Comparative testing of disinfectant and antiseptic products using proposed European suspension testing methods

The development of standard suspension test methods for disinfectants and antiseptics for adoption in Europe is described. Evaluation of a range of disinfectant agents and products currently used in the UK under conditions as proposed for these tests indicates that the majority of products diluted in water of standard hardness showed satisfactory activity producing a 4·5–5 log reduction in viable count within 5 min against Staphylococcus aureus, Pseudomonas aeruginosa, Enterococcus faecium, Proteus mirabilis and Candida albicans in the absence and presence of 1% albumin. All the products, when diluted with distilled water, produced greater than 5 log reduction in 60 min.     

Comparative testing and evaluation of hard-surface disinfectants

Summary The activity of eleven disinfectants againstStaphylococcus aureus, Pseudomonas aeruginosa, andSaccharomyces cerevisiae was determined using a method based on the A.O.A.C. germicidal and detergent sanitizer assay. Based on the activity against the test organisms after 30-and 60-s exposures to each disinfectant, the disinfectant containing chlorine dioxide had the highest biocidal activity in this assay, on a mg/l basis. In addition, a disinfectant containing sodium hypochlorite and a disinfectant containing sodium chlorite performed well, at concentrations below label specifications. The results illustrate the importance of testing disinfectants in the context of their intended use.     

Evaluation of the repeatability and reproducibility of European suspension test methods for antimicrobial activity of disinfectants and antiseptics

A collaborative study to determine the precision of the 1987 Method of test for the antimicrobial activity of disinfectants in food hygiene is described. The repeatability and reproducibility of the test was found to vary according to the nature of the test organism, the type of disinfectant product and the skill of the operator. Results indicate that significant differences in microbicidal effect (ME values) occur within test laboratories between test periods as well as between laboratories, and that much of this variability derives from apparently random variations in the resistance of test strains from day to day and test period to test period. Indications are that although the test is sufficiently reliable to be used as a standard method, adequate test replication must be specified to distinguish borderline pass from borderline fail disinfectant concentrations. The implications of the results in relation to current work on the development of unified European test methods for disinfectants is discussed.     

Evaluation of the repeatability and reproducibility of European suspension test methods for antimicrobial activity of disinfectants and antiseptics.

A collaborative study to determine the precision of the 1987 Method of test for the antimicrobial activity of disinfectants in food hygiene is described. The repeatability and reproducibility of the test was found to vary according to the nature of the test organism, the type of disinfectant product and the skill of the operator. Results indicate that significant differences in microbicidal effect (ME values) occur within test laboratories between test periods as well as between laboratories, and that much of this variability derives from apparently random variations in the resistance of test strains from day to day and test period to test period. Indications are that although the test is sufficiently reliable to be used as a standard method, adequate test replication must be specified to distinguish borderline pass from borderline fail disinfectant concentrations. The implications of the results in relation to current work on the development of unified European test methods for disinfectants is discussed.     

The testing of disinfectants

Although all disinfectant tests have the same final purpose, namely measuring the antimicrobial activity of a chemical substance or preparation, a large number of testing methods has been described. They are subdivided into suspension tests, carrier and surface disinfection tests and other practice-mimicking tests. The suspension tests comprise qualitative and quantitative suspension tests, and, as derived tests, the determination of the phenol coefficient and capacity tests. There is an essential difference between a carrier test and a surface disinfectant test: in the former case the carrier is submerged in the disinfectant solution during the whole exposure time, whereas in the latter case the disinfectant is applied on the carrier for the application time and thereafter the carrier is drying during the exposure.The basic principle now widely accepted is that the antimicrobial efficiency of a disinfectant is examined at three stages of testing.The first stage concerns laboratory tests in which it is verified whether a chemical compound or a preparation possesses antimicrobial activity. For these preliminary screening tests, suspension tests are considered.In the second stage of tests, disinfection procedures and not disinfectants are examined. It is determined under which conditions and at which use-dilution for a given application the preparation is active: the tests simulate real-life situations; such tests are carrier tests for the disinfection of materials by submersion and surface disinfection tests.The last stage takes place in the field, and comprises the in-loco or in-situ tests with as variants the in-use tests, which examine whether, after a normal period of use, germs are still killed by the disinfectant solution.It is the task of the European and international standardization organisations to develop new standards and to elaborate tests, which predict the effectiveness of a preparation in practice under variable circumstances.     

An evaluation of the repeatability and reproducibility of a surface test for the activity of disinfectants

A collaborative study was carried out to determine the precision of a disinfectant surface test method which is currently under consideration for development as a harmonized European standard surface test. Results indicate that significant variation in microbicidal effect occurs both within and between test laboratories despite careful standardization of test conditions, but that the variability may be less than that associated with suspension tests. Indications are that much of this variability derives from random variations in the resistance of the test strains from day to day and, most particularly, from test period to test period both within as well as between laboratories. It is concluded that although the test may be sufficiently reliable to be used as a standard method, adequate replication must be specified to distinguish borderline pass from borderline fail concentrations.     

Topology testing of phylogenies using least squares methods

Background  

The least squares (LS) method for constructing confidence sets of trees is closely related to LS tree building methods, in which the goodness of fit of the distances measured on the tree (patristic distances) to the observed distances between taxa is the criterion used for selecting the best topology. The generalized LS (GLS) method for topology testing is often frustrated by the computational difficulties in calculating the covariance matrix and its inverse, which in practice requires approximations. The weighted LS (WLS) allows for a more efficient albeit approximate calculation of the test statistic by ignoring the covariances between the distances.     

DNA repair test of disinfectants by liquid rec-assay

The DNA-damaging capacity and the mutagenicity of 6 disinfectants were studied by liquid rec-assay and Ames test. 5 disinfectants were found to be positive in DNA-damaging capacity while only one of them showed clear mutagenicity in the Ames test. Liquid rec-assay by direct incubation with S9 mix was the most sensitive method and gave the best correlation between the growth ratio (R 50) and the time lag, both of which compared Rec+ and Rec-. Liquid rec-assay may be useful for detecting the DNA-damaging capacity of chemicals with a strong killing effect.     

三种不同方法检查尿液有形成分结果的比较研究

目的:探讨利用三种不同方法检查尿液有形成分的符合率及其影响因素.方法:采用AX-4280全自动干化学分析仪、IQ200全自动尿液分析仪和人工镜检法联合检测尿液,并对结果进行比较和分析.结果:尿液各种有形成分的检测结果均存在不同程度的假阳性,人工镜检法与AX-4280的符合率为:红细胞71.1%;白细胞76.4%.人工镜检法与IQ200全自动尿液分析仪人工修饰前和人工修饰后结果的符合率分别为:红细胞81.3%、91.5%;白细胞85.9%、93.8%;透明管型81.4%、89.7%,未分类管型52.6%、77.4%:结晶84.1%、92.4%;细菌65.1%、88.2%;精子72.0%、91.5%.以人工镜检为标准,IQ200全自动尿液分析仪人工修饰前和人工修饰后各检测项目的假阳性率分别为:红细胞23.0%、9.3%,白细胞16.4%、6.6%,透明管型22.9%、11.4%,未分类管型90.2%、29.2%.结晶19.004、8.2%,细菌53.7%、11.0%,精子38.9%、9.3%.结论:三种检查方法的联合应用更能提高尿液有形成分检查结果的准确性,为临床诊治提供依据.     

三种检验方法在诊断女性生殖道沙眼衣原体感染的比较研究

目的:比较不同方法对宫颈拭子样本沙眼衣原体的检测效果.方法:采集300例20-50岁无感染症状女性宫颈分泌物,分别采用细胞培养、聚合酶链式反应及胶体金法进行沙眼衣原体检测,培养阳性或两个非细胞培养方法检测为阳性,定为真阳性,称为"扩大金标准".结果:300例受检查者.按"扩大金标准"CT感染者共36例,发病率为12%(36/300),细胞培养、聚合酶链式反应、胶体金法敏感性分别为72.22%、91.67%、52.78%.特异性分别为100%、98.11%、98.86%.阳性预测值分别为100%、86.84%、86.36%.阴性预测值分别为96.35%、98.85%、93.88%.结论:三种检测方法均可用于CT感染的诊断.     

The challenge of testing chemicals for potential carcinogenicity using multiple short-term assays: an analysis of a proposed test battery for hair dyes

Recent reports of the association of hair dyes usage with increased bladder cancer risk in women with the slow NAT-2 acetylator phenotype have resulted both in attempts to identify the putative carcinogen as well as in devising batteries of tests that could be used to screen for such putative carcinogens in hair dye formulations, their intermediates and final products. Analytical studies have reported the presence of traces ( approximately 0.5 ppm) of the carcinogen 4-aminobiphenyl in some hair dye preparations. In parallel, SCCNFP (Scientific Committee on Cosmetic and Non-Food Products Intended for Consumers) has suggested the deployment of a battery of six in vitro assays followed by an in vivo assay. The practicality of deploying and interpreting such a battery is analyzed herein as it is expected to result in 64 and 128 possible test results and SCCNFP does not provide detailed guidance of how the test results are to be interpreted. In this study we have applied a previously described Bayesian approach which takes advantage of the known predictive performances of individual assays, to analyze the possible outcomes of the 6-7 test batteries. While the SCCNFP battery is clearly risk-averse, it is shown that performing all of the assays is not always necessary and moreover it does not necessarily improve predictive performance. Finally, based upon the reported mutagenicity of 4-aminobiphenyl, it is doubtful that this "impurity" would be detected by the test battery.     

Reconsidering association testing methods using single-variant test statistics as alternatives to pooling tests for sequence data with rare variants

Association tests that pool minor alleles into a measure of burden at a locus have been proposed for case-control studies using sequence data containing rare variants. However, such pooling tests are not robust to the inclusion of neutral and protective variants, which can mask the association signal from risk variants. Early studies proposing pooling tests dismissed methods for locus-wide inference using nonnegative single-variant test statistics based on unrealistic comparisons. However, such methods are robust to the inclusion of neutral and protective variants and therefore may be more useful than previously appreciated. In fact, some recently proposed methods derived within different frameworks are equivalent to performing inference on weighted sums of squared single-variant score statistics. In this study, we compared two existing methods for locus-wide inference using nonnegative single-variant test statistics to two widely cited pooling tests under more realistic conditions. We established analytic results for a simple model with one rare risk and one rare neutral variant, which demonstrated that pooling tests were less powerful than even Bonferroni-corrected single-variant tests in most realistic situations. We also performed simulations using variants with realistic minor allele frequency and linkage disequilibrium spectra, disease models with multiple rare risk variants and extensive neutral variation, and varying rates of missing genotypes. In all scenarios considered, existing methods using nonnegative single-variant test statistics had power comparable to or greater than two widely cited pooling tests. Moreover, in disease models with only rare risk variants, an existing method based on the maximum single-variant Cochran-Armitage trend chi-square statistic in the locus had power comparable to or greater than another existing method closely related to some recently proposed methods. We conclude that efficient locus-wide inference using single-variant test statistics should be reconsidered as a useful framework for devising powerful association tests in sequence data with rare variants.     

Selection of evolutionary models for phylogenetic hypothesis testing using parametric methods

Recent molecular studies have incorporated the parametric bootstrap method to test a priori hypotheses when the results of molecular based phylogenies are in conflict with these hypotheses. The parametric bootstrap requires the specification of a particular substitutional model, the parameters of which will be used to generate simulated, replicate DNA sequence data sets. It has been both suggested that, (a) the method appears robust to changes in the model of evolution, and alternatively that, (b) as realistic model of DNA substitution as possible should be used to avoid false rejection of a null hypothesis. Here we empirically evaluate the effect of suboptimal substitution models when testing hypotheses of monophyly with the parametric bootstrap using data sets of mtDNA cytochrome oxidase I and II (COI and COII) sequences for Macaronesian Calathus beetles, and mitochondrial 16S rDNA and nuclear ITS2 sequences for European Timarcha beetles. Whether a particular hypothesis of monophyly is rejected or accepted appears to be highly dependent on whether the nucleotide substitution model being used is optimal. It appears that a parameter rich model is either equally or less likely to reject a hypothesis of monophyly where the optimal model is unknown. A comparison of the performance of the Kishino–Hasegawa (KH) test shows it is not as severely affected by the use of suboptimal models, and overall it appears to be a less conservative method with a higher rate of failure to reject null hypotheses.     

Comparative assessment of toxic effects of surfactants using biotesting methods

This study assesses the comparative sensitivity and possibility of obtaining fast results of various methods of biotesting for several surfactants: Tween 85, sodium dodecyl sulfate (SDS), Fairy dishwashing gel, and Mif washing powder. The following test organisms are used for the study: luminescent bacteria Photobacterium phosphoreum (Beijerinck), preparation of Ecolum luminescent bacteria, unicellular algae Scenedesmus quadricauda (G.M. Smith), infusorian Paramecium caudatum (Ehrenberg), and crustacean Daphnia magna (Straus). It has been revealed that Fairy dishwashing gel possesses the strongest toxicity against the studied test objects. Daphnia and algae are most sensitive to the effects of Fairy and SDS, protozoan and luminescent bacteria are most sensitive to SDS, and Ecolum is most sensitive to Mif washing powder. The tested aquatic organisms and Ecolum are most tolerant to the effect of Tween 85.     

Harnessing prions as test agents for the development of broad-range disinfectants

The development of disinfectants with broad-range efficacy against bacteria, viruses, fungi, protozoa and prions constitutes an ongoing challenge. Prions, the causative agents of transmissible spongiform encephalopathies (TSEs) such as Creutzfeldt-Jakob disease (CJD) or its variant (vCJD) rank among the pathogens with the highest resistance to disinfection. Pilot studies have shown that different procedures devised for prion disinfection were also highly effective against microbial pathogens. This fueled the idea to systematically exploit prions as test pathogens for the identification of new potential broad-range disinfectants. Prions essentially consist of misfolded, aggregated prion protein (PrP) and putatively replicate by nucleation-dependent, or seeded PrP polymerization. Recently, we have been able to establish PrP seeding activity as a quantitative in vitro indicator for the disinfection of 263K scrapie prions on steel wires used as surrogates for medical instruments. The seeding activity on wires re-processed in different disinfectants could be (1) biochemically determined by quantitative protein misfolding cyclic amplification (qPMCA), (2) biologically detected after qPMCA in a cell assay and (3) correctly translated into residual titers of scrapie infectivity. Our approach will substantially facilitate the identification of disinfectants with efficacy against prions as promising candidates for a further microbiological validation of broad-range activity.Key words: cell assay, disinfection, prion, prion protein, protein misfolding cyclic amplification, scrapie, seeding activity, surgical instruments, transmissible spongiform encephalopathies