show Abstracthide AbstractYersinia enterocolitica is a food-borne pathogen that has the potential to cause serious gastrointestinal illness. Because its best characterized virulence factors are expressed when the bacteria are attached to the surface of host cells, it is typically considered an extracellular pathogen. During the infection of macrophages however, there are populations of bacteria that are able to survive within intracellular compartments for long periods of time. Little is known about the role of these bacteria in the overall infection process. In this study we used a next-generation RNA sequencing approach to analyze the gene expression pattern in bacteria attached to the cell surface as well as those located within the intracellular compartments. Differential gene expression was computed for bacterias in nutrient rich growth medium at 26°C to conditioned cell culture medium at 37°C, bacteria in conditioned cell culture medium to bacteria attached to the surface of macrophages and as well as extracellular and intracellular bacteria.