Browsing by Subject "Resistance"

Now showing 1 - 8 of 8
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    Antibiotic resistance in the lower intestinal microbiota of dairy cattle: longitudinal analysis of phenotypic and genotypic resistance.
    (2012-02) Boyer, Timothy Charles
    This research focused on methods of measuring antibiotic resistance and analysis of antibiotic resistance data in dairy cattle that were sampled repeatedly over time. Specific objectives included: characterization and longitudinal analysis of phenotypic antibiotic resistance of commensal Escherichia coli, development of a statistical model for the analysis of low quantity resistance genes measured by quantitative real-time polymerase chain reaction (qPCR), measurement of antibiotic resistance genes in the lower intestinal bacterial communities of dairy cattle that received a short-term therapeutic dose of antibiotic and untreated cattle, and measurement and longitudinal analysis of the quantities of six antibiotic resistance genes in the lower intestinal bacterial communities of dairy cattle. Enteric E. coli collected from dairy cattle over 1.5 years were tested for phenotypic resistance to 17 antimicrobials. A total of 93 phenotypic patterns were observed among 3,402 isolates tested, with a majority (67%) susceptible to all 17 antimicrobials. The most prevalent resistances were to tetracycline, sulfamethoxazole, and streptomycin. Latent class and latent transition analyses were carried out to group the animals into classes according to their resistance phenotypes and to estimate the probabilities of transitioning into and out of classes over time. Probabilities of transitioning to a pan-susceptible class were high, as were the probabilities of remaining in the pan-susceptible class. Probabilities of transitioning form a pan-susceptible class to a resistant class were very low. Measurement of antibiotic resistance genes by qPCR presents challenges for genes that are present in very low quantities. A statistical model was developed to analyze qPCR data made up of a significant proportion of observations that fall below the limit of quantification of a qPCR assay. Computer simulations showed that the statistical model produced less biased estimates of regression parameters than common methods of handling low quantity qPCR data. qPCR was applied to a cohort of dairy cattle that received a five day course of ceftiofur and matched untreated cattle. Quantities of a gene (blaCMY-2) that confers resistance to ceftiofur were measured and analyzed using the statistical model developed for low quantity genes. Treated animals had significantly higher quantities of blaCMY-2 during treatment than untreated animals. By the first day post-treatment, gene quantities had returned to pre-treatment levels. The quantities of six different antibiotic resistance genes were measured by qPCR in the fecal community bacterial DNA of a cattle population that was sampled repeatedly over 2.5 years. Significantly increasing trends over time were observed for three of the six genes conferring resistance to tetracyclines, macrolides, and cephalosporins. Comparison of phenotypic resistance and qPCR data showed that qPCR performed on community DNA is a more sensitive method of detection that phenotypic testing of cultured isolates.
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    Characterization and quantitative trait loci (QTL) mapping of Fusarium head blight resistance-related traits in the Japanese wheat landrace, PI 81791 (Sapporo Haru Komugi Jugo)
    (2010-04) Quirin, Edmund Andrew
    Fusarium head blight (FHB) is a destructive disease of wheat (Triticum aestivum L.). Infection by Fusarium graminearum affects yield and grain quality traits that can lead to substantial economic losses. Developing resistant cultivars has been a major objective of plant breeders for controlling FHB. The objective of this study was to assess FHB resistance in the Japanese landrace, PI 81791 (Sapporo Haru Komugi Jugo), a line that does not possess the widely used Fhb1 QTL for type II resistance. A population of 150 recombinant inbred lines (RILs) was developed from a cross between this genotype and the susceptible variety, Wheaton, and was assessed for several resistance-related traits, including type I and II resistance, post-harvest grain traits, and agronomic traits in four field environments in Minnesota. Type II resistance was also assessed in two greenhouse environments. The RILs were genotyped using 377 microsatellite markers. Composite interval mapping detected QTL for resistance traits on chromosomes 2B, 3A, 3B, 3D, 4A, 4D, 5A, 5B and 6A and for heading date and height on 1B, 2D, 3B and 4D. The resistance QTL on chromosomes 2B, 3B, and 3D explain the largest amount of variation observed for many of the resistance traits analyzed with alleles being inherited from PI 81791. The QTL on chromosome 3B in the interval of Xbarc229 – Xgwm383b appears to be a major novel resistance locus that explains 7 – 21% of the variation observed for various resistance traits. Similar QTL regions to those on chromosome 2B in the interval of Xgwm639b – Xwmc339 and chromosome 3D in the interval of Xwmc533a – Xwmc656 have been previously reported, supporting their use for FHB resistance breeding. Major resistance QTL were also identified on chromosomes 4A, associated with Xbarc233, and 4D, which is associated with the semi-dwarfing gene, Rht-D1. However, these QTL are likely associated with increased susceptibility from PI 81791 and Wheaton, respectively. Additional type II resistance QTL were identified on 3A in greenhouse environments, explaining as much as 23.2 and 15.8% of the phenotypic variation observed.
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    Comics, curriculum and the classroom: the development and implementation of an arts-integrated Holocaust unit
    (2014-08) Johnson, Jeremy Lee
    Traditionally, the Holocaust has been taught to middle school students using a novel like Anne Frank: The Diary of Young Girl. However, with the recent adoption of the Common Core Standards many teachers must incorporate new ways of teaching content, including the use of graphic novels. This study examined how two teachers, an English teacher and reading teacher, worked collaboratively to create and implement a Holocaust unit that asked students to use comics to demonstrate their learning. While the premise of the study was to examine how teachers with no prior experience incorporated graphic novels into their classrooms, the study became something altogether different. I discuss how the teachers relied on me to teach students how to draw figures and explain the conventions of comics with the final goal of creating a research-based comic examining some element from the Holocaust. During this study I was present in the classroom four full days a week. Data collection methods included participant observation, interviews with staff and students and document collection and analysis. Findings could be categorized three ways and include resistance, gender stereotyping and the accuracy and authenticity of student-created comic narratives. Resistance occurred from both teachers and students. The English and reading teachers resisted use of the term "comic" because they considered it not serious enough for a discussion of the Holocaust. The art teacher resisted participation because he felt that comics were a lower form of art that had no place in education. Student resistance came in the form of a young man who, for example, did not believe that the school should be dedicating nine weeks to studying the Holocaust. A second significant finding focused on gendered stereotypes and how assumptions about gender were made visible through students' comments and perceptions of drawing. Interesting gender differences also existed in the ways students drew their final projects with male students' comics exhibiting depersonalization. Information was shared in an almost bullet-point manner whereas female students spent more time developing characters and exploring emotions. The final area of focus was on the ways in which accuracy and authenticity of narratives were brought into question through failure to emphasize citation of sources and inclusion of bibliographies as part of the students' research project, thus devaluing the factual value of their comic Holocaust narratives.
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    Design, Synthesis, and Evaluation of Pyrazinoic Acid-Derived Antituberculars for Drug-Resistant Mycobacterium tuberculosis
    (2022-01) Cole, Malcolm
    Tuberculosis (TB), an infectious disease caused by the pathogen Mycobacterium tuberculosis (Mtb), is a major cause of suffering worldwide. The impact of this disease has been exacerbated by the ongoing coronavirus pandemic, reversing much recent progress that had increased diagnosis and treatment rates in the preceding decade. In addition to ongoing issues related to public health shortcomings and lack of access to treatment, the emergence and spread of resistant strains is an increasing cause for concern. While the antitubercular pipeline has produced a few new antibiotics in the 21st century, more novel treatments are urgently needed to keep abreast of resistant strains. This dissertation describes efforts to create new therapeutic options for resistant TB, centered around pyrazinoic acid (POA), the active form of pyrazinamide (PZA), an important first-line TB drug.Recently, a growing number of reports have highlighted the promise of β-lactam conjugates in selectively targeting resistant organisms. β-lactams are a widely-employed class of antibiotics that target cell wall biosynthesis. Bacteria can evade this activity through expression of β-lactamases, powerful enzymes that destroy the electrophilic β-lactam warhead. However, researchers have learned to take advantage of this resistance mechanism, designing β-lactam conjugates that release a molecular payload following β-lactamase cleavage. This strategy, referred to here as β-lactamase-mediated fragmentation, is explored in great detail in Chapter 1, including descriptions of its discovery and applications in a variety of fields, including diagnostics, cellular imaging, and antibiotic design. Chapter 2 describes our own work in this space, designing β-lactam conjugates bearing POA as a Mtb-selective warhead. This strategy circumvents the most common resistance mechanism against PZA, imparting activity in an Mtb macrophage infection model (where conventional β-lactams are typically ineffective). We also provide preliminary mechanistic evidence that our conjugates act as codrugs, achieving antibacterial activity through action of the β-lactam scaffold as well as the POA warhead. In Chapter 3, we remove the β-lactam scaffold and focus on POA itself, reporting a series of new analogues featuring substitutions on the pyrazine ring. We identify several analogues with improved activity over POA, and use biochemical techniques to demonstrate they are inhibitors of PanD, a putative target of POA. We use the structure of our most active lead and recent structural insights into PanD to design additional inhibitors with comparable antimycobacterial activity, providing proof-of-concept for future structure-based design of new PanD inhibitors.
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    Engaging the dialectic: managerial resistance to change and innovation in corporate America.
    (2012-07) Chermack, Kelly
    This dissertation examines the implementation of FREE, an innovation-based, organization-wide workplace flexibility initiative. Through FREE, the company experienced a massive re-structuring to how, when, and where work was done. From its very inception in the company, the FREE concept critiqued and criticized current norms and assumptions about work in corporate America. During FREE training sessions, managers, in particular, began to oppose and resist the rollout. Evident from fieldwork and ethnographic observations of these training sessions, a dialectic model of change fostered a dialectic model of resistance. Resistance emerged at three levels of abstraction: macro, meso, and micro. Analyses indicate that through the operation of these dialectic processes, managers resisted the very idea of changing work on a grad scale, changes in actual work practices, and/or the change agents. In addition, this resistance prompted changes to the change implementation process and FREE, itself, began to change. This dissertation suggests that resistance to change is rooted in conceptualizations of identity and representations of the self in and out of the organization. This work also proposes that resistance to change bears a significant impact on the implementation of the change, so much so that the implementation adapted over time.
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    Genetic understanding of resistance to foliar phylloxera, Daktulosphaira vitifoliae Fitch, in cold-hardy hybrid grapes
    (2020-06) Yin, Lu
    Phylloxera is an important pest infesting foliage of North American native Vitis species and cold-hardy hybrids between V. vinifera and V. riparia. Currently, chemical control is the only commonly used management method. There is a need to development integrated pest management strategies including the use of resistant varieties (Chapter 1). The effects of foliar phylloxera infestations on four grape varieties were a numeric reduction in unit yield of cluster weight, photosynthesis rate, and photosystem II efficiency. This reduction in cluster weight can be economically important to growers (Chapter 2). Most genetic studies in grape for resistance to phylloxera limited to the root. A previous study using a population, GE1025 (N=~125), detected the first quantitative trait locus (QTL), a ~15-cM region, for foliar resistance on chromosome 14. To fine map the QTL, a larger population, GE1783 (N=~1023), was created and genotyped with the rhAmpSeq technology with conserved haplotype markers across Vitis species. Through selective phenotyping using a 0-7 severity rating scale among other phylloxera severity traits on 188 potential recombinants of GE1783, we fine mapped the QTL to 2.1-4.9 Mbp on chromosome 14. A most probable candidate resistance gene plays a role in gallic acid formation (Chapter 3). To investigate antixenosis as a possible resistance mechanism, leaf trichome density was mapped in GE1025 with genotype-by-sequencing and phenotypic scores collected using a 0-6 trichome density scale at several leaf positions. Evaluations were done on forced dormant cuttings in two years and on field-grown leaves in one year. There was a ~ -0.2 correlation (r) between trichome density and phylloxera resistance. Two regions on chromosomes 1 and 10 were repeatedly detected for multiple trichome density traits. We fine mapped the chromosome 1 QTL to a 140-kb region using selective phenotyping in GE1783. We found insertion/deletion variations of the parents of the population in one candidate pseudogene in this region and three other candidate genes proposed previously (Chapter 4). In all, we identified closely linked markers that can be used for marker-assisted breeding for foliar phylloxera resistance to improve the cold-hardy hybrid grape germplasm and potential candidate resistance genes for future investigations.
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    Hungry Spirits: Anishinaabe resistance and revitalization
    (2014-02) McLeod, Laura Eleanor
    Tribal members of the White Earth Band of Anishinaabe-Ojibway have struggled for generations to maintain their collective rights to Turtle Island, their vast homelands and territories stretching throughout North America, especially through the Upper Great Lakes region where they have lived and traveled for more than 10,000 years as America's first residents and First Nations (Quimby 1960; Wright 1972; Usher et al 1985; Tanner, ed. 1987; Morton and Gawboy 2000). The focus of this dissertation is the struggle of the White Earth Anishinaabe to recover land (LaDuke 2005; Silverstone 1987; Lurie, J. 2003) and protect subsistence rights to hunt and fish in northern Minnesota (Lone Fight 1994). It also represents an ethnography of resistance and revitalization in the face of land loss (Gibson 1978; Lurie, N. 1978) and market debasement (Swenson, ed. 1982; Spry 1983; Shkilnyk 1985) in an increasingly globalized world (Davis, S. 1982, 1991; Davis, W. 1993; Hornborg 1994; Abrahamson 1998; Piot 1999). In 1986 twelve U.S. Congressmen voted in Washington DC to end all land claims held by the White Earth Band (Shipp 1987). However, the Band has never relinquished rights to fish and hunt throughout their territories ceded by treaties of 1837 and later in 1855. Today 93 percent of the reservation's 837,000 acres is controlled by non-Indians: two-thirds held by European American immigrant farmers and individuals who own lake cabins, resorts, or hunting grounds; the U.S. federal government including U.S. Fish and Wildlife Service; State of Minnesota; Becker, Mahnomen, and Clearwater counties (tax forfeiture lands); religious organizations and major corporations. The anthropological research problem is this: how does one analyze and compare relationships between community and market economies (Lofving, ed. 2005; Gudeman 2008)? In their struggle to recover their land base and revitalize their community's economy and well-being, tribal members want to show that a standing forest, one that provides food stuffs (animals and plants), material needs, and medicines, for local community members, has more value than a clearcut forest (Woehrle 1996).
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    Investigations of resistance in American elm (Ulmus americana) to Dutch elm disease (caused by Ophiostoma novo-ulmi)
    (2017-08) Beier, Garrett
    Ophiostoma ulmi and Ophiostoma novo-ulmi, the causal agents of Dutch elm disease (DED), have caused catastrophic losses throughout North America, with millions of elms lost over the past eight decades. Although most genotypes of American elm are highly susceptible to DED, there are some genotypes which show increased resistance. Gaining a better understanding of what makes certain trees resistant has critical implications for developing disease management strategies and screening genotypes for resistance. For these investigations five Ulmus americana cultivars and two wild type U. americana populations were studied. When examining trees for host responses, cultivars exhibited differences in their abilities to compartmentalize infection. There appeared to be several strategies of compartmentalization that cultivars used to survive infection. Barrier zones were found in many of the trees examined, however, their presence did not ensure the trees’ survival. Some cultivars created multiple barrier zones within the same year, helping maintain functional xylem after the earlier barrier zone was breached or circumvented. The only cultivar to consistently display an effective wall 3 reaction zone, was ‘Valley Forge’ in 2016. Anatomical xylem characteristics associated with resistance were also examined. Trees with the lowest disease severity ratings, generally had smaller vessel diameters and higher vessel densities compared with those with the highest disease severity ratings. The potential use and limitations of anatomical xylem characteristics as a preliminary screening method for DED resistance are discussed. Although host factors influence disease resistance, other factors are likely playing a role. The effect of timing of inoculation on disease severity ratings was investigated using wild type U. americana trees. Trees inoculated late in the season (August 4) had lower mean disease severity ratings at all time-points compared with those inoculated early in the season (May 26). Timing of inoculation had a significant effect on disease severity ratings, however, in the year following inoculation there were no significant differences between the groups. In summary, findings from these investigations indicate resistance to DED in American elm is highly complex, involving a wide variety of factors. Implications for management, selection, and future research are discussed.