Invasive pathogenic bacteria invade, survive and replicate inside mammalian cells. These group of pathogens developed sophisticated molecular tool kits to hijack cellular pathways to support bacterial intracellular survival and cause disease. Our laboratory investigates the cellular biology mechanism altered by the pathogens Salmonella and Legionella pneumophila. Salmonella invades intestinal mucosa cells and spread systematically causing diseases that range from gastroenteritis to the most severe typhoid fever. Although most of the patients recover, a small number develop Reiter’s syndrome and chronic arthritis and for immune deficient patients can be life threatening. The efficiency of Salmonella as a pathogen depends on its ability to evade its recognition by the immune system. We are currently investigating cellular mechanisms subverted by Salmonella to promote immune evasion; most specifically the disruption of the pathogen recognition receptor TLR4. L. pneumophila is an emerging respiratory pathogen and the etiological agent of Legionnaires disease. While invasion and intracellular survival of L. pneumophila have been extensively studied in macrophages, the interactions with epithelial cells have received considerably less attention. Because epithelial cells represent an important platform for host-pathogen interactions, we investigate the cellular mechanisms used by L. pneumophila to invade and survive inside lung epithelial cells. Studying the interactions between these cells and Legionella will help in the understanding the infection process and in designing effective treatments.