兽用氟喹诺酮类的抗菌后效应、抗菌后亚抑制浓度效应、亚抑制浓度效应

5种兽医专用氟喹诺酮类抗菌药在体外对猪链球菌、大肠杆菌、多杀性巴氏杆菌均具有不同程度的PAE，最长者可达3.23h。其中对猪大肠杆菌、多杀性巴氏杆菌的PAE略长于对猪链球菌的PAE。各抗菌药对3种细菌同时也具有较PAE更长的抗菌后亚抑制浓度效应（PA-SME），并受诱导PAE的药物浓度、亚抑菌药物浓度（Sub-MIC)及细菌种类的影响。不定期一接种量细菌暴露于各Sub-MIC的药物中也表出现一定的亚抑制浓度效应（SME），且随Sub-MIC的增加而增加。     

氟苯尼考对大肠杆菌K99体外抗菌后效应研究

抗菌后效应（Postantibiotic effect，PAE）是指细菌与抗菌药物短暂接触后，当药物清除或低于最低抑菌浓度（MIC）时，细菌的生长仍然受到持续抑制的现象。近年来，抗菌后效应的研究逐渐受到国内外学者的重视，其研究不断深入，发现几乎所有的抗菌药物都具有PAE。     

氟苯尼考对鳗鲡常见致病菌体外抗菌后效应研究

采用试管液体二倍稀释法测定氟苯尼考对鳗鲡养殖中常见主要致病菌（肠杆菌B01、克雷伯氏菌B12、豚鼠气单胞菌B15和嗜水气单胞菌B20）的最小抑菌浓度（MIC）和最小杀菌浓度（MBC）,用菌落计数法分别测定氟苯尼考在0.5、1、2、4倍于各菌MIC时对鳗鲡致病菌株B01、B12、B15、B20体外抗菌后效应（PAE）。结果氟苯尼考在0.5、1、2、4倍MIC值时对鳗鲡致病菌株B01、B12、B15、B20均具有一定的PAE,且PAE与药物浓度在一定范围内（0.5-4倍MIC）呈剂量依赖关系,当药物浓度达4倍MIC时,PAE明显延长,分别为2.5±0.165、3.0±0.038、5.0±0.090和5.0±0.232h;氟苯尼考对B01、B12、B15、B20的PAE值在2倍MIC时差异较显著,在4倍MIC时对致病菌株B15和B20的PAE几乎无差异。相同浓度氟苯尼考对致病菌株B01和B12的PAE值明显低于B15和B20。结果提示在养殖鳗鲡病害防治中设计投药方案时,对常见致病菌B01、B12、B15和B20感染所造成的细菌性败血症、烂鳃、肝胆肿大等疾病,除了考虑药代动力学和MIC指标外,还需考虑PAE因素,可适当延长给药间隔时间,降低药物对鳗鲡的副作用及对其摄食量和生长的负面影响。     

单诺沙星对大肠杆菌和金葡球菌的体外抗茵后效应

采用菌落计数法测定了单诺沙星在三种不同浓度下对大肠杆菌和金黄色葡萄球菌 (金葡球菌 )的体外抗菌后效应 (PAE)。当药物浓度为 0 .5MIC、2MIC、4MIC时 ,对大肠杆菌的PAE值为 (0 .6 4 6 4± 0 .0 2 94 )h、(1.2 0 77± 0 .0 2 84 )h、(1.6 5 2 9± 0 .0 4 96 )h ;对金葡球菌的PAE值为 (0 .5 6 6 0± 0 .0 0 75 )h、(1.174 6± 0 .0 0 5 7)h、(1.4 913± 0 .0 2 5 7)h。这表明单诺沙星对大肠杆菌、金葡球菌均有不同程度的较强的PAE ,且PAE值与药物浓度呈正相关     

乳酸恩诺沙星对温和气单胞菌的体外抗菌后效应

为研究乳酸恩诺沙星对温和气单胞菌(A.sobria)的体外药效学,采用二倍稀释法测定了乳酸恩诺沙星对温和气单胞菌的最小抑菌浓度(MIC)和最小杀菌浓度(MBC),在此基础上探究在温和气单胞菌的不同生长时期加入乳酸恩诺沙星后对其生长的影响,研究乳酸恩诺沙星不同药物浓度(2×MIC、4×MIC、8×MIC)作用对温和气单胞菌的杀菌动力学和抗菌后效应(PAE)。结果显示,乳酸恩诺沙星对温和气单胞菌的MIC和MBC分别为0.39μg/mL和1.56μg/mL,乳酸恩诺沙星对温和气单胞菌有较强的杀菌作用,其PAE与药物浓度呈正相关。     

6种水产常用抗生素对鳗弧菌的抗菌后效应研究

为了解水产养殖业常用抗生素对鳗弧菌的抗菌后效应,本研究采用试管二倍稀释法测定乳酸恩诺沙星、乳酸诺氟沙星、盐酸沙拉沙星等6种抗生素对鳗弧菌的最小抑菌浓度(MIC);采用菌落计数法测定6种抗生素的抗菌后效应(PAE)。结果显示,6种抗生素在1、2、4倍MIC时对鳗弧菌的PAE分别为:0.17±0.11,1.45±0.21,1.81±0.33(乳酸恩诺沙星);0.54±0.11,0.72±0.12,1.17±0.22(乳酸诺氟沙星);0.52±0.19,0.72±0.25,1.13±0.22(盐酸沙拉沙星);0.46±0.16,0.86±0.16,1.88±0.30(盐酸二氟沙星);0.68±0.21,1.42±0.34,1.91±0.20(盐酸恩诺沙星);0.67±0.13,0.79±0.12,1.25±0.17(烟酸诺氟沙星)。6种抗生素对鳗弧菌均表现出不同程度的抗生素后效应,并随着抗生素浓度的增加,PAE的时间也延长,呈药物剂量依赖模式。     

5种抗菌药物对嗜水气单胞菌的体外抗菌后效应研究

为比较研究水产养殖中几种常见抗菌药物对嗜水气单胞菌(A.hydrophila)的体外抗菌后效应(PAE),本研究选取5种典型的抗菌药物(恩诺沙星、盐酸多西环素、诺氟沙星、氟苯尼考以及甲砜霉素),采用常量肉汤稀释法测定它们对A.hydrophila的最小抑菌浓度(MIC)和最小杀菌浓度(MBC),并在0、1/2 MIC、1 MIC、2 MIC和4 MIC药物浓度下进行PAE诱导,再用活菌计数法测定并记录细菌生长曲线,计算PAE值。结果显示,5种抗菌药物的MIC和MBC分别为0.016和0.023μg/m L(恩诺沙星),0.250和0.500μg/m L(盐酸多西环素),0.250和0.500μg/m L(诺氟沙星),1和4μg/m L(氟苯尼考)以及2和4μg/m L(甲砜霉素);5种抗菌药物在不同浓度下均有一定的PAE,其中盐酸多西环素最长可达2.84 h。本研究结果表明,这5种抗菌药物对A.hydrophila均有相当的PAE,并且在一定范围内呈浓度依赖性。提示在治疗鱼病及临床给药时,可以考虑PAE的独有特性,延长给药间隔,科学用药。     

氟苯尼考及其与多西环素联合的体外抗菌作用

对氟苯尼考 (Florfenicol)及其与多西环素 (Doxycycline)联合的体外抗菌活性、杀菌动力学曲线和抗菌后效应(PAE)作了研究。结果表明 :氟苯尼考对鸡大肠杆菌等 9种标准菌株最小抑菌浓度 (MIC)为 0 .2～ 1.6 mg/L ,与氯霉素相似或略低 ,比甲砜霉素低 1/2～ 1/80 ;对耐氯霉素、甲砜霉素的鸡大肠杆菌、鸡白痢沙门氏菌和猪大肠杆菌临床分离株仍有较强抗菌作用 ;对鸡大肠杆菌和金黄色葡萄球菌的杀菌动力学曲线与甲砜霉素相似 ,表现为低浓度抑菌 (小于 4 MIC值 )、高浓度缓慢杀菌 ;对鸡大肠杆菌和金黄色葡萄球菌的 PAE显著长于甲砜霉素 (P<0 .0 5 ) ,呈浓度依赖性 ,对鸡大肠杆菌的 PAE(1.4 5～ 2 .0 7h)显著长于对金黄色葡萄球菌 (0 .4 8～ 1.18h)。棋盘法测得氟苯尼考与多西环素联合对鸡大肠杆菌、鸡白痢沙门氏菌、猪链球菌和金黄色葡萄球菌均为无关作用 ,对前 3种菌的部分抑菌浓度(FIC)指数值为 1.5 ,联合时的氟苯尼考 MIC值比其单独时减小了 1/2。氟苯尼考以 1∶ 2与多西环素联合时 ,对鸡大肠杆菌和金黄色葡萄球菌的杀菌速率与氟苯尼考单药相比均有所增加 ,当浓度大于或等于 4 MIC时呈现出协同作用 ;对鸡大肠杆菌和金黄色葡萄球菌的 PAE与单药 PAE的较大值相近 ,与相应浓度的单药相比均表现为无关作用。     

单诺沙星在雏鸡体内的药动学及其抗菌后效应研究

本论文以高效液相色谱(HPLC)内标法为定量手段,研究了单诺沙星经静注、口服两种途径给药后在雏鸡体内的药物代谢动力学特征;以菌落计数法测定了单诺沙星对大肠杆菌、金黄色葡萄球菌(金葡球菌)的体外抗菌后效应。静注和内服给药后血药浓度-时间数据分别符合无吸收因素二室开放式模型和一级吸收一室开放式模型。静注给药的主要药动学参数为:t1/2α0.3313h、t1/2β5.9940h、Vd7.5246L/kg、AUC5.6916μg/(mL·h)、CLB0.8935/(kg·h)。内服给药后主要药动学参数为:t1/2Ka0.3029h、t1/2K6.5128h、tmax1.2100h、Cmax0.5159μg/mL、AUC5.1329μg/(mL·h),生物利用度为90.18%。抗菌后效应(PAE)结果如下,浓度分别为0.5MIC、2MIC、4.MIC的单诺沙星对大肠杆菌的PAE测定值分别为(0.6464±0.0294)h,(1.2077±0.0284)h,(1.6529±0.0496)h,对金葡球菌的PAE测定值分别为(0.5660±0.0075)h,(1.1746±0.0057)h,(1.4913±0.0257)h。     

阿莫西林纳米粒对沙门菌的体外抗菌后效应

为指导兽医临床中应用阿莫西林纳米粒治疗沙门菌病的给药方案,利用显微镜直接计数法测定了阿莫西林纳米粒对沙门菌的体外抗菌后效应(PAE)。结果表明:阿莫西林纳米粒在(0.5～4)×MIC的药物浓度范围内对沙门菌产生的PAE约在1.6～4 h,且PAE与药物浓度呈正相关,4×MIC时的PAE值较长,与1×MIC和0.5×MIC时均差异极显著(P<0.01),与2×MIC时差异显著(P<0.05)。结果说明,临床应用阿莫西林纳米粒治疗沙门菌病时,除了考虑药效学指标和药动学参数外,还应考虑PAE因素,可适当延长给药间隔时间。     

Minimum Inhibitory Concentration and Postantibiotic Effect of Amikacin for Equine Isolates of Methicillin-Resistant Staphylococcus aureus In Vitro

Objective— To report the minimum inhibitory concentration (MIC) of amikacin sulfate for equine clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA) and characterize the initial kill and duration of the postantibiotic effect (PAE) for selected strains.
Study Design— Experimental study.
Methods— Isolates of MRSA (n=35) had their amikacin MIC determined using the E-test agar diffusion method. Two isolates with MICs>256 μg/mL limit were further characterized using broth macrodilution. Six distinct isolates with amikacin MICs of 32, 48, 128 (2 isolates) and 500 (2 isolates) μg/mL had PAE determinations made over a range of amikacin concentrations from 31.25–1000 μg/mL using standard culture-based techniques.
Results— Median MIC of the 35 isolates was 32 μg/mL (range 2 to >256 μg/mL). Mean PAE of selected MRSA strains had an overall mean (all amikacin doses) of 3.43 hours (range 0.10–9.57 hours). PAE for MRSA exposed to amikacin at 1000 μg/mL was 6.18 hours (range 3.30–9.57 hours), significantly longer than that for all other concentrations ( P <.0001). There was no statistically significant effect of isolate MIC on PAE.
Conclusions— Isolates had a wide range of MIC; however, growth of all 6 selected strains were inhibited within the range of concentrations tested, including 2 strains with MICs of 500 μg/mL. PAE duration was not influenced by the MIC of amikacin but was significantly longer with treatment at 1000 μg/mL than at lower concentrations.
Clinical Relevance— Clinical isolates of MRSA are susceptible to amikacin at concentrations achieved by regional perfusion: however, the modest duration of PAE observed suggest that further laboratory and in vivo evaluation be conducted before recommending the technique for clinical use.     

五倍子对鳗鲡4株常见病原菌的体外抗菌后效应

采用试管液体二倍稀释法测定中药五倍子对鳗鲡养殖中常见主要致病菌(肠杆菌B01、迟缓爱德华氏菌B09、豚鼠气单胞菌B18和嗜水气单胞菌B27)的最小抑菌浓度(MIC).然后再采用菌落计数法分别测定五倍子在0.25、0.5、1、2、4倍于各菌MIC时对鳗鲡病原菌株B01、B09、B18、B27的体外抗菌后效应(PAE).结...     

五倍子对鳗鲡致病性气单胞菌的体外抗菌后效应

采用试管液体二倍稀释法测定中药五倍子对鳗鲡养殖中致病性气单胞菌(威隆气单胞菌K17、肠棕气单胞菌G03、豚鼠气单胞菌R37和嗜水气单胞菌G06)的最小抑菌浓度(MIC).然后再采用菌落计数法分别测定五倍子在0.25、0.5、1、2、4倍于各菌MIC时对鳗鲡4株致病性气单胞菌K17、G03、R37、G06的体外抗菌后效应(PAE).结果显示:五倍子在0.25、0.5、1、2、4倍MIC值时对鳗鲡4株致病性气单胞菌均具有一定的PAE,且PAE与药液浓度在一定范围内(0.25～4倍MIC)呈剂量依赖性,当药液浓度达4倍MIC时,PAE明显延长(P＜0.05);五倍子对各致病菌株K17、G03、R37、G06的PAE值在1倍MIC浓度以上差异显著(P＜0.05),在4倍MIC时对于致病菌株K17和R37的PAE之间差异较小.结论:试验结果提示,在养殖鳗鲡病害防治中设计投药方案,选用中药五倍子治疗由致病性气单胞菌感染所造成的烂鳃、肝胆肿大、败血症等疾病时,除了考虑药代动力学和MIC指标外,还应考虑PAE因素,可适当延长给药间隔时间,降低药物对鳗鲡的副作用及对其摄食量和生长的负面影响.     

Antibacterial activity of cefquinome against equine bacterial pathogens

Cefquinome is known for its use as an antibacterial drug in cattle and pigs. The objective of this study was to evaluate the antibacterial activity of cefquinome against equine pathogenic bacteria. The minimum inhibitory concentration (MIC) of cefquinome was determined for a total of 205 strains, which had recently been isolated in Europe from diseased horses (respiratory infection, foal septicaemia). The bactericidal activity was tested against 19 strains using the time killing method. The post-antibiotic effect (PAE) and post-antibiotic sub-MIC effect (PA SME) were determined against 12 strains. Cefquinome showed high activity against Actinobacillus equuli and streptococci (MIC(90) of 0.016 and 0.032microg/mL), Enterobacteriaceae (MIC(90)=0.125microg/mL) and staphylococci (MIC(90)=0.5microg/mL). The activity was limited against Rhodococcus spp. and Pseudomonas spp. Cefquinome was shown to be a time dependent bactericidal antibiotic against the target pathogens, killing occurring at a concentration close to the MIC. A PAE of 0.5-10h was calculated against streptococci whereas no PAE was observed for Escherichia coli. A longer PA SME was determined for streptococci (3.3 to >24h with a killing effect) and E. coli (0.5-13.9h). Cefquinome was shown to have a broad spectrum of activity which covers many equine pathogens.     

Pharmacokinetics and tissue distribution of enrofloxacin and its active metabolite ciprofloxacin in calves

The purpose of this study was to establish the pharmacokinetics of enrofloxacin and its metabolite ciprofloxacin in the plasma and interstitial fluid (ISF) following subcutaneous (s.c.) administration of enrofloxacin. Ultrafiltration probes were placed in the s.c. tissue, gluteal musculature, and pleural space of five calves. Each calf received 12.5 mg/kg of enrofloxacin. Plasma and ISF samples were collected for 48 h after drug administration and analyzed by high pressure liquid chromatography. Plasma protein binding of enrofloxacin and ciprofloxacin was measured using a microcentrifugation system. Tissue probes were well tolerated and reliably produced fluid from each site. The mean +/- SD plasma half-life was 6.8 +/- 1.2 and 7.3 +/- 1 h for enrofloxacin and ciprofloxacin, respectively. The combined (ciprofloxacin + enrofloxacin) peak plasma concentration (Cmax) was 1.52 microg/mL, and the combined area under the curve (AUC) was 25.33 microg/mL. The plasma free drug concentrations were 54% and 81% for enrofloxacin and ciprofloxacin, respectively, and free drug concentration in the tissue fluid was higher than in plasma. We concluded that Cmax/MIC and AUC/MIC ratios for free drug concentrations in plasma and ISF would meet suggested ratios for a targeted MIC of 0.06 microg/mL.     

安普霉素及其联合用药对金黄色葡萄球菌体外PAE的研究

本试验采用稀释法去除抗生素。用菌落计数测定细菌生长曲线的方法,分别测定了安普霉素及其与阿莫西林或氨苄西林联用对金黄色葡萄球菌的体外抗生素后效应（PAE）.当药物以2×MIC、4×MIC和8xMIC浓度作用于金黄色葡萄球菌时,安普霉素的体外PAE分别为1．78h、2．49h、3．63h;安普霉素与阿莫西林联用的体外PAE分别为4．13h、6．91h、9．82h;安普霉素与氨苄西林联用的体外PAE分别为3．81h、5．67h、8．45h。结果表明。安普霉素在体外对金黄色葡萄球菌有较长的PAE。且随药物浓度的升高其PAE也相应地延长．呈明显的剂量依赖性;安普霉素与阿莫西林、氨苄西林联用对金黄色葡萄球菌的体外PAE呈现相加或协同作用。     

In vitro and in vivo pharmacodynamic properties of the fluoroquinolone ibafloxacin

The pharmacodynamic properties of a new veterinary fluoroquinolone antimicrobial agent, ibafloxacin, were evaluated. Minimal inhibitory concentrations (MIC), time-kill kinetics, postantibiotic effect (PAE) and postantibiotic subminimal inhibitory concentration effects (PA-SME) were determined against pathogenic canine Gram-negative and Gram-positive bacterial isolates from dermal, respiratory and urinary tract infections. The synergistic interactions between ibafloxacin and its main metabolite, 8-hydroxy-ibafloxacin were investigated. Finally, the efficacy of ibafloxacin was tested in in vivo canine infection models. Ibafloxacin had good activity against Pasteurella spp., Escherichia coli, Klebsiella spp., Proteus spp. and Staphylococcus spp. (MIC90=0.5 microg/mL), moderate activity against Bordetella bronchiseptica, Enterobacter spp. and Enterococcus spp. (MIC50=4 microg/mL) and low activity against Pseudomonas spp. and Streptococcus spp. The time-killing analysis confirmed that ibafloxacin was bactericidal with a broad spectrum of activity. The PAE and PA-SME were between 0.7-2.13 and 1-11.5 h, respectively. Finally, studies in dog models of wound infection and cystitis confirmed the efficacy of once daily oral ibafloxacin at a dosage of 15 mg/kg. Additional studies are needed to better define the importance of AUC/MIC (AUIC) and Cmax/MIC ratios on the outcome of fluoroquinolone therapy in dogs.     

Pharmacokinetics and endometrial tissue concentrations of enrofloxacin and the metabolite ciprofloxacin after i.v. administration of enrofloxacin to mares

Enrofloxacin was administered i.v. to five adult mares at a dose of 5 mg/kg. After administration, blood and endometrial biopsy samples were collected at regular intervals for 24 h. The plasma and tissue samples were analyzed for enrofloxacin and the metabolite ciprofloxacin by high-pressure liquid chromatography. In plasma, enrofloxacin had a terminal half-life (t(1/2)), volume of distribution (area method), and systemic clearance of 6.7 +/- 2.9 h, 1.9 +/- 0.4 L/kg, and 3.7 +/- 1.4 mL/kg/min, respectively. Ciprofloxacin had a maximum plasma concentration (Cmax) of 0.28 +/- 0.09 microg/mL. In endometrial tissue, the enrofloxacin Cmax was 1.7 +/- 0.5 microg/g, and the t(1/2) was 7.8 +/- 3.7 h. Ciprofloxacin Cmax in tissues was 0.15 +/- 0.04 microg/g and the t(1/2) was 5.2 +/- 2.0 h. The tissue:plasma enrofloxacin concentration ratios (w/w:w/v) were 0.175 +/- 0.08 and 0.47 +/- 0.06 for Cmax and AUC, respectively. For ciprofloxacin, these values were 0.55 +/- 0.13 and 0.58 +/- 0.31, respectively. We concluded that plasma concentrations achieved after 5 mg/kg i.v. are high enough to meet surrogate markers for antibacterial activity (Cmax:MIC ratio, and AUC:MIC ratio) considered effective for most susceptible gram-negative bacteria. Endometrial tissue concentrations taken from the mares after dosing showed that enrofloxacin and ciprofloxacin both penetrate this tissue adequately after systemic administration and would attain concentrations high enough in the tissue fluids to treat infections of the endometrium caused by susceptible bacteria.     

Comparison of pharmacodynamic and pharmacokinetic indices of efficacy for 5 fluoroquinolones toward pathogens of dogs and cats

BACKGROUND: Fluoroquinolones are often used interchangeably in dogs and cats. HYPOTHESIS: Predicted therapeutic efficacy differs among fluoroquinolones. ANIMALS: Bacterial pathogens isolated from dogs and cats. METHODS: Using microtube-dilution procedures, percent resistance and 2 pharmacodynamic/pharmacokinetic indices (maximum concentration/minimum inhibitory concentration [Cmax/MIC] [target 0.10] and area under curve/minimum inhibitory concentration [AUC/MIC] [target 0.125]) were compared prospectively at low and high doses (mg/kg) for ciprofloxacin (5 and 20), difloxacin (5 and 10), enrofloxacin (including enrofloxacin+ciprofloxacin) (5 and 20), marbofloxacin (2.5 and 5), and orbifloxacin (2.5 and 7.5). Indices were calculated for organisms represented by < or = 15 isolates. RESULTS: Percent resistance for all Gram-negative (n = 180; 20+/-3%; 39+/-5% for Escherichia coli) and Gram-positive isolates (n = 66; 18+/-3%) did not differ among drugs or organisms. The pattern of Cmax/MIC was generally enrofloxacin+ciprofloxacin > or = enrofloxacin or ciprofloxacin > or = marbofloxacin > or = orbifloxacin > or = difloxacin; and for AUIC/ MIC, enrofloxacin+ciprofloxacin > or = marbofloxacin > or = ciprofloxacin > or = enrofloxacin > difloxacin > orbifloxacin. Among susceptible Gram-negative isolates studied (n = 117), targeted Cmax/MIC or AUC/MIC were achieved in 88% of E. coli, 53% of Proteus mirabilis, and 35% of Pseudomonas aeruginosa; and for susceptible Gram-positive isolates studied (n = 49), 53% of Streptotoccus spp. and Staphylococcus intermedius and 27% of Staphylococcus spp. At the high dose, the proportion of isolates for which a target was reached was: ciprofloxacin, enrofloxacin+ciprofloaxin, and marbofloxacin (77%), enrofloxacin (73%), orbifloxacin (51%), and difloxacin (40%); and at the low dose, enrofloxacin+ciprofloxacin and enrofloxacin (43%), ciprofloxacin (40%), marbofloxacin (39%), orbifloxacin (29%), and difloxacin (28%). CONCLUSIONS: E. coli resistance to fluoroquinolones approximated 40%. For susceptible isolates, enrofloxacin, marbofloxacin, and ciprofloxacin more consistently reached indices associated with predicted efficacy, but only at the high dose.     

In vitro susceptibility of selected veterinary bacterial pathogens to ciprofloxacin, enrofloxacin and norfloxacin.

The minimum inhibitory concentrations (MIC) of ciprofloxacin, enrofloxacin, and norfloxacin were tested for approximately ten clinical isolates of each of Actinobacillus pleuropneumoniae, Actinobacillus suis, Actinomyces pyogenes, Corynebacterium pseudotuberculosis, Erysipelothrix rhusiopathiae, Haemophilus parasuis, Haemophilus somnus, Pasteurella haemolytica, Pasteurella multocida, Rhodococcus equi, Streptococcus equi, Streptococcus suis and Streptococcus zooepidemicus. Ciprofloxacin and enrofloxacin had similar activity and were more active than norfloxacin. All isolates had an MIC of 1.0 microgram/mL or less for ciprofloxacin and enrofloxacin, and these drugs had particularly marked activity against the gram-negative bacteria tested.