After infection, coverslips containing infected BMDMs were washed once with PBS and fixed in 4% paraformaldehyde for 30 minutes at 37uC. Coverslips containing cells were incubated with blocking buffer (PBS, 0.1% Triton X-100, 2% BSA) for 30 minutes at 37uC. The primary antibodies used were: anti-GFP (combination of two monoclonal murine antibodies, Roche, 1:200 dilution) and rabbit polyclonal anti-L. monocytogenes (Difco, 1:2,000 dilution). Secondary antibodies used were Alexa-Fluor conjugated goat antimouse IgG1 and goat anti-rabbit IgG (Invitrogen, 1:1000) respectively. Both primary and secondary antibodies were diluted in block buffer and incubated for one hour at room temperature followed by three washes with TBST buffer (25 mM Tris-HCl pH 8, 150 mM NaCl, 0.1% Triton X-100). Coverslips were mounted with Vectashield mounting medium containing DAPI (Vector Laboratories).