Penetration studies of propoxur and phoxim from eggshell into whole egg after experimental exposure and application in henhouses

The penetration of propoxur and phoxim from eggshell into whole egg was investigated in vitro by spraying eggs directly and in vivo after application of the compounds in henhouses. Although mean concentrations of the compounds on eggshells were up to 23000 microg kg(-1), mean residue concentrations in whole eggs were far below the current maximum residue levels (50 microg kg(-1) for propoxur and 60 microg kg(-1) for phoxim). These results provide the first evidence that propoxur and phoxim do not penetrate from eggshell into whole egg under experimental and field conditions. Subsequently, residue carry-over after egg cracking in households and during a worst-case situation in an egg-cracking plant was investigated. However, when eggs were cracked manually, a negligible contamination of whole egg values occurred. If, in an automated process, eggshells accidentally come into close contact with whole egg, very high residue levels of propoxur and phoxim may be generated time dependently. These results suggest that eggshell contact with whole egg during egg cracking must be avoided to prevent pesticide carry-over.     

饲料中添加强化爱渔灵对凡纳滨对虾生长、存活及免疫指标以及攻毒实验的影响

在实验室条件下研究了强化爱渔灵对凡纳滨对虾(Litopenaeus vannamei)生长、存活和免疫反应的影响。生长实验设计了三种颗粒饲料,分别添加不同含量的强化爱渔灵(0%、0.05%和0.1%),每个处理有6个重复,每个重复对应1个鱼缸,其中有25尾虾。生长实验进行60d,期间每天投喂实验饲料4次,日投饵率为3%。实验结果表明,生长实验40d后,0.1%强化爱渔灵组虾体重(16.76±1.33)g,显著高于0.05%强化爱渔灵组(15.84±0.99)g和对照组(15.40±1.19)g的体重(P<0.05)。两个实验组之间成活率(97.18%～97.60%)没有显著差异,但显著高于对照组的成活率(83.20%)(P<0.05)。通过总血细胞计数(THC)、吞噬百分率、酚氧化酶活力以及杀菌活性等评价了各处理组虾的免疫力。结果表明,0.1%添加组的THC值和吞噬百分率以及酚氧化酶活性显著高于0.05%添加组和对照组。0.1%添加组和0.05%添加组杀菌活性的血清稀释度为1:16,而对照组为1:8。生长实验60d后,对各处理组的虾肌肉注射哈维病毒,两个实验组均未发现死亡率,而对照组的死亡率达43.33%。同时,用白斑综合症病毒感染虾,两个强化爱渔灵添加组在感染7d后的死亡率达到100%,而对照组的死亡率在6d内就达到100%。各处理组虾在感染黄头病毒后的死亡率结果与白斑综合征病毒感染实验结果类似。本研究表明,在饲料中添加0.1%强化爱渔灵可显著改善凡纳滨对虾的生长、成活率以及免疫力。     

Quantitative analysis of tylosin in eggs by high performance liquid chromatography with electrospray ionization tandem mass spectrometry: residue depletion kinetics after administration via feed and drinking water in laying hens

Maximum residue limits (MRLs) have been established by the European Union when tylosin is used therapeutically. They are fixed at 200 microg/kg for eggs. A highly sensitive and selective quantitative liquid chromatography electrospray ionization tandem mass spectrometry (LC/ESI/MS/MS) method suitable for monitoring tylosin residues in eggs to determine its depletion kinetics was developed and validated. For sample pretreatment all samples were liquid-liquid extracted with citrate buffer (pH 5.0) and acetonitrile. Liquid chromatographic separation was carried out on a reversed phase C18 column employing a 0.5% formic acid/acetonitrile gradient system. The tylosin recovery in eggs at a concentration range from 1.0-400 microg/kg was >82% with relative standard deviations between 1.5 and 11.0%. In two experimental studies administrating tylosin via feed (final dosage: 1.5 g/kg) or drinking water (final dosage: 0.5 g/L), no residues above the MRL were found during and after treatment. Moreover, all samples were well below the actual MRL of 200 microg/kg. Therefore, our residue data suggest that a withholding period for eggs is not required when laying hens are treated with tylosin in recommended dosages via feed or drinking water. Keywords: Tylosin; residue; depletion; laying hen; withholding period; mass spectrometry.     

Antimicrobial activity of partially characterized analytes from Bacillus pumilus(B2)

This study was carried out to characterize the antimicrobial substance produced by the strain of Bacillus pumilus (B2) obtained from Novozymes Biologicals Inc. to compare its antimicrobial activity by agar well diffusion assay and bacteriocin activity assay via critical dilution method against seven different strains of Vibrio spp., specifically V. alginolyticus (A01), V. cholerae (C01), V. fluvialis (F01, F02), V herveyii (H), V. mimicus (M01), V. parahaemolyticus (P01) and V. vulnificus (V01, V02). All Vibrio spp. were isolated from the hemolymph and intestine of the white faeces disease‐infected moribund pacific white‐leg shrimp Litopenaeus vannamei (Boone 1931) and one strain (V. harveyi) from its diseased postlarva. The cell‐free neutralized supernatant (CFNS) of B2 showed moderate thermo‐stability being stable up to 70°C for 60 min with, however, reducing activity above 80°C for 20 min. B2 antimicrobials showed a stable activity within the pH ranging from 6 to 10 at room temperature and at 4°C, while residual antimicrobial activity of crude CFNS showed tolerance to salinity up to 7% of sodium chloride below 4°C. No B2 activity was obtained while exposed to proteolytic enzyme, such as proteinase k and pepsin, while its activity kept stable exposed to lipase. Initial B2 characterization for antimicrobial substance in CFNS revealed proteinaceous in nature owing to activity loss against proteolytic enzymes and no lipid moiety activity against lipase, which could be categorized as bacteriocin‐like inhibitory substance having potential application against several strains of Vibrio spp. in aquaculture.