Defense Date


Document Type


Degree Name

Doctor of Philosophy



First Advisor

Dr. Harry P. Dalton


Legionella pneumophila was first recognized as a cause of human pneumonia in 1976 . Since then, much has been learned about the microbiology, pathophysiology and epidemiology of this organism. The features which permit one strain but not another to invade human lung tissue and produce disease remain incompletely understood. This study e valuated several attributes of a virulent and an avirulent strain of L. pneumophila in an attempt to identify characteristics which would distinguish the two. Evaluation of a new medium, buffered egg yolk agar, showed that virulence was maintained after 26 passages, which was the same as the buffered charcoal yeast extract agar used for comparison. However, growth appeared earlier and was heavier on the charcoalcontaining medium. Morphologically, the avirulent strain produced greater numbers of filamentous forms and was found to be encapsulated more frequently. Treatment with polymixin B produced morphologic changes similar to those previously reported but failed to alter the virulence of either strain. No plasmids were found in either strain nor were consistent differences in protein content demonstrated using sodium dodecylsulfate polyacrylamide gel electrophoresis. Both strains reacted less intensely as cultures aged with a monoclonal but not a polyclonal antibody in a direct fluorescent antibody assay . This change was more pronounced when the virulent organism was tested. Chemotactic assays showed similar tendencies when human or guinea pig mononuclear cells were compared to two estuarine species (hogchoker and spot) and one freshwater species (golden shiner minnow) of fish. In vivo results were also similar when two of the three species of fish were tested, suggesting that either the spot or the minnow may be used in evaluation of certain characteristics of L. pneumophila. Organisms were isolated from apparently healthy fish up to 15 days after inoculation in some instances. This suggests that fish may be a possible additional environmental reservoir for Legionella pneumophila.


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