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.     

土壤中兽用抗生素污染对水稻生长的影响

为了解农田土壤兽用抗生素污染对粮食作物水稻生长的潜在影响,选择我国养殖业中常用的抗生素之一土霉素作为目标化合物,试验研究了不同土霉素浓度水平对水稻苗期、生长期生长与产量的影响,探讨了水稻各器官中土霉素积累与土壤中土霉素浓度水平的关系。结果表明,土壤土霉素污染对水稻生长的影响主要发生在苗期,对地下部分的影响显著大于地上部分;苗期地下部生物量、根系活力、叶片叶绿素含量和氧化酶活性随浓度水平(30 mg·kg^-1以上)的升高而显著降低。苗期受到土霉素污染影响的水稻其影响一直可延续至整个生育期,表现在分蘖数降低、产量减少等。土霉素在水稻各器官中的积累量大小顺序:根系> 叶片> 茎秆> 籽粒。水稻对土壤中的土霉素富集能力较小,土霉素由根部向地上部分叶、茎、籽粒的迁移作用也较弱。考虑到当前农田土壤中土霉素污染水平一般较低(多在10 mg·kg^-1以下),且在谷物中土霉素积累水平较低,推断在目前农地土壤中土霉素污染水平下,其对水稻生长的直接危害相对较小。     

嗜水气单胞菌对盐酸多西环素的耐药性获得与消失速率研究

在离体条件下测定了从人工养殖的斑点叉尾蛔患病鱼体上分离的嗜水气单胞菌（Aerowtonas hydrophila）的4个菌株对盐酸多西环素耐药性获得与消失的速率。结果表明：以25℃条件下培养72h为1代,在含有盐酸多西环素的药物培养基中连续传代9次后,盐酸多西环素对A．hydrophila的最小抑制菌浓度（MIC）上升了31倍,MIC由0．05mg／L上升至1．56mg／L;而将已经获得高耐药性的菌株以穿刺法接种在不合药物的BHI（Difco）琼脂培养基中,以4℃条件下保存20d为1代,连续传代5次,供试菌株的耐药性呈现逐渐消失的趋势,至第5次传代后,其MIC由1．56mg／L下降至0．10mg／L。     

Removal of Oxytetracycline in Water by Improved UV Disinfection Process

The removal of oxytetracycline (OTC) in water by UV, UV/TiO2, UV/Zeolite, and UV/Composite photocatalyst with different ratio was investigated respectively with a 32W low voltage mercury lamp. The effects of composite photocatalyst concentration, initial OTC concentration and pH value on degradation were also investigated. It was shown that the UV/Composite photocatalyst with 10% TiO2 and 90% Zeolite was an effective one to remove OTC in water. And in a solution with 50 mg/L OTC in ultrapure water the OTC was removed by 99% within 120 min with the help of 300 mg/L composite photocatalyst. The degradation of OTC by UV/Composite photocatalyst was little influenced by its initial concentration, but influenced by its initial pH. In the environment with pH+2~10, the OTC was removed by more than 95% within 120 min with the help of UV/Composite photocatalyst, when the pH is above 10, the removal rate is rapidly decreased.      

Influence of Characteristic of Zeolite on Loading Nano-TiO2 for Photocatalytic Degradation of Oxytetracyline in Aqueous Solution

The composite photocatalysts were made by using solid dispersion method with nano-TiO2 loaded on hydrophobic or hydrophilic zeolite and zeolite with different pore diameters. The removal and mineralization efficiency of oxytetracycline (OTC) in aqueous solution were investigated under the irradiation of 32 W UV lamps by composite photocatalysts loaded with different ratios of nano-TiO2. The results showed that UV/10%TZ2 (hydrophilic zeolite) achieved a better removal efficiency of OTC than UV/40%TZ1 (hydrophobic zeolite) while UV/15%T5A (hydrophilic zeolite with a pore diameter of 0.5 nm) achieved a better removal efficiency of OTC than UV/10%T13X (hydrophilic zeolite with a pore diameter of 1 nm). That is to certify that the hydrophilic zeolite and zeolite with small pore diameters loaded with nano-TiO2 could achieve better removal effects for OTC in aqueous solution. The OTC that adsorbed on the inside surface of 13X cannot be degraded due to the out range of hydroxyl radicals attack.     

土霉素在锯缘青蟹体内的药物代谢和消除规律

采用高效液相色谱法检测土霉素,研究土霉素口灌给药途径下在锯缘青蟹体内的药代动力学。锯缘青蟹口灌给药土霉素50 mg/kg后,其血浆、肌肉和肝胰脏中的药峰浓度分别为16.78±1.98 mg/L、9.39±2.12μg/g和32.12±6.12μg/g,达峰时间分别为4 h、8 h和4 h。血浆中土霉素浓度-时间关系曲线符合一级吸收的二室开放动力学模型。土霉素在锯缘青蟹体内分布广泛,其表观分布容积(Vd)为2.129 L/kg;分布半衰期(t1/2α)和消除半衰期(t1/2β)分别为3.200 h和47.856 h,总体清除率(CLs)为0.063 mL/(kg.h)。肌肉和肝胰脏中土霉素浓度与时间关系的药动学参数采用统计矩原理分析,其消除半衰期(t1/2 z)分别为60.145 h和71.009 h,总体清除率(CLz)分别为0.054 g/(kg.h)和0.037 g/(kg.h)。土霉素在精巢和卵巢中达峰时间分别为8 h和12 h,峰浓度分别为9.83μg/g和10.26μg/g。给药后24 d时,血浆、肌肉、肝胰脏、精巢和卵巢中土霉素含量都已低于0.10μg/g。土霉素在锯缘青蟹体内消除比较缓慢。     

Pharmacokinetic–pharmacodynamic integration and modelling of oxytetracycline for the calf pathogens Mannheimia haemolytica and Pasteurella multocida

A calf tissue cage model was used to study the pharmacokinetics (PK) and pharmacodynamics (PD) of oxytetracycline in serum, inflamed (exudate) and noninflamed (transudate) tissue cage fluids. After intramuscular administration, the PK was characterized by a long mean residence time of 28.3 hr. Based on minimum inhibitory concentrations (MICs) for six isolates each of Mannheimia haemolytica and Pasteurella multocida, measured in serum, integration of in vivo PK and in vitro PD data established area under serum concentration–time curve (AUC_0–∞)/MIC ratios of 30.0 and 24.3 hr for M. haemolytica and P. multocida, respectively. Corresponding AUC_0–∞/MIC ratios based on MICs in broth were 656 and 745 hr, respectively. PK‐PD modelling of in vitro bacterial time–kill curves for oxytetracycline in serum established mean AUC_0–24 hr/MIC ratios for 3log₁₀ decrease in bacterial count of 27.5 hr (M. haemolytica) and 60.9 hr (P. multocida). Monte Carlo simulations predicted target attainment rate (TAR) dosages. Based on the potency of oxytetracycline in serum, the predicted 50% TAR single doses required to achieve a bacteriostatic action covering 48‐hr periods were 197 mg/kg (M. haemolytica) and 314 mg/kg (P. multocida), respectively, against susceptible populations. Dosages based on the potency of oxytetracycline in broth were 25‐ and 27‐fold lower (7.8 and 11.5 mg/kg) for M. haemolytica and P. multocida, respectively.     

阳离子强度及类型对生物质炭吸附土霉素的影响

以OECD Guideline 106为基础,采用批量平衡法研究不同Ca~(2+)强度(0.01、0.03、0.05、0.08、0.1 mol·L-1)以及不同阳离子类型(0.01 mol·L-1KCl、ZnCl_2、CaCl_2、Al Cl3)对土霉素在3种菠萝皮渣生物质炭(BL350、BL500、BL650)中吸附的影响。结果表明,随着溶液中Ca~(2+)浓度的增加,土霉素在生物质炭中的吸附参数lg Kf逐渐减小趋于稳定,且lg Kf值与CaCl_2浓度之间呈显著负相关(P0.05)。与此同时,Ca~(2+)浓度的增加对低浓度土霉素溶液的吸附影响与高浓度时相比不明显。不同阳离子条件下,Freundlich和Langmuir模型均能较好地对吸附数据进行非线性拟合,平均R2分别是0.922 1、0.946 3。除了土霉素在BL650的Al Cl3介质中1/n接近1,吸附趋于线性外,其他介质条件下的吸附等温线均呈"L"型。4种阳离子对土霉素在3种生物质炭中吸附行为的影响存在较大差异,具体表现为K+与Al3+之间存在显著差异(P0.05),而Zn2+与K+、Al3+之间存在极显著差异(P0.01)。与其他阳离子相比,K+的存在显著降低溶液中土霉素在生物质炭上的吸附强度(1/n)。     

土霉素及镉污染对土壤呼吸及酶活性的影响

随着饲料工业以及畜禽养殖业的规模化发展,抗生素和重金属在土壤环境中同时存在的几率不断增大。为了分析抗生素和重金属对土壤微生物生态系统的影响,以土霉素(OTC)与镉(Cd)为污染物,采用室内培养法,研究了土霉素(OTC)与镉(Cd)单一处理及复合污染对土壤呼吸和酶活性的影响。结果表明,10mg/kg重金属镉单独污染对土壤微生物呼吸表现为先抑制后激活作用,且显著抑制了土壤蔗糖酶、脲酶、磷酸酶活性,对3种酶活性平均抑制率从大到小依次为:蔗糖酶磷酸酶脲酶;1mg/kg土霉素显著激活土壤微生物呼吸,50和200mg/kg土霉素对土壤微生物呼吸的影响呈现出先抑制后激活的规律。各处理浓度下的土霉素对蔗糖酶和脲酶活性均主要表现为抑制作用,对磷酸酶活性的影响呈现出一定的波动性;当土霉素的浓度为1和200mg/kg时,其与10mg/kg镉的复合污染对土壤微生物呼吸及3种酶活性的影响主要为拮抗作用,但当土霉素的浓度为50mg/kg时,与10mg/kg镉的复合污染对土壤微生物呼吸及3种酶活性的影响则主要为协同作用。微生物呼吸对土霉素与镉胁迫更为敏感,最高抑制率和激活率分别可达98.98%和300.82%,土壤酶活性受土霉素和镉污染的影响要弱于它们对土壤微生物呼吸的影响。     

三种抗生素与铜复合污染对土壤过氧化氢酶活性的影响

为分析抗生素与重金属单一及复合污染对土壤过氧化氢酶活性的影响,以三种兽用抗生素恩诺沙星（Enrofloxacin,ENR）、土霉素（Oxytetracycline,OTC）、磺胺二甲嘧啶（Sulfamethazine,SM2）和重金属铜（Cu）为目标污染物,采用高锰酸钾滴定法,研究其对土壤中过氧化氢酶活性的影响。结果表明,单一污染下,中低浓度的ENR各处理对酶活性有一定激活作用,最大激活率为5.52%;OTC处理组随着污染物浓度的增加,对酶活性的抑制作用增大,抑制率最大为8.36%;SM2处理初期,中低浓度处理组对酶有激活作用,最大激活率为7.46%,处理21 d,高浓度处理组对酶活性有显著促进作用,激活率为1.71%。Cu在第28 d时对过氧化氢酶活性表现为抑制。复合污染下,ENR与Cu复合污染组对过氧化氢酶活性的影响随污染浓度增加先抑制后激活;OTC与Cu处理第7 d,各浓度组与对照差异均不显著,14 d后,高浓度组产生抑制作用,抑制率最高为3.58%;SM2与Cu高浓度处理组在第7 d对土壤过氧化氢酶活性表现为明显激活作用,激活率高达10.00%,14 d后转为抑制作用,28 d时抑制率最高为4.49%。研究表明,单一污染下,抗生素对土壤过氧化氢酶的影响与其类型、暴露浓度以及暴露时间有关。复合污染下,抗生素和Cu的交互作用存在差异,表现为拮抗和协同两种作用,不仅与抗生素种类、复合污染浓度比例、暴露时间有关,还与抗生素和Cu配位反应产生复合物的比例有关。