We hypothesized that active interaction between bacteria and host cells was necessary to trigger EGR1 induction. To address this, we infected host epithelial cells with live, heat-killed or live bacteria separated from the host cells by a filter. The maximum induction in the EGR1 was observed with the live bacteria (Figure 3). Heat-killed N. meningitidis, S. pyogenes, H. pylori and N. gonorrhoeae were not able to induce EGR1, suggesting that bacterial viability is important (Figures 3A–D). However, S. Enteritidis could upregulate EGR1 after heat treatment (Figure 3E). After the heat treatment, the bacteria were not washed indicating a possible role of surface molecule or component that is released upon heat treatment might be involved in the upregulation of EGR1 by heat-killed S. Enteritidis. Separation of the bacteria from host cells by using a Millicell 0.4 μm filter inhibited EGR1 induction in cells infected with N. meningitidis, S. pyogenes, H. pylori, N. gonorrhoeae, and S. Enteritidis. This observation indicates that contact between bacterium and the host cell is necessary (Figure 3).