Date of Award

January 2013

Document Type


Degree Name

Doctor of Philosophy (PhD)


Biomedical Sciences

First Advisor

Matthew L. Nilles


The type III secretion system of gram-negative bacterial pathogens is a major virulence factor and functions to modulate host immune responses. Immune modulation occurs in many ways, including direct injection of effector proteins or indirect methods such as the detection of bacterial components by host immune receptors. Knowledge of these immune modulations allows for development of treatment options in an ever-increasing antibiotic-resistance climate. The studies presented here explore both areas of immune modulation. We identify Compound D as a potent inhibitor of the type III secretion system of Yersinia pestis. Through evaluation of effector secretion by bacteria grown in the presence of Compound D, we establish that inhibition of secretion occurs through translocon protein YopD and is also affected by LcrQ and YopD's chaperone, LcrH. Type III Secretion inhibition by Compound D also requires a secretion active state of the type III secretion system as determined by analysis of strains that constitutively secrete effectors. The other study focuses on host recognition of bacterial proteins, specifically the needle protein of type III secretion systems. Via utilization of cells that secrete a measurable signal protein when NF-κB or AP-1 is activated, we show that needle proteins from Yersinia pestis, Salmonella enterica serovar Typhimurium, and Shigella flexneri are capable of activating cells through Toll-like receptors 2 and 4. This interaction appears to be modulated by the N-terminus, that is reported to reside on the outside of the fully formed needle structure, exposed to host receptors. Activation of NF-κB/AP-1 correlates with production of TNF-α in response to needle proteins.