Development of High Performance Liquid Chromatography-Tandem Mass Spectrometry Method for the Detection of Tulathromycin in Swine Plasma

An accurate and precise method for the determination of tulathromycin in swine plasma was developed and validated.Plasma samples were analyzed by high-performance liquid chromatography with tandem mass spectrometry detection （HPLC-MS/MS） using electrospray ionization （ESI）.Tulathromycin was extracted from plasma by precipitation with acetonitrile and separated using a Phenomenex Luna 5 μm C18 column （150 mm×2.0 mm） at a flow rate of 0.25 mL min^-1.Solvent A consisted of 0.002 mol L^-1 ammonium acetate and formic acid （999：1,v/v）,and solvent B was acetonitrile.The mass spectrometer was operated in the selected-ion mode with atmospheric pressure chemical ionization to monitor the respective MH＋ ions,namely,m/z 577.3 for tulathromycin and m/z 679.3 for the internal standard roxithromycin.The calibration curves were linear in a dynamic range of 2.0-500 ng mL^-1 on the column.The accuracy was ranged from 95.25 to 109.75%,and the precision was ranged from 2.81 to 7.72%.The recoveries measured at 3 concentration levels （20,250,and 500 ng mL^-1） were higher than 98%.The method described above is efficient,and has the required accuracy and precision for rapid determination of tulathromycin in plasma.The method was applied to study the pharmacokinetics of tulathromycin in swine,and tulathromycin demonstrated a rapid absorption,wide distribution,and slow elimination after intramuscular administration.

牛源产志贺毒素大肠杆菌血清型及耐药性分析

为了调查青岛地区牛源产志贺毒素大肠杆菌(STEC)的流行情况和耐药情况,本试验对保存的780株牛源大肠杆菌进行PCR鉴定、血清分型以及药敏试验,经测序确认共检出27株STEC,随后对检出的STEC进行了30种血清型的鉴定,鉴定出14株共9种血清型,占定型菌株的51.9%,其中以O78、O2、O45血清型为主且O78占定型菌株的14.8%,为优势血清型。药敏试验结果显示,27株STEC对四环素、氨苄西林的耐药率分别为88.9%和81.5%;对氟苯尼考、磷霉素、恩诺沙星、萘啶酸、头孢噻呋、链霉素、甲氧苄啶-磺胺甲噁唑的耐药率介于11.1%~59.3%;对卡那霉素具有较高敏感性,耐药率仅为7.4%;所有受试菌株均对阿米卡星、环丙沙星和左氧氟沙星敏感。本试验结果对青岛地区牛源STEC的治疗提供理论依据。