Shigella flexneri is a Gram negative, intracellular pathogen responsible for bacillary dysentery in humans. To achieve infection of the human colonic epithelium, S. flexneri must adapt to varying environmental conditions, including fluctuations in pH, osmolarity, and nutrient and oxygen availabilities. The plaque assay is commonly used to measure the ability of S. flexneri to invade epithelial cells, grow intracellularly, and spread intercellularly to adjacent cells. However, as traditionally performed, this assay is of limited use in testing the virulence of Shigella in response to many of the conditions encountered in the host. I have modified the plaque assay to identify factors contributing to the virulence of S. flexneri under the anaerobic conditions present in the colon. This assay demonstrated that the Feo transport system that acquires anaerobically abundant ferrous iron, as well as the transcription factors ArcA, Fnr, and Fur, impact Shigella plaque formation in anoxic environments. Transcriptional analyses indicated that anaerobic conditions activated expression of feoABC in S. flexneri. Anaerobiosis also repressed genes encoding two other iron transport systems that allow plaque formation by S. flexneri in aerobic environments, the ABC transporter Sit and the Iuc/Iut aerobactin siderophore synthesis and acquisition system that binds ferric iron, the dominant form of iron under aerobic conditions. The anaerobic regulators ArcA and Fnr induced expression of feoABC. Additionally, ArcA represses transcription of iucABCDiutA and fur. fur encodes a transcriptional regulator that is activated in the presence of iron and is responsible for repression of genes encoding iron acquisition systems and the sRNA RyhB that affects synthesis of iron-storage proteins including many TCA cycle enzymes. ArcA is a redox regulator known for redirecting metabolism upon oxygen depletion by down-regulating TCA cycle and aerobic respiratory enzymes and inducing fermentation and anaerobic respiratory complexes. However, ArcA regulation of fur and its downstream targets offers S. flexneri a means to coordinate energy and carbon metabolism with that of iron availability in response to environmental redox conditions. / text

No description available.

Zugl.: Marburg, University, Diss., 2008.

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

No description available.

Thesis (Ph. D.)--University of Hong Kong, 1997. / Includes bibliographical references (leaf 129-150).

Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

Thesis (Ph.D.)--University of Hong Kong, 1997. / Includes bibliographical references (leaf 129-150) Also available in print.

OBJETIVO: Determinar la resistencia antibiótica de las cepas de Shigella aisladas en el Hospital Daniel A. Carrión MATERIALES Y METODOS: Se resembraron las 159 cepas de Shigella aisladas del 01 de Enero 1999 al 31 de Diciembre del 2001, siendo viables 111 de ellas con las que se desarrollo el estudio. RESULTADOS: De las 111 cepas, 89 provenían de muestras de heces (80%), 73 eran flexneri (67%), la resistencia a Ampicilina fue 81%, a Cloramfenicol 72%, a Cotrimoxazol 72%, a Amikacina 13%, a Gentamicina 9%, a Ácido Nalidíxico 14%, a Norfloxacina 1%, a Ciprofloxacina 2%; la resistencia múltiple más frecuente fue a 6 antibióticos con 36 cepas (32.4%), y el patrón de resistencia más frecuente fue Ampicilina, Sultamicilina, Cloramfenicol, Doxiciclina, Cotrimoxazol, Tetraciclina con 22 cepas (19.8%). CONCLUSIONES: Shigella flexneri se constituye en la cepa más frecuentemente aislada, se evidencia una leve disminución de la resistencia a Ampicilina y Cloramfenicol, y una progresión de la resistencia a Ácido Nalidíxico y Cotrimoxazol, sin cambios significativos en la resistencia a los Aminoglucósidos y las Quinolonas.

Thesis (M.A.)--Central Connecticut State University, 2002. / Thesis advisor: Michael A. Davis. " ... in partial fulfillment of the requirements for the degree of Master of Arts in Biology." Includes bibliographical references. Also available via the World Wide Web.