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Biomedical subjects

K L Schroeder

Publications and source records attributed to K L Schroeder.

18 recordsLinked to original sources
PubMed2006

Role of 2,4-diacetylphloroglucinol-producing fluorescent Pseudomonas spp. in the defense of plant roots.

Plants have evolved strategies of stimulating and supporting specific groups of antagonistic microorganisms in the rhizosphere as a defense against diseases caused by soilborne plant pathogens owing to a lack of genetic resistance to some of the most common and widespread soilborne pathogens. Some of the best examples of natural microbial defense of plant roots occur in disease suppressive soils. Soil suppressiveness against many different diseases has been described. Take-all is an important root disease of wheat, and soils become suppressive to take-all when wheat or barley is grown continuously in a field following a disease outbreak; this phenomenon is known as take-all decline (TAD). In Washington State, USA and The Netherlands, TAD results from the enrichment during monoculture of populations of 2,4-diacetylphloroglucinol (2,4-DAPG)-producing Pseudomonas fluorescens to a density of 10 (5) CFU/g of root, the threshold required to suppress the take-all pathogen, Gaeumannomyces graminis var. tritici. 2,4-DAPG-producing P. fluorescens also are enriched by monoculture of other crops such as pea and flax, and evidence is accumulating that 2,4-DAPG producers contribute to the defense of plant roots in many different agroecosystems. At this time, 22 distinct genotypes of 2,4-DAPG producers (designated A - T, PfY and PfZ) have been defined by whole-cell repetitive sequence-based (rep)-PCR analysis, restriction fragment length polymorphism (RFLP) analysis of PHLD, and phylogenetic analysis of PHLD, but the number of genotypes is expected to increase. The genotype of an isolate is predictive of its rhizosphere competence on wheat and pea. Multiple genotypes often occur in a single soil and the crop species grown modulates the outcome of the competition among these genotypes in the rhizosphere. 2,4-DAPG producers are highly effective biocontrol agents against a variety of plant diseases and ideally suited for serving as vectors for expressing other biocontrol traits in the rhizosphere.

Cluster Analysis↗
PubMed2000

Genotypic and phenotypic diversity of phlD-containing Pseudomonas strains isolated from the rhizosphere of wheat.

Production of 2,4-diacetylphloroglucinol (2,4-DAPG) in the rhizosphere by strains of fluorescent Pseudomonas spp. results in the suppression of root diseases caused by certain fungal plant pathogens. In this study, fluorescent Pseudomonas strains containing phlD, which is directly involved in the biosynthesis of 2,4-DAPG, were isolated from the rhizosphere of wheat grown in soils from wheat-growing regions of the United States and The Netherlands. To assess the genotypic and phenotypic diversity present in this collection, 138 isolates were compared to 4 previously described 2, 4-DAPG producers. Thirteen distinct genotypes, one of which represented over 30% of the isolates, were differentiated by whole-cell BOX-PCR. Representatives of this group were isolated from eight different soils taken from four different geographic locations. ERIC-PCR gave similar results overall, differentiating 15 distinct genotypes among all of the isolates. In most cases, a single genotype predominated among isolates obtained from each soil. Thirty isolates, representing all of the distinct genotypes and geographic locations, were further characterized. Restriction analysis of amplified 16S rRNA gene sequences revealed only three distinct phylogenetic groups, one of which accounted for 87% of the isolates. Phenotypic analyses based on carbon source utilization profiles revealed that all of the strains utilized 49 substrates and were unable to grow on 12 others. Individually, strains could utilize about two-thirds of the 95 substrates present in Biolog SF-N plates. Multivariate analyses of utilization profiles revealed phenotypic groupings consistent with those defined by the genotypic analyses.

Anti-Bacterial Agents↗
PubMed1998

Root-surface caries in rats and humans: inhibition by a non-antimicrobial property of tetracyclines.

The incidence of root caries has been found to increase as the population ages and as edentulism becomes less prevalent due to improved dental awareness and care, and as exposure of roots due to gingival recession has also increased in the elderly. The mechanism of root caries is thought to be mediated by both bacterial and mammalian proteases produced by plaque and the periodontal tissues, respectively. In the current study, a rat model of periodontal disease was used in which gnotobiotic rats were infected intra-orally with a periodontal pathogen (P. gingivalis). Infecting the rats with P. gingivalis increased the collagenase activity in the gingival tissue in association with severe alveolar bone loss. Treating P. gingivalis-infected rats with doxycycline or CMT-1 prevented the destruction of the periodontium by MMPs, thus preventing exposure of roots to subgingival bacterial plaque and host tissue collagenases and the subsequent development of root caries. In addition, a low-dose doxycycline (LDD, 20 mg bid, non-antimicrobial dose) for 3 months was used in humans predisposed to increased root caries as the result of heavy use of smokeless (chewing) tobacco, causing gingival recession, subgingival plaque accumulation with Gram-negative bacteria, increased gingival crevicular fluid flow (GCF), and elevated GCF collagenase. Daily administration of LDD in smokeless tobacco patients reduced the GCF collagenase and prevented the further development of root caries.

Adult↗
PubMed1990

P.L. 99-252--implications for dentists and their clinical practice.

This paper is one of a series attempting to determine the impact of Public Law 99-252, the Comprehensive Smokeless Tobacco Health Education Act of 1986, on decreasing smokeless tobacco use. Potential indicators are discussed that could be used by the dental profession to determine the efficacy of the profession's involvement in existing and future prevention and cessation efforts relative to this law. In this review, six major areas are considered for measuring declines in smokeless tobacco use relative to the role of the dental health practitioner. These areas encompass the following: (1) the dental profession's knowledge of smokeless tobacco health hazards, (2) dental practitioners' involvement in measuring changes in use patterns, (3) the influence dentists have with their patients and community in decreasing smokeless tobacco use, (4) the general attitude and intention to quit on the part of dental patients, (5) active governmental involvement efforts, and (6) health effects of smokeless tobacco that might be used for identifying decreasing smokeless tobacco use. Within each of these six broad categories, more specific indicators for measuring the impact of P.L. 99-252 relative to the dental profession were considered.

Dentists↗
PubMed1990

An epilogue to evaluating the impact of P.L. 99-252 on decreasing smokeless tobacco use.

In a previous paper, "Evaluating the Impact of P.L. 99-252 on Decreasing Smokeless Tobacco Use," the context of this law and the theoretical framework for an evaluation plan for measuring its impact were described. In this paper, the methodology and selected findings from this project as well as their implications are discussed. This discussion includes the identification of the six indicators considered to be the most relevant, valid, reliable, accessible, and practical for measuring the impact of this law on decreasing smokeless tobacco use, as well as a report on the feasibility analysis of three of these indicators. Pilot data on two indicators--pounds of smokeless tobacco sold and incidence rates of tobacco-induced leukoplakia--are presented and analyzed.

Adult↗
PubMed1988

Morphologic and immunohistochemical evidence of human papillomavirus capsid antigen in smokeless tobacco keratoses from juveniles and adults.

Seventy-seven tissue samples from patients with either degree I, II, or III smokeless tobacco keratoses were examined. The tissues were evaluated for the presence of human papillomavirus (HPV) antigen by immunocytochemical staining. Capsid antigen could be identified in sixteen cases (20.78%). This investigation further supports the concept that smokeless tobacco-associated leukoplakias can be correlated with HPV infection.

Adolescent↗
PubMed1988

Personality profiles associated with smokeless tobacco use patterns.

The purpose of this study was to examine the personality characteristics of male dippers and chewers of smokeless tobacco. The study objective was to determine any differences in personality characteristics between dippers and chewers of smokeless tobacco and nonusers. A survey at a southeastern university provided a sample of 289 males, of which 55 (19%) were smokeless tobacco users. Each subject was administered a demographic data sheet and Cattell's Sixteen Personality Factor Questionnaire (16 PF). Smokeless tobacco users were categorized as snuff dippers or tobacco chewers, and comparisons of personality characteristics were made between persons who exclusively dipped, persons who exclusively chewed, persons who dipped and chewed, and persons who did neither. The results of the study indicated that smokeless tobacco use is primarily a White male habit; very few Blacks or other racial groups consumed smokeless tobacco among this population. Significant (p less than 0.05) personality differences between snuff dippers and tobacco chewers were noted. Snuff dippers were more socially outgoing, enthusiastic, imaginative and group dependent than chewers. Chewers were found to be more uncompromising, critical in outlook and practical and less easily influenced by others than dippers.

Adolescent↗
PubMed1988

Proposed definition of a smokeless tobacco user based on "potential" nicotine consumption.

This study examined and operationally defined "light," "moderate," and "heavy" users of smokeless tobacco according to the potential amounts of nicotine consumed per week from chewing tobacco and/or snuff products. Fifty adult male smokeless tobacco users ranging in ages from 18-85 were tested to determine nicotine content of smokeless tobacco products consumed. The smokeless tobacco products were blindly analyzed by gas chromatography to determine nicotine content. Mean nicotine yield per week was calculated by multiplying the number of cans and/or pouches used per week and placed on a normal probability distribution. The mean nicotine yielded 238 mg/wk and the categories emerged as "light" less than or equal to 87 mg/wk, "moderate" 88-388 mg/wk and "heavy" users greater than or equal to 389 mg/wk. Differences regarding type of user (light, moderate, heavy) were crossed tabbed with educational levels, years of smokeless tobacco use, age the habit was initiated, perception of harm and whether habit forming, and reason for using smokeless tobacco.

Adolescent↗
PubMed1988

Screening for smokeless tobacco-associated lesions: recommendations for the dental practitioner.

The increasing use of smokeless tobacco and the accumulating list of associated health hazards including cancer and cardiovascular effects should be of concern to the dentist. This study documents both concern from patients' perceptions and clinical examinations of their smokeless tobacco-associated lesions. Implications for the dentists' practice among adolescents and young adults are discussed.

Adolescent↗
PubMed1987

Bimodal initiation of smokeless tobacco usage: implications for cancer education.

One hundred fifty (150) randomly chosen adult male subjects (average age 37) drawn from a university general dental clinic were classified by self-report into three equal categories of fifty smokeless tobacco users, fifty cigarette smokers (non-smokeless tobacco users), and fifty non-tobacco users. According to questionnaire results, a bimodal curve was exhibited among smokeless tobacco users with the two peaks of initiation at ages 12 and 18 compared to a unimodal age of initiation for cigarette smokers at age 16. Two different cohorts of smokeless tobacco users based on age of initiation were observed with differences reported in level of education, urban versus rural origin, average length of time in using smokeless tobacco, and the type of smokeless tobacco product used. Young initiators appeared to be primarily from rural communities having a strong parental or familial influence when initiating smokeless tobacco usage, whereas older initiators appeared to be primarily from more urbanized regions with peer influences as the most significant for initiating smokeless tobacco usage. Other characteristics associated with one or the other cohort were also reported, pointing to different educational measures that may be necessary for prevention and intervention, based on the age of initiating smokeless tobacco usage, as well as place of residence.

Adult↗
PubMed1987

An analysis of print and audiovisual materials to prevent smokeless tobacco use.

We analyzed 28 examples of smokeless tobacco educational print and audiovisual materials based on two criteria: (1) strength of the scientific bases for the selected materials, and (2) appropriateness of the materials for the known populations at risk to smokeless tobacco ever-use. We concluded that these materials in general are authoritative and provide the cancer educator with a solid scientific basis to initiate a primary prevention strategy. Nonetheless, some updating of materials to include the latest scientific findings (eg, cardiovascular and physiological/addictive effects) is needed. In terms of appropriateness of materials, we noted that the focus of materials was correctly targeted to young, white males; however, most materials tended to be aimed at seventh grade and beyond reading and social levels. Few, if any, materials were aimed at the other group at risk to smokeless tobacco adoption, namely youth in the early elementary grades. Consequently, while smokeless tobacco educational materials are generally authoritative, the cancer educator must still customize both the selection of materials and the educational approach to populations at risk.

Audiovisual Aids↗
PubMed1977

Quantification of flow in a dynamic phantom using Rb81-Kr81m, and a Nal detector.

Blood flow can be measured by monitoring the count rate of Krypton-81m after its parent, Rubidium-81 (a potassium analogue), has been deposited in the tissue. The steady-state Kr-81m count rate reflects both production by decay of Rb-81 and washout due to blood flow. Its use is theoretically superior to that of Xenon-133 for quantification of blood flow (cc/min per 100 gm) since: (1) multiple flow measurements can be obtained from a single arterial injection, (2) flow-dependent changes in the count rate of Kr-81m provide a steady-state measure of specific flow, and (3) errors due to uptake in fat are eliminated. The count rate of Kr-81m was measured as a function of flow in a dynamic phantom with a NaI crystal, suing both pure cyclotron-produced Rb-81 and commercially available samples with as much as 25% contamination from Rb-82m. The phantom was calibrated by measuring the flow-rate constants with Xe-133. No significant difference was found between the flow-rate constant measured with three pure samples. The ratio of the zero-flow Kr-81m count rate to the rate observed in the presence of flow showed excellent correlation with calibrated flow over a range of rate constant from 0 to 0.02 sec (-1). This study suggests that regional specific flow can be measured in vivo with currently available Nal detecting systems after the intra-arterial injection of Rb-81.

Blood Flow Velocity↗