基因探针试验检测大肠杆菌不耐热肠毒素的初步应用

本文报道用LT基因探针试验检测了从已排除其它肠道致病菌的急性腹泻病人粪便标本中挑出的109株大肠杆菌(每例病人1株),同时用平板免疫溶血试验及家兔肠段结扎试验检测ETEC进行比较。结果LT基因探针试验检出率最高,达66.06%,比平板免疫溶血试验的6.42%及家兔肠段结扎试验的5.50%均高了约10倍,证实了LT基因探针试验具有极高度的敏感性,适合于一次过地大量筛选出含毒素基因的菌株。     

霍乱沾棒一步法快速诊断技术现场应用的效果观察

目的了解霍乱沾棒一步法检测霍乱弧菌的特异性和敏感性及现场应用的效果。方法以O1群霍乱弧菌、非O1群霍乱弧菌和引起腹泻的主要肠道致病菌制成菌悬液模拟粪便标本,并与常规细菌培养法平行检测霍乱流行期间的粪便标本进行比较。结果霍乱沾棒一步法的灵敏度为105cfu/ml,与非O1群霍乱弧菌和主要肠道致病菌无交叉反应;129份粪便标本的现场检测与常规细菌培养法结果一致。结论霍乱沾棒一步法具有快速、简单、准确和适用于基层单位使用的优点,值得推广应用。     

协同凝集反应在细菌性痢疾快速诊断上的应用

本文利用SPA—COA反应,采用增菌基增菌、离心集菌、弃除粪便悬液,对临床怀疑为“菌痢”的病人粪便标本进行快速病源检测,结果与常规细菌培养法基本一致。并对解决反应中细菌量的问题和排除粪便悬液中非特异性凝集的问题进行讨论。     

大肠艾希氏菌不耐热肠毒素基因探针和单向免疫溶血试验及其它方法对比

比较了鉴定产不耐热肠毒素(LT)大肠艾希氏菌(ETEC-LT)的基因探针和单向免疫溶血试验(SRIH)检测河南、广东、湖北腹泻病人分离物的效果。26株LT基因探针阳性菌株中,24株SRIH阳性;2株SRIH阴性菌株,1株酶联免疫吸附试验(ELISA),被动免疫溶血试验(PIH)和Y-1肾上腺细胞试验均为阳性,另1株未经后三种方法检查。48株LT基因探针阴性菌株中,46株SRIH阴性,2株SRIH阳性菌株,1株ELISA,PIH种Y-1均阳性,另1株未经后三种方法检查。 1979年Dallas等完成了肠毒性大肠艾希氏菌(ETEC)不耐热肠毒素(LT)基因克隆,随后制备了LT基因探针,成功地用于临床和外环境标本ETEC-LT_4的检查,为ETEC-LT+的鉴定和流行病学研究提供了有用的工具。为了解该探针DNA与我国ETEC-LT+菌株的同源性,评价其实用价值,我们制备了LT探针,检查了河南、广东、湖北省腹泻病人粪便分离物,并与其它LT测定免疫学方法及培养细胞试验进行了比较。     

常用大肠埃希氏菌LT检测方法的比较

近十年来,在腹泻的病原研究中发现,产肠毒素性大肠埃希氏菌(ETEC)感染率最高.ETEC菌产生LT(不耐热)和ST(耐热)两种肠毒素,可引起腹泻.目前检测LT的方法很多,有动物试验、免疫学方法、基因探针技术等,1994年本室对常用的平板免疫溶血试验法、家兔肠袢试验法和Biken’s试验法三种检测方法进行比较,报告如下:1 材料与方法1.1 菌株来源 试验菌株系近几年我省从腹泻病人粪便标本中分离,共256株,其中34株LT阳性株经北京药品生物制品检定所鉴定证实.6株标准菌株:LT阳性2株,LT—ST阳性2株,LT阴性2株,由北京药品生物制品检定所提供.     

实时荧光定量PCR快速检测无菌性体液革兰阳/阴性细菌感染

目的　探讨将实时荧光定量PCR（qPCR）检测细菌16S rRNA基因用于快速判断无菌性体液革兰阳/阴性细菌感染,并评价其分析性能。方法　以细菌16S rRNA基因为目标设计通用引物、通用探针及革兰阴性（GN）菌探针,对14种标准菌株、20种临床菌株、白色念珠菌、乙型肝炎病毒(HBV)、人基因组及阴性对照进行qPCR检测,评价该方法引物和探针的通用性和特异性及检测限。以104 cfu/ml菌悬液、阴性对照的循环域（Ct）值99%置信区间下限分别作为尿路、其他无菌性体液细菌感染判定的分界值。用271例临床无菌性体液标本评价qPCR法的临床效能。结果　通用探针-qPCR,所有实验菌株检测为阳性。GN探针-qPCR,所有实验革兰阴性菌株检测为阳性。通用探针的检测限为1×101～1×102 cfu/ml。GN探针的检测限可低至1.0×101 cfu/ml。判定尿路、其他无菌性体液细菌感染的分界值分别为23.76、29.37。结论　应用细菌16S rRNA基因通用探针和GN探针的qPCR方法通用性好、特异性强、检测限低,可快速检测临床无菌性体液常见细菌感染,为临床提供准确、可靠的病原学诊断依据。     

TaqMan-MGB探针实时荧光定量PCR联合检测难辨梭菌菌属基因及毒素基因方法学的建立

目的 建立一种简便、快速难辨梭菌菌属鉴定及其毒素基因筛查的荧光定量PCR检测方法。方法 采用TaqMan-MGB探针，通过real-time PCR分析系统，同时检测难辨梭菌菌属基因磷酸丙糖异构酶（Tpi）、A毒素（TcdA）、B毒素（TcdB）及缺失部分基因的A毒素（TcdAT），从特异度、灵敏度及其抗干扰性等方面评价该方法，并联合全自动酶联荧光免疫系统（VIDAS）检测50 例临床不明原因腹泻病例粪便标本探讨其应用价值。结果 难辨梭菌非产毒株 Tpi 基因（tpi）的检测下限是6×10^-2 CFU/μl，产毒株 tpi、tcdA、tcdB、tcdAT 的检测下限为 6×10^-1 CFU/μl；难辨梭菌非产毒株tpi检测下限批内、批间变异率分别为2.1%和2.3%；产毒株tpi、tcdA、tcdB、tcdAT的检测下限批内、批间变异率依次为3.0%和3.4%、2.9%和3.2%、5.3%和5.7%、2.7%和2.8%。临床常见分离菌株及梭菌属其他细菌对检测无干扰。50 例不明原因腹泻病例粪便标本中，采用TaqMan-MGB 探针实时荧光 PCR 与 VIDAS 酶标免疫检测 39 例阴性标本其符合率为 100%；6 例两方法检测均为阳性；3例VIDAS酶标免疫检测为可疑及2例为阴性，经TaqMan-MGB探针实时荧光PCR检测为A-/B＋菌株。结论 建立的TaqMan-MGB探针实时荧光定量PCR具有高通量、高灵敏度和重复性好的特性，且可筛查携带缺失部分基因的TcdA难辨梭菌菌株。     

嗜水气单胞菌TaqMan实时PCR检测方法的建立

目的 建立嗜水气单胞菌TaqMan实时PCR实验室检测方法.方法 根据嗜水气单胞菌主要黏附素基因(aeromonas hydrophila major adhesion gene,ahe)的保守序列设计引物和TaqMan探针.引物选取200～700 nmol/L 6个浓度梯度,探针选取100～400 nmol/L 4个浓度梯度,以完全随机设计资料的方差分析分别优化引物和探针的浓度.以45株霍乱弧菌、20株副溶血弧菌、10株河流弧菌、4株拟态弧菌、5株创伤弧菌、1株溶藻弧菌、1株弗尼斯弧菌、5株沙门菌属细菌、10株志贺菌属细菌和2株类志贺邻单胞菌为对照,评价该方法的特异性.对所建立的方法进行菌液灵敏度检测和DNA灵敏度检测,并将嗜水气单胞菌人工污染健康人的粪便,实验室内评价该方法从粪便中检测嗜水气单胞菌的能力.结果 6组引物浓度所得的循环阈值(cycle threshold,Ct)分别为(x±s):20.69±0.33、20.72±0.21、20.81±0.12、20.74±0.12、20.51±0.16和20.69±0.11,选择上下游引物的浓度为200 nmol/L(F=1.33,P=0.28),4组探针浓度所得的Ct值分别为(x±s):20.56±0.08、20.82±0.05、20.82±0.11和20.9±0.09,选择探针的浓度为100 nmol/L(F=5.26,P=0.01).该方法DNA的榆测下限为100 fs/μl,纯菌液的检测下限为80 CFU/ml,粪便中嗜水气单胞菌的检测下限为8×103CFU/ml,人工粪便标本增菌8 h后的检测下限为8 CFU/ml.该方法对其他细菌的染色体无扩增.结论 以aha基因为目标检测片段建立的嗜水气单胞菌实时PCR方法灵敏度高、特异度强,可用于纯菌和粪便标本中嗜水气单胞菌的快速检测.     

实时荧光PCR快速检测粪便中艰难梭菌方法

目的:建立实时荧光PCR快速检测艰难梭菌的方法。方法:以艰难梭菌磷酸丙糖异构酶(tpi)基因的保守序列为模板设计和合成特异性引物和荧光标记探针,建立实时荧光PCR检测体系,通过检测含有艰难梭菌标准菌株浓度为106-10 CFU/ml的细菌培养物及加标模拟样本进行敏感性分析,并对其特异性和干扰性进行评价。结果:该方法只对艰难梭菌进行特异性扩增,其他常见的病原菌均不能扩增;整个检测过程只需要2 h,对艰难梭菌菌悬液可检测至10 CFU/ml细菌,对加标粪便样本可检测至1000 CFU/ml细菌。结论:本研究建立的实时荧光PCR检测艰难梭菌方法具有快速、特异、敏感性高等优点,能实现对艰难梭菌的快速检测。     

微型寡核苷酸芯片检测脑脊液病原菌研究与应用

目的建立快速检测脑脊液标本中常见病原菌的微型寡核苷酸芯片。方法根据脑脊液中常见病原菌16S rRNA基因序列设计通用引物和检测探针;探针固定于尼龙膜上制成寡核苷酸芯片;通用引物扩增病原菌DNA并标记生物素,产物与芯片进行反向杂交检测;对该体系的敏感性和特异性进行了测试,并检测了32例临床病原菌感染的脑脊液标本。结果所有实验菌株均只与芯片上相应探针杂交。该法最低可检测出10 CFU/ml的大肠埃希菌;32例临床本的检测结果与常规鉴定法完全一致。结论该寡核苷酸芯片法能够准确、敏感、快速地检测脑脊液标本中的病原菌。     

Fermented Wheat Aleurone Enriched With Probiotic Strains LGG and Bb12 Modulates Markers of Tumor Progression in Human Colon Cells

Fermentation of dietary fiber by the microflora enhances the levels of effective metabolites, which are potentially protective against colon cancer. The specific addition of probiotics may enhance the efficiency of fermentation of wheat aleurone, a source of dietary fiber. We investigated the effects of aleurone, fermented with fecal slurries with the addition of the probiotics LGG and Bb12 (aleurone⁺), on cell growth, apoptosis, and differentiation, as well as expression of genes related to growth and apoptosis using two different human colon cell lines (HT29: adenocarcinoma cells; LT97: adenoma cells). The efficiency of fermentation of aleurone was only slightly enhanced by the addition of LGG/Bb12, resulting in an increased concentration of butyrate. In LT97 cells, the growth inhibition of aleurone⁺ was stronger than in HT29 cells. In HT29 cells, a cell cycle arrest in G₀/G₁ and the alkaline phosphatase activity, a marker of differentiation, were enhanced by the fs aleurone⁺. Treatment with all fermentation supernatants resulted in a significant increase in apoptosis and an upregulation of genes involved in cell growth and apoptosis (p21 and WNT2B). In conclusion, fs aleurone⁺ modulated markers of cancer prevention, namely inhibition of cell growth and promotion of apoptosis as well as differentiation.     

Enterotoxigenic and necrotizing Escherichia coli in human diarrhoea in Spain

Enterotoxigenic Escherichia coli (ETEC) strains of serotype 0153: K-:H45 CFA/I⁺ STa⁺ were associated with two outbreaks of neonatal diarrhoea that occurred in two different hospitals of Madrid, in one of which several children died. Two other outbreaks were associated with ETEC strains of serotypes 0159: K-: H21 (LT⁺) and 0159: K-: H4 (LT⁺ STa⁺) without CFA/I and CFA/II colonization factors. Necrotizing E. coli (NTEC) strains of serotype 06: K13, producing the cytotoxic necrotizing factor CNFI and -haemolysin, were also associated with two outbreaks of neonatal diarrhoea that occured in a hospital in Madrid and in a hospital in Talavera de la Reina. The results of the characterization of some ETEC and NTEC strains isolated from sporadic cases of diarrhoea are also discussed.Corresponding author.     

Serotypes and colonization factors of enterotoxigenic Escherichia coli isolated in various countries

One hundred and six enterotoxigenic E. coli (ETEC) isolated from many geographical areas were serotyped and investigated for the presence of colonization factor antigens CFA/I and CFA/II, the expression of mannose-resistant haemagglutination (MRHA) and the levels of surface hydrophobicity. CFA/I was found in 6 (17%) of 36 LT⁺STa⁺ strains and in 15 (54%) of 28 STa⁺ strains; CFA/II was found in 16 (44%) of 36 LT⁺STa⁺ strains. None of 42 LT⁺ strains showed CFA/I or CFA/II. CFA/I was found in ETEC of serotypes O63:K?:H?, O78:K80, O128:K67 and O153:K?:H45, whereas CFA/II was found in serotypes O6:H?, O6:K15:H16 and 06:K?:H40. Of the 69 CFA/I^? CFA/II^? ETEC strains, 9 (13%) showed MRHA with some of the seven erythrocyte species used and 21 (30%) were hydrophobic. Among the 21 hydrophobic strains CFA-negative we have detected: (i) 6 LT⁺ strains of serogroup O25 negative for MRHA, (ii) 5 strains O159 (4 LT⁺ and 1 LT⁺ STa⁺) also negative for MRHA, and (iii) 3 STa⁺ strains of serotype O27:K?:H7 that haemagglutinated calf and sheep erythrocytes when grown on Minca-Is. The 106 ETEC strains belonged to 20 different 0 serogroups. However, 77 (73%) were of one of nine serogroups (O6, O8, O25, O27, O78, O148, O153, O159 and O167). E. coli strains belonging to O6 and O153 groups predominated among ETEC isolated in Spain, O159 strains in the Central African Republic, O25 and O148 strains in Japan, and O15 and O78 strains in India.     

Studies on cholera carriers

Cholera carrier studies in the Philippines in 1964-66 showed a prevalence rate of 21.7% among household contacts of cholera patients, and 8.4% in occupants of houses next door to one where a cholera patient lived, as opposed to 0.34% in the general population. The duration of the carrier state among 19 household carriers isolated for examination varied from 5 to 19 days. The vibrio concentration in the stool of contact carriers was 10²-15⁵ per gram, as compared with 10⁶-19⁹ per ml of rice-water stool in cholera cases.     

Fish Oil Enhances T Cell Function and Tumor Infiltration and Is Correlated With a Cancer Prevention Effect in HER-2/neu But Not PyMT Transgenic Mice

Few studies have explored the effects of omega-3 polyunsaturated fatty acid (n-3 PUFA) supplementation on immune modulation in murine models of mammary carcinogenesis. HER-2/neu and PyMT mice were randomized to 2 dietary interventions: AIN-93G-based diet with 1) 11% of diet (per gram weight) as corn oil (CO) or 2) 10% of diet as menhaden fish oil plus 1% of diet as corn oil (FO). FO significantly reduced the incidence and multiplicity of tumors (P < 0.001) in HER-2/neu, but not PyMT mice. FO-fed mice had significantly larger splenocyte counts than CO-fed mice in both the HER-2/neu and PyMT models; and in both models this was comprised of an increase in most cell types, including Gr-1⁺/CD11b⁺ cells. T cells from FO-fed HER-2/neu mice produced significantly more interleukin-2 (P = 0.004) and interferon-γ (P = 0.012) in response to in vitro stimulation with anti-CD3 (0.5 µg/ml). Lastly, FO-fed HER-2/neu mice had significantly more tumor immune infiltrates than CO-fed mice, including NK1.1⁺, F4/80⁺, and Gr-1⁺/CD11b⁺ cells (P ≤ 0.05). Greater Th1 cytokine production and significantly more tumor immune infiltrates in FO-fed Her2/neu mice may account for the cancer prevention effect of fish oil in this model.     

新生儿HBV血清标志物及免疫状态与乙型肝炎疫苗无/弱应答的关系

目的 探讨新生儿HBV血清标志物及免疫状态对乙型肝炎（乙肝）疫苗无/弱应答的影响。方法 选择2011年7月至2013年7月太原市第三人民医院妇产科HBsAg阳性孕产妇及其足月新生儿386对,按我国0-1-6月免疫接种程序对新生儿进行乙肝疫苗接种并随访至12月龄。采用化学发光法检测孕产妇、新生儿及其12月龄（婴儿）的外周血HBV血清标志物HBsAg、抗-HBs、HBeAg、抗-HBe和抗-HBc水平;利用流式细胞术及ELISA检测新生儿及婴儿的外周血TLR3蛋白表达量及T淋巴细胞亚群、B淋巴细胞、树突状细胞（DCs）数量和Th1/Th2型细胞因子水平。结果 新生儿HBV血清标志物以“HBeAg⁺抗-HBe⁺”、“HBsAg⁺HBeAg⁺抗-HBe⁺”、“HBsAg⁺”和“HBV血清标志物全阴,HBVM^-”为主;“HBeAg⁺抗-HBe⁺”模式下婴儿乙肝疫苗无/弱应答率为5.2%,低于其他3种模式的20.0%、40.0%和22.5%。4种主要HBV血清学模式下婴儿的CD₄⁺ T淋巴细胞和CD₈⁺ T淋巴细胞数量、新生儿及婴儿IL-6水平差异有统计学意义。“HBeAg⁺抗-HBe⁺”模式下新生儿及婴儿的IL-6水平均高于“HBVM^-”模式;新生儿及婴儿的IL-6水平均与抗-HBs水平呈正相关;血清IL-6水平>1 112.0 pg/ml的新生儿发生乙肝疫苗无/弱应答的风险下降了61.4%（OR=0.386,95% CI：0.266～0.561,P<0.001）。结论 新生儿“HBeAg⁺抗-HBe⁺”模式及高水平IL-6者的乙肝疫苗无/弱应答率较低,新生儿各血清学标志物组合模式与免疫状态的关系有待进一步研究。     

Energy-restricted diets result in higher numbers of CD4, CD8, immunoglobulins (A, M, and G), and CD45RA cells in spleen and CD4, immunoglobulin A, and CD45RA cells in colonic lamina propria of rats

Dietary energy restriction (ER) offers certain health benefits, particularly when ER is controlled through manipulation of dietary fats. Our hypothesis is that cellular immunity is modulated by dietary ER. Furthermore, we believe that the immune response may differ between spleen and colon because their lymphatic and vascular organization is different. The objective of the study was to test this hypothesis by determining the effects of dietary ER through manipulation of energy intake from high-fat (HF) diets on the expression and frequency of the CD4⁺ (T-helper/T-inducer) and CD8⁺ (T-cytotoxic/T-suppressor) cells, CD45RA (B-cell–specific marker), and immunoglobulins (Ig) A-, G-, and M-bearing cells in spleen and colon in rats by immunohistochemical method. Rats fed the HF diet had a significantly (P < .05) reduced number of immune cells as compared with those fed ER diets. Energy-restricted diet–fed rats showed higher (P < .05) numbers of CD4⁺, CD8⁺, IgA, IgM, IgG, and CD45RA cells in spleen and CD4⁺, IgA, and CD45RA cells in colonic lamina propria. The IgA-containing cells were markedly higher in the colon compared with the spleen. No change occurred in the number of IgM- and IgG-containing cells in colonic tissues between groups, except for the 20% ER group where IgM-labeled cells were higher (P < .05) compared with HF and 40% ER groups. These findings suggest that ER may modulate adaptive immune function and that CD4⁺ and IgA cells may serve as biological indicators for dietary energy-modulated immunoresponse in spleen and colon, respectively.     

Gestational vitamin A deficiency reduces the intestinal immune response by decreasing the number of immune cells in rat offspring

ObjectivesVitamin A (VA) is a critical micronutrient for life, especially during growth and development. There is a close relationship between VA deficiency (VAD) and the morbidity of diarrhea in the clinical setting. However, the regulatory mechanisms of VA are not clearly understood.MethodsSpecific-pathogen–free Wistar rats received a diet with or without VA before gestation. The offspring were submitted to an abdominal injection of Escherichia coli lipopolysaccharide. After the challenge, which lasted for 12 h, the serum retinol was detected by high-performance liquid chromatography, and the level of immunoglobulin A in the stool was analyzed by enzyme-linked immunosorbent assay. The lymphocyte immunophenotypes were evaluated with the use of flow cytometry with samples collected from the spleen, the mesenteric lymph nodes, Peyer patches, and intestinal intraepithelial lymphocytes.ResultsEarly life VAD, independent of the lipopolysaccharide challenge, significantly decreased serum retinol level and CD8⁺ intestinal intraepithelial lymphocytes. The level of immunoglobulin A secretion and percentages of splenic CD4⁺CD8⁺ T cells were affected by the interaction effects of the lipopolysaccharide challenge and VAD treatment. Gestational VAD significantly increased the percentages of B cells in the mesenteric lymph nodes and decreased the percentages of CD11 _C⁺ dendritic cells and CD4⁺CD25⁺ T cells from the Peyer patches. The lipopolysaccharide challenge only significantly increased percentages of splenic CD4⁺CD25⁺ T cells. The intestinal tissue of the pups with VAD displayed mild inflammation.ConclusionsGestational or early life VAD decreases the numbers of immune cells in offspring, which may partly suppress the activities of the mucosal immune responses in the intestine. This suggests that more attention should be given to the VA nutritional state of children and women of reproductive age.     

Health risks in wastewater irrigation: Comparing estimates from quantitative microbial risk analyses and epidemiological studies

The combination of standard quantitative microbial risk analysis (QMRA) techniques and 10,000-trial Monte Carlo risk simulations was used to estimate the human health risks associated with the use of wastewater for unrestricted and restricted crop irrigation. A risk of rotavirus infection of 10^-2 per person per year (pppy) was used as the reference level of acceptable risk. Using the model scenario of involuntary soil ingestion for restricted irrigation, the risk of rotavirus infection is ~10^-2 pppy when the wastewater contains 10⁶ Escherichia coli per 100 ml and when local agricultural practices are highly mechanised. For labour-intensive agriculture the risk of rotavirus infection is ~10^-2 pppy when the wastewater contains 10⁵ E. coli per 100 ml; however, the wastewater quality should be 10⁴ E. coli per 100 ml when children under 15 are exposed. With the model scenario of lettuce consumption for unrestricted irrigation, the use of wastewaters containing 10⁴E. coli per 100 ml results in a rotavirus infection risk of ~10^-2 pppy; however, again based on epidemiological evidence from Mexico, the current WHO guideline level of 1,000 E. coli per 100 ml should be retained for root crops eaten raw.     

The toxicity of dimethoate to predatory coleoptera: Developing an approach to risk analysis for broad-spectrum pesticides

Topical toxicity bioassays were undertaken with the organophosphate compound dimethoate, O, O-dimethyl S-methylcarbamoylmethyl phosphorodithioate, against six species of predatory Coleoptera that are recognized predators of cereal aphids: the staphylinid Tachyporus hypnorum, the coccinellid Coccinella septempunctata and the carabids Demetrias atricapillus, Trechus quadristriatus, Bembidion obtusum and Nebria brevicollis. LD₅₀ values for formulated dimethoate, diluted in water, varied between 3.4 and 98.8 ng a.i. insect^–1 and 1.45 and 18.20 g a.i. g^–1 body weight. These values were similar to those obtained in another study by Wiles and Jepson (1992) for the pyrethroid insecticide deltamethrin, (S)-alphacyano-3-phenoxybenzyl (1R)-cis-3-(2,2-dibromovinyl)-2,2,-dimethylcyclopropanecarboxylate. Hazard ratios were calculated for dimethoate and deltamethrin by dividing recommended field mass application rate in g a.i. ha^–1 by LD₅₀ in g a.i. insect^–1: this gave an indication of potential direct exposure hazard. The range of values for dimethoate (3,441 to 100,000) were well in excess of those for deltamethrin (28.6 to 500) because of its greater field application rate (340 g a.i. ha^–1 compared with 6.25 g ai ha^–1). LT₅₀s were determined for adult C. septempunctata exposed to wheat leaves treated with either dimethoate or deltamethrin at full or half field rate within in-situ bioassays. At both rates, the dimethoate LT₅₀s were shorter, ranging at full rate from 0.06 to 7.70 h, between 2 and 96 h after treatment, compared with 1.04 to 20.89 h after the same time intervals for deltamethrin. At half-field rate, the equivalent LT₅₀ ranges were 0.52 to 13.65 h for dimethoate and 3.75 to 31.76 h for deltamethrin. The relative toxicities of the two insecticides, expressed as the ratio of log (x+1) LT₅₀ deltamethrin:dimethoate, narrowed greatly between 2 and 24 h, especially in the full rate treatment, indicating a more rapid loss of dimethoate than deltamethrin from foliage in the field shortly after spray application. The ecotoxicological consequences of exposure to dimethoate and deltamethrin are compared relative to their differing mass application rates, physicochemical properties and environmental fate. The role and value of laboratory-based toxicological testing within risk analysis procedures is discussed.