Foster Levy

East Tennessee State University, Johnson City, Tennessee, United States

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Publications (17)49.21 Total impact

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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.
    Chemotherapy 01/2010; 56(5):411-6. · 2.07 Impact Factor
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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.
    Statistics in Medicine 09/2009; 28(29):3626-42. · 2.04 Impact Factor
  • Foster Levy, Shannon Hill, Tim McDowell
    The American Biology Teacher 01/2009; · 0.39 Impact Factor
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    Foster Levy
    The American Biology Teacher 01/2009; · 0.39 Impact Factor
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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.
    Chest 12/2008; 135(4):1019-23. · 7.13 Impact Factor
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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.
    Epidemiology and Infection 10/2008; 137(4):581-90. · 2.87 Impact Factor
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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.
    Journal of Hospital Infection 06/2007; 66(1):59-64. · 2.86 Impact Factor
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    Journal of environmental health 12/2006; 69(4):48, 51. · 1.01 Impact Factor
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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.
    Infectious Diseases Society of America 2004 Annual Meeting; 10/2004
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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.
    Journal of Clinical Microbiology 07/2004; 42(6):2792-5. · 4.07 Impact Factor
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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.
    Journal of Antimicrobial Chemotherapy 03/2004; 53(2):371-4. · 5.34 Impact Factor
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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.
    Infectious Diseases Society of America 2003 Annual Meeting; 10/2003
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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.
    New Phytologist 08/2002; 155(3):437 - 447. · 6.74 Impact Factor
  • E S Walker, F 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.
    Evolution 07/2001; 55(6):1110-22. · 4.86 Impact Factor
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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 beta-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 beta-lactam antimicrobials (all except cefamandole). Significant correlations in MICs were uncovered among all pairs of four beta-lactam antimicrobials in both producers and non-producers of beta-lactamase. In contrast, cefamandole MICs were correlated only with ceftriaxone and penicillin, and these were limited to beta-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 beta-lactamase producing isolates in the population, but the observation of significant decreases in susceptibility limited to beta-lactamase-producing isolates suggests that the underlying factors were different forms of beta-lactamase, beta-lactamase-dependent modifiers and/or additional factors.
    Journal of Antimicrobial Chemotherapy 03/2000; 45(2):175-82. · 5.34 Impact Factor
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    F 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.
    Heredity 05/1999; 82 Pt 4:422-31. · 4.11 Impact Factor
  • 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.

Publication Stats

102 Citations
49.21 Total Impact Points

Institutions

  • 1999–2010
    • East Tennessee State University
      • • Department of Biological Sciences
      • • Department of Internal Medicine
      Johnson City, Tennessee, United States
  • 2002
    • University of Exeter
      Exeter, England, United Kingdom