Defense Date


Document Type


Degree Name

Master of Science


Microbiology & Immunology

First Advisor

Francine Marciano-Cabral


Acanthamoeba culbertsoni (A. culbertsoni) is an amphizoic amoeba that is the causative agent of Granulomatous Amoebic Encephalitis (GAE), an often fatal central nervous system infection that is seen most frequently in severely immunocompromised patients and is characterized by hemorrhagic and necrotic lesions of the brain as well as varying degrees of granuloma formation. A.culbertsoni isolates have also been identified in a few cases of Amoebic Keratitis, a painful, sight-threatening corneal infection that disproportionately affects contact lens users irrespective of immune status. Common features of both infections include amoebic interaction with host extracellular matrix (ECM) components as requisites for both attachment to, and subsequent invasion of, host tissues to facilitate disease establishment. Previous studies have demonstrated that pathogenic species of Acanthamoeba , such as A.culbertsoni, bind to the ECM proteins Laminin-1 and Collagen I to a greater extent than non-pathogenic species. It has also been documented in the literature that secreted Acanthamoeba proteases have the ability to degrade components of the extracellular matrix. The role of amoebic proteases in mediating the attachment and invasion processes is not entirely understood. Initial experiments conducted in the present study revealed secretion of approximately 150 and 55-kDa serine proteases during attachment as well as invasion of the ECM by A. culbertsoni. However, inhibition of these serine proteases using phenylmethylsulfonyl fluoride (PMSF) did not diminish the ability of amoebae to attach or invade. It was demonstrated that secretion of the observed proteases occurred in a constitutive rather than substrate-induced manner and that amoebae secrete these proteases under a number of different conditions. Additionally, a 140-kDa membrane-associated serine protease was identified which may prove to play a role in focal proteolytic degradation. Collectively, our results suggest that attachment to extracellular matrix components is mediated through non-protease-dependent mechanisms. We also suggest that ECM invasion by A.culbertsoni is predominately a mechanical process that may be supplemented or enhanced by focal proteolytic degradation of extracellular matrix components by membrane-associated proteases.


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Date of Submission

August 2011