Andrew Camilli

Dual roles of plcA in Listeria monocytogenes pathogenesis

The plcA gene of Listeria monocytogenes encodes a secreted phosphatidylinositol‐speciftc phospholi‐pase C (PI‐PLC). Recent studies have established that transposon mutations within plcA result in avirulence for mice and pleiotropic effects when examined in tissue‐culture models of infection. Genetic analysis reveals that many of the effects of the transposon insertions are due to loss of readthrough transcription from plcA into the downstream gene prfA, which encodes an essential transcription factor of numerous L. monocytogenes virulence genes. Construction of an in‐frame deletion within plcA had no effect on expression of prfA thus allowing direct assignment of a role of the PI‐PLC in pathogenesis. PI‐PLC was shown to play a significant role in mediating escape of L. monocytogenes from phagosomes of primary murine macrophages. Interestingly, this defect manifested itself in vivo in the liver but not in the spleen of infected mice.

CHAPTER 4 – Strategies to Identify Bacterial Pathogenicity Factors

This chapter focuses on the various biochemical, immunological, and genetic strategies that are successfully employed by microbiologists to identify the bacterial pathogenicity factors. In addition, speculation on the utilization of several postgenomic strategies that are currently being developed is presented in an attempt to illuminate future methodologies, which should prove useful in further discoveries. A listing of each technique along with a brief description of some of their advantages and disadvantages is addresses in the chapter. The chapter also deals with the use of a broader definition of pathogenicity factor that includes any factor produced by a pathogen that plays a role in its survival, multiplication, or spread to new hosts. It also describes many of the genetic strategies that have been employed throughout the last few decades of the twentieth century to facilitate identification of bacterial pathogenicity factors. Each technique, as described, can result in identification of a bacterial gene that is required for production of a putative pathogenicity factor.