The application of photodynamic therapy (PDT) has aimed at destroying tumor cells and microbiological control in infections. Experimentation in vitro with individual elements of a biological system enables the study of mechanism of action and provides directions to in vivo applications where cancer coexists with normal cells and microorganisms, whether opportunistic or not. The action of the combined set of elements leads to a different behavior from each of the components isolated. In this study, we created a simple model to investigate the effects of PDT (1) on the coculture of macrophages (2) and melanoma cells (3) infected with E. coli (4) under different combinations. Comparing the 4 individual elements of the system interacting with each other to all of them interacting together, we found that macrophage phagocytosis depends on the order in which the elements are exposed to PDT. That indicates the behavior of macrophages depends on their relationship with the microenvironment. Applying the photodynamic effect to each component separately or to all of them together results in different outcomes. These in vitro experiments provide pathways to understand or to design new and more efficient applications of PDT.