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For a long time lysozyme was only known for its antimicrobial activity against Gram-positive bacteria.

Our results on Gram-negative bacteria are:

• Lysozyme permeabilizes both the outer and inner membranes of Escherichia coli.
• Pore size and quantity were higher with dry-heated lysozyme compared to the native protein. 

Effect of lysozyme on Escherichia coli membranes visualised using atomic force microscopy (1 µm white bar) 

E. coli K12	E. coli with native lysozyme	E. coli with dry-heated lysozyme

Studies using lipopolysaccharide (LPS) and endothelial cell (CMEC) monolayer, models of the E. coli outer and inner membranes, respectively, have shown that:

• Lysozyme has a high affinity for the LPS monolayer into which it inserts as long as polysaccharide moieties are present, causing reorganisation of the monolayer.
• Dry-heated lysozyme has a stronger affinity for the LPS monolayer and causes more radical reorganisation than native lysozyme.
• Lysozyme absorbs and inserts into the CMEC monolayer causing severe modifications in lipid packing.

 
Our study demonstrates the different actions of lysozyme and expands the spectrum of its activities and the environmental conditions in which this protein can act.