Hypothesis formulation and testing in aquatic bioassays: a deterministic model approach

The paper examines the significance of toxicant kinetics information obtained from aquatic toxicity bioassays and bioconcentration tests. The data, bioconcentration kinetics and acute mortality versus exposure-duration information for juvenile American flagfish (Jordanella foridae) exposed to 1,4-dichlorobenzene, are interpreted in terms of a one-compartment, first-order kinetics model. The output of the model is used to formulate a testable hypothesis regarding the comparison of toxicant kinetics derived from both bioconcentration test exposures and toxicity bioassays. The model's estimates of the toxicant body burden attained at mortality are compared with theoretical and observed body burdens from literature sources. The use of a simple, deterministic residue-based, one-compartment, first-order kinetics model to evaluate existing data, as well as to formulate hypotheses to direct experimental designs, is examined.     

Sensitivity of bacterial vs. acute Daphnia magna toxicity tests to metals

The objectives of this study were to evaluate the sensitivity of two bacterial tests commonly used in metal toxicity screening — the Vibrio fischeri bioluminescence inhibition test and the Pseudomonas putida growth inhibition test — in comparison to the standard acute Daphnia magna test, and to estimate applicability of the selected methods to the toxicity testing of environmental samples. The D. magna acute test proved to be more sensitive to cadmium (Cd), zinc (Zn) and manganese (Mn) than the two bacterial assays, whereas P. putida seems to be the most sensitive species to lead (Pb). Manganese appears to be slightly toxic to D. magna and non-toxic to the two selected bacteria. This leads to the conclusion that even in regions with high background concentrations, manganese would not act as a confounding factor. Low sensitivity of V. fischeri to heavy metals questions its applicability as the first screening method in assessing various environmental samples. Therefore, it is not advisable to replace D. magna with bacterial species for metal screening tests. P. putida, V. fischeri and/or other bacterial tests should rather be applied in a complex battery of ecotoxicological tests, as their tolerance to heavy metals can unravel other potentially present toxic substances and mixtures, undetectable by metal-sensitive species.     

Empirical evaluation of two-sample statistical tests for differences of stepping phase during insect walking

In order to determine which statistical tests can validly be applied to data that describe a temporal relationship between two or more repetitive movements by an animal, we evaluated empirically seven two-sample tests that seemed potentially useful: Student's t test, the Watson Williams test for means, the variance-ratio F test, the Watson Williams test for the concentration parameter k, the Wallraff test, the Mann Whitney test and the Watson U² test. Evaluations were carried out on the timing (phases) of bursts of muscular activity in one leg relative to those in another during free walking in cockroaches. Each statistical test was evaluated by dividing randomly a single parent set of data into two subsets, each subset containing about half the original data set. This division was repeated 400 times, thus generating 400 different pairs of subsets. Each statistical test was used separately on the pairs of subsets to test the null hypothesis that the two samples of each pair came from the same population;; this procedure generated 400 statistics for each test, one for each pair of subsets. An estimate of the reliability of each statistical test was obtained by comparing the number of times the test actually indicated a significant difference between subsets to the number of times it might be expected to do so out (20 out of 400 when tested at the 5% level of significance). This procedure was repeated on ten different sets of data. The outcome of the evaluation suggested that, from an empirical point of view, Student's t, the Mann Whitney, the Wallraff and the Watson U² tests may be useful in assessing differences among the data we analyzed. The variance-ratio F test and the Watson Williams test for the concentration parameter k were clearly not usable. The Watson Williams test for means might be useful in some circumstances. Performing an arcsine transformation of the data did not significantly alter these results. Possible causes of the inapplicability of some of these tests to phase data are discussed.     

生态毒理试验中的连续流系统设计及控制

长期连续流试验中,毒物浓度波动主要归因于毒物稀释系统的故障。为了提高毒性数据质量,毒物浓度水平监控是必不可少的.本文对现有连续流试验系统中的毒物稀释器作了改进,采用计量泵输送毒物和稀释水,提高毒物稀释系统的精确度。同时,在连续流试验系统中配置了实时监控系统(RTMS).RTMS由泵、样品室、分析仪器、记录仪等组成.在56d试验中,RTMS随时提供毒物稀释器运行的最新情况,各级毒物浓度变异系数在2.16%-6.13%之间。系统的运行成功为规范中、长期毒性试验提供了技术保证.       

Evaluation of acute and chronic toxicity of selected compounds in higher plants using cell culture

Summary The feasibility of using plant cell culture to measure toxicity was determined by investigating the toxicological effects of three chemical compounds, allyl alcohol, propargylglycine, and cadmium chloride, on cell cultures ofCatharanthus roseus G. Don (Madagascar periwinkle). Suspension cultures ofC. roseus were maintained in modified B5 medium and transferred every 5 d. Five-day-old cell cultures were exposed to various concentrations (10,3,1,0.3,0.1,0.03,0.01,0.003,0.001,0.0003,0.0001, 0.00003, and 0.0 mM) of the toxicants in both acute and chronic toxicity tests. In the acute test, cells were exposed to the toxicant for 24 h, washed three times with sterile medium, and plated in petri plates with an equal volume of 1.4% agar medium. Cells in the chronic test were plated with an equal volume of 1.4% agar medium containing various concentrations of the toxicant. Cells were incubated 28 d at 30°C in the dark. The colonies were counted and the results plotted as percent survival versus toxicant concentration. The results indicate, at the concentrations tested, thatC. roseus assay may be feasible in that it fulfills the criteria for a practical assay (e.g., rapid, simple, quantifiable, and reproducible). This work was submitted to the faculty of Miami University in partial fulfillment of the requirements for the degree of Master of Environmental Science, Institute of Environmental Sciences.     

Biochemical Characterization and Phylogenetic Analysis Based on 16S rRNA Sequences for V-Factor Dependent Members of <Emphasis Type="Italic">Pasteurellaceae</Emphasis> Derived from Laboratory Rats

Phylogenetic analysis based on 16S rRNA sequences with sequence data of some bacterial species of Pasteurellaceae related to rodents deposited in GenBank was performed along with biochemical characterization for the 20 strains of V-factor dependent members of Pasteurellaceae derived from laboratory rats to obtain basic information and to investigate the taxonomic positions. The results of biochemical tests for all strains were identical except for three tests, the ornithine decarboxylase test, and fermentation tests of D(+) mannose and D(+) xylose. The biochemical properties of 8 of 20 strains that showed negative results for the fermentation test of D(+) xylose agreed with those of Haemophilus parainfluenzae complex. By phylogenetic analysis, the strains were divided into two clusters that agreed with the results of the fermentation test of xylose (group I: negative reaction for xylose, group II: positive reaction for xylose). The clusters were independent of other bacterial species of Pasteurellaceae tested. The sequences of the strains in group I showed 99.7–99.8% similarity and the strains in group II showed 99.3–99.7% similarity. None of the strains in group I had a close relation with Haemophilus parainfluenzae by phylogenetic analysis, although they showed the same biochemical properties. In conclusion, the strains had characteristic biochemical properties and formed two independent groups within the “rodent cluster” of Pasteurellaceae that differed in the results of the fermentation test of xylose. Therefore, they seemed to be hitherto undescribed taxa in Pasteurellaceae.     

Effect of food concentration on the chronic toxicity of sodium dodecyl sulphate to Daphnia magna

Food concentration supplied during subchronic and chronic toxicity tests, is one of the most important factors that might influence the response of test organisms to toxicants. The green microalga Scenedesmus incrassatulus was used as food for the cladoceran Daphnia magna, in a chronic toxicity test with the toxicant sodium dodecyl sulphate (SDS). Test concentrations were 0.625, 1.25, and 2.5 mg l^-1 of SDS, equivalent to 1/40, 1/20, and 1/10 of the average 48-h LC50 previously determined. Food concentrations were 9.5, 19, and 38 mg l^-1 (dry wt.). Survival and reproduction were recorded, and the data were analyzed using a life-table approach. After 55 days, the main findings were as follows:

Evaluation of non-culture diagnosis of invasive meningococcal disease by polymerase chain reaction (PCR)

Antibiotic treatment prior to transport or admission to hospital has reduced the proportion of cases of invasive meningococcal disease (IMD) from which Neisseria meningitidis can be isolated by standard microbiological techniques. Identification of meningococci by polymerase chain reaction (PCR) was assessed in relation to microbiological diagnosis for cases over a 4-year period between 1998 and 2001. A screening assay for the IS1106 gene was used to detect meningococcal DNA and five additional assays for siaD and orf-2 genes were performed to determine the serogroup. PCR results were compared with results of bacteriological culture, other laboratory test results and clinical data. The sensitivity of the PCR assay for culture-confirmed cases was 98.5%. The specificity of the assay was 96% based on test results for patients from whom other bacteria were isolated, children with viral meningitis and afebrile negative controls. The siaD B/C/W-135 and Y as well as the orf-2 gene for serogroup A PCR assays were able to determine the serogroup for 75.2% of cases that were positive by PCR screening assay. When isolates from patients with IMD were tested by both agglutination and PCR, the results agreed in all cases. PCR is a useful tool for diagnosis of IMD when Gram stain and culture tests are negative due to antibiotic treatment prior to collection of samples for microbiological analyses.     

Search for nucleic acid influencing, as well as membrane active, potential cancerostatic fungal metabolites using microbiological and cytological screening methods]

A prescreening program including microbiological and cytological assays was employed in search of potential cancerostatic antibiotics in crude extracts of mushrooms. The microbiological tests based on agar diffusion techniques consist of prophage induction test and BIP-test. All active compounds selected by these microbiological models are potential inhibitors of nucleic acid metabolism. Cytological assays on leukemia L 1210 cells have been carried out by microscopic examination and by evaluation using an electronic particle counter. Activity was expressed as decrease of the number of single cells caused by agglutination or lysis of cells, changes in cell surface area, dye exclusion, and increase of cell volume. A wide variety of mushrooms was demonstrated to exhibit interesting activities in some of these screening systems. The influence of primary metabolic products of mushrooms on microbiological models was studied additionally. In vivo assays have not yet been accomplished.     

灭蚊真菌贵阳腐霉Pythium guiyangense对大鼠的长期安全性测试

为了解灭蚊真菌贵阳腐霉Pythium guiyangense对大鼠是否有长期毒性作用。将大鼠120只随机分4组,经饮水口服贵阳腐霉菌丝体。菌丝剂量分别为200mg/kg、100mg/kg、50mg/kg,对照组饮自来水。分别于试验期的90d和180d各组取鼠总数的1/3处死进行检查,剩余1/3大鼠待停用菌丝体悬液2周后处死。观察大鼠一般情况、血常规、肝肾功能等各项生化和组织学指标。结果表明各组大鼠均发育正常,精神食欲好,体重增加;血液学、生化指标变化无明显的剂量-效应关系;内脏系数无异常;对重要脏器的解剖学及组织学检查未见明显异常。本研究结果证明灭蚊真菌贵阳腐霉对大鼠是安全的,从而为其在防治蚊虫的推广应用中的安全性提供了重要的毒理学依据。     

灭蚊真菌贵阳腐霉Pythium guiyangense对大鼠的长期安全性测试

为了解灭蚊真菌贵阳腐霉Pythium guiyangense对大鼠是否有长期毒性作用。将大鼠120只随机分4组,经饮水口服贵阳腐霉菌丝体。菌丝剂量分别为200mg/kg、100mg/kg、50mg/kg,对照组饮自来水。分别于试验期的90d和180d各组取鼠总数的1/3处死进行检查,剩余1/3大鼠待停用菌丝体悬液2周后处死。观察大鼠一般情况、血常规、肝肾功能等各项生化和组织学指标。结果表明各组大鼠均发育正常,精神食欲好,体重增加;血液学、生化指标变化无明显的剂量-效应关系;内脏系数无异常;对重要脏器的解剖学及组织学检查未见明显异常。本研究结果证明灭蚊真菌贵阳腐霉对大鼠是安全的,从而为其在防治蚊虫的推广应用中的安全性提供了重要的毒理学依据。     

Current and emerging polymyxin resistance diagnostics: A systematic review of established and novel detection methods

The emergence of polymyxin resistance, due to transferable mcr genes, threatens public and animal health as there are limited therapeutic options. As polymyxin is one of the last-line antibiotics, there is a need to contain the spread of its resistance to conserve its efficacy. Herein, we describe current and emerging polymyxin resistance diagnostics to inform faster clinical diagnostic choices. A literature search in diverse databases for studies published between 2016 and 2020 was performed. English articles evaluating colistin resistance methods/diagnostics were included. Screening resulted in the inclusion of 93 journal articles. Current colistin resistance diagnostics are either phenotypic or molecular. Broth microdilution is currently the only gold standard for determining colistin MICs (minimum inhibitory concentration). Phenotypic methods comprise of agar-based methods such as CHROMagar™ Col-APSE, SuperPolymyxin, ChromID^® Colistin R, LBJMR and LB medium; manual MIC-determiners viz., UMIC, MICRONAUT MIC-Strip and ComASP Colistin; automated antimicrobial susceptibility testing systems such as BD Phoenix, MICRONAUT-S, MicroScan, Sensititre and Vitek 2; MCR-detectors such as lateral flow immunoassay (LFI) and chelator-based assays including EDTA- and DPA-based tests, that is, combined disk test, modified colistin broth-disk elution (CBDE), Colispot, and Colistin MAC test as well as biochemical colorimetric tests, that is, Rapid Polymyxin NP test and Rapid ResaPolymyxin NP test. Molecular methods only characterize mobile colistin resistance; they include PCR, LAMP and whole-genome sequencing. Due to the faster turnaround time (≤3 h), improved sensitivity (84%–100%) and specificity (93.3%–100%) of the Rapid ResaPolymyxin NP test and Fastinov^®, we recommend this test for initial screening of colistin-resistant isolates. This can be followed by CBDE with EDTA or the LFI as they both have 100% sensitivity and a specificity of ≥94.3% for the rapid screening of mcr genes. However, molecular assays such as LAMP and PCR may be considered in well-equipped clinical laboratories.     

Pyrolysis mass spectrometry characterisation and numerical taxonomy ofAeromonas spp.

Reference strains (2) and 29 isolates ofAeromonas spp. from clinical material and environmental specimens were characterised in traditional biochemical tests, and in pyrolysis mass spectrometry, which gives data reflecting whole-cell composition. Numerical taxonomic analyses of the data sets were compared with conventional identification at species level, and pathogenic potential, as inferred from the origin of the isolates. Clustering with conventional test reaction patterns showed, for each of the species represented, a clearly defined core group of typical isolates, surrounded by a halo of aberrant strains. One further cluster comprised strains intermediate betweenA. caviae andA. hydrophila, and one strain was grossly atypical in both analyses. Clustering from pyrolysis data corresponded less well with species identification. Broadly, the biochemical division between core and halo strains was supported in pyrolysis forA. caviae andA. sobria, but the main group ofA. hydrophila in pyrolysis comprised strains clustering in the core and halo groups of this species, and three strains intermediate betweenA. hydrophila andA. caviae in biochemical tests. Two further pyrolysis clusters comprised core and halo strains ofA. hydrophila. However, pyrolysis clustering correlated well with inferred pathogenicity, showing four clusters of probable pathogens, six clusters of probable nonpathogens, and one two member cluster of doubtful status. Most strains that clustered in the species haloes, or in species-intermediate groups in biochemical tests, were non-human isolates, or were isolated in the absence of symptomatic infection. The correlation of inferred pathogenicity with biochemical clustering was poorer than that with pyrolysis clustering.Abbreviations CTRP conventional test reaction pattern - PyMS pyrolysis mass spectrometry     

Reduced water intake: Implications for rodent developmental and reproductive toxicity studies

In developmental and reproductive toxicity studies, drinking water is a common means of delivering the test agent. Reduced consumption of toxicant-containing water raises questions about indirect effects of reduced maternal fluid consumption resulting from unpalatability, versus direct effects of the test compound. Issues to consider include: objective assessment of dehydration and thirst, the relative contributions of innate and learned behaviors to drinking behavior and flavor preference, and the objective assessment of physiologic stress. Not only do lab animals under ad lib conditions consume more water than the minimum required to maintain fluid balance, animals faced with water restriction have substantial physiologic capacity for protection of metabolic processes. Measures of blood biochemistry can provide quantifiable, objective indications of fluid balance, but changes in these parameters could result from other causes such as effects of a test toxicant. Consummatory behaviors in response to perceived need are highly influenced by learning. Hence, the drinking behavior, water intake, and flavor acceptance/preference of animals used in toxicology experiments could be subject to learning experiences with the test compound. Physiological symptoms of stress produced by water deprivation may be distinguishable from the symptoms associated with other generalized stressors, such as food deprivation, but doing so may be beyond the scope of most developmental or reproductive toxicity studies. Use of concurrent controls, paired to test groups for water consumption, could help distinguish between the direct effects of a test toxicant as opposed to effects of reduced water consumption alone. Birth Defects Res (Part B), 86:157–175, 2009. ©2009 Wiley-Liss, Inc.     

Response of Fresh-Water Protozoan Artificial Communities to Metals*

An artificial fresh-water protozoan community was subjected to different concentrations of Zn and Cu in a test system consisting of Plexiglas troughs through which pond water flowed continuously. Although the % survival of colonizing species exposed to Cu or Zn fluctuated greatly at each concentration, the range of toxicity for each compound allowed comparison of protozoa with other organisms with respect to resistance to heavy metal toxicity. Individual protozoan species also were exposed for 3 hr to Zn, Cu, Cr, phenol, Pb, Mn, Co, HNO₃, acetic acid, Al, Sn, and HCl to derive time to death curves. Protozoa tested appeared to be more resistant than Daphnia to phenol, K₂C₂O₇, and Cu; however, some species were more sensitive than Daphnia to Zn, nitric acid, and HCl. This suggests that the sensitivity of protozoa to toxicants may be either more or less than that of macroinvertebrates and that information does not suffice to predict sensitivity. Moreover, the relative sensitivity of protozoa to various toxicants will not always be the same, i.e. species X may be twice as tolerant to a toxicant as species Y but its relative sensitivity may be quite different for another toxicant.     

A novel design for estimating relative accuracy of screening tests when complete disease verification is not feasible

The accuracy (sensitivity and specificity) of a new screening test can be compared with that of a standard test by applying both tests to a group of subjects in which disease status can be determined by a gold standard (GS) test. However, it is not always feasible to administer a GS test to all study subjects. For example, a study is planned to determine whether a new screening test for cervical cancer ("ThinPrep") is better than the standard test ("Pap"), and in this setting it is not feasible (or ethical) to determine disease status by biopsy in order to identify women with and without disease for participation in a study. When determination of disease status is not possible for all study subjects, the relative accuracy of two screening tests can still be estimated by using a paired screen-positive (PSP) design in which all subjects receive both screening tests, but only have the GS test if one of the screening tests is positive. Unfortunately in the cervical cancer example, the PSP design is also infeasible because it is not technically possible to administer both the ThinPrep and Pap at the same time. In this article, we describe a randomized paired screen-positive (RPSP) design in which subjects are randomized to receive one of the two screening tests initially, and only receive the other screening test and GS if the first screening test is positive. We derive maximum likelihood estimators and confidence intervals for the relative accuracy of the two screening tests, and assess the small sample behavior of these estimators using simulation studies. Sample size formulae are derived and applied to the cervical cancer screening trial example, and the efficiency of the RPSP design is compared with other designs.     

Toxicity testing of polymer materials for dialysis equipment: is there any need forin vivo testing?

In an earlier work, slightly more than 650 plastic materials, intended for use in medical devices, were tested with a battery of chemical, as well asin vitro andin vivo biological tests. An analysis showed that only a limited number of the tests used were actually necessary to obtain the same pass or fail decision as that obtained using the full test battery. This prompted us to prescreen all new materials with a small test battery consisting of the two most discriminating chemical tests and anin vitro cell growth inhibition test. The present work is a report of our findings after testing another 155 materials using this prescreen system.For each single one of the 155 tested materials the same decision on whether or not to use the material in the intended medical device would have been reached without anyin vivo testing. In no single case in a total of 851in vivo tests did an eluate that had passed thein vitro cell test give rise to a reactionin vivo. Thus, among the tests on living systems the cell test alone seems to be sensitive enough to provide sufficient information. Nothing appears to be gained from thein vivo animal tests. However, some of the materials that passed the prescreening tests later failed in one or several of the chemical tests. Both nonspecific chemical tests and tests for specific molecules seem to detect undesirable levels of leachable substances not detected by the prescreening system. Therefore these tests should not be abandoned. Abandoning unnecessaryin vivo testing, on the other hand, would save considerable costs.     

Biochemical tests for identification of mycelial cultures of basidiomycetes

Twenty-four biochemical tests have been developed to identify basidiomycetes from mycelial cultures. Eleven are designated ‘instant tests’ because results are obtained within 24 h; ten of these test for specific enzymes, the other is based on a reaction between vanillin and unknown fungal metabolites. The remaining thirteen tests require incubation periods ranging from 1 to 4 days and are thus designated ‘incubated tests’. Sixteen of these tests were applied first to identified isolates of Peniophora sacrata, Sclerotium rolfsii, Stereum purpureum and Trametes versicolor. They distinguished these species satisfactorily, so these sixteen tests, and eight others devised subsequently, were applied to unidentified basidiomycetes isolated from diseased roots of fruit crops. The results of these tests enabled the isolates to be placed in seven groups. All isolates in a particular group were morphologically similar which further suggested that each group might correspond to a species and that isolates could be defined on the basis of biochemical tests.     

Effectiveness of plastic matrix lures and traps against Bactrocera dorsalis and Bactrocera cucurbitae in Hawaii

Trapping trials were conducted in two locations on the island of Hawaii with plastic‐matrix formulations of methyl eugenol (ME) (1‐2‐dimethoxy‐4‐allylbenzene) and cuelure (CL) [4‐(p‐acetoxyphenyl)‐2‐butanone] in traps with or without a toxicant (2, 2‐dichlorovinyl dimethyl phosphate, DDVP) against wild fly populations of oriental fruit fly, Bactrocera dorsalis (Hendel) and melon fly, Bactrocera cucurbitae (Coquillett) respectively. Both 5 g disks and 10 g cones of ME and 2 g plugs of CL caught flies for >9 months which varied relative to the population fluctuations. In all of these trials a one‐way entrance design trap caught more flies than the toxicant‐baited trap. The similar‐sized entrance holes (0.70 cm) of the latter may have slowed the dispersal of the toxicant vapour, thus causing flies to be repelled or killed outside the entrance to the trap when DDVP vapour was evolving at a maximum rate. The effect decreased as the toxicant aged. One‐way entrance traps are appropriate where toxicant traps are not allowed (e.g. organic farms), present a health hazard (e.g. yards with children), or would need to be replaced more frequently than lures. The results of these studies are discussed in relation to areawide fruit fly suppression programs where large populations of these flies are persistent, as well as to detection programs in areas where fruit flies have not established.     

MULTIPLE PREFERENCE TESTS CAN PROVIDE MORE INFORMATION ON CONSUMER PREFERENCES*

Preference testing is used for a variety of reasons. Traditionally, a consumer completes one preference test. However, consumers may not be consistent in their preferences and, therefore, multiple preference tests would be necessary. This research investigated the preference responses of consumers during four preference tests on the same pair of products. Results showed that many of the consumers switched their preference through the series of four tests. Although the basic conclusion drawn from the first test or by any of the four tests was the same in this study, the overall percentages of consumers who preferred product “A” from the four tests were not always similar to one another, nor did the results of the first preference test show the degree of preference that existed for some products. Multiple preference tests may provide more information that is useful to researchers or marketers than a single preference test. Inconsistent responses should be included in data analysis to avoid distortion of preference patterns.