Term of Award

Winter 2003

Degree Name

Master of Science

Document Type and Release Option

Thesis (restricted to Georgia Southern)


Department of Biology

Committee Chair

Laura B. Regassa

Committee Member 1

James B. Claiborne

Committee Member 2

Alison Morrison-Shetlar

Committee Member 3

Susan Edwards


Actinobacillus pleuropnenmoniae is the causative agent of porcine pleuropneumonia, a highly contagious and often fatal respiratory tract disease of pigs. The Apx toxins are primary virulence factors of this pathogen, with Apxl and ApxII being produced by all highly virulent strains in North America. Further characterization of these hemolytic toxins is needed to fully understand their role in disease and elucidate the environmental signals and genes that affect their production during infection. The goal of this project was to examine environmental signals that could be involved in regulation of the Apxl and ApxII toxins. To pursue this goal, toxin production was examined in relation to growth phase, quorum sensing, and oxygen tension. Changes in the hemolytic activity, the production of extracellular toxin and/or levels of mRNA were measured. It was found that ApxII was regulated by growth-phase, with maximal production occurring during late exponential or early stationary phase. Also, there was a slight increase, less than two fold, in ApxII production that may be due to quorum sensing. Finally, comparable amounts of Apxl and ApxII toxins were produced anaerobically under both our liquid and solid media growth conditions.


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