Corynebacterium pseudotuberculosis (Cp) is the causative agent of caseous lymphadenitis (CLA), a chronic bacterial disease of sheep and goats characterized by granulomatous
inflammation of Iymph nodes. CLA is prevalent worldwide and causes considerable economic losses to the sheep and goat industries. The ability of Cp to persist as a facultative intracellular parasite is considered an important feature in the pathogenesis of CLA. The present study provides the basis for identifying the host and bacterial factors mediating entry of Cp into phagocytic and non-phagocytic cells and evaluates the possible significance of cell invasion in the pathogenesis and epidemiology of CLA. The aims were to investigate the cell tropism of Cp and to characterize the hostpathogen interactions and mechanisms involved in cell invasion by analyzing the in-vitro ability of the bacterium to enter murine 1774 macrophages and epithelial buffalo green monkey (BGM) cells. By means of a gentamicin invasion assay and bright field light microscopy, Cp was shown to enter and multiply within macrophages and actively invade epithelial cells. Scanning electron microscopy revealed that the bacterium seemed to adhere to the BGM cells in clusters and induce its uptake via a "zipper-like" mechanism of engulfment. Using a variety of compounds that act on eukaryotic cell structures, the entry process was found to involve various host signal transduction events and the reorganization of the actin cytoskeleton.