Foster Levy

East Tennessee State University, جونسون سيتي، تينيسي, Tennessee, United States

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Publications (20)48.77 Total impact

  • Foster Levy · Elaine S. Walker
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    ABSTRACT: We monitored a population of Carolina Hemlocks in northwestern North Carolina for four years to examine the rate and pattern of decline in response to infestation by Adelges tsugae (Hemlock Woolly Adelgid). Our yearly census of hemlock condition and severity of the adelgid infestation included trees of all sizes. We estimated declines in condition as the portions of the leaf canopy that were lost. Initially, infestation occurred throughout the population but was severe in only a small cluster of individuals. Within 1 year, the area of severe infestation increased in size to encompass 48% of the population. In another region of the population, there was a cluster of relatively healthy individuals comprised largely of seedlings. Of the 4 size-classes of trees, sapling-sized individuals experienced the highest rates of decline in condition. Most trees declined to poor health within 3 years of an observation of moderate to severe infestation.
    No preview · Article · Jul 2014
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    ABSTRACT: Increasingly frequent reports of vancomycin treatment failures for serious methicillin-resistant Staphylococcus aureus (MRSA) infections provide impetus for comparative in vitro studies to assess the activity of newer antimicrobial agents against a range of MRSA isolates. A sample of 168 MRSA derived from a long-term MRSA collection was subjected to susceptibility testing to telavancin, daptomycin, linezolid, tigecycline and vancomycin by broth micro-dilution. Data were reviewed for sporadic occurrence of isolates with reduced susceptibility. Analyses were performed to test for temporal trends toward decreasing susceptibility and to compare susceptibility of isolates from different infection sites. No MRSA isolate from any time period was resistant to test antibiotics. For daptomycin, linezolid and tigecycline, there were no susceptibility differences between the pre- and postclinical availability periods. All newer agents were active against MRSA isolates with minimum inhibitory concentrations (MICs) of vancomycin >1 mg/l, but there were significant correlations in susceptibility among several pairs of antibiotics. Telavancin and other newer antistaphylococcal agents were fully active against MRSA from various infection sites including isolates with vancomycin MIC >1 mg/l.
    No preview · Article · Oct 2010 · Chemotherapy
  • Scotland C Leman · Foster Levy · Elaine S Walker
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    ABSTRACT: Accurate assessment of disease dynamics requires a quantification of many unknown parameters governing disease transmission processes. While infection control strategies within hospital settings are stringent, some disease will be propagated due to human interactions (patient-to-patient or patient-to-caregiver-to-patient). In order to understand infectious transmission rates within the hospital, it is necessary to isolate the amount of disease that is endemic to the outside environment. While discerning the origins of disease is difficult when using ordinary spatio-temporal data (locations and time of disease detection), genotypes that are common to pathogens, with common sources, aid in distinguishing nosocomial infections from independent arrivals of the disease. The purpose of this study was to demonstrate a Bayesian modeling procedure for identifying nosocomial infections, and quantify the rate of these transmissions. We will demonstrate our method using a 10-year history of Morexella catarhallis. Results will show the degree to which pathogen-specific, genotypic information impacts inferences about the nosocomial rate of infection.
    No preview · Article · Dec 2009 · Statistics in Medicine
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    Foster Levy · Shannon Hill · Tim McDowell

    Preview · Article · Jan 2009 · The American Biology Teacher
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    Foster Levy

    Preview · Article · Jan 2009 · The American Biology Teacher
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    ABSTRACT: In the United States, cases of human blastomycosis are largely described in defined geographic areas, with Mississippi reporting the highest prevalence of disease in the southeast region. The infection is uncommonly recognized in mountainous areas, and our previous report of blastomycosis in the southern Appalachian mountains of northeast Tennessee appeared to be an exception to the usual disease distribution. Our current retrospective study was undertaken to determine whether blastomycosis has persisted as an endemic fungal infection in our northeast Tennessee geographic area and whether epidemiologic features have changed over a 25-year time period. Results show that clinical aspects of the disease have remained fairly constant with few exceptions; mass-type pulmonary lesions have become more common, and itraconazole has emerged as the therapy of choice. Most notably, however, are the observations that blastomycosis persists as a major endemic fungal infection in our mountain region, more than half of all cases occurring during the period from 1996 to 2005 were found in a core area centered on two counties, Washington and Unicoi; three of five counties surrounding the core counties experienced rate increases compared to our previous study. These findings suggest a further expansion of this endemic fungal disease beyond the core region.
    No preview · Article · Dec 2008 · Chest
  • F Levy · S C Leman · F A Sarubbi · E S Walker
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    ABSTRACT: We report an objective examination of nosocomial transmission events derived from long-term (10-year) data from a single medical centre. Cluster analysis, based on the temporal proximity of genetically identical isolates of the respiratory pathogen Moraxella catarrhalis, identified 40 transmission events involving 33 of the 52 genotypes represented by multiple isolates. There was no evidence of highly transmissible or outbreak-prone genotypes. Although most clusters were small (mean size 3.6 isolates) and of short duration (median duration 25 days), clustering accounted for 38.7% of all isolates. Significant risk factors for clustering were multi-bed wards, and winter and spring season, but bacterial antibiotic resistance, manifested as the ability to produce a beta-lactamase was not a risk factor. The use of cluster analysis to identify transmission events and its application to long-term data demonstrate an approach to pathogen transmission that should find wide application beyond hospital populations.
    No preview · Article · Oct 2008 · Epidemiology and Infection
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    ABSTRACT: Nosocomial outbreaks of infection due to non-typeable Haemophilus influenzae (NTHi) are rarely described. There are a few published reports that suggest that elderly patients with underlying pulmonary disease are at risk and that person-to-person spread is key to disease transmission. During the summer months of 2005, we documented an outbreak of NTHi infections in a Veterans Affairs nursing home. Thirteen patients developed conjunctivitis or lower respiratory infection involving a beta-lactamase-negative biotype III NTHi isolate, with an indistinguishable SmaI macrorestriction pattern. Patients were elderly males usually with underlying cardiac and pulmonary disease. A case-control study failed to demonstrate any specific significant risk factor for NTHi infection and there was no evidence of spatial clustering of cases within the nursing home. A random throat culture survey involving nursing home patients during the outbreak showed that only one of 19 persons was colonized with NTHi. The outbreak concluded following appropriate treatment and an emphasis on universal and respiratory droplet precautions. All patients recovered and a specific inciting event for the outbreak was never defined. Literature review revealed a spectrum of responses to nosocomial NTHi infections and a lack of consensus regarding the infection control approach towards NTHi outbreaks.
    No preview · Article · Jun 2007 · Journal of Hospital Infection
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    Scott A Reynolds · Foster Levy · Elaine S Walker

    Preview · Article · Dec 2006 · Journal of environmental health
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    ABSTRACT: To improve the success of vegetative propagation of Sciadopitys verticillata, stem cuttings were subjected to three treatments designed to minimize the accumulation of a latex-like sap at the cut ends of stems. A 24-hour soak in water before a hormone dip significantly enhanced rooting success and root mass. The water soak pretreatment was more beneficial to hardwood cuttings compared with softwood cuttings. Cuttings from shade-grown source trees showed the highest rooting success, but source tree age, height, and place of origin were not important factors. The water-insoluble latex-like sap had strong antibacterial activity against 3 of 11 bacterial species tested, but activity was not related to bacterial Gram reaction or the bacterial natural environment. In contrast, pine resins and latexes from selected angiosperms showed no antibacterial activity. The antibacterial component of the Sciadopitys latex-like sap was heat stable and therefore probably not protein based.
    Preview · Article · Dec 2006 · HortScience: a publication of the American Society for Horticultural Science
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    ABSTRACT: statement on introduc -tory college level science courses (Halyard 1993) challenges those responsible for such courses: "Laboratory activities should fea-ture experimental procedures that require students to think about, select, generate, test, and evaluate the effectiveness of hypotheses and the scope of their results." As fac-ulty in a university where multiple lab sections are taught by graduate teaching assistants or part-time temporary faculty, we find it dif-ficult to provide the individual at-tention required to monitor projects conducted by small groups or indi-vidual students (Dimaculangan et al. 2000; Lunsford 2003; Norton et al. 1997; Ortiz 1994; Stager 1994; Tolman 1999). Like Grant and Vatnick (1998), "we lack the resources to supervise large numbers of independently active learners that populate our introductory courses," and conse-quently have adopted what they call bounded inquiry: "…students' research questions and study sub-jects are instructor constrained but hypotheses…are not a priori speci- Data sharing among multiple lab sections increases statistical power of data analyses and informs student-generated hypotheses. We describe how to collect, organize, and manage data to support replicate and rolling inquiry models, with three illustrative examples of activities from a population-level biology course for science majors.
    Full-text · Article · Jan 2006
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    ABSTRACT: Background: Methicillin-resistant S. aureus (MRSA) is a widespread nosocomial infection problem. Consequently, hospitalized patients have been treated with mupirocin ointment to eliminate nasal carriage of MRSA. Following frequent usage for decolonization in the 1990s, mupirocin resistance was relatively high (32%) at a Veterans Affairs Medical Center (VAMC). By 2001, resistance declined to 4% in concert with prescription control. The goals of this study were to determine if mupirocin resistance remained low, to examine resistance in a facility with a different patient population and mupirocin usage history, and to assess the incidence of mupirocin resistance in coagulase-negative staphylococci. Methods: A point-prevalence survey of staphylococci isolated from the nares of 50 VAMC patients in 2003 showed the incidence of mupirocin resistance in S. aureus was rare (3%) but resistance was relatively high (39%) in S. epidermidis. At the nearby community hospital (CH), mupirocin was used for wound treatment but not for programmatic decolonization. Results: Nevertheless, in both species mupirocin resistance levels at the CH (S. aureus - 2%; S. epidermidis - 40%) paralleled those at the VAMC. Archived data from 1997-8 showed the CH had a mupirocin resistance incidence of 27% in MRSA, a level not significantly different from that at the VAMC during the same time period. Thus, coincident temporal patterns were uncovered at the two medical centers; in S. aureus, high incidences of resistance declined precipitously over time, but S. epidermidis supports a current high rate of resistance. Interspecific gene exchange is known to occur and mupirocin resistance could be transferred from S. aureus to S. epidermidis using VAMC isolates, but transfer out of S. epidermidis was uncommon. Conclusion: Thus, S. epidermidis appears to accumulate mupirocin resistance and that species has the potential for long-term gene retention in the absence of apparent selective pressure.
    No preview · Conference Paper · Oct 2004
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    ABSTRACT: Susceptibility to mupirocin was assessed in methicillin-resistant Staphylococcus aureus isolates selected from eras corresponding to differences in usage rate and prescription policies at a Veterans Affairs medical center. The eras studied encompassed from the time of introduction of the drug to its widespread use, through recommended judicious use, and finally to subsequent stringent administrative control. Prescriptions declined from 3.0 to 0.1 per 1,000 patient days. Precipitous declines first in the numbers of isolates with high-level resistance (from 31% to 4%) and then in those with low-level resistance (from 26% to 10%) accompanied prescription control.
    Full-text · Article · Jul 2004 · Journal of Clinical Microbiology
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    F Levy · E S Walker
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    ABSTRACT: The hypothesis that BRO-1 selectively replaced the BRO-2 isoform of the Moraxella catarrhalis BRO beta-lactamase was tested by examining the temporal distribution, antibiotic resistance and epidemiological characteristics of isolates from a long-term collection at a single locale. A rapid, one-step PCR assay conducted on 354 isolates spanning 1984-1994 distinguished bro alleles in over 97% of the beta-lactamase-producing isolates. Probes of dot blots were used to distinguish PCR failure from non-beta-lactamase-mediated penicillin resistance. BRO-2 isolates comprised 0-10% of the population per year with no evidence of a decline over time. All beta-lactamase producers exceeded the clinical threshold for penicillin resistance. Bimodality of penicillin MICs for beta-lactamase producers was caused by variation within BRO-1 rather than differences between BRO-1 and BRO-2. Non-beta-lactamase factors also confer resistance to penicillin and may contribute to the BRO-1 bimodality. The 13 BRO-2 isolates were associated with diverse genotypes within which there was evidence of epidemiologically linked clusters. The exclusive association of BRO-2 with four unrelated genotypes suggested maintenance of BRO-2 by recurrent mutation or horizontal exchange. The relative rarity of BRO-2 throughout the study, the absence of a declining temporal trend, and genetic diversity within BRO-2 all failed to support the hypothesis that BRO-2 was more common in the past and has been selectively replaced by BRO-1.
    Preview · Article · Mar 2004 · Journal of Antimicrobial Chemotherapy
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    ABSTRACT: Background. Following an increase in resistance to mupirocin in methicillin-resistant Staphylococcus aureus and a subsequent decline that accompanied prescription restrictions at the James H. Quillen VA Medical Center, a study was conducted to determine whether coagulase-negative staphylococci (CNS) serve as reservoirs of mupirocin resistance. Methods: A point prevalence study of staphylococci in the nares of 50 patients was conducted at the James H. Quillen VA Medical Center Nursing Home. For one isolate of each species from each patient, antibiograms and pulsed-field gel electrophoresis genotypes were characterized. Conjugations were performed to determine whether resistances could transfer across species. Results: S. aureus and S. epidermidis were the two most common species (n=33 and 29, respectively) with 12 mixed species occurrences. Mupirocin resistance was absent in S. aureus, but that species showed significantly higher incidences of resistance to methicillin, ciprofloxacin, clindamycin and erythromycin and 16 of 33 isolates had identical resistance profiles. In contrast, mupirocin resistance was common in S. epidermidis (55% resistant). S. epidermidis also had significantly higher incidences of resistance to gentamicin, SXT and tetracycline. Antibiogram diversity was significantly higher in S. epidermidis as evidenced by 23 of the 29 isolates with unique patterns. Although the relatively low antibiogram diversity in S. aureus may suggest clonality, both species were characterized by high genetic diversity. A suite of resistances, including mupirocin resistance, was capable of interspecific transfer via conjugation. Conclusion: Within a single nursing home, CNS had the characteristics of an antibiotic reservoir--they harbored many resistances, some of which were not found in S. aureus; those resistances were found in a wide diversity of combinations; the two species co-occurred; and resistances could be transferred across species via conjugation.
    No preview · Conference Paper · Oct 2003
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    Stacy I. Taylor · Foster Levy
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    ABSTRACT: Summary • Tests for adaptation to three different soils inhabited by subspecific taxa within Phacelia dubia and for preadaptation to a serpentine soil were conducted to examine the plausibility of an endemic-to-endemic evolutionary pathway. Each taxon performed optimally on its home soil, demonstrating edaphic specialization. None survived on the serpentine. • Hydroponic assays for tolerance to two serpentine factors, elevated magnesium: calcium and elevated nickel, were conducted on population samples and maternal half sib families. Performance was estimated by root length and rosette diameter while leaf dissection served as an indicator of developmental maturity. • Both nickel and magnesium: calcium of typical serpentine inhibited all three taxa. However, the granite outcrop endemic var. georgiana tolerated higher magnesium: calcium than other taxa, its tolerance exceeded that found on its home soil, and there was developmental variation among sibships. • The tolerance uncovered in the endemic var. georgiana suggests that a specialized endemic taxon may encompass variation that could lead to preadaptation to a novel habitat and therefore serve as the raw material for speciation rather than represent an evolutionary dead end.
    Preview · Article · Aug 2002 · New Phytologist
  • Elaine S. Walker · Foster Levy
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    ABSTRACT: The evolution of antibiotic resistance provides a well-documented, rapid, and recent example of a selection driven process that has occurred in many bacterial species. An exhaustive collection of Moraxella catarrhalis that spans a transition to chromosomally encoded penicillin resistance was used to analyze genetic changes accompanying the transition. The population was characterized by high haplotypic diversity with 148 distinct haplotypes among 372 isolates tested at three genomic regions. The power of a temporally stratified sample from a single population was highlighted by the finding of high genetic diversity throughout the transition to resistance, population numbers that remained high over time, and no evidence of departures from neutrality in the allele frequency spectra throughout the transition. The direct temporal analysis documented the persistence, antibiotic status, and haplotypic identity of strains undergoing apparent clonal expansions. Several haplotypes that were beta-lactamase nonproducers in early samples converted to producers in later years. Maintenance of genetic diversity and haplotype conversions from sensitive to resistant supported the hypothesis that penicillin resistance determinants spread to a diverse array of strains via horizontal exchange. Genetic differentiation between sample years, estimated by F(ST), was increasing at a rate that could cause complete haplotype turnover in less than 150 years. Widespread linkage disequilibrium among sites within one locus (copB) suggested recent mutation followed by clonal expansion. Nonrandom associations between haplotypes and resistance phenotypes provided further evidence of clonal expansion for some haplotypes. Nevertheless, the population structure was far from clonal as evidenced by a relatively low frequency of disequilibria both within sites at a second locus (M46) as well as between loci. The haplotype-antibiotic resistance association that was accompanied by gradual haplotype turnover is consistent with a hypothesis of genetic drift at marker loci with directional selection at the resistance locus.
    No preview · Article · Jul 2001 · Evolution
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    ABSTRACT: A retrospective, population analysis of antimicrobial susceptibility patterns was performed on Moraxella catarrhalis isolates recovered from a single medical centre to detect temporal trends and infer potential mechanisms of reduced susceptibility. The duration of this study, June 1984 to July 1994, encompassed the period during which the frequency of β-lactamase production expanded from 30 to 96% in the population. MICs of penicillin G, cefamandole, ceftriaxone, amoxycillin/clavulanate, imipenem, clarithromycin, tetracycline, ciprofloxacin and trimethoprim/sulphamethoxazole for a representative sample of 375 isolates were determined. Analyses were conducted to test for variation in susceptibility among isolates, correlations of susceptibility levels among different antimicrobial agents, and temporal patterns in susceptibility. All antimicrobials except clarithromycin displayed significant differences among isolates within years, and mean MICs of all antimicrobial agents except tetracycline and clarithromycin varied significantly between years. Temporal trends to a reduction in susceptibility were detected to four of five β-lactam antimicrobials (all except cefamandole). Significant correlations in MICs were uncovered among all pairs of four β-lactam antimicrobials in both producers and non-producers of β-lactamase. In contrast, cefamandole MICs were correlated only with ceftriaxone and penicillin, and these were limited to β-lactam producing isolates; cefamandole and amoxycillin/clavulanate showed a correlation limited to non-producing isolates. For some antimicrobials, trends toward decreasing susceptibility may have been caused by an increased proportion of β-lactamase producing isolates in the population, but the observation of significant decreases in susceptibility limited to β-lactamase-producing isolates suggests that the underlying factors were different forms of β-lactamase, β-lactamase-dependent modifiers and/or additional factors.
    No preview · Article · Mar 2000 · Journal of Antimicrobial Chemotherapy
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    Foster Levy · CL Neal
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    ABSTRACT: For neutral genes, uniparental inheritance is expected to reduce effective population size relative to biparentally inherited genes. In finite populations, the ensuing genetic drift can cause stronger spatial and temporal differentiation. An intrapopulation polymorphism in chloroplast DNA was used to examine relative spatial and temporal population structure of chloroplast and allozyme markers in the annual plant Phacelia dubia. There was significant differentiation among populations at chloroplast markers but not for allozyme loci. A fine-scale analysis showed significant structure among sites within populations for chloroplast markers and local heterozygote deficiencies at allozyme loci. These spatial analyses suggest that gene flow via pollen exceeds that via seed. Temporal variation in chloroplast markers, assessed over a 10-year period, was evident in two of four populations, and allozyme loci were characterized by temporal variation in rare-allele frequencies. Population structure appeared to be related to the intensity and type of human disturbance influencing each population. Habitat destruction promoted isolation and enhanced differentiation, whereas mowing increased seed dispersal and reduced differentiation for chloroplast markers. At this time, genetic drift appears to be the primary force shaping chloroplast gene frequencies.
    Preview · Article · May 1999 · Heredity
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    Foster Levy · Tim Mcdowell
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    ABSTRACT: O ver fifty universities, colleges, and com-munity colleges are listed among the members of the American Association of Botanical Gardens and Arboreta; an internet search uncovers many more campus arboreta, whether planted in discrete areas or dispersed throughout the campus. Biology teachers commonly use their arboreta for instruction in tree identification or to provide live mate-rial for studying plant morphology. In general, however, the myriad examples of evolution-ary and horticultural diversity in these arbo-reta remain an underutilized resource. At East Tennessee State University we have suc-cessfully used arboretum-based activities to illustrate such biological fundamentals as spe-cies concepts, phylogenetic biogeography (the use of evolutionary relationships to infer the origin of current distribution patterns), and mutational genetic variation. The three Above is Magnolia x soulangiana 'Alexandrina', M. denudata, and M. liliiflora. The cultivar 'Alexandrina' is just one of many crosses between M. denudata and M. liliiflora.
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