterium psychrophilum and two antimicrobial agents, oxytetracycline and flumequine, commonly used in aquaculture. Planktonic and biofilm cells were exposed to a minimum inhibitory concentration (MIC), to a 3 × MIC concentration and to an environmental concentration level of each antimicrobial in 96-well microtitre plates after which growth on agar plates was measured. The type strain NCIMB1947 of F. psychrophilum was further used to study the development of antimicrobial resistance in biofilm cells. The results suggest that at high bacterial densities (>10(7) CFU mL(-1)), biofilm cells of F. psychrophilum are less susceptible to antimicrobial agents. Furthermore, the results imply that biofilm cells of F. psychrophilum may rapidly develop resistance to both oxytetracycline and flumequine if exposed to subinhibitory concentrations of these antimicrobials.

Oxytetracycline hydrochloride vital labelling revisited: the case of Dicentrarchus labrax and Diplodus puntazzo

The main objective of this study was to determine the optimal oxytetracycline hydrochloride (OTC) dosage for otolith marking in Dicentrarchus labrax and Diplodus puntazzo. Adult reared individuals of these two species were marked with OTC intraperitoneal injections at three recommended doses (25, 45 and 60 mg kg(-1) fish) and a blank. Fishes were monitored for 36-49 days from when they were marked. The effectiveness of the otolith marking was inversely related to the OTC dosage. The injections were found to have deleterious effects at the highest dosages: (1) mortality was nearly 0% during the first 4 days but then it suddenly rose to 85-100% depending on the fish and treatment, (2) no daily growth increments were formed after marking and (3) no or negative somatic growth was observed. These results suggest that most of the current studies using OTC marking for estimating mortality of wild fishes use an observation period between marking the fishes and releasing that is too short to allow the deleterious effects of OTC to be detected. Species-specific experiments for assessing the long-term mortality should be undertaken when OTC marking is used on wild fishes.

Dispositions and residue depletion of enrofloxacin and its metabolite ciprofloxacin in muscle tissue of giant freshwater prawns (Macrobrachium rosenbergii)

Fates and residue depletion of enrofloxacin (ER) and its metabolite ciprofloxacin (CP) were examined in giant freshwater prawns, Macrobrachium rosenbergii, following either single oral (p.o.) administration of ER at a dosage of 10 mg/kg body weight (b.w.) or medicated-feed treatment at the feeding concentration of 5 g/kg of feed for five consecutive days. The concentrations of ER and CP in prawn muscle tissues were measured simultaneously using high-performance liquid chromatography (HPLC) equipped with a fluorescence detector. Muscle tissue concentrations of ER and CP were below the detection limit (LOD, 0.015 microg/g for ER; 0.025 microg/g for CP) after 360 and 42 h, following single p.o. administration respectively. Peak muscle concentration (C(max)) of ER was 1.98 +/- 0.22 microg/g whereas CP was measurable at concentrations close to the detection limit of the analytical method after p.o. administration at a single dosage of 10 mg/kg b.w. The concentration of ER in prawn muscle tissue with respect to time was analyzed with a non-compartmental pharmacokinetic model. The elimination half-life and area under the curve of ER were 39.33 +/- 7.27 h and 168.7 +/- 28.7 microg x h/g after p.o. administration at a single dose of 10 mg/kg x b.w. respectively. In medicated-feed treated group, ER was detectable in prawn muscle tissue 11 days postdosing at the dose of 5 g/kg of feed for five consecutive days, which is the value corresponding to the maximum residue limit (MRL) of ER in animal products. The maximum concentrations of ER and CP were 2.77 +/- 0.91 and 0.06 +/- 0.006 microg/g during medicated-feed treatment and postdosing respectively. The values of elimination half-life and absorption half-life of ER after single p.o. administration at a dosage of 10 mg/kg b.w. corresponded well with the values determined from medicated-feed treated group, showing 41.01 +/- 6.62 and 11.36 +/- 3.15 h respectively in M. rosenbergii. Based on data derived from this study, to avoid the ER residue in prawn muscle, it should take at least 11 days postcessation of medicated feed containing ER at the dose concentration of 5 g/kg of feed twice a day at a rate of 1% of total body weight for five consecutive days to wash out the drug from the muscle of M. rosenbergii.

Species differences in pharmacokinetics and pharmacodynamics

Veterinary medicine faces the unique challenge of having to treat many types of domestic animal species, including mammals, birds, and fishes. Moreover, these species have evolved into genetically unique breeds having certain distinguishable characteristics developed by artificial selection. The main challenge for veterinarians is not to select a drug but to determine, for the selected agent, a rational dosing regimen because the dosage regimen for a drug in a given species may depend on its anatomy, biochemistry, physiology, and behaviour as well as on the nature and causes of the condition requiring treatment. Both between- and within-species differences in drug response can be explained either by variations in drug pharmacokinetics (PK) or drug pharmacodynamics (PD), the magnitude of which varies from drug to drug. This chapter highlights selected aspects of species differences in PK and PD and considers underlying physiological and patho-physiological mechanisms in the main domestic species. Particular attention was paid to aspects of animal behaviour (food behaviour, social behavior, etc.) as a determinant of interspecies differences in PK or/and PD. Modalities of drug administration are many and result not only from anatomical, physiological and/or behavioural differences across species but also from management options. The latter is the case for collective/group treatment of food-producing animals, frequently dosed by the oral route at a herd or flock level. After drug administration, the main causes of observed inter-species differences arise from species differences in the handling of drugs (absorption, distribution, metabolism, and elimination). Such differences are most common and of greatest magnitude when functions which are phylogenetically divergent between species, such as digestive functions (ruminant vs. non-ruminant, carnivore vs. herbivore, etc.), are involved in drug absorption. Interspecies differences also exist in drug action but these are generally more limited, except when a particular targeted function has evolved, as is the case for reproductive physiology (mammals vs. birds vs. fishes; annual vs. seasonal reproductive cycle in mammals; etc.). In contrast, for antimicrobial and antiparasitic drugs, interspecies differences are more limited and rather reflect those of the pathogens than of the host. Interspecies difference in drug metabolism is a major factor accounting for species differences in PK and also in PD (production or not of active metabolites). Recent and future advances in molecular biology and pharmacogenetics will enable a more comprehensive view of interspecies differences and also between breeds with existing polymorphism. Finally, the main message of this review is that differences between species are not only numerous but also often unpredictable so that no generalisations are possible, even though for several drugs allometric approaches do allow some valuable interspecies extrapolations. Instead, each drug must be investigated on a species-by-species basis to guarantee its effective and safe use, thus ensuring the well-being of animals and safeguarding of the environment and human consumption of animal products.

gyrA and parC Mutations and associated quinolone resistance in Vibrio anguillarum serotype O2b strains isolated from farmed Atlantic cod (Gadus morhua) in Norway

MIC testing of Vibrio anguillarum isolates recovered from diseased farmed Atlantic cod revealed oxolinic acid MICs of < or =0.001, 0.06, and 16 microg ml(-1). Single gyrA Ser-Ile substitutions were identified at position 83 of the intermediate and resistant strains, while a parC Ser-Leu substitution at position 85 was found only in the resistant strain.

Pharmacokinetics of enrofloxacin in Korean catfish (Silurus asotus)

The objective of this study was to evaluate the pharmacokinetic profile of enrofloxacin and its active metabolite, ciprofloxacin, in Korean catfish after intravenous and oral administrations. Enrofloxacin was administered to Korean catfish by a single intravenous and oral administrations at the dose of 10 mg/kg body weight. The plasma concentrations from intravenous and oral administrations of enrofloxacin were determined by LC/MS. Pharmacokinetic parameters from both routes were described to have a two-compartmental model. After intravenous and oral administrations of enrofloxacin, the elimination half-lives (t(1/2,beta)), area under the drug concentration-time curves (AUC), oral bioavailability (F) were 17.44 +/- 4.66 h and 34.13 +/- 11.50 h, 48.1 +/- 15.7 microgxh/mL and 27.3 +/- 12.4 microgxh/mL, and 64.59 +/- 4.58% respectively. The 3.44 +/- 0.81 h maximum concentration (C(max)) of 1.2 +/- 0.2 microg/mL. Ciprofloxacin, an active metabolite of enrofloxacin, was detected at all the determined time-points from 0.25 to 72 h, with the C(max) of 0.17 +/- 0.08 microg/mL for intravenous dose. After oral administration, ciprofloxacin was detected at all the time-points except 0.25 h, with the C(max) of 0.03 +/- 0.01 microg/mL at 6.67 +/- 2.31 h. Ciprofloxacin was eliminated with terminal half-life t(1/2,beta) of 52.08 +/- 17.34 h for intravenous administration and 52.43 +/- 22.37 h for oral administration.

In vitro susceptibility of antibiotics against Vibrio spp. and Aeromonas spp. isolated from Penaeus monodon hatcheries and ponds

Susceptibility patterns to 16 different antibiotics were investigated against pathogenic Vibrio spp. and Aeromonas spp. isolated from shrimp culture hatcheries and ponds in India. Thirteen species of Vibrio (N = 90) and two species of Aeromonas (N = 7) isolates were tested by agar disk diffusion. The results show that 100% of the isolates were resistant to ampicillin, and that 43.2% and 47.4% were sensitive to chlortetracycline and erythromycin, respectively. Susceptibility patterns of another 160 isolates belonging to the genera Vibrio and Aeromonas obtained from the water samples of shrimp hatcheries and ponds were tested against six commonly used antibiotics. Results indicate that isolates from the hatcheries were more resistant to antimicrobials than isolates from the ponds. The minimum inhibitory concentrations of five antibiotics against the different Vibrio spp. and Aeromonas spp. were determined. Ciprofloxacin was found to be the most effective in controlling the isolates from hatcheries and ponds compared with the other antibiotics used in the study. Our results reveal that antibiotic-resistant bacteria are widespread in the shrimp culture hatcheries and ponds in India. Potential risk to human health was not addressed in this study and remains to be elucidated.

Enrofloxacin pharmacokinetics in the European cuttlefish, Sepia officinalis, after a single i.v. injection and bath administration

Enrofloxacin pharmacokinetics were studied in European cuttlefish, Sepia officinalis, after a single 5 mg/kg i.v. injection or a 2.5 mg/L 5 h bath. A pilot study with two animals was also performed following a 10 mg/kg p.o. administration. The concentration of enrofloxacin in hemolymph was assayed using high-performance liquid chromatography (HPLC) and pharmacokinetic parameters were derived from compartmental methods. In the i.v. study, the terminal half-life (t(1/2)), apparent volume of distribution, and systemic clearance were respectively 1.81 h, 385 mL/kg, and 4.71 mL/min/kg. Following bath administration the t(1/2), peak hemolymph concentration (C(max)), and area under the curve to infinity (AUC(0-infinity)) were 1.01 h, 0.5 +/- 0.12 mug/mL, and 0.98 microg.h/mL, respectively. After oral administration, the t(1/2), C(max), and AUC(0-infinity) were 1.01 h, 10.95 microg/mL, 26.71 mug.h/mL, respectively. The active metabolite of enrofloxacin, ciprofloxacin, was not detected in any samples tested. The hemolymph concentration was still above minimum inhibitory concentration (MIC) values for shrimp and fish bacterial isolates at 6 h after i.v. administration, therefore, a dose of 5 mg/kg i.v. every 8-12 h is suggested for additional studies of efficacy. The C(max) value for the water bath was lower than for the i.v. study, but a bath of 2.5 mg/L for 5 h once to twice daily is suggested for additional studies to test efficacy against highly susceptible organisms. Although only two animals were used for the oral study, a dose of 10 mg/kg produced hemolymph concentrations of enrofloxacin that were in a range consistent with therapeutic efficacy in other species.

Evaluation of a method of intracoelomic catheterization in koi

OBJECTIVE

To develop an easy and safe method for catheterization and determine the pharmacokinetics of a single dose of enrofloxacin after intracoelomic administration in koi.

DESIGN

Prospective study.

ANIMALS

20 healthy koi.

PROCEDURE

6 koi were anesthetized with tricaine methanesulfonate, and a 23-gauge, three-fourths-inch butterfly catheter was inserted into the coelomic cavity and secured. Catheters were flushed daily for 6 days with 0.4 mL of sterile saline (0.9% NaCl) solution containing heparin (100 units of heparin in 250 mL of saline solution) without removing koi from the aquarium. At the end of the sixth day (144 hours), each of the 6 catheterized koi and 6 uncatheterized (control) koi was anesthetized individually. Enrofloxacin (10 mg/kg [4.5 mg/lb]) was administered to catheterized koi via the injection port and to control koi via a 23-gauge needle in the same site as the catheter placement. A pharmacokinetics study was performed on multiple plasma samples to validate the efficiency of the catheter. Reliability of the catheterization method was determined in 8 koi.

RESULTS

All 6 catheters remained patent and effective for the 6 days prior to the start of the pharmacokinetics study. Results for the 2 routes of administration were comparable, and all koi survived the study without any detectable clinical problems.

CONCLUSIONS AND CLINICAL RELEVANCE

An intracoelomic catheter was effective and safe when maintained in koi for at least 6 days. This would be highly beneficial for veterinarians, clients, and fish, especially when intracoelomic administration of a drug would require daily or more frequent dosing.

The efficacy of a single intraperitoneal injection of oxolinic acid in the treatment of bacterial infections in goldsinny wrasse (Ctenolabrus rupestris) and corkwing wrasse (Symphodus melops) studied under field and laboratory conditions

The efficacy of a single intraperitoneal injection of oxolinic acid to control an outbreak of atypical Aeromonas salmonicida infection in goldsinny wrasse (Ctenolabrus rupestris) and in the treatment of systemic vibriosis in corkwing wrasse (Symphodus melops) was examined. In addition a field study was performed to examine the effect of medication on the survival rate of goldsinny wrasse in Atlantic salmon cages. Four groups of wild caught goldsinny wrasse, each of 50 fish, were treated with an intraperitoneal injection of propylene glycol:saline (50:50) (control) or 50 mg/kg oxolinic acid at a concentration of 50 mg/mL. Three days after medication the fish in all groups were treated by an intraperitoneal injection of prednisolone acetate and an increase in seawater temperature from 9.0 to 11.5 degrees C. Cumulative mortalities were 18% in the two groups treated with oxolinic acid and 94 and 100% in the unmedicated control groups, giving a 'relative percentage survival' (RPS) value of 82%. A laboratory maintained population of originally wild caught corkwing wrasse experiencing high daily mortality was treated with oxolinic acid (50 mg/kg) or propylene glycol:saline (control). Cumulative mortalities were 84% (control) and 42% (oxolinic acid medicated group) giving an RPS value of 50%. In a field investigation using goldsinny wrasse approximately 30% were medicated with oxolinic acid (50 mg/kg) prior to stocking in cages with Atlantic salmon. In two of three cages the cumulative mortality was significantly lower (P = 0.025 and P < 0.001) in the medicated groups.

Class 1 integrons mediate antibiotic resistance in the fish pathogen Aeromonas salmonicida worldwide

The presence of class 1 integrons was investigated in 38 sulfonamide-resistant strains of Aeromonas salmonicida subsp. salmonicida, atypical A. salmonicida and Escherichia coli conjugants with R plasmids originating from A. salmonicida. The strains originated from Finland, France, Japan, Norway, Scotland, Switzerland, and the United States. Additional resistance determinants in strains with class 1 integrons were also determined. Of 21 strains containing a class 1 integron, 19 had a single gene cassette, 1 strain had two cassettes, and 1 strain was found to lack an integrated gene cassette. In the integrons with single cassettes, aadA2 was present in eight strains, dfr16 in five strains, and aadA1 and dfrIIc in three strains each. In the integron with two cassettes, qacG and orfD were present. Tetracycline resistance was observed in 20 of the integron-positive strains, caused by the determinants Tet A and Tet E, in which Tet A frequently was associated with Tn1721. Class 1 integrons seem to be important in mediating antibiotic resistance also in the marine environment. The gene cassettes reported in this study are all described in bacteria associated with humans, and this demonstrates once more how the common gene pool is shared between organisms belonging to different environments.

A global non-conjugative Tet C plasmid, pRAS3, from Aeromonas salmonicida

Two 11.8 kb non-conjugative, but mobilizable R plasmids designated pRAS3.1 and pRAS3.2 were isolated from Aeromonas salmonicida subspecies salmonicida and atypical A. salmonicida, respectively. Differences between the plasmids were of minor extent and they are considered as being variants of the same plasmid, pRAS3. The genes repA, repB, mobA, mobC, mobD, and mobE were organized similar to corresponding genes in the small, mobilizable plasmid pTF-FC2 isolated from Acidithiobacillus ferrooxidans (previously Thiobacillus ferrooxidans). The nucleotide identity between these genes from pRAS3.1 and pTF-FC2 ranged from 89.5 to 98.2%. The tetA(C), tetR(C), and approximately 960 base pairs adjacent to tetR(C) were highly similar to the nucleotide sequence in pSC101. Plasmid pRAS3 was also found in a Scottish A. salmonicida strain, and appears to be identical to the R plasmid pJA8102-2 isolated from A. salmonicida in Japan.

Functional Tn5393-like transposon in the R plasmid pRAS2 from the fish pathogen Aeromonas salmonicida subspecies salmonicida isolated in Norway

Tn5393c containing strA-strB was identified as part of R plasmid pRAS2 from the fish pathogen Aeromonas salmonicida subsp. salmonicida. This is the first time an intact and active transposon in the Tn5393 family has been reported in an ecological niche other than an agricultural habitat.

Pharmacokinetic and depletion studies of sarafloxacin after oral administration to eel (Anguilla anguilla)

The pharmacokinetics of sarafloxacin applied by oral gavage at a dose of 15 mg/kg b.w. was studied in eel (Anguilla anguilla) at water temperature of 24 degrees C. Sarafloxacin levels were determined using high performance liquid chromatography with a quantitation limit of 0.07 microg/ml or gram. The time to peak plasma concentration, Tmax, was 12 hr and peak concentration, Cmax, was 2.64 microg/ml. The absorption rate constant (k(a)) was 0.23 hr(-1) (r=0.996). The drug disposition curve after Tmax was fitted to a two-compartment open model. The distribution rate constant (alpha) was 0.085 hr(-1) (r=0.972), and the half-life (t(1,2alpha)) was 8.15 hr. The elimination rate constant (beta) was 0.023 hr(-1) (r=0.909), and the half-life (t(1/2beta)) was 30.13 hr. The estimated area under the curve, AUC, was 56.7 microg.hr/ml. The peak concentrations of drug in liver, kidney, muscle, and skin were 13.39 (12 hr), 5.53 (12 hr), 1.82 (24 hr), and 0.78 microg/g (40 hr), respectively. The time for sarafloxacin mean levels to fall below detectable limits in the plasma, muscle, and skin were 7 days but for the liver and kidney were 14 days.

Single-dose pharmacokinetics of flumequine in halibut (Hippoglossus hippoglossus) and turbot (Scophthalmus maximus)

Flumequine was administered to halibut (Hippoglossus hippoglossus) and turbot (Scophthalmus maximus) intravenously (i.v.) and orally (p.o.) at a dose of 10 mg/ kg bodyweight, and as a bath-treatment at a dose of 10 mg/L water for 2 h, using identical experimental designs. The study was performed in seawater with a salinity of 3% and a temperature of 10.3+/-0.4 degrees C (halibut) and 18.0+/-0.3 degrees C (turbot). Pharmacokinetic modelling of the data showed that flumequine had quite similar pharmacokinetic properties in halibut and turbot. Following intravenous administration, the volumes of distribution at steady state (Vss) were 2.99 L/kg (halibut) and 3.75 L/kg (turbot). Plasma clearances (Cl) were 0.12 L/kg (halibut) and 0.17 L/h x kg (turbot) and the elimination half-lives (t(1/2lambdaz)) were calculated to be 32 h (halibut) and 34 h (turbot). Mean residence times (MRT) were 25.1 h (halibut) and 22.2 h (turbot). Following oral administration, the t(1/2lambdaz) were 43 h (halibut) and 42 h (turbot). Maximal plasma concentrations (tmax) were 1.4 mg/L (halibut) and 1.9 mg/L (turbot), and were observed 7 h post administration in both species. The oral bioavailabilities (F) were calculated to 56% (halibut) and 59% (turbot). Following bath administration maximal plasma concentrations were 0.08 mg/L (halibut) and 0.14 mg/ L (turbot), and were observed 0 h (halibut) and 3 h (turbot) after the end of the bath. The bioavailability in halibut following a 2-h bath treatment was 5%.

Absorption and excretion of cefquinome in coho salmon (Oncorhynchus kisutch) in freshwater at 10 degrees C

The absorption and elimination of cefquinome in serum and tissues of coho salmon were studied. The study was performed in freshwater at 10 degrees C with fish weighing 100 +/- 5 g (mean and standard deviation). Single doses of 5, 10 and 20 mg/kg were administered intraperitoneally to 30 fish for each dose. The maximum concentration occurred in the following order; kidney and liver > serum > muscle > brain. The pharmacokinetic analysis and predictive withdrawal times were calculated using only the dose of 20 mg/kg body weight. The peak cefquinome concentrations (Cmax) in serum (3.35 +/- 0.45 micrograms/ml) and muscle (2.87 +/- 0.53 micrograms/g) were achieved at 12 h. In the brain, the Cmax was 2.18 micrograms/g at 6 h. The half-lives (t1/2) in serum, muscle, brain, liver and kidney were 20.56, 8.93, 9.35, 113.61 and 119.48 h, respectively. With the detection limit of 0.015 microgram/g for the cefquinome, the predicted withdrawal time with 95% confidence for muscle tissue was 104.2 h at 10 degrees C for the 20 mg/kg dose. The results suggest that cefquinome could be efficacious and safe for the consumer in treating bacterial diseases of coho salmon in fresh water. Nevertheless, future studies are required in order to determine an adequate dose with the corresponding withdrawal times.

Pharmacokinetics of a discontinuous absorption process of oxolinic acid in turbot, Scophthalmus maximus, after a single oral administration

1. The pharmacokinetics of oxolinic acid have been studied in 500 g turbot (Scophthalmus maximus). The fish were kept in seawater at 16 degrees C with a 15 h/9 h photoperiod. Oxolinic acid was administered orally via a stomach tube at a single dose of 10 mg/kg of body weight. Serum concentrations of oxolinic acid were determined by a (HPLC) using liquid phase extraction with an internal standard and a fluorescence detection. 2. The pharmacokinetic process was not significantly sex-influenced. The short elimination phase of the oxolinic acid in turbot after oral administration was similar to the elimination after intravascular administration. The serum concentration profile of oxolinic acid was better described by a discontinuous absorption model than by compartment models using continuous absorption processes. The absorption of oxolinic acid in turbot was characterized by two distinct phases after a lag time of about 2 h. A time (Tmax) of 12 h was necessary to reach the peak serum concentration (Cmax) of 1.41 microg/ml. The oral bioavailability was 27.9%. 3. Based on the minimum inhibitory concentration for susceptible strains, and especially Vibrio anguillarum, the oxolinic acid could be effective in turbot after an oral treatment of 10 mg/kg/day.

Pharmacokinetics of oxytetracycline in the red pacu (Colossoma brachypomum) following different routes of administration

Oxytetracycline (OTC) pharmacokinetics were studied in the red pacu (Colossoma brachypomum) following intravenous (i.v.) and intramuscular (i.m.) administration at a dose of 5 mg/kg body weight. OTC plasma concentrations were determined by high-performance-liquid-chromatography (HPLC). A non-compartmental model was used to describe plasma drug disposition after OTC administration. Following i.m. administration, the elimination half-life (t1/2) was 62.65 +/- 1.25 h and the bioavailability was 49.80 +/- 0.01%. After i.v. administration the t1/2 was 50.97 +/- 2.99 h, the Vd was 534.11 +/- 38.58 mL/kg, and CI(b) was 0.121 +/- 0.003 mL/min x kg. The 5 mg/kg i.v. dose used in this experiment resulted in up to 48 h plasma concentrations of OTC above the reported MIC values for some strains of fish pathogens such as Aeromonas hydrophila, A. liquefaciens, A. salmonicida, Cytophaga columnaris, Edwardsiella ictaluri, Vibrio anguillarium, V. ordalii, V. salmonicida and Yeersinia ruckeri. These MIC values are below the susceptible range (4 microg/mL) listed by the National Committee for Clinical Laboratory Standards (NCCLS) as determined by the NCCLS susceptibility interpretive criteria.

Application of a modified disc diffusion technique to antimicrobial susceptibility testing of Vibrio anguillarum and Aeromonas salmonicida clinical isolates

Two techniques for antimicrobial susceptibility testing of Vibrio anguillarum and Aeromonas salmonicida strains were compared. The first method was the reference test that determines Minimal Inhibitory Concentrations (MIC); the second was a modified diffusion test that measures the Inhibitory Concentrations in Diffusion (ICD) by carrying out the diffusion test with five discs of differing contents. ICD measurement was not applicable for the susceptibility testing of oxytetracycline and sulfadimethoxine. On the other hand, a good correlation between the MICs and the ICDs was observed for oxolinic acid, sarafloxacin, chloramphenicol and trimethoprim. Moreover, the ICD values were close to those obtained for the MIC values. A. salmonicida resistant strains were detected by ICD determination. Thus, ICD could be used instead of MIC for oxolinic acid, sarafloxacin, trimethoprim and chloramphenicol susceptibility testings. The ICD technique is easy to carry out and is not dependent on the growth characteristics of bacteria.

Comparative single-dose pharmacokinetics of four quinolones, oxolinic acid, flumequine, sarafloxacin, and enrofloxacin, in Atlantic salmon (Salmo salar) held in seawater at 10 degrees C

Quinolones are currently the most commonly used group of antimicrobial agents in Norwegian aquaculture. The aims of this study were to examine and compare the pharmacokinetic properties of the quinolones oxolinic acid, flumequine, sarafloxacin, and enrofloxacin after intravascular and oral administration to Atlantic salmon (Salmo salar) by using identical experimental designs. The study was performed in seawater at 10.2 +/- 0.2 degree C with Atlantic salmon weighing 240 +/- 50 g (mean +/- standard deviation). The bioavailability varied considerably among the four quinolones. Following oral administration of medicated feed, the bioavailabilities of oxolinic acid, flumequine, sarafloxacin, and enrofloxacin were 30.1, 44.7, 2.2, and 55.5%, respectively. Taking the different dosages (25 mg/kg of body weight for oxolinic acid and flumequine and 10 mg/kg for sarafloxacin and enrofloxacin) into account, enrofloxacin showed the highest maximum concentration in plasma, followed by flumequine, oxolinic acid, and sarafloxacin. Following intravenous administration, the volumes of distribution at steady state of oxolinic acid, flumequine, sarafloxacin, and enrofloxacin were 5.4, 3.5, 2.3, and 6.1 liters/kg, respectively. Hence, all the quinolones showed good tissue penetration in Atlantic salmon. The elimination half-life of three of the quinolones, oxolinic acid, flumequine, and sarafloxacin, was less than or equal to 24 h, with oxolinic acid showing the shortest (18.2 h). On the other hand, the elimination half-life of enrofloxacin was estimated to be 34.2 h, almost twice that of oxolinic acid. This study showed that flumequine and enrofloxacin had better pharmacokinetic properties, compared with those of oxolinic acid, in Atlantic salmon held in seawater.

gyrA mutations in quinolone-resistant isolates of the fish pathogen Aeromonas salmonicida

gyrA mutations in quinolone-resistant isolates of Aeromonas salmonicida have been detected by using PCR to amplify the quinolone resistance-determining region of gyrA and subsequent cloning and sequencing of PCR products. Comparison of nucleotide and derived amino acid sequences of PCR products from quinolone-susceptible and -resistant bacteria revealed a serine 83-to-isoleucine substitution in the gyrase A protein of resistant isolates. One of the resistant isolates differed from the other by a two- to fourfold-higher MIC of the fluoroquinolone enrofloxacin and carried an additional alanine 67-to-glycine substitution, which may contribute to the higher level of resistance.