How does lysozyme penetrate through the bacterial outer membrane?

Lysozyme fails to penetrate through the outer membrane of stationary phase cells of Escherichia coli when it is simply added to suspensions of plasmolyzed cells. Lysozyme penetrates the outer membrane only when these cells are exposed to a mild osmotic shock in the presence of EDTA and lysozyme. In the presence of Mg2+, the outer membrane is stabilized sufficiently so that there is no lysozyme penetration during osmotic shock. If Mg2+ is added after an osmotic shock has been used to cause lysozyme to penetrate a destabilized outer membrane, the outer membrane is stabilized once again. In this case however, cells are converted to spheroplasts by the lysozyme which has gained access to the murein layer prior to the addition of Mg2+. Mg2+ stabilizes the outer membranes of these spheroplasts sufficiently so that they remain immune to lysis even in the absence of osmotic stabilizers such as sucrose. These results are discussed in terms of current information on the structure of the murein layer and the outer membrane.