Lysozyme attacks peptidoglycan, which are found in Gram-positive bacteria. I know someone who uses lysozyme to lyse Escherichia coli, which is Gram-negative. How is that possible? Can lysozyme lyse all bacteria, independently of their Gram status? Does anybody have information on how long I should leave lysozyme in a bacterial solution for it to be effective?
Gram-negative bacteria also have peptidoglycan which can be degraded by lysozyme. However they have an outer membrane lying outside the peptidoglycan layer and this will block lysozyme action.
Because of this if you intend to treat Gram-negative bacteria with lysozyme it is necessary to add something that will disrupt the outer membrane—the usual choice is EDTA since removal of magnesium ions by chelation will destabilise the outer membrane.