Lysozyme exert a strong antibacterial activity by hydrolysing peptidoglycan, a vital component of the bacterial cell wall, ultimately leading to osmotic lysis. To survive the bactericidal action of lysozyme when their outer membrane is permeabilised, Gram-negative bacteria produce various types of lysozyme inhibitors that allow them to survive. The latter are grouped in three distinct families and structural domains comprising this superfamily share the structure of PliI (periplasmic lysozyme inhibitor of I-type lysozyme), characteristic of invertebrate species. PliI achieves its inhibitory action via an insertion of a loop containing the conserved SGxY motif into the active center of I-type lysozymes PMID:21146533,PMID:25664745.