Identity and resistance in social work leadership is a fairly recent area in the study of leadership. A significant amount of the literature discusses leadership, identity and resistance from the standpoint of managerialism, where the leader’s character is defined by their response to managing and eliminating staff workplace resistance. This study offers a contrasting approach to the managerial notions of leadership, identity and resistance. This study examines social work leadership in the context of the justice-oriented resistance work leaders do and how their identities inform the strategies they engage. A small qualitative study was done from a critical perspective to better understand how social work leaders in the social services engage in resistance work when encountering social injustices in their organization. The findings were organized around three central themes form the interviews. The first theme was how the participants understood resistance or what were they fighting for in their work. Participants were fighting for respectful relationships with service users, and fighting against the implications of social inequalities embedded in policies and directives that are not beneficial to service users. The second theme focused on the strategies the participants engaged in their resistance work. Participants identified the deliberate use of language, awareness and activation of values, and the use of their power and role as leaders. The third theme was how their identities influenced the resistance work they engaged in. The participants drew on their personal histories which have framed their identities to inform the manner in which they resist: to take up certain value positions in their work, to be critical and unafraid in their resistance, and to have strong loyalties to their communities. The results of this study extend the literature on leadership by highlighting resistance not in a passive manner but in the sense of consciously taking actions with consequences. It was apparent the participants engaged in micro political actions and adopted strategies to counter the negative effects of policies and attitudes that promote social inequalities. / Thesis / Master of Social Work (MSW)

No description available.

Resistance to antimalarial drugs continues to be a major obstacle in controlling and eradicating malaria. The identification of genetic markers of resistance is vital for disease management but they can be difficult to predict before resistance arises in the field. This thesis describes an alternative approach to gene identification, combining an in vivo experimental evolution model, Linkage Group Selection (LGS) and Solexa genome re-sequencing. Here this model was used to resolve the genetic basis of chloroquine and artemisinin resistance in the rodent malaria parasite Plasmodium chabaudi. AS-30CQ is a parasite with high resistance to chloroquine and resistance to artemisinin. It was crossed with the genetically different drug-sensitive strain AJ. The resulting progeny were selected with drugs and backcrossed to the sensitive parent. Both crosses were treated with increasing concentrations of chloroquine and artemisinin. The frequency of markers from the sensitive parasite were analysed in order to characterize the signatures of drug selection. Three loci involved progressively in chloroquine resistance were identified on chromosomes 11, 3 and 2. One main locus on chromosome 2 was identified with artemisinin selection. The Solexa platform was used to re-sequence the genomes of both AS-30CQ and its sensitive progenitor, AS-sens. The differences between the two genomes were integrated with the LGS data to identify: 1) a strong candidate for the main CQresistance determinant - a putative amino acid transporter on chromosome 11 (aat1) 2) two candidates for high level chloroquine resistance on chromosome 3. and 3) a mutation in ubp1 gene on chromosome 2 that is likely to contribute to the highest level of chloroquine resistance and be main determinant of the artemisinin resistance phenotype. In addition the last section of this thesis describes two otherwise isogenic clones showing low- and high levels of chloroquine resistance were grown competitively to evaluate the effect of these mutations on parasite fitness. The highly resistant strain demonstrated a loss of fitness in relation to its more sensitive progenitor and was outcompeted in untreated and low-treated infections.

Baseline data on susceptibility levels to azinphosmethyl and permethrin were generated on five field-collected populations of the pink bollworm, Pectinophora gossypiella (Saunders), from Arizona and Southern California, relative to a standard susceptible laboratory strain. The field strains showed less than 2-fold resistance to azinphosmethyl but exhibited variable levels (1.3- to 18.3-fold) of resistance to permethrin. Resistance of pink bollworms to permethrin seems to be correlated with the pattern of insecticide-use prevalent in the localities studied. Strains from Yuma, Phoenix and Westmoreland exhibited highest levels of resistance to permethrin. Synergism of permethrin with an oxidase inhibitor, piperonyl butoxide (PBO), and an esterase inhibitor, S,S,S-tributyl phosphorotrithioate (DEF), produced less than 2-fold synergism in the Yuma strain. Results suggest that nonmetabolic factor(s) may be involved in permethrin resistance of the Yuma field strain since neither PBO nor PBO/DEF combination suppressed resistance completely. It is possible that pink bollworm resistance is at least partially conferred by the khr-gene. Rearing of two field strains collected from Marana and Yuma under insecticide-free conditions resulted in reversion of resistance in four and five generations, respectively, to levels close to that found in the susceptible laboratory strain. Permethrin-resistance in these field strains is unstable and is apparently in its early phase of development. Monitoring of resistance in field strains should be performed preferably in the F₁ generation. Subsequently, selection studies were performed on both larval and adult stages to investigate the capacity of the pink bollworm to develop resistance in both life-stages. Selection of larvae with both azinphosmethyl and permethrin resulted in higher levels of resistance in larvae than in adults. Results suggest that azinphosmethyl possesses a low degree of selectivity for development of resistance in pink bollworm adults. Fourteen to 16 generations of selection with azinphosmethyl and permethrin produced ca. 2- and 9-fold resistance, respectively, in the adult stage. A laboratory-selected strain showing ca. 13-fold resistance was used in reciprocal crosses with a susceptible laboratory strain. The F₁ results suggested that inheritance of permethrin resistance was autosomal and partially dominant. Chi-square analysis of responses of backcross progeny indicated that resistance seems to be conferred by a major gene under the influence of minor gene(s).

MSc (Med), Epidemiology and Biostatistics, Faculty of Health Sciences, University of the Witwatersrand / Introduction Given the increasing prevalence of non-typhoidal salmonella in humans, especially as an opportunistic illness associated with HIV, enhanced surveillance for non-typhoidal salmonella (NTS), including screening for antibiotic resistance, is conducted annually in South Africa. We aimed to determine whether there is an association between trimethoprim-sulfamethoxazole (TMP-SMX) prophylaxis and multi-drug resistant NTS infection, to establish whether various factors modify the relationship between TMP-SMX resistance and invasive NTS infection, to examine whether these associations vary by province, and to quantify the resistance rates of NTS to a range of antibiotics. Methods This study was a secondary analysis of enhanced surveillance data on NTS collected between 2003 and 2005. We used descriptive methods to assess the prevalence of NTS by year, province and serotype, and to determine the prevalence of four MDR patterns. Univariate and multivariate regression models were used to investigate the relationships between TMP-SMX prophylaxis and MDR NTS. Univariate logistic regression was used to assess the relationship between invasive NTS and TMP-SMX resistance. Results TMP-SMX prophylaxis is associated with the ACKSSuT pattern (OR 1.91, 95% CI 1.14 – 3.19, p=0.0080) and the AKSSuT MDR pattern (OR 2.00, 95% CI 1.26 – 3.15, p=0.0015). Being on TMP-SMX prophylaxis is associated with an increased odds of having at least one of the four MDR patterns investigated (OR 1.43, 95% CI 1.00 – 2.04, p=0.0388). We also found high rates of resistance to all antibiotics tested except for ciprofloxacin and imipenem. The highest resistance rate was observed for sulfamethoxazole (>75.85%). S. enterica Isangi isolates showed the highest levels of resistance, with 94.43% having at least one MDR pattern. Other factors significantly associated with MDR NTS were ESBL production, prior treatment with antibiotics, HIV status and resistance to TMP-SMX. Discussion and conclusions Isolates from patients on TMP-SMX prophylaxis were associated with an increased odds of having the ACKSSuT and AKSSuT MDR patterns, not taking into account other explanatory factors. These associations did not remain significant when possible confounders were taken into account. Despite the threat of increased multi-drug resistance, TMP-SMX prophylaxis remains important in certain clinical settings.

Chau Sze-lok. / Thesis submitted in: December 2002. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2003. / Includes bibliographical references (leaves 221-245). / Abstracts in English and Chinese. / ABSTRACT (English) --- p.i / ABSTRACT (Chinese) --- p.iii / ACKNOWLEDGMENT --- p.v / LIST OF CONTENTS --- p.vii / LIST OF TABLES --- p.xiv / LIST OF FIGURES --- p.xvii / ABBREVIATIONS --- p.xx / TERMS --- p.xxi / Chapter CHAPTER 1 --- INTRODUCTION --- p.1 / (PART A) / Chapter 1.1 --- Acinetobacter spp --- p.1 / Chapter 1.2 --- Clinical importance of Acinetobacter --- p.4 / Chapter 1.3 --- Resistance mechanisms / Chapter 1.3.1 --- Intrinsic resistance --- p.7 / Chapter 1.3.2 --- Acquired resistance --- p.15 / Chapter 1.4 --- Resistance in Acinetobacter --- p.21 / Chapter 1.4.1 --- The efflux system in Acinetobacter --- p.22 / Chapter 1.4.2 --- Other antibiotic resistance mechanisms in Acinetobacter --- p.23 / (PART B) / Chapter 1.5 --- Methods used in this study --- p.29 / Chapter 1.6 --- Rationale of this study --- p.35 / Chapter 1.7 --- Objectives --- p.37 / Chapter CHAPTER 2 --- MATERIALS AND METHODS --- p.39 / Chapter 2.1 --- Bacterial strains and isolates / Chapter 2.1.1 --- Isolates for studying blaIMP-4 --- p.39 / Chapter 2.1.2 --- Isolates for studying adeB --- p.39 / Chapter 2.1.3 --- Isolates for investigation of other efflux pump(s)in Acinetobacter GDG3 --- p.40 / Chapter 2.1.4 --- Isolates for studying the distribution of efflux pumps --- p.40 / Chapter 2.1.5 --- Reference strains --- p.41 / Chapter 2.2 --- Materials / Chapter 2.2.1 --- Sources of materials --- p.42 / Chapter 2.2.2 --- Buffers and solutions --- p.45 / Chapter 2.3 --- Instruments and software --- p.46 / Chapter 2.4 --- General bacteriological techniques / Chapter 2.4.1 --- Bacteriological dientification --- p.47 / Chapter 2.4.2 --- Stock isolates --- p.48 / Chapter 2.4.3 --- Retrieval of isolates --- p.48 / Chapter 2.5 --- General molecular biology techniques / Chapter 2.5.1 --- Agarose gel electrophoresis --- p.49 / Chapter 2.5.2 --- Polymerase chain reaction (PCR) --- p.50 / Chapter 2.5.3 --- Amplified Ribosomal Restriction DNA Analysis (ARDRA) --- p.51 / Chapter 2.5.4 --- Pulsed field gel electrophoresis (PFGE) --- p.53 / Chapter 2.5.5 --- Minimal inhibitory concentration (MIC) --- p.55 / Chapter 2.5.6 --- Antibiotic sensitivity test - disc diffusion test --- p.56 / Chapter 2.5.7 --- Detection of the presence of the common resistance mechanisms --- p.57 / Chapter 2.5.8 --- TA Cloning --- p.60 / Chapter 2.5.9 --- DNA Sequencing --- p.62 / Chapter 2.5.10 --- Sequence analysis --- p.64 / Chapter 2.5.11 --- CYBR Green Assay --- p.65 / Chapter 2.5.12 --- Complementary DNA (cDNA) preparation --- p.66 / Chapter 2.5.13 --- Real time RT-PCR --- p.67 / Chapter 2.5.14 --- Construction of Genome Walker Libraries --- p.69 / Chapter 2.6 --- "Selection of acinetobacters from ICU, blood culture and other clinical isolates" / Chapter 2.6.1 --- Isolates from existing stock cultures --- p.71 / Chapter 2.6.2 --- New isolates obtained for this study --- p.71 / Chapter 2.7 --- Study of expression level of the blaIMP-4 gene / Chapter 2.7.1a --- Verification of the specificity of primers for blaIMP-4 --- p.72 / Chapter 2.7.1b --- Verfication of the specificity of primers for 16S rRNA gene --- p.73 / Chapter 2.7.1c --- Construction of standard curve --- p.76 / Chapter 2.7.2 --- Expression levels of blaIMP-4 and meropenem MICin blaIMP-4+ blood culture isolates --- p.77 / Chapter 2.7.3 --- Intra-assay reproducibility --- p.11 / Chapter 2.7.4 --- Detection of the production of metallo-β-lactamase --- p.77 / Chapter 2.8 --- Study of adeABC expression / Chapter 2.8.1 --- Determination of the presence of the adeB gene --- p.78 / Chapter 2.8.2 --- Entirety of the adeABC operon --- p.79 / Chapter 2.8.3 --- Expression level of the adeB gene --- p.82 / Chapter 2.8.4 --- Expression levels of adeB in sets of serial isolates --- p.84 / Chapter 2.8.5 --- Intra-assay reproducibility --- p.84 / Chapter 2.8.6 --- Inter-assay reproducibility --- p.84 / Chapter 2.9 --- Investigation of other efflux pumps in acinetobacter genomic DNA group3 / Chapter 2.9.1 --- Detection of adeB homologue in a genomic DNA group 3isolate --- p.85 / Chapter 2.9.2 --- Chromosome walking of the adeB-like genes --- p.87 / Chapter 2.9.3 --- Sequences of AdeE and AdeY and their comparison --- p.105 / Chapter 2.9.4 --- Topology prediction of AdeE and AdeY --- p.105 / Chapter 2.9.5 --- The role of the putative pump AdeE --- p.106 / Chapter 2.10 --- Distribution of AdeB and the putative efflux pumps AdeE and AdeY in acinetobacters from different bacterial collections / Chapter 2.10.1 --- Distribution of adeB and the putative pumps (adeE and adeY) in blood cultures (1997-2000) --- p.113 / Chapter 2.10.2 --- Confirmation of the identity of the amplification products of adeE and ade Y in blood culture isolate (1997-2000) --- p.115 / Chapter 2.10.3 --- The presence of adeE in GDG 3 acinetobacters from different sources --- p.116 / Chapter 2.10.4 --- "The presence of adeB, adeE and adeY in antibiotic susceptibility" --- p.116 / Chapter 2.10.5 --- "adeB, adeE and adeY and the clonally and epidemiologically related sets of isolates" --- p.116 / Chapter 2.10.6 --- "adeB, adeE and adeY and the blaIMP-4+ isolates" --- p.116 / Chapter CHAPTER 3 --- "SELECTION OF ACINETOBACTERS FROM ICU, BLOOD CULTURE AND OTHER CLINICAL ISOLATES" --- p.119 / Chapter 3.1 --- Results / Chapter 3.1.1 --- Isolates from existing stock cultures --- p.119 / Chapter 3.1.2 --- New isolates obtained for this study --- p.127 / Chapter 3.2 --- Discussion / Chapter 3.2.1 --- Identification of clonally related isolates by PFGE --- p.129 / Chapter 3.2.2 --- Correlation between the presence of common resistance mechanisms and the changes in antimicrobial susceptibility --- p.129 / Chapter 3.2.3 --- Development of resistance in serial isolates --- p.131 / Chapter CHAPTER 4 --- STUDY OF blaIMP-4 EXPRESSION --- p.133 / Chapter 4.1 --- Results / Chapter 4.1.1 --- Study of expression level of the blaIMP-4 gene --- p.134 / Chapter 4.1.2 --- Expression levels of blaIMP-4 and meropenem MIC in blaIMP-4+ blood culture isolates --- p.136 / Chapter 4.1.3 --- Intra-assay reproducibility \ --- p.37 / Chapter 4.1.4 --- Detection of the production of metallo-β-lactamase --- p.140 / Chapter 4.2 --- Discussion / Chapter 4.2.1 --- Dissociation curve --- p.140 / Chapter 4.2.2 --- Reproducibility of real time RT-PCR --- p.140 / Chapter 4.2.3 --- Relationship between mRNA level of blaIMP-4 and the meropenem MIC --- p.142 / Chapter CHAPTER 5 --- STUDY OF adeABC EXPRESSION --- p.145 / Chapter 5.1 --- Results / Chapter 5.1.1 --- Determination of the presence of the adeB gene --- p.145 / Chapter 5.1.2 --- Entirety of the adeABC operon --- p.146 / Chapter 5.1.3 --- Expression level of the adeB gene --- p.148 / Chapter 5.1.4 --- Expression levels of adeB in sets of serial isolates --- p.151 / Chapter 5.1.5 --- Intra-assay reproducibility --- p.154 / Chapter 5.1.6 --- Inter-assay reproducibility --- p.154 / Chapter 5.2 --- Discussion / Chapter 5.2.1 --- Detection of adeB --- p.156 / Chapter 5.2.2 --- Entirety of the adeABC operon --- p.156 / Chapter 5.2.3 --- Reproducibility of real time RT-PCR --- p.157 / Chapter 5.2.4 --- Relationship between adeB-mRNA level and antimicrobial susceptibility --- p.157 / Chapter CHAPTER 6 --- INVESTIGATION OF OTHER EFFLUX PUMPS IN ACINETOBACTER GENOMIC DNA GROUP3 --- p.159 / Chapter 6.1 --- Results / Chapter 6.1.1 --- Detection of adeB homologue in a genomic DNA group3 isolate --- p.159 / Chapter 6.1.2 --- Chromosome walking of the adeB-like genes --- p.162 / Chapter 6.1.3 --- Sequences of AdeE and AdeY and their comparison --- p.173 / Chapter 6.1.4 --- Topology prediction of AdeE and AdeY --- p.175 / Chapter 6.1.5 --- The role of the putative pump AdeE --- p.177 / Chapter 6.2 --- Discussion / Chapter 6.2.1 --- The AdeE RND transporter --- p.181 / Chapter 6.2.2 --- The theoretical AdeY protein --- p.183 / Chapter CHAPTER 7 --- DISTRIBUTION OF AdeB AND THE PUTATIVE EFFLUX PUMPS AdeE and AdeY IN ACINETOBACTERS FROM DIFFERENT BACTERIAL COLLECTIONS --- p.184 / Chapter 7.1 --- Results / Chapter 7.1.1 --- Distribution of adeB and the putative pumps (adeE and ade Y) in blood cultures (1997-2000) --- p.184 / Chapter 7.1.2 --- Confirmation of the identity of the amplification products of adeE and adeY in blood culture isolates (1997-2000) --- p.187 / Chapter 7.1.3 --- The presence of adeE in GDG 3 acinetobacters from different sources --- p.195 / Chapter 7.1.4 --- "The presence of adeB, adeE and ade Y in antibiotic susceptibility" --- p.196 / Chapter 7.1.5 --- "adeB, adeE and adeY and the clonally and epidemiologically related sets of isolates" --- p.202 / Chapter 7.1.6 --- "adeB, adeE and adeY and the blaIMP-4+ isolates" --- p.202 / Chapter 7.2 --- Discussion / Chapter 7.2.1 --- PCR-RFLP typing --- p.205 / Chapter 7.2.2 --- Distribution of adeB --- p.205 / Chapter 7.2.3 --- Distribution of adeE --- p.206 / Chapter 7.2.4 --- Distribution of adeY --- p.207 / Chapter 7.2.5 --- Distribution of adeE and adeY in GDG 3 isolates --- p.207 / Chapter CHAPTER 8 --- GENERAL DISCUSSION --- p.209 / Chapter 8.1 --- Significance of adeB and the putative pumps (adeE and adeY) --- p.211 / Chapter CHAPTER 9 --- CONCLUSION --- p.218 / Chapter 9.1 --- Conclusion --- p.218 / Chapter 9.2 --- Future Plan --- p.219 / REFERENCES --- p.221 / APPENDIX --- p.246 / Appendix1 --- p.246 / Appendix2 --- p.247 / Appendix3 --- p.252 / Appendix4 --- p.253 / Appendix5 --- p.259

There is at present great interest in large ships capable of carrying substantial cargo at speeds in excess of 40 knots. At the same time, there are large gaps in our understanding of the hydrodynamics, structural engineering, and economics of high-speed vessels. Monohulls, catamarans, trimarans, surface effect ships, and air cushion vehicles are considered in the present work. The total resistance of these vehicles is divided into separate components which are estimated using different methods. Skin-friction is estimated using Grigson's algorithm which gives much better predictions of flat plate skin-friction than the traditional ITTC method. Wave resistance of displacement hulls is estimated using Michell's thin-ship theory: a similar theory is used for the wave resistance of travelling pressure distributions. Several simple formulae are derived that can be used in the preliminary design stage of catamarans to estimate optimum demihull separation. Memetic algorithm techniques are used to find vessels with minimum (calm-water) total resistance. Optimal geometric parameters are found for vessels of 1200 tonnes under a variety of geometric limitations and constraints on upright stability, at design speeds of 50 knots and 75 knots. Estimates are made of the principal weight components of the optimal vessels. Empirical formulae for the efficiencies of powerplants and propulsors then enable estimates to be made of the maximum range, the cargo capacity, and the fuel consumption. / Thesis (M.Sc.)--School of Mathematical Sciences, 2005.

Étude de la Sous-Classe B3 et des Inhibiteurs des Métallo β-Lactamases En raison de l'introduction dagents antibactériens, les bactéries ont développé divers moyens de résistance. Le plus commun, déjà fortement développé, est la production denzymes qui hydrolysent la forme la plus largement répandue d'agent antibactérien, les antibiotiques à noyau β-lactame (Frère 1995). Ces enzymes, appelées β-lactamases, ont deux origines. Les β-lactamases à sérine correspondant aux classe A, C et D auraient évolué à partir dune DD-transpeptidase ancestrale, alors que les métallo β-lactamases (MBLs), nont pour linstant aucun ancêtre connu (Ambler 1980) (Matagne et al. 1999). Les MBLs sont importantes médicalement, puisqu'elles peuvent hydrolyser la plupart des β-lactames, y compris les carbapénèmes, qui échappent à l'activité des enzymes à sérine les plus actives (Rasmussen et al. 1997). Un transfert des MBLs entre espèce est également envisageable, du fait que certains gènes codant pour ces enzymes sont présents sur des plasmides (Osano et al. 1994) (Laraki et al. 1999). Les inhibiteurs classiques des β-lactamases à sérine active ont peu ou pas d'effet sur les MBLs et dans certains cas ils peuvent même être hydrolysés par les MBLs. Les MBLs sont produites, comme les β-lactamases à sérine, dans le périplasme des bactéries Gram-négatives ou sont sécrétées par les bactéries Gram-positives, cependant elles ont un mode d'action différent. À la différence des β-lactamases à sérine qui emploient une sérine dans leur site actif pour hydrolyser le noyau β-lactame, les MBLs utilisent lion zinc (Bush et al. 1995). Puisque ces enzymes ne présentent pas le même besoin en ions zinc pour faire preuve dune activité maximale, un débat continuel est mené afin de savoir si les MBLs utilisent un ou deux ions zinc dans leur site actif in vivo. Les MBLs forment un groupe hétérogène qui a été divisé en sous-groupes B1, B2 et B3 par similitude de séquence et spécificité de substrat (Galleni et al. 2001) (Garau et al. 2004). C'est l'hétérogénéité de cette classe qui a rendu la recherche d'un inhibiteur générique difficile. Divers inhibiteurs de MBLs ont été décrits; ceux-ci incluent le captopril, un inhibiteur compétitif des MBLs qui sest avéré efficace contre les enzymes mono-zinc BcII et CphA (Heinz et al. 2003). L'acide thiomandelique s'est avéré un inhibiteur à large spectre pour le composé racémique, avec des valeurs de Ki en-dessous de 1 µM, pour toutes les enzymes testées des sous-classes B1 et B3; bien qu'il ait été inefficace sur CphA du sous-groupe B2 (Mollard et al. 2001). Les hydrazones de sulfonyle inhibent IMP-1, le plus bas Ki étant de 0.7 µM, mais ont un effet limité sur d'autres enzymes B1 telles que BcII (Siemann et al. 2002). Les acides succiniques substitués inhibent également IMP-1 montrant des valeurs dIC50 impressionnantes mais aucune valeur de Ki nest donnée (Toney et al. 2001). L'incubation de CphA avec les β-lactames, moxalactame et céfoxitine, cause l'inactivation de l'enzyme par les produits de la réaction, mais ces inactivateurs sont des substrats pour les enzymes des sous-classes B1 et B3 (Zervosen et al. 2001). La recherche dinhibiteurs s'est tout naturellement concentrée sur les variants IMP et VIM, qui sont des MBLs portées par un plasmide; pour linstant, aucun inhibiteur identifié nest efficace sur tous les sous-groupes (Jin et al. 2004) (Kurosaki et al. 2005) (Siemann et al. 2002). La première partie de cette étude s'est concentrée sur lidentification de molécules modèles potentiellement inhibitrices de MBLs pouvant être développées en inhibiteurs à large spectre des MBLs. Par le criblage nous avons identifié trois modèles différents susceptibles de donner des inhibiteurs efficaces; lun deux est capable de chélater l'espèce mono-zinc, lacide 2,4 pyridine dicarboxylique; un autre est spécifique de FEZ-1, le N,3-Dihydroxy-5-(4-hydroxybenzoyl) benzamide et le dernier est efficace contre toutes les MBLs testées, lacide [(3-Mercaptopropanoyl)amino](phenyl) propanoic. Les résultats obtenus montrent des constantes dinhibition allant du micromolaire au nanaomolaire. La sous-classe B3 contient la MBL L1, dont le spectre daction est le plus large. Cette enzyme peut hydrolyser un éventail de substrats tel que les pénicillines, les céphalosporines et les carbapénèmes (Crowder et al. 1998). Elle partage le repliement αβ/βα et le site di-zinc des autres MBLs mais cest un tétramère, une caractéristique unique parmi les β-lactamases (Saino et al. 1982) (Bicknell et al. 1985). La forme tétramerique de L1 la rend plus difficile à étudier par des techniques telles que la spectroscopie de résonance magnétique nucléaire ou la spectrométrie de masse. Par conséquent, pour la deuxième partie de cette étude, nous avons décidé d'étudier L1, visant à trouver les conditions dans lesquelles l'enzyme était présente comme monomère, sans besoin de mutation. Les résultats que nous avons obtenus étaient imprévus et nous ont menés à examiner une méthode de production d'apo-enzyme pour les MBLs. L'enzyme a pu facilement être dénaturée et le zinc être enlevé. L'activité a été trouvée après renaturation suite à l'addition de zinc. Cette étude pourrait être poursuivie à l'avenir, les résultats préliminaires obtenus ici sont peu concluants, mais présentent un intérêt cinétique ainsi quun bénéfice à l'étude des MBLs commencée dans ce travail. Le nombre de MBLs connues augmente constamment et la caractérisation de chaque enzyme doit être accomplie pour gagner une pleine compréhension des β-lactamases, afin quil reste un espoir d'empêcher la diffusion supplémentaire de la résistance bactérienne. Pour cette raison le but de la troisième partie de cette étude était de caractériser plus profondément la MBL, GOB-1 de Chryseobacterium meningosepticum. L'analyse de sa séquence en acides aminés, par Bellais et al. 2000 place GOB-1 dans la sous-classe B3 en dépit de son unique résidu liant le zinc Gln116. Nous avons produit GOB-1 en utilisant un vecteur d'expression basé sur le système dexpression du phage T7 et avons purifié l'enzyme. Des mutants de GOB-1 ont été créés par mutagénèse dirigée du résidu liant le zinc Gln116. Une étude cinétique détaillée a alors été réalisée en présence et absence de zinc additionnel montrant que GOB-1 est une enzyme très efficace, capable dhydrolyser efficacement tous les β-lactames testés. Les mutants du résidu Gln116 de GOB-1, produits par mutagénèse dirigée ont montré une perte d'activité qui ne peut pas être corrigée par addition de zinc, démontrant ainsi que GOB-1 n'est pas une enzyme hybride des sous-classes B2 et B3, comme cela avait été précédemment suggéré (Garau et al. 2004), mais plutôt une enzyme nouvelle et améliorée de la sous-classe B3, utilisant les dispositifs structuraux précédemment utilisés par les enzymes de la sous-classe B2 mais en améliorant l'effet.

Graduation date: 1991

Microbiological detection of foodborne pathogens is ineffective for monitoring critical control points (CCP) within a slaughter/processing Hazard Analysis and Critical Control Point (HACCP) system. Pathogens are usually absent from carcass surfaces and their uneven distribution makes it difficult to obtain a representative sample. However, microbiological testing can be applied within a HACCP plan to validate and verify the effectiveness of decontamination procedures designed to control hazards. With proper data collection, the reduction of an indicator group at a point in processing can indicate that a specific pathogen is being effectively controlled, especially when pathogen levels are too low to allow confirmation of process control, as they typically are in beef slaughter processing. Since E. coli O157:H7 has been shown to have some acid resistance, the ability of typical indicator organisms to accurately predict the reduction of this pathogen by carcass decontamination procedures has been a concern. Obtaining potential indicator bacteria from the same environmental reservoir as E. coli O157:H7 may provide non-pathogenic indicators with similar heat- and acid-resistance characteristics suitable for use in processing plant environments for validation and verification of carcass decontamination treatments within HACCP plans. Potential indicator bacteria were isolated from hides of cattle at slaughter facilities in Arizona, Georgia, and Texas and compared with isolates of E. coli O157:H7 from the same locations to determine similarity in acid- and heat-resistance characteristics. After evaluation at 2 heating temperatures (55 and 65??C) and 3 pH levels (3.0, 4.0, and 5.0), it was determined that several potential indicator bacteria were slightly more resistant than E. coli O157:H7 to heating and acid treatment. The greatest reduction in numbers for E. coli O157:H7 and indicator bacteria occurred at pH 3.0 and temperature of 65??C. Counts of bacteria grown at pH 4.0 and 5.0 were not significantly different. Testing indicated that several of the isolates from cattle hides would make good process control indicators since the indicator bacteria were reduced by heating or acid conditions at similar or greater rates when compared to E. coli O157:H7, providing an increased level of security that pathogens have been reduced in processing.