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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Prevention of the neutrophil-induced mammary epithelial damage during bovine mastitis

Lauzon, Karoline. January 2005 (has links)
Reduction of milk production following acute bovine mastitis causes important economic losses. In this study, two experiments were conducted to asses the ability of different antioxidants to prevent neutrophil (PMN)-induced mammary damage in acute bovine mastitis. First, a co-culture model composed of bovine mammary epithelial cell line (MAC-T cells) and bovine PMN activated by phorbol myristate acetate was used. Activated PMN release reactive oxygen species that are cytotoxic for bovine epithelial cells. Addition of dimethylthiourea or bathocuproinic acid did not induce any protective effect. On the other hand, addition of catechin, deferoxamine or glutathione ethyl ester (GEE) significantly reduced PMN-induced cytotoxicity in a dose-dependent manner as demonstrated by lower levels of released lactate dehydrogenase (LDH). The second experiment was undertaken with the last three antioxidants to evaluate their protective effects in vivo. A model of LPS-induced mastitis on dairy cows was used. The extent of cell damages was evaluated by measuring quarter milk levels of LDH and 4-methylumbelliferyl N-acetyl beta-D-glucosaminidase ( NAGase) at varying intervals before and after intramammary infusions of LPS, with or without antioxidants. Milk levels of haptoglobin and bovine serum albumin were also analysed. Catechin and GEE did not induce any protective effect whereas infusions of deferoxamine, a chelator of iron, decreased milk levels of LDH, NAGase and haptoglobin hence suggesting a protective effect against PMN-induced damage. Deferoxamine did not interfere with PMN migration into the mammary gland. Additionally, deferoxamine inhibited bacterial growth in vitro but did not affect PMN's ability to phagocytize live Escherichia coli. Overall, our results suggest that local infusion of deferoxamine may be an effective tool to protect mammary tissue against PMN-induced oxidative stress during bovine mastitis.
2

Biological and molecular characterization of South African bacteriophages infective against Staphylococcus aureus subsp. aureus Rosenbach 1884, casual agent of bovine mastitis.

Basdew, Iona Hershna. 27 November 2013 (has links)
Bacteriophage therapy has been exploited for the control of bacterial diseases in fauna, flora and humans. However, the advent of antibiotic therapy lead to a cessation of most phage research. Recently, the problem of antibiotic resistance has rendered many commonly used antibiotics ineffective, thereby renewing interest in phage therapy as an alternative source of control. This is particularly relevant in the case of bovine mastitis, an inflammatory disease of bovine mammary glands, caused by strains such as Staphylococcus aureus subsp. aureus Rosenbach 1884. Antibiotic resistance (primarily towards penicillin and methicillin) by staphylococcal strains causing mastitis is regularly reported. Phage therapy can provide a stable, effective and affordable system of mastitis control with little to no deleterious effect on the surrounding environment or the affected animal itself. Several studies have delved into the field of biocontrol of bovine mastitis using phages. Results are variable. While some phage-based products have been commercialized for the treatment of S. aureus-associated infections in humans, no products have yet been formulated specifically for the strains responsible for bovine mastitis. If the reliability of phage therapy can be resolved, then phages may become a primary form of control for bovine mastitis and other bacterial diseases. This study investigated the presence of S. aureus and its phages in a dairy environment, as well as the lytic ability of phage isolates against antibiotic-resistant strains of mastitic S. aureus. The primary goals of the thesis were to review the available literature on bovine mastitis and its associated control, and then to link this information to the use of phages as potential control agents for the disease, to conduct in vitro bioassays on the selected phages, to conduct phage sensitivity assays to assess phage activity against different chemical and environmental stresses, to morphologically classify the selected phages using transmission electron microscopy, to characterize the phage proteins using one-dimensional electrophoresis, and lastly, to characterize phage genomes, using both electrophoresis as well as full genome sequencing. Twenty-eight phages were isolated and screened against four strains of S. aureus. Only six phages showed potential for further testing, based on their wide host range, high titres and common growth requirements. Optimal growth conditions for the host S. aureus strain was 37°C for 12hr. This allowed for optimal phage replication. At an optimal titre of between 6.2x10⁷ to 2.9x10⁸ pfu.mlˉ¹(at 10ˉ⁵ dilution of phage stock), these phages were able to reduce live bacterial cell counts by 64-95%. In addition, all six phages showed pathogenicity towards another 18 S. aureus strains that were isolated from different milk-producing regions during a farm survey. These six phages were named Sabp-P1, Sabp-P2, Sabp-P3, Sabp-P4, Sabp-P5 and Sabp-P6. Sensitivity bioassays, towards simulated environmental and formulation stresses were conducted on six identified phages. Phages Sabp-P1, Sabp-P2 and Sabp-P3 showed the most stable replication rates at increasing temperatures (45-70°C), in comparison to phages Sabp-P4, Sabp-P5 and Sabp-P6. The effect of temperature on storage of phages showed that 4ºC was the minimum temperature at which phages could be stored without a significant reduction in their lytic and replication abilities. Furthermore, all phages showed varying levels of sensitivity to chloroform exposure, with Sabp-P5 exhibiting the highest level of reduction in activity (74.23%) in comparison to the other phages. All six phages showed optimal lytic ability at pH 6.0-7.0 and reduced activity at any pH above or below pH 6.0-7.0. Exposure of phages to varying glycerol concentrations (5-100%) produced variable results. All six phages were most stable at a glycerol concentration of 10-15%. Three of the six isolated phages, Sabp-P1, Sabp-P2 and Sabp-P3, performed optimally during the in vitro assays and were used for the remainder of the study. Morphological classification of phages Sabp-P1, Sabp-P2 and Sabp-P3 was carried out using transmission electron microscopy. All three phages appeared structurally similar. Each possessed an icosahedral head separated from a striated, contractile tail region by a constricted neck region. The head capsules ranged in diameter between 90-110nm with the tail length ranging from 150-200nm in the non-contractile state and 100-130nm in the contractile state. Rigid tail fibres were also visible below the striated tail. The major steps in the virus replicative cycle were also documented as electron micrographs. Ultra-thin sections through phage plaques were prepared through a modification of traditional methods to speed up the process, with no negative effects on sample integrity. The major steps that were captured in the phage replicative cycle were (1) attachment to host cells, (2) replication within host cells, and, (3) release from cells. Overall results suggested that all three phages are strains from the order Caudovirales and are part of the Myoviridae family. A wealth of information can be derived about an organism based on analysis of its proteomic data. In the current study, one-dimensional electrophoretic methods, sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), and ultra-thin layer isoelectric focusing (UTLIEF), were used to analyse the proteins of three phages, Sabp-P1, Sabp-P2 and Sabp-P3, in order to determine whether these strains differed from each other. SDS-PAGE analysis produced unique protein profiles for each phage, with band fragments ranging in size from 8.86-171.66kDa. Combined similarity matrices showed an 84.62% similarity between Sabp-P1 and Sabp-P2 and a 73.33% similarity between Sabp-P1 and Sabp-P3. Sabp-P2 showed a 69.23% similarity to Sabp-P3. UTLIEF analysis showed protein isoelectric charges in the range of pI 4.21-8.13, for all three phages. The isoelectric profiles for each phage were distinct from each other. A combined similarity matrix of both SDS-PAGE and UTLIEF data showed an 80.00% similarity between phages Sabp-P1 and Sabp-P2, and a 68.29% similarity between Sabp-P1 and Sabp-P3. Sabp-P2 showed a 70.59% similarity to Sabp-P3. Although the current results are based on putative protein fragments analysis, it can be confirmed that phages Sabp-P1, Sabp-P2 and Sabp-P3 are three distinct phages. This was further confirmed through genomic characterization of the three staphylococcal phages, Sabp-P1, Sabp-P2 and Sabp-P3, using restriction fragment length analysis and whole genome sequencing. Results showed that the genomes of phages Sabp-P1, Sabp-P2 and Sabp-P3 were all different from each other. Phages Sabp-P1 and Sabp-P3 showed sequence homology to a particular form of Pseudomonas phages, called "giant" phages. Phage Sabp-P3 showed sequence homology to a Clostridium perfringens phage. Major phage functional proteins (the tail tape measure protein, virion structural proteins, head morphogenesis proteins, and capsid proteins) were identified in all three phages. However, although the level of sequence similarity between the screened phages and those already found on the databases, enabled preliminary classification of the phages into the order Caudovirales, family Myoviridae, the level of homology was not sufficient enough to assign each phage to a particular type species. These results suggest that phage Sabp-P1 might be a new species of phage within the Myoviridae family. One longer-term objective of the study is to carry out complete assembly and annotation of all the contigs for each phage. This will provide definitive conclusions in terms of phage relatedness and classification. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2012.
3

Fatores fisiológicos, clínicos e farmacológicos, determinantes de resíduos de antimicrobiano no leite, avaliados em protocolos terapêuticos de mastite em bovinos leiteiros / Evaluation of some physiological, clinical and pharmacological factors to antimicrobials residues in milk under different management and therapeutic protocols

Roberto Bellizia Raia Junior 04 April 2006 (has links)
Atualmente a terapia e as práticas de manejo da mastite estão baseadas na administração de agentes antimicrobianos com ampla atividade contra os microrganismos mais comuns desta doença. Os fármacos são administrados diretamente no canal da teta e/ou por sistêmica. Os tratamentos com antimicrobianos são realizados durante o período seco como terapia preventiva, ou durante o período de lactação como terapia curativa. O leite produzido por animais tratados pode conter resíduos do medicamento. A presença de resíduos de antimicrobianos no leite constitui um risco para a saúde pública devido ao fenômeno de múltipla resistência, bem como uma causa de perdas econômicas, considerando a fabricação de queijo e iogurte, entre outros derivados lácteos. A proposta deste estudo foi avaliar alguns fatores que contribuem para a ocorrência de resíduos em vacas tratadas além do período recomendado para descarte. Os fatores avaliados foram: fisiológico, como a produção leiteira; clínico, como a mastite e farmacológico como a via de administração e o fármaco utilizado. Foi usado um teste comercial para a detecção de resíduos (Delvotest®) por inibição microbiológica. Entre os fatores estudados, foi demonstrada a influência da produção leiteira, ou seja, animais com produção leiteira maior do que 20L/dia apresentaram menor ocorrência de resíduo (39,5%), quando comparado com aqueles com produção menor do que 20L/dia (70,7%) e a diferença foi significante (P < 0,0001). Entre os fatores clínicos foi determinado que a presença e intensidade do processo inflamatório contribuem para a ocorrência de resíduos. Deste modo, entre os quartos com mastite clínica tratados o nível de resíduo foi 47,7%, os quartos com mastite subclínica tratados apresentaram 34,9% e os controles 9,5% (quartos sem mastite tratados) e a diferença entre os três grupos foi significante (P = 0,0381, P = 0,0008, P = 0,0209). Ao se comparar a ocorrência de resíduos no leite de quartos tratados durante a lactação (41,9%) com os resíduos nos quartos que receberam a terapia de vaca seca (23,2%) foi observado um maior nível entre os grupos tratados durante a lactação e a diferença foi significante (P < 0,0001). Em relação aos fatores farmacológicos, a via de aplicação bem como o grupo farmacológico do antimicrobiano utilizado no tratamento foram demonstradas diferenças estatísticas tanto para os diversos antimicrobianos, quanto para as vias de administração. Um maior nível de resíduo foi observado entre os grupos farmacológicos em quartos tratados por via intramamária com aminoglicosídeos (gentamicina) (66,7%). E o maior nível de resíduo foi observado quando ambas as vias foram utilizadas simultaneamente, tanto para aminoglicosídeos (93,7%), quanto para betalactâmicos (100%). O conhecimento de que o pKa dos antimicrobianos irá determinar diferentes níveis de distribuição nos órgãos e tecidos sustenta a hipótese que a via de administração pode influenciar a presença de resíduos de antimicrobianos no leite. Conseqüentemente, o uso simultâneo das duas vias de administração, uma prática comum, contribuiu também para um alto risco da ocorrência de resíduos de antimicrobianos. Deve-se ressaltar que a redução da presença de resíduos no leite não depende apenas de normas e regulamentos, mas envolve uma orientação aos produtores e aos veterinários para controlar e/ou prevenir os fatores de risco. Assim, os resultados deste estudo irão contribuir para esclarecer alguns aspectos importantes para um melhor entendimento da ocorrência de resíduo no leite além do período recomendado para descarte. / Current mastitis therapy and management practices are base on the administration of antimicrobial agents with high activity against most common mastitis bacterial pathogens. Drugs are administrated directly into the teat canal and/or systemically. Antibiotic treatments are performed during the dry period as preventive therapy, or during the lactating periods as therapeutic cure. Milk produced from treated animals may contain drug residues. The presence of antibiotic residues in milk constitutes a public health risk due to the multi-resistance phenomenon, as well as, a source of economical losses, considering the industries of cheese and yogurts, among others dairy products. The purpose of this study was evaluated some factors that contribute to the occurrence of residues in treated cows beyond the recommended discarded period. The evaluated factors were: physiological, as milk production, clinical, as mastitis and pharmacological, as routes and antimicrobials. It was used a commercial test for residues detection (Delvotest®) by microbiological inhibition. Among the clinical factors it was demonstrated the influence of the milk production, so animals with milk production higher than 20 L/day showed lower occurrence of residues (39.5%), compared to the ones with less than 20 L/day (70.7%) the difference was significant (P<0.0001). Among the clinical factors it was determinated that the presence of inflammatory process and the intensity of it, contributes to the presence of residues. Therefore, among the clinical mastitis treated quartes the level of residues was 47.7%, while the subclinical treated quartes showed 34.9% and, the control ones 9.5% (i.e. treated quartes without mastitis) and the difference among the three groups was significant (P=0.0381, P=0.0008, P=0.0209).Comparing the residues in milk from treated quartes during lactation (41.9%) with the quartes that received the dry cow therapy (23.2%) it was observed a higher level of residues among the groups treated during the lactation and the difference was significant (P<0.0001). Among the pharmacological factors, the routes as well the pharmacological group of the antimicrobials used in the treatment showed statistical differences either among the antimicrobials as well as the administration routes. A high level of residues was observed among pharmacological groups in quartes treated by intramammarian route with aminoglicosides (gentamicin) (66.7%). And, the highest level of residues was observed when both route where used simultaneously, either with aminoglicosides (93.7%) as well as with betalactamics (100%). The knowledge that different pKa among the antimicrobials will determine the level of distribution in different organs and tissues, support the hypothesis that the administration route could influence the presence of residues of antibiotics in milk. Consequently, the simultaneous use of both administration routes, a very usual practice, could also contributes to a higher risk of antimicrobial residue occurrence. To reduce this possibility, it is not only a matter of Regulatory Affairs, but also involves the dairy farmers and veterinarians\' proper orientation about how to avoid and to control the risk factors, therefore, the results of this study will contribute to clarify some important aspects to a better understanding of the occurrence of residues in milk beyond the recommend discard period.

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