Such infections caused by sorts of intracellular microorganisms there is a relationship between bacterial pathogens and host macrophages. Mononuclear phagocytes are active effector cells to intracellular infectious organisms and they kill those infectious agents by both oxygen dependent and independent pathways. During the infection there is a complex and dynamic interaction between host macrophages and bacterial pathogens. The majority of studies examining bacterial survival within macrophages, have measured viability of the total bacterial population and instead of viability, dead and live bacteria, which are being together have been overlooked. These results often give an incomplete picture of the dynamics of the infection.

In our study, human monocyte derived macrophages were infected by two Salmonella typhi strains at a cell ratio of 10 bacteria per one macrophage (10:1). Specimens were examined by both culture and LIVE/DEAD BacLight staining system which allow us to see dead and live bacteria directly. At the end of 24 hours it was found that clinical strain was more resistant than standard strain. With Bac- Light stain it was possible for us to observe bactericidal effects of macrophages.