Differences In Frequency Of Detection Research Articles

Progress towards a commercial PCR-based seed assay for Acidovorax avenae subsp. citrulli

To develop a commercial-scale PCR-based assay for Acidovorax avenae subsp. citrulli in watermelon seed, parameters for immunomagnetic separation (IMS) were optimized. Optimal conditions for target cell recovery included 40 μg of polyclonal anti-AAC antibody per 10 immunomagnetic beads (IMBs) for coating, ca. 2.5 × 10 IMBs per sample and immunocapture for one hour at 4°C. These parameters consistently facilitated the recovery of A. avenae subsp. citrulli cells from suspensions containing ca.10 CFU/ml. Using lots contaminated with artificially infested seeds (10 A. avenae subsp. citrulli CFU/seed), IMS-PCR detected the pathogen in 25% and 87.5% of samples (n=10,000 seeds) with 0.01 and 0.1% infestation, respectively. For seedlots with similar infestation levels, the detection frequencies for the seedling grow-out assay (SGO) were 12.5% and 37.5%; however, the difference in detection frequency between SGO and IMS-PCR was not statistically significant. While liquid enrichment improved the detection sensitivity of IMS-PCR 100-fold, the difference in detection frequency between enrichment IMS-PCR and IMS-PCR was not statistically significant for seed samples contaminated with artificially and naturally infested seeds. These results suggest that IMS-PCR has great potential as an effective alternative to SGO for the detection of A. avenae subsp. citrulli in commercial watermelon seedlots.

Establishing Site Specific Reference Levels for Fungi in Outdoor Air for Building Evaluation

Culturable airborne fungal spore sampling at five building sites during 2002–2003 provided a bank of outdoor data (102 samples total) to evaluate differences in levels of individual species of airborne fungi during the morning and afternoon hours. A minimum of 15 (outdoor) airsamples was collected at each site, and data were segregated into morning (beforenoon) and afternoon subsets. Significant differences in airborne levels for all detected fungal types between the morning and afternoon subsets were determined for each site, using a direct calculation of probability. Significance was defined by differences in frequency of detection above the combined median (p = 0.90 or greater) for the respective fungal type. The levels of various species of fungi in the outdoor air varied significantly between morning and afternoon data sets at all five sites, with no pattern by species, time of day, or location. Levels of Penicillium, Aspergillus, or other fungal species associated with problematic buildings if detected outdoors, can be significantly greater in the morning or afternoon (or exhibit no significant difference) on any given day. The data does not indicate laboratory analysis as a major contributor to the variability exhibited in bioaerosols, and underscores the necessity of collecting sufficient number of samples in the outdoor air in both the morning and afternoon to prevent bias when comparing a suspect indoor environment to outdoor conditions.

Comparison of Whole-Tissue and Xylem Fluid Collection Techniques to Detect Xylella fastidiosa in Grapevine and Oleander.

Xylella fastidiosa is the xylem-limited bacterium that causes Pierce's disease of grapevine and oleander leaf scorch. Detection of this pathogen prior to symptom development is critical for improved management of the disease. Enzyme-linked immunosorbent assay (ELISA) and polymerase chain reaction (PCR) currently are used for routine detection of the pathogen; however, both detection methods are limited by low titer or patchy distribution of the bacterium within a host plant. In the study reported here, we directly compared X. fastidiosa detection in whole-tissue samples with xylem fluid samples from grapevine and oleander. Collection of xylem fluid samples improved sensitivity of pathogen detection by ELISA (41.0%) compared with whole-tissue samples (20.5%) in asymptomatic grapevine. Additionally, pathogen detection in asymptomatic grapevine by PCR also was improved when xylem samples were tested (66.7%) compared with whole-tissue samples (23.1%). There were no differences in frequency of detection of X. fastidiosa in symptomatic grapevines by ELISA or PCR dependent upon sample collection method. Assays of xylem fluid samples did not improve detection of X. fastidiosa in symptomatic or asymptomatic oleander compared with assays of whole tissue. Finally, in a direct comparison of ELISA and PCR, we found no significant differences in frequencies of positive grapevine or oleander samples detected.

Bioaerosol data distribution: probability and implications for sampling in evaluating problematic buildings.

Airborne fungal contamination in the indoor environment is a substantial contributor to indoor air quality (IAQ) problems, yet there are no set numerical standards by which to evaluate air sampling data. Intuitively appealing is the operational model that the indoor air should not be significantly different from the outdoor air, but determining what is "significant" as well as where to sample and how many samples to collect to determine significance have not been firmly established. The purpose of this study was to determine the number of samples and their locations necessary to determine significant differences in airborne fungi between the ambient and indoor environments. Sampling results from several hundred air samples for culturable fungi from various sites were used to derive a probability of detection in the outdoor air for problematic or "marker" fungal species. Under the assumption that indoor fungal growth results in an increase in the probability of detection for a given fungal species, mathematical probability dictates the number of samples necessary in the indoor (target zone) and in the outdoor (reference zone) air to demonstrate significance. Ultimately, it is the sparse distribution of the problematic species that drives the number of required samples to demonstrate a significant difference, which varies depending upon the level of significance desired. Therefore, the number of samples in each zone can be adjusted to reach a target difference in detection frequency, or an investigator can assess a sampling scheme to identify the differences in detection frequency that show significance.

Maximal Airway Response in Adolescents with Long-Term Asthma Remission and Persisting Airway Hypersensitivity: Its Profile and the Effect of Inhaled Corticosteroids

Many children with asthma go into long-term clinical remission at adolescence, but bronchial hyperresponsiveness (BHR) persists in some of these subjects. BHR in asthma is characterized by an increase in sensitivity and in maximal airway response to bronchoconstrictor stimuli. The aims of this study were to compare the profiles of maximal airway response between adolescents with asthma remission and adolescents with symptomatic asthma to a similar degree of airway hypersensitivity, and to determine whether maximal airway response in adolescents with asthma remission is reduced by prolonged treatment with inhaled corticosteroids. A high-dose methacholine inhalation test was performed in 46 adolescents with long-term asthma remission (remission group) and 44 adolescents with symptomatic asthma (symptomatic group). Subjects exhibiting a maximal response plateau in the remission group were administered inhaled budesonide (400 microg bid, budesonide/remission group, n = 15) or identical placebo (placebo/remission group, n = 15) for 6 months, and the subjects in the symptomatic group were administered the same regimen of budesonide (budesonide/symptomatic group, n = 17). The plateau level was measured after 3 months and 6 months of treatment. Thirty-four subjects (73.9%) in the remission group featured a maximal response plateau on the dose-response curve to methacholine, whereas 19 subjects (43.2%) in the symptomatic group had a plateau (p = 0.003). In neither the placebo/remission group nor the budesonide/remission group did the plateau level change significantly over the 6-month period, whereas budesonide markedly decreased the level in the budesonide/symptomatic group. The difference in frequency of detection of a plateau between the remission group and the symptomatic group, as well as the difference in its response to treatment with budesonide between the two groups, suggests that inflammatory changes impact the maximal airway response in symptomatic asthmatic adolescents but not in adolescents with asthma remission.

A Probability Model for Evaluating Building Contamination from an Environmental Event

ABSTRACT Asbestos dust and bioaerosol sampling data from suspected contaminated zones in buildings allowed development of an environmental data evaluation protocol based on the differences in frequency of detection of a target contaminant between zones of comparison. Under the assumption that the two test zones of comparison are similar, application of population proportion probability calculates the significance of observed differences in contaminant levels. This was used to determine whether levels of asbestos dust contamination detected after a fire were likely the result of smoke-borne contamination, or were caused by pre-existing/background conditions. Bioaerosol sampling from several sites was also used to develop the population proportion probability protocol. In this case, significant differences in indoor air contamination relative to the ambient conditions were identified that were consistent with the visual observations of contamination. Implicit in this type of probability analysis is a definition of “contamination” based on significant differences in contaminant levels relative to a control zone. Detection of a suspect contaminant can be assessed as to possible sources(s) as well as the contribution made by pre-existing (i.e., background) conditions, provided the test and control zones are subjected to the same sampling and analytical methods.

Effect of Tillage Practices on Vertical Distribution of Phytophthora sojae.

The vertical distribution of Phytophthora sojae was investigated in soil samples collected in the spring of 1994 from soybean fields at 62 locations in Illinois, Indiana, Iowa, and Minnesota. In the fall of 1995, soil samples were collected from 18 additional locations in Illinois and Iowa. Each location consisted of a pair of no-till and conventional-till fields, and soil samples were collected from arbitrarily selected locations in each field at 0- to 7.5-cm and 7.5- to 15-cm depths. Separate intensive sampling was made in the spring of 1995 from two pairs of adjacent no-till and conventional-till fields at the Iowa State University Northeast Research Farm, in which samples were collected from 0- to 30-cm depth in increments of 5 cm. Samples were assayed for P. sojae with the use of a leaf-disk bioassay. In the 1994 regional samples, there was greater recovery of P. sojae (P ≤ 0.05) at 0- to 7.5-cm depth in the no-till samples than in the conventional-till samples for all states except Minnesota. The fall 1995 samples from Illinois followed a similar trend (P = 0.05); whereas samples from Iowa showed no significant difference between tillage systems. At depths greater than 7.5 cm, there was generally no difference in detection frequency of P. sojae between tillage systems. Samples from the Northeast Research Farm followed patterns of vertical distribution similar to those of the regional samples. In no-till fields, the detection frequency of P. sojae was greatest near the soil surface; two to three times greater than that of the conventional-till fields at this depth. In the conventional-till fields, however, the frequency of recovery peaked at 20 cm and was comparable at these depths to those of no-till fields. There was a positive correlation between the percentage of leaf disks colonized and residue dry weights in the no-till fields (r = 0.84, P = 0.04; and r = 0.86, P = 0.03) but not in the conventional-till fields (r = -0.06, P = 0.90; and r = -0.60, P = 0.17). The recovery of P. sojae in greater frequency near the soil surface in no-till fields than in conventional-till fields suggests that the potential for damping-off may be greater in no-till fields than in conventional-till fields.

Role of ground water on hexachlorocyclohexane (lindane) detections in surface water in western Canada

AbstractInterrelationships between surface water and groundwater dynamics of α‐ and γ‐hexachlorocyclohexane (HCH) were investigated by determining their detection frequency and concentrations in surface water that originated primarily from surface runoff of snow and rain and in surface water that originated from ground water. In the prairie ecozone in Saskatchewan, where lindane (γ‐HCH) is currently used, lindane and α‐HCH were detected in about 50% of water samples taken from lakes and ponds that are recharged primarily by surface runoff (N = 43 sites). Maximum concentrations for lindane and α‐HCH were 0.011 and 0.004 μg/L, respectively. Isomers of HCH were not detected in any of the eight prairie springs that were examined (N = 10 samples). These springs originate from ground water located beneath agricultural lands. In the montane ecozone of Alberta where lindane is not used for agricultural purposes, only α‐HCH was detected frequently in the Waterton and Athabasca rivers. From 1976 to 1992, α‐HCH was detected in 81% of water samples from the Waterton River with no significant difference in detection frequency through the year (χ2 for 12 months = 14.6, d.f. = 11, p = 0.20, N = 163 samples). The site on the Waterton River is located downstream from a series of large lakes with multiyear storage of surface water. In contrast, discharge for the Athabasca River originates primarily from surface water during summer and ground water during winter. Detection frequency for α‐HCH during these seasons was 53% and 2%, respectively, with the annual pattern a normal distribution. These results indicate that HCH isomers were not detected frequently in surface waters that originate from ground water.

Frequency Sampling and Type II Errors

Probabilities of detecting frequency differences based on data obtained by random sampling were determined by computer simulation. Artificial, monotypic populations of known frequency were generated and sampled. Sample sizes of 100, 200, 500, and 1,000 plots were used to compare baseline populations of 20, 50, and 80%O frequency to populations having progressively larger or smaller frequencies. Probabilities of detecting a difference in frequency from baseline populations were empirically estimated from 10,000 comparisons using a test of proportions (P<0.05). Results indicated that the power of the test was substantially reduced at lower sample sizes. Equating the probability of Type I and Type II errors at 0.05 resulted in sample sizes of approximately 500 plots being needed to statistically distinguish between differences of plus or minus 10%01 frequency.

Raman difference spectroscopy of tertiary and quaternary structure changes in methaemoglobins.

There have been several resonance Raman scattering investigations of the effect of inositol hexaphosphate (IHP) on methaemoglobins. In those studies the sensitivity for detecting frequency differences was limited to 1-2 cm-1, and consequently frequency differences were not detected although spectral intensity differences due to changes in spin equilibria were. Shelnutt et al. recently reported on the observation of frequency differences induced by changes in the quaternary structure of chemically modified deoxyhaemoglobins. An improved Raman difference spectroscopic technique with 0.1 cm-1 sensitivity allowed the detection of these differences. We report here the application of this technique to a series of methaemoglobins with and without the addition of IHP. In addition to the intensity changes resulting from changes in the spin equilibria, we have observed frequency differences. In all liganded methaemo-globins that we examined a decrease in frequency of the mode in the 1,370 cm-1 region was observed on addition of IHP. In those in which a quaternary structure change is known to occur the frequency difference is greater than 0.5 cm-1. In those in which no quaternary structure change occurs [metHbA(CN-) and methHbA(N-3)] the frequency difference is smaller (approximately 0.15 cm-1).

Reciprocal Spreading Effects on Frequency Discrimination

The reciprocal spreading phenomenon tells us that short-duration signals are poorly defined in the frequency domain, while line spectra exist only for signals of infinite duration. Formally, ΔfΔt = CONST describes how “effective” bandwidth and “effective” duration are constrained by a reciprocal relation. The value of the constant is unique to the envelope of the signal and varies considerably for the types of signal envelopes that occur in actual waveforms. Only a few studies have examined frequency discrimination at short durations where reciprocal spreading effects might be important. Liang and Chistovich found that for durations less than about 40 msec, the difference limen for frequency is proportional to signal bandwidth. To investigate this bandwidth hypothesis in more detail, several different waveforms were selected as envelopes for short-duration sinusoids. These included a rectangular, a Gaussian, two exponentials, and a gamma function, which were equated for “effective” bandwidth. From the ΔtΔf = CONST relation, it can be seen that sinusoids with these different envelopes have different “effective” durations, and we might expect that this would have some effectjon the ability to detect frequency differences. The experimental results indicate that such is indeed the case: wide differences are observed for these signals that are nominally equivalent in bandwidth. [This research was supported by the National Institutes of Health, Public Health Service, U. S. Department of Health, Education, and Welfare, and an NIMH—Postdoctoral Fellowship.]