Simultaneous determination of fluoroquinolones and tetracyclines in chicken muscle using HPLC with fluorescence detection

A multiresidue method has been developed which allows for the simultaneous determination of both fluoroquinolones and tetracyclines in chicken muscle. Samples were extracted with a mix of acetonitrile and 0.1 M citrate, 150 mM MgCl(2), pH 5.0. After centrifugation and evaporation, the extracts could be analyzed by liquid chromatography with fluorescence detection. Good recoveries (63-95%) were obtained from samples fortified with a mix of five fluoroquinolones and three tetracyclines, with satisfactory relative standard deviations. Limits of detection were 0.5 ng/g (danofloxacin), 1 ng/g (oxytetracycline, ciprofloxacin, enrofloxacin), 1.5 ng/g (tetracycline), 2 ng/g (difloxacin) and 5 ng/g (sarafloxacin, chlortetracycline). Enrofloxacin and its metabolite ciprofloxacin, as well as oxytetracycline were determined in enrofloxacin and oxytetracycline incurred chicken muscle using this method.     

Determination of residues of enrofloxacin and its metabolite ciprofloxacin in biological materials by capillary electrophoresis

A method for the analysis of enrofloxacin and ciprofloxacin in chicken muscle using marbofloxacin as internal standard is proposed. Clean-up and pre-concentration of the samples are effected by solid-phase extraction and determination is carried out by capillary electrophoresis using a photodiode array detector. The calibration graphs are linear for enrofloxacin and ciprofloxacin from 10 to 300 μg/kg. The method recoveries for enrofloxacin and ciprofloxacin are 74 and 54%, respectively. The limit of detection for the two compounds is lower than 25 μg/kg, which allows the detection of positive muscle samples at the required maximum residue limits.     

Liquid chromatography analysis of enrofloxacin and ciprofloxacin in chicken blood spotted on filter-paper disks

A simple, low-cost, sensitive and selective LC method was developed for the determination of enrofloxacin and ciprofloxacin in chicken blood. The method was applied to whole blood from a chicken using dried blood spots on filter paper disks. The detection limits of enrofloxacin and ciprofloxacin (100 microl of whole blood on a disk) were 0.005 and 0.01 microg/ml, respectively. The whole procedure was verified in intra-laboratory studies (recoveries of both compounds were above 90%), and its applicability was tested with blood from the chicken receiving enrofloxacin in a single oral dose at a level of 10 mg/kg body mass. The method permits the use of a small volume of blood from a chicken and should be useful for pharmacokinetic studies.     

Simultaneous determination of danofloxacin and N-desmethyldanofloxacin in cattle and chicken edible tissues by liquid chromatography with fluorescence detection

A rugged, simple, and selective method for the determination of danofloxacin and its primary metabolite, N-desmethyldanofloxacin, in cattle (liver, muscle, kidney, and fat) and chicken (liver and muscle) tissues was developed. The method is selective for danofloxacin and N-desmethyldanofloxacin over other veterinary important fluoroquinolones, such as enrofloxacin, ciprofloxacin, norfloxacin, and ofloxacin. Selectivity is achieved through a combination of extraction, chromatography, and fluorescence detection. The analytes were extracted from homogenized tissues using a methanolperchloric-phosphoric acid solution. After centrifugation, direct injection of extraction supernate was possible. The limit of quantitation was 20 pg on column. Separation was achieved on an Inertsil C₈ (5 μm, 100 Å) column with dimensions of 250×4.6 mm I.D. The mobile phase consisted of 0.05 M phosphate buffer (pH 3.5)-acetonitrile (88:12). A fluorescence detector was utilized with an excitation wavelenght of 280 nm and an emission wavelength of 440 nm. The assay was accurate and reproducible within the range of 10 to 500 ng/g for both danofloxacin and N-desmethyldanofloxacin. Intra-assay accuracy was between 98 and 101%, and precision was less than 4%. Inter-assay accuracy was between 99 and 102%, while precision was less than 2%. Recoveries for both analytes over the dynamic range were greater than 90% for all the tissues.     

Simultaneous determination of residual veterinary drugs in bovine, porcine, and chicken muscle using liquid chromatography coupled with electrospray ionization tandem mass spectrometry

A simple and rapid method using liquid chromatography coupled with electrospray ionization tandem mass spectrometry (LC/MS/MS) for the simultaneous determination of 130 veterinary drugs and their metabolites in bovine, porcine, and chicken muscle was developed. The drugs (1 to 10 ng/g, in muscle) were extracted from bovine, porcine, or chicken muscles with acetonitrile-methanol (95:5, v/v), and the extracts were delipidated with n-hexane saturated with acetonitrile. The extracts were evaporated, dissolved with methanol, analyzed by liquid chromatography with gradient elution on a C18 column, and determined by electrospray ionization tandem mass spectrometry. The detection limits ranged from 0.03 to 3 ng/g. The quantitation limits ranged from 0.1 to 10 ng/g. One hundred eleven, 122, and 123 drugs from bovine, porcine, and chicken muscle respectively showed recoveries between 70 and 110%.     

Simultaneous determination and confirmation of chloramphenicol, thiamphenicol, florfenicol and florfenicol amine in chicken muscle by liquid chromatography-tandem mass spectrometry

A reliable and sensitive liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) confirmation method has been developed for the simultaneous determination of chloramphenicol (CAP), thiamphenicol (TAP), florfenicol (FF), and florfenicol amine (FFA) in chicken muscle. Samples were extracted with basic ethyl acetate, defatted with hexane, and cleaned up on Oasis MCX cartridges. LC separation was achieved on a XTerra C(18) column with gradient elution using a mobile phase composed of acetonitrile and water at a flow rate of 0.20 mL/min. The analysis was carried out on a triple-quadrupole tandem mass spectrometer in the multiple reaction monitoring (MRM) mode via electrospray interface operated in the positive and negative ionization modes, with deuterated chloramphenicol-d5 (d(5)-CAP) as the internal standard. The method validation was performed according to the criteria of Commission Decision 2002/657/EC. Four identification points were obtained for each analyte with one precursor ion and two product ions. Limits of detection (LODs) were 0.1 microg/kg for CAP, 0.2 microg/kg for FF and 1 microg/kg for TAP and FFA in chicken muscle. Linear calibration curves were obtained over concentration ranges of 0.3-20 microg/kg for CAP, 0.5-20 microg/kg for FF and 3-100 microg/kg for TAP and FFA in tissues. Mean recoveries of the 4 analytes ranged from 95.1% to 107.3%, with the corresponding intra- and inter-day variation (relative standard deviation, R.S.D.) less than 10.9% and 10.6%, respectively. The decision limit (CCalpha) and detection capability (CCbeta) of the method were also reported.     

Validation of an HPLC-UV method according to the European Union Decision 2002/657/EC for the simultaneous determination of 10 quinolones in chicken muscle and egg yolk

Herein two different methods are proposed for the determination of 10 quinolones (enoxacin, ofloxacin, norfloxacin, ciprofloxacin, danofloxacin, enrofloxacin, sarafloxacin, oxolinic acid, nalidixic acid and flumequine) in chicken muscle and egg yolk. Two different HPLC systems were used comparatively and the respective methods were fully validated. The analytes were initially extracted from chicken muscle and egg yolk and purified by a solid phase extraction using LiChrolut RP-18 cartridges. Recoveries varied between 96.6 and 102.8% for chicken muscle and 96.4-102.8% for egg yolk. HPLC separation was performed at 25 degrees C using an ODS-3 PerfectSilTarget (250 mmx4 mm) 5 microm analytical column (MZ-Analysentechnik, Germany). The mobile phase consisted of a mixture of 0.1% trifluoroacetic acid (TFA)-ACN-CH3OH, delivered by a gradient program, different for each method. In both cases caffeine was used as internal standard at the concentration of 7.5 ng/microL. Column effluent was monitored using a photodiode array detector, set at 275 and 255 nm. The developed methods were validated according to the criteria of Commission Decision 2002/657/EC. The LODs for chicken muscle varied between 5.0 and 12.0 microg/kg and for egg yolk was 8.0 microg/kg for all examined analytes.     

Effective separation and simultaneous determination of seven fluoroquinolones by capillary electrophoresis with diode-array detector

A simple, rapid and accurate method has been developed for effective separation and simultaneous determination of lomefloxacin, gatifloxacin, enoxacin, ciprofloxacin, ofloxacin, enrofloxacin and pefloxacin residues in porcine tissue by capillary electrophoresis with diode-array detector. The separation conditions were investigated and optimized. The sample was extracted with acetonitrile, and a mixture consisted of 25 mM NaH(2)PO(4), 25 mM Na(2)B(4)O(7) and 25 mM H(3)BO(3) (pH 9.0) was used as a running buffer. A linear relationship between concentration and peak area for each compound was obtained in the concentration range of 0.5-100 mg/L with a correlation coefficient greater than 0.9994. For analysis of porcine tissue, the detection limits of lomefloxacin, gatifloxacin, enoxacin, ciprofloxacin, ofloxacin, enrofloxacin and pefloxacin were 0.013, 0.012, 0.023, 0.040, 0.037, 0.035 and 0.034 mg/kg, respectively. The recoveries are in the range of 72-93%. The intra-day precision is less than 5%, and the inter-day precision is less than 10%. The proposed method has high resolution, speed and the extremely small sample volume required. It can permit to confirm the presence of the studied seven fluoroquinolones in porcine tissue at the required maximum residue limit (MRL) level.     

不同温度下恩诺沙星及其代谢物在斑点叉尾鲖各组织中的残留及消除规律比较

分别在18℃和28℃水温下, 以20 mg/(kg·d)鱼体质量对斑点叉尾鲙给药恩诺沙星, 连续灌胃7d。给药后在不同的时间点取样, 用高效液相色谱荧光检测器检测, 研究恩诺沙星及其主要代谢产物环丙沙星在斑点叉尾鲙体内(血液、肌肉、皮肤、肝脏和肾脏)的残留消除规律。结果表明, 恩诺沙星在不同组织、不同水温消除速率不同: 水温为18℃, 皮肤、肝脏、肾脏和肌肉中的消除曲线方程分别为C=1022.1e–0.034t、C=2601.3e–0.046t、C=2903.6e–0.072t和C=1186.5e–0.036t, 消除半衰期分别为31.79d、45.29d、16.15d和35.54d; 水温为28℃, 皮肤、肝脏、肾脏和肌肉中的消除曲线方程分别为C=8805.5e–0.04t、C=3154e–0.08t、C=4145.1e–0.1t和C=1302.1e–0.068t, 消除半衰期分别为18.33d、6.26d、12.44d和10.34d。恩诺沙星在斑点叉尾鲙体内可代谢为环丙沙星, 恩诺沙星在斑点叉尾鲙体内的代谢速度较慢, 代谢物环丙沙星在斑点叉尾鲙体内的消除速度比恩诺沙星快; 在18℃水温下, 斑点叉尾鲙肉中的恩诺沙星和环丙沙星完全消除需要150d以上; 在28℃水温下, 斑点叉尾鲙肉中的恩诺沙星和环丙沙星完全消除需要120d。在实验条件下, 建议水温为18℃和28℃时, 休药期分别为3240℃·日和4200℃·日。     

Multiresidue confirmation of beta-agonists in bovine retina and liver using LC-ES/MS/MS

Misuse of numerous beta-agonist drugs for their growth promoting effects in livestock production requires significant regulatory enforcement activities worldwide. The proof of illegal drug use needed for regulatory action usually requires the high degree of specificity derived from mass spectrometric analysis of suspect tissues and body fluids. In this paper, we describe a multiresidue screening method for confirmation of nine beta-agonist compounds in bovine liver and retina. A wide range of analyte structures was selected in order to demonstrate applicability to other chemically related beta-agonists for which standards are not currently available. The class-specific method, which is based on mixed mode cation exchange/reverse phase solid phase extraction, reverse phase gradient LC separation using a cyanopropyl-silica phase, and tandem mass spectrometry (MS/MS) in the multiple reaction monitoring (MRM) mode, yields high analyte recoveries at the target level of 1 ppb (ng/g). In addition, acquisition of multiple MRM transitions for each analyte permits simultaneous confirmation of beta-agonists at the level of 1 ppb in liver and retina by using intensity ratios between fragment ions and protonated molecules. Estimated values for the limit of quantification (LOQ) for individual beta-agonists were 0.08-0.3 ppb in liver and 0.02-0.5 in retina; the estimated limits of confirmation, using accepted criteria from international regulatory agencies, were 0.25-0.8 ppb in liver and 0.1-1 ppb in retina. This method should be useful in supporting regulatory enforcement programs that monitor beta-agonist misuse.     

Pharmacokinetics and tissue distribution of enrofloxacin and its metabolite ciprofloxacin in the Chinese mitten-handed crab, Eriocheir sinensis

The pharmacokinetics of enrofloxacin and its active metabolite ciprofloxacin were investigated in the Chinese mitten-handed crab after a single intramuscular injection of enrofloxacin at 5.0mg/kg body weight. The tissue concentrations of enrofloxacin and ciprofloxacin were determined simultaneously by a high-performance liquid chromatography (HPLC) method. The data were analyzed with Practical Pharmacokinetic Program 3P97. The highest average concentrations of enrofloxacin in liver, muscle, gill, and hemolymph were 3.93, 12.42, 16.73, and 11.04 microg/g (ml), respectively. The elimination half-lives (t(1/2beta)) for enrofloxacin were 92.42, 64.86, 38.80, and 52.39 h, respectively. The AUC(0-infinity) values for enrofloxacin were 304.80, 260.74, 288.30, and 269.24 microg h/ml, respectively. Ciprofloxacin could be detected in all four tissues. The respective values of main pharmacokinetics parameters Cmax, t(1/2beta), and AUC(0-infinity) were 0.52 microg/g (ml), 38.38 h, and 35.06 microg h/ml for liver; 0.24 microg/g (ml), 65.36 h, and 25.64 microg h/ml for muscle; 0.10 microg/g (ml), 112.88 h, and 11.57 microg h/ml for gill; and 0.30 microg/g (ml), 93.33 h, and 39.99 microg h/ml for hemolymph.     

Simple and sensitive determination of five quinolones in food by liquid chromatography with fluorescence detection

A simple and sensitive high-performance liquid chromatographic (HPLC) method has been developed for the determination of five different quinolones: enrofloxacin, ciprofloxacin, sarafloxacin, oxolinic acid and flumequine in pork and salmon muscle. The method includes one extraction and clean-up step for the five quinolones together which are detected in two separated HPLC runs by means of their fluorescence. The proposed analytical method involves homogenizing of the tissue sample with 0.05 M phosphate buffer, pH 7.4 and clean-up by Discovery DS-18 cartridges. For chromatographic separation a Symmetry C(18) column is used in two different runs: (1) ciprofloxacin, enrofloxacin and sarafloxacin with acetonitrile-0.02 M phosphate buffer pH 3.0 (18:82) as mobile phase and the detector at excitation wavelength: 280 nm and emission wavelength 450 nm; and (2) oxolinic acid and flumequine with acetonitrile-0.02 M phosphate buffer pH 3.0 (34:66) as mobile phase and excitation wavelength: 312 nm and emission wavelength: 366 nm. Detection limit was as low as 5 ng g(-1), except for sarafloxacin which had a limit of 10 ng g(-1). Standard curves using blank muscle tissues spiked at different levels showed a good linear correlation coefficient, r(2) higher than 0.999 for all quinolones.     

Simultaneous analysis of fluoroquinolones and xanthine derivatives in serum by molecularly imprinted matrix solid-phase dispersion coupled with liquid chromatography

A new molecularly imprinted polymer was synthesized using ofloxacin and theophylline as template and methacryclic acid as function monomer and it was employed as a special dispersant of matrix solid-phase dispersion for selective extraction of fluoroquinolones (ofloxacin, ciprofloxacin and enrofloxacin) and xanthine (caffeine and theophylline) from human serum samples. To eliminate the influences of template leaking on quantitative analysis, acetonitrile-trifluoracetic acid (99:1, v/v) was used as the template removing solution. By using water and acetonitrile-trifluoracetic acid (99.5:0.5, v/v) as the washing and elution solvent, respectively, satisfactory recoveries and clean enough chromatogram could obtained. Good linearity of all the analytes was observed in a range of 0.35-150 μg g(-1) with the correlation coefficient (r(2))≥0.9991. The recoveries of spiked human serum samples were in a range of 89.5-104.0% for fluoroquinolones and xanthine derivatives with RSD less than of 5.0%.     

Automated multi-residue isolation of fluoroquinolone antimicrobials from fortified and incurred chicken liver using on-line microdialysis and high-performance liquid chromatography with programmable fluorescence detection

Isolation of the quinolones, sarafloxacin (SAR), oxolinic acid (OXA), and flumequine (FMQ), from fortified chicken liver tissues, and SAR incurred chicken liver tissues was achieved by combined liquid–liquid extraction and aqueous on-line microdialysis using the automated trace enrichment of dialysates (ASTED) system. Analysis of tissue isolates after ASTED clean-up was performed using reversed-phase HPLC and programmable fluorescence detection. Overall recoveries of SAR, OXA and FMQ from samples fortified over a concentrations range of 1–100 ppb were 94, 97 and 87% with overall inter-assay variability of 4.2, 4.1 and 3.6%, respectively. Chicken liver samples incurred with SAR at three concentration levels also were tested by the ASTED method. The method exhibited high peak resolution (3.4–4.2 on average), a high signal-to-noise ratio, and demonstrated good precision. The ASTED–HPLC method overall had a lower limit of detection (LOD) of 0.2 ppb, and a limit of quantitation (LOQ) of 1 ppb.     

Simultaneous measurement of pazufloxacin,ciprofloxacin, and levofloxacin in human serum by high-performance liquid chromatography with fluorescence detection

In this study, three fluoroquinolones, pazufloxacin, ciprofloxacin and levofloxacin, were simultaneously determined in spiked human serum by high-performance liquid chromatography (HPLC) method with fluorescence detection. Chromatography was performed using a C₈ column with an isocratic mobile phase consisting of 1% triethylamine (pH 3.0)/acetonitrile (86/14, v/v). Protein precipitation was conducted using perchloric acid and methanol. The calibration curves for the three fluoroquinolones were linear over concentrations ranging from 0.1 to 20.0 μg/mL. The within-day and between-day coefficients of variation obtained from three fluoroquinolones were less than 7%, and relative errors ranged from −1.6% to 9.3%. Mean recoveries of pazufloxacin, ciprofloxacin, and levofloxacin from spiked human serum were 97%, 88%, and 90%, respectively. The proposed method proved to be simple and reliable for the determination of three fluoroquinolones.     

Quantification of cerebrospinal fluid transport across the cribriform plate into lymphatics in rats

A major pathway by which cerebrospinal fluid (CSF) is removed from the cranium is transport through the cribriform plate in association with the olfactory nerves. CSF is then absorbed into lymphatics located in the submucosa of the olfactory epithelium (olfactory turbinates). In an attempt to provide a quantitative measure of this transport, 125I-human serum albumin (HSA) was injected into the lateral ventricles of adult Fisher 344 rats. The animals were killed at 10, 20, 30, 40, and 60 min after injection, and tissue samples, including blood (from heart puncture), skeletal muscle, spleen, liver, kidney, and tail were excised for radioactive assessment. The remains were frozen. To sample the olfactory turbinates, angled coronal tissue sections anterior to the cribriform plate were prepared from the frozen heads. The average concentration of 125I-HSA was higher in the middle olfactory turbinates than in any other tissue with peak concentrations achieved 30 min after injection. At this point, the recoveries of injected tracer (percent injected dose/g tissue) were 9.4% middle turbinates, 1.6% blood, 0.04% skeletal muscle, 0.2% spleen, 0.3% liver, 0.3% kidney, and 0.09% tail. The current belief that arachnoid projections are responsible for CSF drainage fails to explain some important issues related to the pathogenesis of CSF disorders. The rapid movement of the CSF tracer into the olfactory turbinates further supports a role for lymphatics in CSF absorption and provides the basis of a method to investigate the novel concept that diseases associated with the CSF system may involve impaired lymphatic CSF transport.     

氯霉素在罗非鱼体内的代谢和消除规律

水产养殖动物口服氯霉素后可能在可食组织中造成残留,本文通过以50mg/kg鱼体重的氯霉素(CAP)的剂量对尼罗罗非鱼单次口灌给药,采用HPLC和GC-ECD分析方法研究了CAP在罗非鱼体内的代谢和消除规律。给药0.5h后,CAP在血浆和肝脏中的浓度均迅速上升,分别为4288.01±1285.53ng/mL和5214.18±1105.62ng/g,2h达到峰值22246.42±355.84ng/mL和25717.47±1740.66ng/g;而肌肉中CAP却上升较慢,2h仅为7744.08±2118.74ng/g,8h才达到峰值13232.89±1612.74ng/g,峰值仅约为血浆和肝脏的1/2。CAP在罗非鱼肌肉和肝脏中的消除速度均较慢,但肌肉比肝脏稍快,肌肉中第96d CAP降至为0.07±0.01ng/g,而肝脏中第120d尚在0.1ng/g以上,为0.25±0.06ng/g。肌肉和肝脏浓度常用对数-时间消除曲线方程分别为y=-0.0966x+5.4292;y=-0.053x+4.7258,二者的T1/2β为7.14d和13.08d。若要使CAP在罗非鱼肌肉和肝脏中的浓度降至0.1ng/g以下,则休药期分别需80.47d和132.61d。试验表明CAP在罗非鱼组织中消除缓慢,尤其在肝脏中,因此肝脏可以作为CAP残留监测的首选组织。       

Hyperglycemia compensates for diet-induced insulin resistance in liver and skeletal muscle of rats

High-fat and high-sucrose diets increase the contribution of gluconeogenesis to glucose appearance (glc R(a)) under basal conditions. They also reduce insulin suppression of glc R(a) and insulin-stimulated muscle glycogen synthesis under euglycemic, hyperinsulinemic conditions. The purpose of the present study was to determine whether these impairments influence liver and muscle glycogen synthesis under hyperglycemic, hyperinsulinemic conditions. Male rats were fed a high-sucrose, high-fat, or low-fat, starch control diet for either 1 (n = 5-7/group) or 5 wk (n = 5-6/group). Studies involved two 90-min periods. During the first, a basal period (BP), [6-3H]glucose was infused. In the second, a hyperglycemic period (HP), [6-3H]glucose, [6-14C]glucose, and unlabeled glucose were infused. Plasma glucose (BP: 111.2 +/- 1.5 mg/dl; HP: 172.3 +/- 1.5 mg/dl), insulin (BP: 2.5 +/- 0.2 ng/ml; HP: 4.9 +/- 0.3 ng/ml), and glucagon (BP: 81.8 +/- 1.6 ng/l; HP: 74.0 +/- 1.3 ng/l) concentrations were not significantly different among diet groups or with respect to time on diet. There were no significant differences among groups in the glucose infusion rate (mg x kg(-1) x min(-1)) necessary to maintain arterial glucose concentrations at approximately 170 mg/dl (pooled average: 6.4 +/- 0.8 at 1 wk; 6.4 +/- 0.7 at 5 wk), percent suppression of glc R(a) (44.4 +/- 7.8% at 1 wk; 63.2 +/- 4.3% at 5 wk), tracer-estimated net liver glycogen synthesis (7.8 +/- 1.3 microg x g liver(-1) x min(-1) at 1 wk; 10.5 +/- 2.2 microg x g liver(-1) x min(-1) at 5 wk), indirect pathway glycogen synthesis (3.7 +/- 0.9 microg x g liver(-1) x min(-1) at 1 wk; 3.4 +/- 0.9 microg x g liver(-1) x min(-1) at 5 wk), or tracer-estimated net muscle glycogenesis (1.0 +/- 0.3 microg x g muscle(-1) x min(-1) at 1 wk; 1.6 +/- 0.3 microg x g muscle(-1) x min(-1) at 5 wk). These data suggest that hyperglycemia compensates for diet-induced insulin resistance in both liver and skeletal muscle.     

High level of quinolone resistance in <Emphasis Type="Italic">Escherichia coli</Emphasis> from healthy chicken broilers

The development of resistance to quinolones (nalidixic acid, ciprofloxacin and enrofloxacin) in 2006–2008 was evaluated in 317 strains of Escherichia coli isolated from healthy chicken broilers from various farms. The isolates (2006/2007/2008) showed a high resistance to nalidixic acid (87/85/67 %), ciprofloxacin (CIP) (49/54/29 %) and enrofloxacin (ENR) (52/42/22 %). Nalidixic acid-resistant isolates with low level of MIC for CIP and ENR represented a single mutation; intermediary MIC for CIP and ENR were related to two mutations and high level resistance MIC for CIP (≥4 mg/L) and ENR (≥16 mg/L) represented three mutations (two in gyrA and one in parC). There was a correlation between the phenotype reading of high-level resistance and mutations in gyrA (Ser83Leu, Asp87Tyr or Asp87Asn) and parC (Ser80Ile) gene. Plasmid-mediated quinolone-resistance qnrS gene was detected in one Escherichia coli strain with a high level of ciprofloxacin resistance. Our results demonstrate the increase in occurrence of multiresistant E. coli strains with a high level of chromosomal and plasmid resistance to fluoroquinolones.     

Determination of α- and β-trenbolone in bovine muscle and liver by liquid chromatography with fluorescence detection

A sensitive and rapid high-performance liquid chromatographic screening method is described for the determination of anabolic steroid trenbolone in bovine muscle and liver. Trenbolone was analyzed as α- and β-trenbolone. Samples were extracted with ethyl acetate and cleaned up on a silica solid-phase extraction (SPE) cartridge. Liver samples were cleaned up on a multifunctional SPE cartridge before using a silica SPE cartridge. Analysis of α- and β-trenbolone was performed by reversed-phase high-performance liquid chromatography (HPLC) with a fluorescence detector. The detection limits for this method were estimated to be 0.2 and 1.0 ng/g in bovine muscle and liver, respectively. The mean recoveries spiked in muscle at 2 ng/g and in liver at 10 ng/g were over 80%.