Figure 1. Remodeling of the cell wall architecture in L. monocytogenes when growing extracellularly in two different broth media or inside eukaryotic cells may affect exposure and function of ActA and the invasins InlA and InlB. (A) The different structure of the cell wall in bacteria grown in BHI or minimal media influences ActA association with the peptidoglycan and also probably its degree of exposure on the cell surface; (B) Based on data collected with L. monocytogenes grown in minimal medium, which show that ActA, InlA and InlB are all required for bacterial invasion of epithelial cells,²² a model is proposed in which ActA could promote bacterial early attachment via its interaction with heparan-sulfate proteoglycan receptor (HSPG-R). This stage would be followed by InlA/E-Cadherin and/or InlB/Met interactions ultimately responsible for mediating bacterial entry. Different colors in the peptidoglycan denote changes in the cell wall architecture. Abbreviations: PRS: proline-rich sequences; LRR: leucine-rich repeats; GW: GW-rich domain; EC1-EC5: extracellular immunoglobulin-like domains reported for E-Cadherin. The putative role(s) played by InlA and InlB in intracellular L. monocytogenes remain unknown.